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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0402085 | Jakob Hansen | Jakob Hansen, Alexei Khokhlov, Igor Novikov | Properties of four numerical schemes applied to a scalar nonlinear
scalar wave equation with a GR-type nonlinearity | 9 pages, 8 Postscript figures | Int.J.Mod.Phys. D13 (2004) 961 | 10.1142/S021827180400502X | null | gr-qc | null | We study stability, dispersion and dissipation properties of four numerical
schemes (Iterative Crank-Nicolson, 3'rd and 4'th order Runge-Kutta and
Courant-Fredrichs-Levy Non-linear). By use of a Von Neumann analysis we study
the schemes applied to a scalar linear wave equation as well as a scalar
non-linear wave equation with a type of non-linearity present in GR-equations.
Numerical testing is done to verify analytic results. We find that the method
of lines (MOL) schemes are the most dispersive and dissipative schemes. The
Courant-Fredrichs-Levy Non-linear (CFLN) scheme is most accurate and least
dispersive and dissipative, but the absence of dissipation at Nyquist
frequency, if fact, puts it at a disadvantage in numerical simulation. Overall,
the 4'th order Runge-Kutta scheme, which has the least amount of dissipation
among the MOL schemes, seems to be the most suitable compromise between the
overall accuracy and damping at short wavelengths.
| [
{
"created": "Thu, 19 Feb 2004 16:12:50 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Mar 2005 03:14:22 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Hansen",
"Jakob",
""
],
[
"Khokhlov",
"Alexei",
""
],
[
"Novikov",
"Igor",
""
]
] | We study stability, dispersion and dissipation properties of four numerical schemes (Iterative Crank-Nicolson, 3'rd and 4'th order Runge-Kutta and Courant-Fredrichs-Levy Non-linear). By use of a Von Neumann analysis we study the schemes applied to a scalar linear wave equation as well as a scalar non-linear wave equation with a type of non-linearity present in GR-equations. Numerical testing is done to verify analytic results. We find that the method of lines (MOL) schemes are the most dispersive and dissipative schemes. The Courant-Fredrichs-Levy Non-linear (CFLN) scheme is most accurate and least dispersive and dissipative, but the absence of dissipation at Nyquist frequency, if fact, puts it at a disadvantage in numerical simulation. Overall, the 4'th order Runge-Kutta scheme, which has the least amount of dissipation among the MOL schemes, seems to be the most suitable compromise between the overall accuracy and damping at short wavelengths. |
gr-qc/0602117 | Achamveedu Gopakumar | Thibault Damour, Achamveedu Gopakumar | Gravitational Recoil during Binary Black Hole Coalescence using the
Effective One Body Approach | 46 pages, new figures and discussions, to appear in PRD | Phys.Rev. D73 (2006) 124006 | 10.1103/PhysRevD.73.124006 | null | gr-qc astro-ph | null | Using the Effective One Body approach, that includes nonperturbative resummed
estimates for the damping and conservative parts of the compact binary
dynamics, we compute the recoil during the late inspiral and the subsequent
plunge of non-spinning black holes of comparable masses moving in
quasi-circular orbits. Further, using a prescription that smoothly connects the
plunge phase to a perturbed single black hole, we obtain an estimate for the
total recoil associated with the binary black hole coalescence. We show that
the crucial physical feature which determines the magnitude of the terminal
recoil is the presence of a ``burst'' of linear momentum flux emitted slightly
before coalescence. When using the most natural expression for the linear
momentum flux during the plunge, together with a Taylor-expanded $(v/c)^4$
correction factor, we find that the maximum value of the terminal recoil is
$\sim 74$ km/s and occurs for a mass ratio $m_2/m_1 \simeq 0.38$. We comment,
however, on the fact that the above `best bet estimate' is subject to strong
uncertainties because the location and amplitude of the crucial peak of linear
momentum flux happens at a moment during the plunge where most of the
simplifying analytical assumptions underlying the Effective One Body approach
are no longer justified. Changing the analytical way of estimating the linear
momentum flux, we find maximum recoils that range between 49 and 172 km/s.
(Abridged)
| [
{
"created": "Tue, 28 Feb 2006 14:36:50 GMT",
"version": "v1"
},
{
"created": "Thu, 18 May 2006 12:30:20 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Damour",
"Thibault",
""
],
[
"Gopakumar",
"Achamveedu",
""
]
] | Using the Effective One Body approach, that includes nonperturbative resummed estimates for the damping and conservative parts of the compact binary dynamics, we compute the recoil during the late inspiral and the subsequent plunge of non-spinning black holes of comparable masses moving in quasi-circular orbits. Further, using a prescription that smoothly connects the plunge phase to a perturbed single black hole, we obtain an estimate for the total recoil associated with the binary black hole coalescence. We show that the crucial physical feature which determines the magnitude of the terminal recoil is the presence of a ``burst'' of linear momentum flux emitted slightly before coalescence. When using the most natural expression for the linear momentum flux during the plunge, together with a Taylor-expanded $(v/c)^4$ correction factor, we find that the maximum value of the terminal recoil is $\sim 74$ km/s and occurs for a mass ratio $m_2/m_1 \simeq 0.38$. We comment, however, on the fact that the above `best bet estimate' is subject to strong uncertainties because the location and amplitude of the crucial peak of linear momentum flux happens at a moment during the plunge where most of the simplifying analytical assumptions underlying the Effective One Body approach are no longer justified. Changing the analytical way of estimating the linear momentum flux, we find maximum recoils that range between 49 and 172 km/s. (Abridged) |
1711.04526 | Andronikos Paliathanasis | N. Dimakis, Alex Giacomini and Andronikos Paliathanasis | (Compactified) black branes in four dimensional f(R)-gravity | 13 pages, 3 figures, title changed, minor corrections, new
references, accepted version for publication at Physics Letter B | null | 10.1016/j.physletb.2017.12.059 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new family of analytical solutions in a four dimensional static spacetime
is presented for $f\left( R\right) $-gravity. In contrast to General
Relativity, we find that a non trivial black string/ring solution is supported
in vacuum power law $f\left( R\right) $-gravity for appropriate values of the
parameters characterizing the model and when axisymmetry is introduced in the
line element. For the aforementioned solution, we perform a brief investigation
over its basic thermodynamic quantities.
| [
{
"created": "Mon, 13 Nov 2017 11:10:25 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Dec 2017 09:14:41 GMT",
"version": "v2"
}
] | 2018-01-17 | [
[
"Dimakis",
"N.",
""
],
[
"Giacomini",
"Alex",
""
],
[
"Paliathanasis",
"Andronikos",
""
]
] | A new family of analytical solutions in a four dimensional static spacetime is presented for $f\left( R\right) $-gravity. In contrast to General Relativity, we find that a non trivial black string/ring solution is supported in vacuum power law $f\left( R\right) $-gravity for appropriate values of the parameters characterizing the model and when axisymmetry is introduced in the line element. For the aforementioned solution, we perform a brief investigation over its basic thermodynamic quantities. |
1605.00326 | Israel Quiros | Israel Quiros, Ricardo Garc\'ia-Salcedo, Tame Gonzalez, F. Antonio
Horta-Rangel, Joel Saavedra | Brans-Dicke Galileon and the Variational Principle | 20 pages, no figures. The content of this paper is specially
recommended to those graduate and postgraduate students who are interested in
the study of modifications of general relativity such as scalar-tensor and
$f(R)$ theories. Bibliographic references added, minor additions to the text.
Acknowledgements modified | null | 10.1088/0143-0807/37/5/055605 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper is aimed at a (mostly) pedagogical exposition of the derivation of
the motion equations of certain modifications of general relativity. Here we
derive in all detail the motion equations in the Brans-Dicke theory with the
cubic self-interaction. This is a modification of the Brans-dicke theory by the
addition of a term in the Lagrangian which is non-linear in the derivatives of
the scalar field: it contains second-order derivatives. This is the basis of
the so-called Brans-Dicke Galileon. We pay special attention to the variational
principle and to the algebraic details of the derivation. It is shown how
higher order derivatives of the fields appearing in the intermediate
computations cancel out leading to second order motion equations. The reader
will find useful tips for the derivation of the field equations of
modifications of general relativity such as the scalar-tensor theories and
$f(R)$ theories, by means of the (stationary action) variational principle. The
content of this paper is specially recommended to those graduate and
postgraduate students who are interested in the study of the mentioned
modifications of general relativity.
| [
{
"created": "Mon, 2 May 2016 00:17:13 GMT",
"version": "v1"
},
{
"created": "Wed, 4 May 2016 18:02:55 GMT",
"version": "v2"
}
] | 2016-08-24 | [
[
"Quiros",
"Israel",
""
],
[
"García-Salcedo",
"Ricardo",
""
],
[
"Gonzalez",
"Tame",
""
],
[
"Horta-Rangel",
"F. Antonio",
""
],
[
"Saavedra",
"Joel",
""
]
] | This paper is aimed at a (mostly) pedagogical exposition of the derivation of the motion equations of certain modifications of general relativity. Here we derive in all detail the motion equations in the Brans-Dicke theory with the cubic self-interaction. This is a modification of the Brans-dicke theory by the addition of a term in the Lagrangian which is non-linear in the derivatives of the scalar field: it contains second-order derivatives. This is the basis of the so-called Brans-Dicke Galileon. We pay special attention to the variational principle and to the algebraic details of the derivation. It is shown how higher order derivatives of the fields appearing in the intermediate computations cancel out leading to second order motion equations. The reader will find useful tips for the derivation of the field equations of modifications of general relativity such as the scalar-tensor theories and $f(R)$ theories, by means of the (stationary action) variational principle. The content of this paper is specially recommended to those graduate and postgraduate students who are interested in the study of the mentioned modifications of general relativity. |
2012.05154 | Neven Bili\'c | Nicolas R. Bertini, Neven Bilic and Davi C. Rodrigues | Primordial perturbations and inflation in a holography inspired
Gauss-Bonnet cosmology | 32 pages, 2 figures, major revision: introduction expanded, an
algebraic mistake corrected, Sections III.A and III.B substantially revised,
one figure added, basic conclusions unchanged, nine references added,
Acknowledgments corrected, accepted in PRD | Phys. Rev. D 105, 023509 (2022) | 10.1103/PhysRevD.105.023509 | RBI-ThPhys-2020-48 | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider an action for gravity that, in addition to the Einstein-Hilbert
term, contains a function of the Ricci scalar and the Gauss-Bonnet invariant.
The specific form of the function considered is motivated by holographic
cosmology. At background level the field equations imply modified Friedmann
equations of the same form as those in the holographic cosmology. We calculate
the cosmological perturbations and derive the corresponding power spectra
assuming a general $k$-inflation. We find that the resulting power spectra
differ substantially from those obtained in both holographic and standard
cosmology. The estimated spectral index and tensor-to-scalar ratio are
confronted with the Planck results.
| [
{
"created": "Wed, 9 Dec 2020 16:45:17 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Dec 2020 10:46:17 GMT",
"version": "v2"
},
{
"created": "Mon, 26 Jul 2021 08:32:18 GMT",
"version": "v3"
},
{
"created": "Wed, 26 Jan 2022 10:02:12 GMT",
"version": "v4"
}
] | 2022-01-27 | [
[
"Bertini",
"Nicolas R.",
""
],
[
"Bilic",
"Neven",
""
],
[
"Rodrigues",
"Davi C.",
""
]
] | We consider an action for gravity that, in addition to the Einstein-Hilbert term, contains a function of the Ricci scalar and the Gauss-Bonnet invariant. The specific form of the function considered is motivated by holographic cosmology. At background level the field equations imply modified Friedmann equations of the same form as those in the holographic cosmology. We calculate the cosmological perturbations and derive the corresponding power spectra assuming a general $k$-inflation. We find that the resulting power spectra differ substantially from those obtained in both holographic and standard cosmology. The estimated spectral index and tensor-to-scalar ratio are confronted with the Planck results. |
gr-qc/0005130 | Edward Malec | Edward Malec | Diffusion of the electromagnetic energy due to the backscattering off
Schwarzschild geometry | 16 pages, typos corrected | Phys.Rev. D62 (2000) 084034 | 10.1103/PhysRevD.62.084034 | null | gr-qc astro-ph | null | Electromagnetic waves propagate in the Schwarzschild spacetime like in a
nonuniform medium with a varying refraction index. A fraction of the radiation
scatters off the curvature of the geometry. The energy of the backscattered
part of an initially outgoing pulse of electromagnetic radiation can be
estimated, in the case of dipole radiation, by a compact formula depending on
the initial energy, the Schwarzschild radius and the pulse location. The
magnitude of the backscattered energy depends on the frequency spectrum of the
initial configuration. This effect becomes negligible in the short wave limit,
but it can be significant in the long wave regime. Similar results hold for the
massless scalar fields and are expected to hold also for weak gravitational
waves.
| [
{
"created": "Wed, 31 May 2000 11:11:39 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Jun 2000 12:42:03 GMT",
"version": "v2"
},
{
"created": "Mon, 11 Sep 2000 13:58:40 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Malec",
"Edward",
""
]
] | Electromagnetic waves propagate in the Schwarzschild spacetime like in a nonuniform medium with a varying refraction index. A fraction of the radiation scatters off the curvature of the geometry. The energy of the backscattered part of an initially outgoing pulse of electromagnetic radiation can be estimated, in the case of dipole radiation, by a compact formula depending on the initial energy, the Schwarzschild radius and the pulse location. The magnitude of the backscattered energy depends on the frequency spectrum of the initial configuration. This effect becomes negligible in the short wave limit, but it can be significant in the long wave regime. Similar results hold for the massless scalar fields and are expected to hold also for weak gravitational waves. |
1009.4388 | Jorgen Rasmussen | Jorgen Rasmussen | On hidden symmetries of extremal Kerr-NUT-AdS-dS black holes | 7 pages | J.Geom.Phys.61:922-926,2011 | 10.1016/j.geomphys.2011.01.006 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well known that the Kerr-NUT-AdS-dS black hole admits two linearly
independent Killing vectors and possesses a hidden symmetry generated by a
rank-2 Killing tensor. The near-horizon geometry of an extremal Kerr-NUT-AdS-dS
black hole admits four linearly independent Killing vectors, and we show how
the hidden symmetry of the black hole itself is carried over by means of a
modified Killing-Yano potential which is given explicitly. We demonstrate that
the corresponding Killing tensor of the near-horizon geometry is reducible as
it can be expressed in terms of the Casimir operators formed by the four
Killing vectors.
| [
{
"created": "Wed, 22 Sep 2010 15:28:14 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Sep 2010 08:42:41 GMT",
"version": "v2"
}
] | 2011-03-02 | [
[
"Rasmussen",
"Jorgen",
""
]
] | It is well known that the Kerr-NUT-AdS-dS black hole admits two linearly independent Killing vectors and possesses a hidden symmetry generated by a rank-2 Killing tensor. The near-horizon geometry of an extremal Kerr-NUT-AdS-dS black hole admits four linearly independent Killing vectors, and we show how the hidden symmetry of the black hole itself is carried over by means of a modified Killing-Yano potential which is given explicitly. We demonstrate that the corresponding Killing tensor of the near-horizon geometry is reducible as it can be expressed in terms of the Casimir operators formed by the four Killing vectors. |
2003.02646 | Vladimir Dzhunushaliev | Vladimir Dzhunushaliev and Vladimir Folomeev | Spinor field solutions in $F\left(B^2\right)$ modified Weyl gravity | 11pages | null | 10.1142/S0218271820500947 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider modified Weyl gravity where a Dirac spinor field is nonminimally
coupled to gravity. It is assumed that such modified gravity is some
approximation for the description of quantum gravitational effects related to
the gravitating spinor field. It is shown that such a theory contains solutions
for a class of metrics which are conformally equivalent to the Hopf metric on
the Hopf fibration. For this case, we obtain a full discrete spectrum of the
solutions and show that they can be related to the Hopf invariant on the Hopf
fibration. The expression for the spin operator in the Hopf coordinates is
obtained. It is demonstrated that this class of conformally equivalent metrics
contains: (a) a metric describing a toroidal wormhole without exotic matter;
(b) a cosmological solution with a bounce and inflation; and (c) a transition
with a change in metric signature. A physical discussion of the results is
given. \end{abstract}
| [
{
"created": "Tue, 3 Mar 2020 11:18:23 GMT",
"version": "v1"
},
{
"created": "Mon, 11 May 2020 08:56:42 GMT",
"version": "v2"
}
] | 2020-11-18 | [
[
"Dzhunushaliev",
"Vladimir",
""
],
[
"Folomeev",
"Vladimir",
""
]
] | We consider modified Weyl gravity where a Dirac spinor field is nonminimally coupled to gravity. It is assumed that such modified gravity is some approximation for the description of quantum gravitational effects related to the gravitating spinor field. It is shown that such a theory contains solutions for a class of metrics which are conformally equivalent to the Hopf metric on the Hopf fibration. For this case, we obtain a full discrete spectrum of the solutions and show that they can be related to the Hopf invariant on the Hopf fibration. The expression for the spin operator in the Hopf coordinates is obtained. It is demonstrated that this class of conformally equivalent metrics contains: (a) a metric describing a toroidal wormhole without exotic matter; (b) a cosmological solution with a bounce and inflation; and (c) a transition with a change in metric signature. A physical discussion of the results is given. \end{abstract} |
2307.13588 | Fatemeh Sadeghi | Behrouz Mirza, Parichehr Kangazian Kangazi and Fatemeh Sadeghi | A class of rotating metrics in the presence of a scalar field | 12 pages and 4 figures | Eur. Phys. J. C (2023) 83:1161 | 10.1140/epjc/s10052-023-12255-7 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a class of three parameter static and axially symmetric metrics
that reduce to the Janis-Newman-Winicour (JNW) and $ \gamma$-metrics in certain
limits of the parameters. We obtain rotating form of the metrics that are
asymptotically flat, stationary and axisymmetric. In certain values of the
parameters, the solutions represent the rotating JNW metric, rotating $
\gamma$-metric and Bogush-Gal'tsov (BG) metric. The singularities of rotating
metrics are investigated. Using the light-ring method, we obtain the quasi
normal modes (QNMs) related to rotating metrics in the eikonal limit. Finally,
we investigate the precession frequency of a test gyroscope in the presence of
the rotating metrics.
| [
{
"created": "Tue, 25 Jul 2023 15:47:08 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Nov 2023 17:23:30 GMT",
"version": "v2"
}
] | 2023-12-21 | [
[
"Mirza",
"Behrouz",
""
],
[
"Kangazi",
"Parichehr Kangazian",
""
],
[
"Sadeghi",
"Fatemeh",
""
]
] | We consider a class of three parameter static and axially symmetric metrics that reduce to the Janis-Newman-Winicour (JNW) and $ \gamma$-metrics in certain limits of the parameters. We obtain rotating form of the metrics that are asymptotically flat, stationary and axisymmetric. In certain values of the parameters, the solutions represent the rotating JNW metric, rotating $ \gamma$-metric and Bogush-Gal'tsov (BG) metric. The singularities of rotating metrics are investigated. Using the light-ring method, we obtain the quasi normal modes (QNMs) related to rotating metrics in the eikonal limit. Finally, we investigate the precession frequency of a test gyroscope in the presence of the rotating metrics. |
0707.0864 | Vladislav Vaganov | Vladislav Vaganov | Self-gravitating radiation in AdS(d) | 21 pages, 4 figures, JHEP style; revised version | null | null | DAMTP-2007-66 | gr-qc hep-th | null | We study spherically symmetric equilibrium configurations of self-gravitating
massless thermal radiation in asymptotically anti-de Sitter space. In d=4, it
was shown by Page and Phillips that there is a maximum red-shifted temperature,
maximum mass and maximum entropy. For higher central densities, the
temperature, mass and entropy undergo an infinite series of damped
oscillations, corresponding to unstable configurations. We extend this work to
all dimensions $d\geq 3$. We find that in $4\leq d\leq 10$, the behaviour is
similar to the d=4 case. In $d\geq 11$, the temperature, mass and entropy are
monotonic functions of the central density, asymptoting to their maxima as the
central density goes to infinity. In d=3, an exact solution is given by a slice
of the AdS C-metric.
| [
{
"created": "Thu, 5 Jul 2007 19:59:30 GMT",
"version": "v1"
},
{
"created": "Sat, 7 Jul 2007 02:00:31 GMT",
"version": "v2"
},
{
"created": "Tue, 24 Jul 2007 19:59:50 GMT",
"version": "v3"
},
{
"created": "Thu, 2 Aug 2007 19:39:22 GMT",
"version": "v4"
}
] | 2007-08-02 | [
[
"Vaganov",
"Vladislav",
""
]
] | We study spherically symmetric equilibrium configurations of self-gravitating massless thermal radiation in asymptotically anti-de Sitter space. In d=4, it was shown by Page and Phillips that there is a maximum red-shifted temperature, maximum mass and maximum entropy. For higher central densities, the temperature, mass and entropy undergo an infinite series of damped oscillations, corresponding to unstable configurations. We extend this work to all dimensions $d\geq 3$. We find that in $4\leq d\leq 10$, the behaviour is similar to the d=4 case. In $d\geq 11$, the temperature, mass and entropy are monotonic functions of the central density, asymptoting to their maxima as the central density goes to infinity. In d=3, an exact solution is given by a slice of the AdS C-metric. |
0803.3162 | Alessandro Nagar | Thibault Damour, Alessandro Nagar, Mark Hannam, Sascha Husa, Bernd
Brugmann | Accurate Effective-One-Body waveforms of inspiralling and coalescing
black-hole binaries | 25 pages, 15 figures. Improved discussion about errors on numerical
relativity data. Version published in Phys. Rev. D | Phys.Rev.D78:044039,2008 | 10.1103/PhysRevD.78.044039 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Effective-One-Body (EOB) formalism contains several flexibility
parameters, notably $a_5$, $\vp$ and $\a$. We show here how to jointly
constrain the values of these parameters by simultaneously best-fitting the EOB
waveform to two, independent, numerical relativity (NR) simulations of
inspiralling and/or coalescing binary black hole systems: published
Caltech-Cornell {\it inspiral} data (considered for gravitational wave
frequencies $M\omega\leq 0.1$) on one side, and newly computed {\it
coalescence} data on the other side. The resulting, approximately unique,
"best-fit" EOB waveform is then shown to exhibit excellent agreement with NR
coalescence data for several mass ratios. The dephasing between this best-fit
EOB waveform and published Caltech-Cornell inspiral data is found to vary
between -0.0014 and +0.0008 radians over a time span of $\sim 2464M$ up to
gravitational wave frequency $M\omega= 0.1$, and between +0.0013 and -0.0185
over a time span of 96M after $M\omega=0.1$ up to $M\omega=0.1565$. The
dephasings between EOB and the new coalescence data are found to be smaller
than: (i) $\pm 0.025$ radians over a time span of 730M (11 cycles) up to
merger, in the equal mass case, and (ii) $\pm 0.05$ radians over a time span of
about 950M (17 cycles) up to merger in the 2:1 mass-ratio case. These new
results corroborate the aptitude of the EOB formalism to provide accurate
representations of general relativistic waveforms, which are needed by
currently operating gravitational wave detectors.
| [
{
"created": "Fri, 21 Mar 2008 13:17:22 GMT",
"version": "v1"
},
{
"created": "Fri, 29 Aug 2008 09:12:04 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Damour",
"Thibault",
""
],
[
"Nagar",
"Alessandro",
""
],
[
"Hannam",
"Mark",
""
],
[
"Husa",
"Sascha",
""
],
[
"Brugmann",
"Bernd",
""
]
] | The Effective-One-Body (EOB) formalism contains several flexibility parameters, notably $a_5$, $\vp$ and $\a$. We show here how to jointly constrain the values of these parameters by simultaneously best-fitting the EOB waveform to two, independent, numerical relativity (NR) simulations of inspiralling and/or coalescing binary black hole systems: published Caltech-Cornell {\it inspiral} data (considered for gravitational wave frequencies $M\omega\leq 0.1$) on one side, and newly computed {\it coalescence} data on the other side. The resulting, approximately unique, "best-fit" EOB waveform is then shown to exhibit excellent agreement with NR coalescence data for several mass ratios. The dephasing between this best-fit EOB waveform and published Caltech-Cornell inspiral data is found to vary between -0.0014 and +0.0008 radians over a time span of $\sim 2464M$ up to gravitational wave frequency $M\omega= 0.1$, and between +0.0013 and -0.0185 over a time span of 96M after $M\omega=0.1$ up to $M\omega=0.1565$. The dephasings between EOB and the new coalescence data are found to be smaller than: (i) $\pm 0.025$ radians over a time span of 730M (11 cycles) up to merger, in the equal mass case, and (ii) $\pm 0.05$ radians over a time span of about 950M (17 cycles) up to merger in the 2:1 mass-ratio case. These new results corroborate the aptitude of the EOB formalism to provide accurate representations of general relativistic waveforms, which are needed by currently operating gravitational wave detectors. |
1412.8666 | Alireza Sepehri | M. R. Setare, A. Sepehri | Stability of cylindrical thin shell wormhole during evolution of
universe from inflation to late time acceleration | 18 pages, 6 figures.v2, accepted in JHEP | null | 10.1007/JHEP03(2015)079 | null | gr-qc | http://creativecommons.org/licenses/by/3.0/ | In this paper, we consider the stability of cylindrical wormholes during
evolution of universe from inflation to late time acceleration epochs. We show
that there are two types of cylindrical wormholes. The first type is produced
at the corresponding point where k black F-strings are transited to BIon
configuration. This wormhole transfers energy from extra dimensions into our
universe, causes inflation, loses it's energy and vanishes. The second type of
cylindrical wormhole is created by a tachyonic potential and causes a new phase
of acceleration. We show that wormhole parameters grow faster than the scale
factor in this era, overtake it at ripping time and lead to the destruction of
universe at big rip singularity.
| [
{
"created": "Sun, 28 Dec 2014 09:16:24 GMT",
"version": "v1"
},
{
"created": "Fri, 13 Feb 2015 11:21:05 GMT",
"version": "v2"
}
] | 2015-06-23 | [
[
"Setare",
"M. R.",
""
],
[
"Sepehri",
"A.",
""
]
] | In this paper, we consider the stability of cylindrical wormholes during evolution of universe from inflation to late time acceleration epochs. We show that there are two types of cylindrical wormholes. The first type is produced at the corresponding point where k black F-strings are transited to BIon configuration. This wormhole transfers energy from extra dimensions into our universe, causes inflation, loses it's energy and vanishes. The second type of cylindrical wormhole is created by a tachyonic potential and causes a new phase of acceleration. We show that wormhole parameters grow faster than the scale factor in this era, overtake it at ripping time and lead to the destruction of universe at big rip singularity. |
2006.08918 | Alvin Chua | Alvin J. K. Chua, Michele Vallisneri | On parametric tests of relativity with false degrees of freedom | 4 pages, 2 figures | null | null | null | gr-qc astro-ph.IM stat.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | General relativity can be tested by comparing the binary-inspiral signals
found in LIGO--Virgo data against waveform models that are augmented with
artificial degrees of freedom. This approach suffers from a number of logical
and practical pitfalls. 1) It is difficult to ascribe meaning to the stringency
of the resultant constraints. 2) It is doubtful that the Bayesian model
comparison of relativity against these artificial models can offer actual
validation for the former. 3) It is unknown to what extent these tests might
detect alternative theories of gravity for which there are no computed
waveforms; conversely, when waveforms are available, tests that employ them
will be superior.
| [
{
"created": "Tue, 16 Jun 2020 04:29:32 GMT",
"version": "v1"
}
] | 2020-06-17 | [
[
"Chua",
"Alvin J. K.",
""
],
[
"Vallisneri",
"Michele",
""
]
] | General relativity can be tested by comparing the binary-inspiral signals found in LIGO--Virgo data against waveform models that are augmented with artificial degrees of freedom. This approach suffers from a number of logical and practical pitfalls. 1) It is difficult to ascribe meaning to the stringency of the resultant constraints. 2) It is doubtful that the Bayesian model comparison of relativity against these artificial models can offer actual validation for the former. 3) It is unknown to what extent these tests might detect alternative theories of gravity for which there are no computed waveforms; conversely, when waveforms are available, tests that employ them will be superior. |
2010.11908 | Torben Frost | Torben C. Frost and Volker Perlick (ZARM, University of Bremen,
Bremen, Germany) | Lightlike Geodesics and Gravitational Lensing in the Spacetime of an
Accelerating Black Hole | 37 pages, 13 figures; updated and added new references, corrected
typos, minor changes and additions in the text, (e.g., black holes in uniform
motion, brief discussion of accelerating black holes with NUT charge,
extended discussion of the shadow), modified figure fonts | Class. Quantum Grav. 38, 085016 (2021) | 10.1088/1361-6382/abe0f5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The C-metric is a solution to Einstein's vacuum field equation that describes
an accelerating black hole. In this paper we discuss the propagation of light
rays and the resulting lensing features in this metric. We first solve the
lightlike geodesic equation using elliptic integrals and Jacobi elliptic
functions. Then we fix a static observer in the region of outer communication
of the C-metric and introduce an orthonormal tetrad to parameterise the
directions of the light rays ending at the position of the observer using
latitude-longitude coordinates on the observer's celestial sphere. In this
parameterisation we rederive the angular radius of the shadow, we formulate a
lens equation, and we derive the redshift and the travel time of light rays. We
discuss the relevance of our theoretical results for detecting accelerating
black holes described by the C-metric and for distinguishing them from
non-accelerating black holes.
| [
{
"created": "Thu, 22 Oct 2020 17:43:34 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Jan 2021 12:51:58 GMT",
"version": "v2"
}
] | 2021-06-09 | [
[
"Frost",
"Torben C.",
"",
"ZARM, University of Bremen,\n Bremen, Germany"
],
[
"Perlick",
"Volker",
"",
"ZARM, University of Bremen,\n Bremen, Germany"
]
] | The C-metric is a solution to Einstein's vacuum field equation that describes an accelerating black hole. In this paper we discuss the propagation of light rays and the resulting lensing features in this metric. We first solve the lightlike geodesic equation using elliptic integrals and Jacobi elliptic functions. Then we fix a static observer in the region of outer communication of the C-metric and introduce an orthonormal tetrad to parameterise the directions of the light rays ending at the position of the observer using latitude-longitude coordinates on the observer's celestial sphere. In this parameterisation we rederive the angular radius of the shadow, we formulate a lens equation, and we derive the redshift and the travel time of light rays. We discuss the relevance of our theoretical results for detecting accelerating black holes described by the C-metric and for distinguishing them from non-accelerating black holes. |
1511.05999 | Sergey G. Klimenko | S. Klimenko, G. Vedovato, M. Drago, F. Salemi, V. Tiwari, G. A. Prodi,
C. Lazzaro, K. Ackley, S. Tiwari, C. F. Da Silva Cost- and G. Mitselmakher | Method for detection and reconstruction of gravitational wave transients
with networks of advanced detectors | 9 pages, 4 figures, 1 table | Phys. Rev. D 93, 042004 (2016) | 10.1103/PhysRevD.93.042004 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a method for detection and reconstruction of the
gravitational-wave (GW) transients with the networks of advanced detectors.
Originally designed to search for transients with the initial GW detectors, it
uses significantly improved algorithms, which enhances both the low-latency
searches with rapid localization of GW events for the electro-magnetic followup
and high confidence detection of a broad range of the transient GW sources. In
the paper we present the analytic framework of the method. Following a short
description of the core analysis algorithms, we introduce a novel approach to
the reconstruction of the GW polarization from a pattern of detector responses
to a GW signal. This polarization pattern is a unique signature of an arbitrary
GW signal that can be measured independent from the other source parameters.
The polarization measurements enable rapid reconstruction of the GW waveforms,
sky localization and helps identification of the source origin.
| [
{
"created": "Wed, 18 Nov 2015 22:10:18 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Dec 2015 00:45:47 GMT",
"version": "v2"
},
{
"created": "Fri, 22 Jan 2016 16:03:22 GMT",
"version": "v3"
}
] | 2016-02-17 | [
[
"Klimenko",
"S.",
""
],
[
"Vedovato",
"G.",
""
],
[
"Drago",
"M.",
""
],
[
"Salemi",
"F.",
""
],
[
"Tiwari",
"V.",
""
],
[
"Prodi",
"G. A.",
""
],
[
"Lazzaro",
"C.",
""
],
[
"Ackley",
"K.",
""
],
[
"Tiwari",
"S.",
""
],
[
"Cost-",
"C. F. Da Silva",
""
],
[
"Mitselmakher",
"G.",
""
]
] | We present a method for detection and reconstruction of the gravitational-wave (GW) transients with the networks of advanced detectors. Originally designed to search for transients with the initial GW detectors, it uses significantly improved algorithms, which enhances both the low-latency searches with rapid localization of GW events for the electro-magnetic followup and high confidence detection of a broad range of the transient GW sources. In the paper we present the analytic framework of the method. Following a short description of the core analysis algorithms, we introduce a novel approach to the reconstruction of the GW polarization from a pattern of detector responses to a GW signal. This polarization pattern is a unique signature of an arbitrary GW signal that can be measured independent from the other source parameters. The polarization measurements enable rapid reconstruction of the GW waveforms, sky localization and helps identification of the source origin. |
0903.0067 | Davood Momeni | D. Momeni, H. Gholizade | A note on constant curvature solutions in cylindrically symmetric metric
$f(R)$ Gravity | 13 pages,Typos corrected and references added, accepted for
publication in "International journal of modern physics D"(IJMPD), Conclusion
and more notes is added,replaced with the published version, The title is
changed | Int.J.Mod.Phys.D18:1719-1729,2009 | 10.1142/S0218271809015266 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the previous work we introduced a new static cylindrically symmetric
vacuum solutions in Weyl coordinates in the context of the metric f(R) theories
of gravity\cite{1}. Now we obtain a 2-parameter family of exact solutions which
contains cosmological constant and a new parameter as $\beta$. This solution
corresponds to a constant Ricci scalar. We proved that in $f(R)$ gravity, the
constant curvature solution in cylindrically symmetric cases is only one member
of the most generalized Tian family in GR. We show that our constant curvature
exact solution is applicable to the exterior of a string. Sensibility of
stability under initial conditions is discussed.
| [
{
"created": "Sat, 28 Feb 2009 11:42:15 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Mar 2009 16:36:04 GMT",
"version": "v2"
},
{
"created": "Mon, 30 Mar 2009 08:12:54 GMT",
"version": "v3"
},
{
"created": "Fri, 29 May 2009 15:03:20 GMT",
"version": "v4"
},
{
"created": "Thu, 22 Oct 2009 09:24:06 GMT",
"version": "v5"
},
{
"created": "Mon, 9 Nov 2009 12:36:39 GMT",
"version": "v6"
},
{
"created": "Wed, 21 Apr 2010 07:20:02 GMT",
"version": "v7"
}
] | 2010-04-23 | [
[
"Momeni",
"D.",
""
],
[
"Gholizade",
"H.",
""
]
] | In the previous work we introduced a new static cylindrically symmetric vacuum solutions in Weyl coordinates in the context of the metric f(R) theories of gravity\cite{1}. Now we obtain a 2-parameter family of exact solutions which contains cosmological constant and a new parameter as $\beta$. This solution corresponds to a constant Ricci scalar. We proved that in $f(R)$ gravity, the constant curvature solution in cylindrically symmetric cases is only one member of the most generalized Tian family in GR. We show that our constant curvature exact solution is applicable to the exterior of a string. Sensibility of stability under initial conditions is discussed. |
1106.6238 | Hing Tong Cho | H. T. Cho, A. S. Cornell, Jason Doukas, and Wade Naylor | Angular Eigenvalues of Higher-Dimensional Kerr-(A)dS Black Holes with
Two Rotations | 10 pages, no figures. To appear in the proceedings of 2011 Shanghai
Asia-Pacific School and Workshop on Gravitation | null | 10.1142/S201019451200431X | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, following the work of Chen, L\"u and Pope, we present the
general metric for Kerr-(A)dS black holes with two rotations. The corresponding
Klein-Gordon equation is separated explicitly, from which we develop
perturbative expansions for the angular eigenvalues in powers of the rotation
parameters with $D\geq 6$.
| [
{
"created": "Thu, 30 Jun 2011 14:19:58 GMT",
"version": "v1"
}
] | 2015-05-28 | [
[
"Cho",
"H. T.",
""
],
[
"Cornell",
"A. S.",
""
],
[
"Doukas",
"Jason",
""
],
[
"Naylor",
"Wade",
""
]
] | In this paper, following the work of Chen, L\"u and Pope, we present the general metric for Kerr-(A)dS black holes with two rotations. The corresponding Klein-Gordon equation is separated explicitly, from which we develop perturbative expansions for the angular eigenvalues in powers of the rotation parameters with $D\geq 6$. |
2306.01054 | Tuhin Malik | K. Nobleson and Sarmistha Banik and Tuhin Malik | Unveiling a universal relationship between the f(R) parameter and
neutron star properties | 10 pages, 7 figures, 3 tables | null | 10.1103/PhysRevD.107.124045 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In recent years, modified gravity theories have gained significant attention
as potential replacements for the general theory of relativity. Neutron stars,
which are dense compact objects, provide ideal astrophysical laboratories for
testing these theories. However, understanding the properties of neutron stars
within the framework of modified gravity theories requires careful
consideration of the presently known uncertainty of equations of state (EoS)
that describe the behavior of matter at extreme densities.
In this study, we investigate three realistic EoS generated using a
relativistic mean field framework, which covers the currently known
uncertainties in the stiffness of neutron star matter. We then employ a
Bayesian approach to statistically analyze the posterior distribution of the
free parameter $\alpha$ of the $f(R)$ gravity model, specifically $f(R) = R +
\alpha R^2$. By using this approach, we are able to account for our limited
understanding of the interiors of neutron stars as well as the uncertainties
associated with the modified gravity theory.
We impose observational constraints on our analysis, including the maximum
mass, and the radius of a neutron star with a mass of $1.4 M_{\odot}$ and $2.08
M_{\odot}$, which are obtained from X-ray NICER observations. By considering
these constraints, we are able to robustly investigate the relationship between
the $f(R)$ gravity model parameter $\alpha$ and the maximum mass of neutron
stars.
Our results reveal a universality relationship between the $f(R)$ gravity
model parameter $\alpha$ and the maximum mass of neutron stars. This
relationship provides insights into the behavior of neutron stars in modified
gravity theories and helps us understand the degeneracies arising from our
current limited knowledge of the interiors of neutron stars and the free
parameter $\alpha$ of the modified gravity theory.
| [
{
"created": "Thu, 1 Jun 2023 18:00:40 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Jul 2023 14:50:27 GMT",
"version": "v2"
}
] | 2023-07-20 | [
[
"Nobleson",
"K.",
""
],
[
"Banik",
"Sarmistha",
""
],
[
"Malik",
"Tuhin",
""
]
] | In recent years, modified gravity theories have gained significant attention as potential replacements for the general theory of relativity. Neutron stars, which are dense compact objects, provide ideal astrophysical laboratories for testing these theories. However, understanding the properties of neutron stars within the framework of modified gravity theories requires careful consideration of the presently known uncertainty of equations of state (EoS) that describe the behavior of matter at extreme densities. In this study, we investigate three realistic EoS generated using a relativistic mean field framework, which covers the currently known uncertainties in the stiffness of neutron star matter. We then employ a Bayesian approach to statistically analyze the posterior distribution of the free parameter $\alpha$ of the $f(R)$ gravity model, specifically $f(R) = R + \alpha R^2$. By using this approach, we are able to account for our limited understanding of the interiors of neutron stars as well as the uncertainties associated with the modified gravity theory. We impose observational constraints on our analysis, including the maximum mass, and the radius of a neutron star with a mass of $1.4 M_{\odot}$ and $2.08 M_{\odot}$, which are obtained from X-ray NICER observations. By considering these constraints, we are able to robustly investigate the relationship between the $f(R)$ gravity model parameter $\alpha$ and the maximum mass of neutron stars. Our results reveal a universality relationship between the $f(R)$ gravity model parameter $\alpha$ and the maximum mass of neutron stars. This relationship provides insights into the behavior of neutron stars in modified gravity theories and helps us understand the degeneracies arising from our current limited knowledge of the interiors of neutron stars and the free parameter $\alpha$ of the modified gravity theory. |
1204.0091 | Vladimir Ivashchuk | A. A. Golubtsova and V. D. Ivashchuk | Exact solutions in gravity with a sigma model source | 22 pages, Latex, several phrases and 4 refs. are addes, few typos are
eliminated | General Relativity and Gravitation, 44, No 10, 2571-2594 (2012) | 10.1007/s10714-012-1415-7 | ICG-PFUR-12-03/1v2 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a D-dimensional model of gravity with non-linear "scalar fields"
as a matter source. The model is defined on the product manifold M, which
contains n Einstein factor spaces. General cosmological type solutions to the
field equations are obtained when n-1 factor spaces are Ricci-flat, e.g. when
one space M_1 of dimension d_1 > 1 has nonzero scalar curvature. The solutions
are defined up to solutions to geodesic equations corresponding to a sigma
model target space. Several examples of sigma models are presented. A subclass
of spherically-symmetric solutions is studied and a restricted version of
"no-hair theorem" for black holes is proved. For the case d_1 =2 a subclass of
latent soliton solutions is singled out.
| [
{
"created": "Sat, 31 Mar 2012 09:58:03 GMT",
"version": "v1"
},
{
"created": "Tue, 8 May 2012 13:50:42 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Golubtsova",
"A. A.",
""
],
[
"Ivashchuk",
"V. D.",
""
]
] | We consider a D-dimensional model of gravity with non-linear "scalar fields" as a matter source. The model is defined on the product manifold M, which contains n Einstein factor spaces. General cosmological type solutions to the field equations are obtained when n-1 factor spaces are Ricci-flat, e.g. when one space M_1 of dimension d_1 > 1 has nonzero scalar curvature. The solutions are defined up to solutions to geodesic equations corresponding to a sigma model target space. Several examples of sigma models are presented. A subclass of spherically-symmetric solutions is studied and a restricted version of "no-hair theorem" for black holes is proved. For the case d_1 =2 a subclass of latent soliton solutions is singled out. |
gr-qc/0410015 | Sayandeb Basu | Sayandeb Basu | Perturbation theory in covariant canonical quantization | 15 pages, no figures. Version 2. Introduction significantly
restructured to put this work in porper context. Contents unchanged, few
references added | Phys.Rev. D71 (2005) 084001 | 10.1103/PhysRevD.71.084001 | UCD-04-27 | gr-qc | null | I investigate a new idea of perturbation theory in covariant canonical
quantization. I present preliminary results for a toy model of a harmonic
oscillator with a quartic perturbation, and show that this method reproduces
the quantized spectrum of standard quantum theory. This result indicates that
when the exact solutions to classical equations are not known, covariant
canonical quantization via perturbation theory could be a viable approximation
scheme for finding observables, and suggests a physically interesting way of
extending the scope of covariant canonical quantization in quantum gravity
| [
{
"created": "Mon, 4 Oct 2004 20:33:31 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Dec 2004 04:16:41 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Basu",
"Sayandeb",
""
]
] | I investigate a new idea of perturbation theory in covariant canonical quantization. I present preliminary results for a toy model of a harmonic oscillator with a quartic perturbation, and show that this method reproduces the quantized spectrum of standard quantum theory. This result indicates that when the exact solutions to classical equations are not known, covariant canonical quantization via perturbation theory could be a viable approximation scheme for finding observables, and suggests a physically interesting way of extending the scope of covariant canonical quantization in quantum gravity |
1410.1486 | Steven Carlip | S. Carlip | Black Hole Thermodynamics | Invited review article. A few parts based on an earlier review,
arXiv:0807.4520. To appear in Int. J. Mod. Phys. D and in "One Hundred Years
of General Relativity: Cosmology and Gravity," edited by Wei-Tou Ni (World
Scientific, Singapore, 2015). v2: added references and appendix | null | 10.1142/S0218271814300237 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The discovery in the early 1970s that black holes radiate as black bodies has
radically affected our understanding of general relativity, and offered us some
early hints about the nature of quantum gravity. In this chapter I will review
the discovery of black hole thermodynamics and summarize the many independent
ways of obtaining the thermodynamic and (perhaps) statistical mechanical
properties of black holes. I will then describe some of the remaining puzzles,
including the nature of the quantum microstates, the problem of universality,
and the information loss paradox.
| [
{
"created": "Mon, 6 Oct 2014 18:37:55 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Aug 2015 00:04:20 GMT",
"version": "v2"
}
] | 2015-08-27 | [
[
"Carlip",
"S.",
""
]
] | The discovery in the early 1970s that black holes radiate as black bodies has radically affected our understanding of general relativity, and offered us some early hints about the nature of quantum gravity. In this chapter I will review the discovery of black hole thermodynamics and summarize the many independent ways of obtaining the thermodynamic and (perhaps) statistical mechanical properties of black holes. I will then describe some of the remaining puzzles, including the nature of the quantum microstates, the problem of universality, and the information loss paradox. |
1905.03118 | Anuradha Samajdar | Anuradha Samajdar and Tim Dietrich | Waveform systematics for binary neutron star gravitational wave signals:
Effects of spin, precession, and the observation of electromagnetic
counterparts | 10 pages, 4 figures, 3 tables | Phys. Rev. D 100, 024046 (2019) | 10.1103/PhysRevD.100.024046 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Extracting the properties of a binary system emitting gravitational waves
relies on models describing the last stages of the compact binary coalescence.
In this article, we study potential biases inherent to current tidal waveform
approximants for spinning and precessing systems. We perform a Bayesian study
to estimate intrinsic parameters of highly spinning binary neutron star
systems. Our analysis shows that one has to include the quadrupolar deformation
of the neutron stars due to their rotation once dimensionless spins above $\chi
\sim 0.20$ are reached, otherwise the extracted intrinsic parameters are
systematically biased. We find that at design sensitivity of Advanced LIGO and
Virgo, it seems unlikely that for GW170817-like sources a clear imprint of
precession will be visible in the analysis of the signal employing current
waveform models. However, precession effects might be detectable for unequal
mass configurations with spins larger than $\chi>0.2$. We finalize our study by
investigating possible benefits of a combined gravitational wave and
electromagnetic detection. The presence of electromagnetic counterparts help in
reducing the dimensionality of the parameter space with constraints on the sky
location, source distance, and inclination. However, we note that although a
small improvement in the estimation of the tidal deformability parameter is
seen in these cases, changes in the intrinsic parameters are overall very
small.
| [
{
"created": "Wed, 8 May 2019 14:51:34 GMT",
"version": "v1"
}
] | 2019-07-31 | [
[
"Samajdar",
"Anuradha",
""
],
[
"Dietrich",
"Tim",
""
]
] | Extracting the properties of a binary system emitting gravitational waves relies on models describing the last stages of the compact binary coalescence. In this article, we study potential biases inherent to current tidal waveform approximants for spinning and precessing systems. We perform a Bayesian study to estimate intrinsic parameters of highly spinning binary neutron star systems. Our analysis shows that one has to include the quadrupolar deformation of the neutron stars due to their rotation once dimensionless spins above $\chi \sim 0.20$ are reached, otherwise the extracted intrinsic parameters are systematically biased. We find that at design sensitivity of Advanced LIGO and Virgo, it seems unlikely that for GW170817-like sources a clear imprint of precession will be visible in the analysis of the signal employing current waveform models. However, precession effects might be detectable for unequal mass configurations with spins larger than $\chi>0.2$. We finalize our study by investigating possible benefits of a combined gravitational wave and electromagnetic detection. The presence of electromagnetic counterparts help in reducing the dimensionality of the parameter space with constraints on the sky location, source distance, and inclination. However, we note that although a small improvement in the estimation of the tidal deformability parameter is seen in these cases, changes in the intrinsic parameters are overall very small. |
1805.05919 | Avirup Ghosh | C. Fairoos, Avirup Ghosh and Sudipta Sarkar | Boundary Conservation from Bulk Symmetry | Essay received honourable mention in the `Gravity Research Foundation
2018 Awards for Essays on Gravitation` | Int.J.Mod.Phys. D27 (2018) no.14, 1847023 | 10.1142/S0218271818470235 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The evolution of the black hole horizon can be effectively captured by a
fictitious membrane fluid living on the stretched horizon. We show that the
dynamics of this boundary matter arises from the invariance of the bulk action
under local symmetries in the presence of the inner boundary. If general
covariance is broken in a semi-classical treatment of a quantum field near a
black hole horizon, we argue that it can be restored by the inclusion of a
quantum flux into the membrane conservation equation which is exactly equal to
the Hawking flux.
| [
{
"created": "Tue, 15 May 2018 17:21:59 GMT",
"version": "v1"
}
] | 2018-12-04 | [
[
"Fairoos",
"C.",
""
],
[
"Ghosh",
"Avirup",
""
],
[
"Sarkar",
"Sudipta",
""
]
] | The evolution of the black hole horizon can be effectively captured by a fictitious membrane fluid living on the stretched horizon. We show that the dynamics of this boundary matter arises from the invariance of the bulk action under local symmetries in the presence of the inner boundary. If general covariance is broken in a semi-classical treatment of a quantum field near a black hole horizon, we argue that it can be restored by the inclusion of a quantum flux into the membrane conservation equation which is exactly equal to the Hawking flux. |
1404.6081 | Hyeong-Chan Kim | Inyong Cho and Hyeong-Chan Kim | Inflationary Tensor Perturbation in Eddington-inspired Born-Infeld
gravity | 14 pages, 4 figures | Phys. Rev. D 90, 024063 (2014) | 10.1103/PhysRevD.90.024063 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the tensor perturbation in the inflation model driven by a
massive-scalar field in Eddington-inspired Born-Infeld gravity. For short
wave-length modes, the perturbation feature is very similar to that of the
usual chaotic inflation. For long wave-length modes, the perturbation exhibits
a peculiar rise in the power spectrum which may leave a signature in the cosmic
microwave background radiation.
| [
{
"created": "Thu, 24 Apr 2014 10:46:59 GMT",
"version": "v1"
}
] | 2014-07-30 | [
[
"Cho",
"Inyong",
""
],
[
"Kim",
"Hyeong-Chan",
""
]
] | We investigate the tensor perturbation in the inflation model driven by a massive-scalar field in Eddington-inspired Born-Infeld gravity. For short wave-length modes, the perturbation feature is very similar to that of the usual chaotic inflation. For long wave-length modes, the perturbation exhibits a peculiar rise in the power spectrum which may leave a signature in the cosmic microwave background radiation. |
1112.2134 | Alexey Golovnev | Alexey Golovnev | On the Hamiltonian analysis of non-linear massive gravity | 8 pages; minor changes; one of the references and the sign of the
potential term are corrected; the reference list is expanded | Physics Letters B 707 (2012), pp. 404-408 | 10.1016/j.physletb.2011.12.064 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we present a very simple and independent argument for the
absence of the Boulware-Deser ghost in the recently proposed potentially
ghost-free non-linear massive gravity. The limitation is that, in its simple
form, the argument is, in a sense, non-constructive and less explicit than the
standard approach. However, the formalism developed here may prove to be useful
for discussing the formal aspects of the theory.
| [
{
"created": "Fri, 9 Dec 2011 16:08:54 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Dec 2011 16:54:25 GMT",
"version": "v2"
}
] | 2012-01-11 | [
[
"Golovnev",
"Alexey",
""
]
] | In this paper we present a very simple and independent argument for the absence of the Boulware-Deser ghost in the recently proposed potentially ghost-free non-linear massive gravity. The limitation is that, in its simple form, the argument is, in a sense, non-constructive and less explicit than the standard approach. However, the formalism developed here may prove to be useful for discussing the formal aspects of the theory. |
2204.10396 | Medine Ildes | Medine Ildes and Metin Arik | Analytic Solutions of Brans-Dicke Cosmology: Early Inflation and Late
Time Accelerated Expansion | null | null | 10.1142/S0218271822501310 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate the most general exact solutions of Brans-Dicke cosmology by
choosing the scale factor "a" as the new independent variable. It is shown that
a set of three field equations can be reduced to a constraint equation and a
first order linear differential equation. Thus this new set of equations is
solvable when one supplies one of the following pairs of functions: ({\Phi}(a),
\r{ho}(a)), ({\Phi}(a), V(a)) or ({\Phi}(a), H(a)). A universe with a single
component energy-matter density is studied. It is seen that when there is no
constant energy density, the Hubble function still contains a constant term
which causes exponential expansion. This constant is expressed in terms of the
initial values of the universe. An early universe and the present universe with
dark energy are studied. In addition late time accelerated expansion is also
explained with cosmic domain walls. If we take Brans-Dicke parameter w>4*10^4
formulas of the Hubble function reduce to solutions of {\Lambda}CDM cosmology.
Therefore comparison of our results with recent observations of type Ia
supernovae indicates that eighty-nine percent of present universe may consist
of domain walls while rest is matter.
| [
{
"created": "Thu, 21 Apr 2022 20:28:42 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Jul 2022 16:36:33 GMT",
"version": "v2"
}
] | 2023-02-15 | [
[
"Ildes",
"Medine",
""
],
[
"Arik",
"Metin",
""
]
] | We investigate the most general exact solutions of Brans-Dicke cosmology by choosing the scale factor "a" as the new independent variable. It is shown that a set of three field equations can be reduced to a constraint equation and a first order linear differential equation. Thus this new set of equations is solvable when one supplies one of the following pairs of functions: ({\Phi}(a), \r{ho}(a)), ({\Phi}(a), V(a)) or ({\Phi}(a), H(a)). A universe with a single component energy-matter density is studied. It is seen that when there is no constant energy density, the Hubble function still contains a constant term which causes exponential expansion. This constant is expressed in terms of the initial values of the universe. An early universe and the present universe with dark energy are studied. In addition late time accelerated expansion is also explained with cosmic domain walls. If we take Brans-Dicke parameter w>4*10^4 formulas of the Hubble function reduce to solutions of {\Lambda}CDM cosmology. Therefore comparison of our results with recent observations of type Ia supernovae indicates that eighty-nine percent of present universe may consist of domain walls while rest is matter. |
0704.2994 | Robert Bluhm | R. Bluhm | Spontaneous Lorentz Violation, Gravity, and Nambu-Goldstone Modes | 3 pages, talk given at the 11th Marcel Grossmann Meeting, Berlin,
Germany, July 2006; typos corrected | null | 10.1142/9789812834300_0110 | null | gr-qc | null | A brief summary is presented of recent work examining the fate of the
Nambu-Goldstone modes in gravitational theories with spontaneous Lorentz
violation.
| [
{
"created": "Mon, 23 Apr 2007 12:55:01 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Apr 2008 17:39:23 GMT",
"version": "v2"
}
] | 2016-11-15 | [
[
"Bluhm",
"R.",
""
]
] | A brief summary is presented of recent work examining the fate of the Nambu-Goldstone modes in gravitational theories with spontaneous Lorentz violation. |
2205.07962 | Yijun Wang | Yijun Wang, Kris Pardo, Tzu-Ching Chang, Olivier Dor\'e | Constraining the Stochastic Gravitational Wave Background with
Photometric Surveys | 7 pages, 2 figures; updated with minor text changes | Phys. Rev. D 106, 084006 (2022) | 10.1103/PhysRevD.106.084006 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The detection of the Stochastic Gravitational Wave Background (SGWB) is
essential for understanding black hole populations, especially for supermassive
black hole binaries. The recent promising results from various Pulsar Timing
Array (PTA) collaborations allude to an imminent detection. In this paper, we
investigate the relative astrometric gravitational wave detection method, which
can contribute to SGWB studies in the microhertz range. We consider the Roman
Space Telescope and Gaia as candidates and quantitatively discuss the survey
sensitivity in both the frequency and spatial domains. We emphasize the
importance of survey specific constraints on performance estimates by
considering mean field of view (FoV) signal subtraction and angular power
spectrum binning. We conclude that if the SGWB is at a similar level as in PTA
estimates, both Roman and Gaia have the potential to detect this
frequency-domain power excess. However, both Roman and Gaia are subject to FoV
limitations, and are unlikely to be sensitive to the spatial pattern of the
SGWB.
| [
{
"created": "Mon, 16 May 2022 19:59:19 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Oct 2022 18:13:39 GMT",
"version": "v2"
}
] | 2022-10-14 | [
[
"Wang",
"Yijun",
""
],
[
"Pardo",
"Kris",
""
],
[
"Chang",
"Tzu-Ching",
""
],
[
"Doré",
"Olivier",
""
]
] | The detection of the Stochastic Gravitational Wave Background (SGWB) is essential for understanding black hole populations, especially for supermassive black hole binaries. The recent promising results from various Pulsar Timing Array (PTA) collaborations allude to an imminent detection. In this paper, we investigate the relative astrometric gravitational wave detection method, which can contribute to SGWB studies in the microhertz range. We consider the Roman Space Telescope and Gaia as candidates and quantitatively discuss the survey sensitivity in both the frequency and spatial domains. We emphasize the importance of survey specific constraints on performance estimates by considering mean field of view (FoV) signal subtraction and angular power spectrum binning. We conclude that if the SGWB is at a similar level as in PTA estimates, both Roman and Gaia have the potential to detect this frequency-domain power excess. However, both Roman and Gaia are subject to FoV limitations, and are unlikely to be sensitive to the spatial pattern of the SGWB. |
1311.6891 | Llu\'is Bel | Ll. Bel | Phantom mass gravitational effects | 5 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I derive the basic relativistic corrections to the equations of motion of
test particles and light rays in the field of a source with active mass $m$,
including the phantom mass density that any such source generates when a
modification of Newton's action at a distance includes a long range term. The
technical framework of this paper is that of Einstein's theory of gravitation
at the linear approximation with respect to the mass parameter $m$.
| [
{
"created": "Wed, 27 Nov 2013 07:54:57 GMT",
"version": "v1"
}
] | 2013-11-28 | [
[
"Bel",
"Ll.",
""
]
] | I derive the basic relativistic corrections to the equations of motion of test particles and light rays in the field of a source with active mass $m$, including the phantom mass density that any such source generates when a modification of Newton's action at a distance includes a long range term. The technical framework of this paper is that of Einstein's theory of gravitation at the linear approximation with respect to the mass parameter $m$. |
1912.11309 | Masahiko Taniguchi | Tomohiro Inagaki, Masahiko Taniguchi | Gravitational waves in Modified Gauss-Bonnet Gravity | 14 pages, 7 figures | International Journal of Modern Physics D, Vol. 29(2020) 2050072 | 10.1142/S0218271820500728 | HUPD1915 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the gravitational waves in modified Gauss-Bonnet gravity. Applying
the metric perturbation around a cosmological background, we obtain explicit
expressions for the wave equations. It is shown that the speed of the traceless
mode is equal to the speed of light. An additional massive scalar mode appears
in the propagation of the gravitational waves. To find phenomena beyond the
general relativity the scalar mode mass is calculated as a function of the
background curvature in some typical models.
| [
{
"created": "Tue, 24 Dec 2019 12:15:46 GMT",
"version": "v1"
},
{
"created": "Sun, 31 May 2020 07:17:25 GMT",
"version": "v2"
}
] | 2020-08-25 | [
[
"Inagaki",
"Tomohiro",
""
],
[
"Taniguchi",
"Masahiko",
""
]
] | We study the gravitational waves in modified Gauss-Bonnet gravity. Applying the metric perturbation around a cosmological background, we obtain explicit expressions for the wave equations. It is shown that the speed of the traceless mode is equal to the speed of light. An additional massive scalar mode appears in the propagation of the gravitational waves. To find phenomena beyond the general relativity the scalar mode mass is calculated as a function of the background curvature in some typical models. |
0809.1131 | Ahmad Sheykhi | A. Sheykhi and M. Allahverdizadeh | Higher dimensional slowly rotating dilaton black holes in AdS spacetime | 11 pages, 1 figure, the version to appear in Phys. Rev. D | Phys.Rev.D78:064073,2008 | 10.1103/PhysRevD.78.064073 | null | gr-qc | http://creativecommons.org/licenses/by/3.0/ | In this paper, with an appropriate combination of three Liouville-type
dilaton potentials, we obtain the higher dimensional charged slowly rotating
dilaton black hole solution for asymptotically anti-de Sitter spacetime. The
angular momentum and the gyromagnetic ratio of such a black hole are determined
for the arbitrary values of the dilaton coupling constant. It is shown that the
dilaton field modifies the gyromagnetic ratio of the rotating dilaton black
holes.
| [
{
"created": "Sat, 6 Sep 2008 04:35:17 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Sep 2008 05:32:10 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Sheykhi",
"A.",
""
],
[
"Allahverdizadeh",
"M.",
""
]
] | In this paper, with an appropriate combination of three Liouville-type dilaton potentials, we obtain the higher dimensional charged slowly rotating dilaton black hole solution for asymptotically anti-de Sitter spacetime. The angular momentum and the gyromagnetic ratio of such a black hole are determined for the arbitrary values of the dilaton coupling constant. It is shown that the dilaton field modifies the gyromagnetic ratio of the rotating dilaton black holes. |
1007.3304 | Jose Socorro Garcia | J. Socorro and Marco D'Oleire | Inflation from Supersymmetric Quantum Cosmology | 14 pages, latex2e, To appear in Phys. Rev. D | Phys.Rev.D82:044008,2010 | 10.1103/PhysRevD.82.044008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive a special scalar field potential using the anisotropic Bianchi type
I cosmological model from canonical quantum cosmology under determined
conditions in the evolution to anisotropic variables $\beta_\pm$. In the
process, we obtain a family of potentials that has been introduced by hand in
the literature to explain cosmological data. Considering supersymmetric quantum
cosmology, this family is scanned, fixing the exponential potential as more
viable in the inflation scenario $\rm V (\phi) = V_0 \,e^{-\sqrt{3}\phi}$.
| [
{
"created": "Mon, 19 Jul 2010 23:15:34 GMT",
"version": "v1"
}
] | 2014-11-21 | [
[
"Socorro",
"J.",
""
],
[
"D'Oleire",
"Marco",
""
]
] | We derive a special scalar field potential using the anisotropic Bianchi type I cosmological model from canonical quantum cosmology under determined conditions in the evolution to anisotropic variables $\beta_\pm$. In the process, we obtain a family of potentials that has been introduced by hand in the literature to explain cosmological data. Considering supersymmetric quantum cosmology, this family is scanned, fixing the exponential potential as more viable in the inflation scenario $\rm V (\phi) = V_0 \,e^{-\sqrt{3}\phi}$. |
1905.05216 | Steven Carlip | S. Carlip | How to Hide a Cosmological Constant | Fourth award, Gravity Research Foundation 2019 Awards for Essays on
Gravitation; based in part on arXiv:1809.08277; 5 pages | null | 10.1142/S0218271819430041 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Naive calculations in quantum field theory suggest that vacuum fluctuations
should induce an enormous cosmological constant. What if these estimates are
right? I argue that even a huge cosmological constant might be hidden in Planck
scale fluctuations of geometry and topology---what Wheeler called `spacetime
foam'---while remaining virtually invisible macroscopically.
| [
{
"created": "Mon, 13 May 2019 18:06:34 GMT",
"version": "v1"
}
] | 2020-01-08 | [
[
"Carlip",
"S.",
""
]
] | Naive calculations in quantum field theory suggest that vacuum fluctuations should induce an enormous cosmological constant. What if these estimates are right? I argue that even a huge cosmological constant might be hidden in Planck scale fluctuations of geometry and topology---what Wheeler called `spacetime foam'---while remaining virtually invisible macroscopically. |
2302.14333 | Subenoy Chakraborty | Roshni Bhaumik, Sourav Dutta, and Subenoy Chakraborty | Noether Symmetry analysis in Chameleon Field Cosmology | 19 pages, 4 figures | null | 10.1142/S0217751X2250018X | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | This work deals with chameleon field cosmology (a scalar field nonminimally
coupled to cold dark matter) in the background of flat
Friedmann-Lemaitre-Robertson-Walker (FLRW) space-time. Both classical and
quantum cosmology have been investigated using Noether symmetry analysis of the
underlying physical system. The Wheeler-DeWitt (WD) equation has been
constructed on the minisuperspace and solutions have been obtained using
conserved charge.
| [
{
"created": "Tue, 28 Feb 2023 06:02:30 GMT",
"version": "v1"
}
] | 2023-03-01 | [
[
"Bhaumik",
"Roshni",
""
],
[
"Dutta",
"Sourav",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | This work deals with chameleon field cosmology (a scalar field nonminimally coupled to cold dark matter) in the background of flat Friedmann-Lemaitre-Robertson-Walker (FLRW) space-time. Both classical and quantum cosmology have been investigated using Noether symmetry analysis of the underlying physical system. The Wheeler-DeWitt (WD) equation has been constructed on the minisuperspace and solutions have been obtained using conserved charge. |
gr-qc/0408069 | Daniel Barraco | A. E. Dominguez and D. E. Barraco | Newtonian limit of the singular f(R) gravity in the Palatini formalism | 9 pages | Phys.Rev. D70 (2004) 043505 | 10.1103/PhysRevD.70.043505 | null | gr-qc astro-ph hep-th | null | Recently D. Vollick [Phys. Rev. D68, 063510 (2003)] has shown that the
inclusion of the 1/R curvature terms in the gravitational action and the use of
the Palatini formalism offer an alternative explanation for cosmological
acceleration. In this work we show not only that this model of Vollick does not
have a good Newtonian limit, but also that any f(R) theory with a pole of order
n in R=0 and its second derivative respect to R evaluated at Ro is not zero,
where Ro is the scalar curvature of background, does not have a good Newtonian
limit.
| [
{
"created": "Thu, 19 Aug 2004 21:56:03 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Dominguez",
"A. E.",
""
],
[
"Barraco",
"D. E.",
""
]
] | Recently D. Vollick [Phys. Rev. D68, 063510 (2003)] has shown that the inclusion of the 1/R curvature terms in the gravitational action and the use of the Palatini formalism offer an alternative explanation for cosmological acceleration. In this work we show not only that this model of Vollick does not have a good Newtonian limit, but also that any f(R) theory with a pole of order n in R=0 and its second derivative respect to R evaluated at Ro is not zero, where Ro is the scalar curvature of background, does not have a good Newtonian limit. |
gr-qc/0209097 | Osvaldo M. Moreschi | Osvaldo M. Moreschi | Intrinsic angular momentum in general relativity | 4 pages, 2 figures | Class.Quant.Grav. 21 (2004) 5409-5426 | 10.1088/0264-9381/21/23/008 | null | gr-qc | null | There are several definitions of the notion of angular momentum in general
relativity. However non of them can be said to capture the physical notion of
intrinsic angular momentum of the sources in the presence of gravitational
radiation. We present a definition which is appropriate for the description of
intrinsic angular momentum in radiative spacetimes. This notion is required in
calculations involving radiation of angular momentum, as for example is
expected in binary coalescence of black holes.
| [
{
"created": "Wed, 25 Sep 2002 19:09:05 GMT",
"version": "v1"
},
{
"created": "Fri, 2 May 2003 17:47:55 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Moreschi",
"Osvaldo M.",
""
]
] | There are several definitions of the notion of angular momentum in general relativity. However non of them can be said to capture the physical notion of intrinsic angular momentum of the sources in the presence of gravitational radiation. We present a definition which is appropriate for the description of intrinsic angular momentum in radiative spacetimes. This notion is required in calculations involving radiation of angular momentum, as for example is expected in binary coalescence of black holes. |
1511.02019 | Titus K Mathew | Paxy George and Titus K Mathew | Holographic Ricci dark energy as running vacuum | 10 pages | null | 10.1142/S0217732316500759 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Holographic Ricci dark energy has been proposed ago has faced with problems
of future singularity. In the present work we consider the Ricci dark energy
with an additive constant in it's density as running vacuum energy. We have
analytically solved the Friedmann equations and also the role played by the
general conservation law followed by the cosmic components together. We have
shown that the running vacuum energy status of the Ricci dark energy helps to
remove the possible future singularity in the model. The additive constant in
the density of the running vacuum played an important role, such that, without
that, the model predicts either eternal deceleration or eternal acceleration.
But along with the additive constant, equivalent to a cosmological constant,
the model predicts a late time acceleration in the expansion of the universe,
and in the far future of the evolution it tends to de Sitter universe.
| [
{
"created": "Fri, 6 Nov 2015 10:09:29 GMT",
"version": "v1"
}
] | 2016-05-25 | [
[
"George",
"Paxy",
""
],
[
"Mathew",
"Titus K",
""
]
] | Holographic Ricci dark energy has been proposed ago has faced with problems of future singularity. In the present work we consider the Ricci dark energy with an additive constant in it's density as running vacuum energy. We have analytically solved the Friedmann equations and also the role played by the general conservation law followed by the cosmic components together. We have shown that the running vacuum energy status of the Ricci dark energy helps to remove the possible future singularity in the model. The additive constant in the density of the running vacuum played an important role, such that, without that, the model predicts either eternal deceleration or eternal acceleration. But along with the additive constant, equivalent to a cosmological constant, the model predicts a late time acceleration in the expansion of the universe, and in the far future of the evolution it tends to de Sitter universe. |
2108.12670 | Bikram Ghosh | Bikram Ghosh and Saugata Mitra | Wormhole solutions in $f(R)$ gravity theory for Chaplygin gas scenario | null | Int.J.Mod.Phys.A 36 (2021) 18, 2150119 | 10.1142/S0217751X21501190 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present paper deals with some wormhole solutions which are obtained by
taking two different shape functions along with zero tidal force. For obtaining
wormhole solutions, anisotropic fluid and a equation of state
$p_t=-\frac{a}{\rho}$ related by Chaplygin gas are considered where $\rho$ is
the energy density, $p_t$ is tangential pressure and $a$ is positive constant.
Energy conditions are examined for two different models, and it is found that a
major energy conditions are satisfied in a region.
| [
{
"created": "Sat, 28 Aug 2021 16:07:00 GMT",
"version": "v1"
}
] | 2021-08-31 | [
[
"Ghosh",
"Bikram",
""
],
[
"Mitra",
"Saugata",
""
]
] | The present paper deals with some wormhole solutions which are obtained by taking two different shape functions along with zero tidal force. For obtaining wormhole solutions, anisotropic fluid and a equation of state $p_t=-\frac{a}{\rho}$ related by Chaplygin gas are considered where $\rho$ is the energy density, $p_t$ is tangential pressure and $a$ is positive constant. Energy conditions are examined for two different models, and it is found that a major energy conditions are satisfied in a region. |
1912.04636 | Mohammad Ali Gorji | Mohammad Ali Gorji, Alireza Allahyari, Mohsen Khodadi, Hassan
Firouzjahi | Mimetic Black Holes | 26 pages, 4 figures, matches published version | Phys. Rev. D 101, 124060 (2020) | 10.1103/PhysRevD.101.124060 | YITP-20-20 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we look for the vacuum static spherically symmetric solution
in the mimetic gravity scenario based on the conformal invariance principle.
The trivial solution is a stealth Schwarzschild black hole with scalar hair
where the mimetic field does not contribute to the background. However, a
solution with two naked singularities shows up when the mimetic scalar field
contributes to the background. We show that one of these singularities is the
same as the singularity at the center of standard Schwarzschild black hole
while the other appears due to caustics formation. However, we construct the
mimetic black hole solution by gluing the exterior static spherically symmetric
solution to a time-dependent anisotropic spacetime describing the interior of
the black hole. It is shown that these two solutions match continuously on the
surface of the apparent horizon. Some physical properties of the corresponding
mimetic black holes are discussed.
| [
{
"created": "Tue, 10 Dec 2019 10:53:24 GMT",
"version": "v1"
},
{
"created": "Fri, 13 Mar 2020 15:19:17 GMT",
"version": "v2"
},
{
"created": "Tue, 16 Jun 2020 10:53:58 GMT",
"version": "v3"
}
] | 2020-07-08 | [
[
"Gorji",
"Mohammad Ali",
""
],
[
"Allahyari",
"Alireza",
""
],
[
"Khodadi",
"Mohsen",
""
],
[
"Firouzjahi",
"Hassan",
""
]
] | In this paper, we look for the vacuum static spherically symmetric solution in the mimetic gravity scenario based on the conformal invariance principle. The trivial solution is a stealth Schwarzschild black hole with scalar hair where the mimetic field does not contribute to the background. However, a solution with two naked singularities shows up when the mimetic scalar field contributes to the background. We show that one of these singularities is the same as the singularity at the center of standard Schwarzschild black hole while the other appears due to caustics formation. However, we construct the mimetic black hole solution by gluing the exterior static spherically symmetric solution to a time-dependent anisotropic spacetime describing the interior of the black hole. It is shown that these two solutions match continuously on the surface of the apparent horizon. Some physical properties of the corresponding mimetic black holes are discussed. |
gr-qc/0512158 | Orfeu Bertolami | M.C. Bento, O. Bertolami, M.J. Rebou\c{c}as, P.T. Silva | Generalized Chaplygin gas model, supernovae and cosmic topology | Revtex 4, 8 pages, 10 figures, 1 table; version to match the
published one | Phys.Rev.D73:043504,2006 | 10.1103/PhysRevD.73.043504 | null | gr-qc astro-ph hep-ph hep-th | null | In this work we study to which extent the knowledge of spatial topology may
place constraints on the parameters of the generalized Chaplygin gas (GCG)
model for unification of dark energy and dark matter. By using both the
Poincar\'e dodecahedral and binary octahedral spaces as the observable spatial
topologies, we examine the current type Ia supernovae (SNe Ia) constraints on
the GCG model parameters. We show that the knowledge of spatial topology does
provide additional constraints on the $A_s$ parameter of the GCG model but does
not lift the degeneracy of the $\alpha$ parameter.
| [
{
"created": "Wed, 28 Dec 2005 12:14:21 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Apr 2006 10:58:19 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Bento",
"M. C.",
""
],
[
"Bertolami",
"O.",
""
],
[
"Rebouças",
"M. J.",
""
],
[
"Silva",
"P. T.",
""
]
] | In this work we study to which extent the knowledge of spatial topology may place constraints on the parameters of the generalized Chaplygin gas (GCG) model for unification of dark energy and dark matter. By using both the Poincar\'e dodecahedral and binary octahedral spaces as the observable spatial topologies, we examine the current type Ia supernovae (SNe Ia) constraints on the GCG model parameters. We show that the knowledge of spatial topology does provide additional constraints on the $A_s$ parameter of the GCG model but does not lift the degeneracy of the $\alpha$ parameter. |
1311.2874 | Zeeshan Yousaf | M. Sharif and Z. Yousaf | Expansion-free Cylindrically Symmetric Models | 16 pages | Can. J. Phys. 90(2012)865 | 10.1139/p2012-070 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper investigates cylindrically symmetric distribution of an-isotropic
fluid under the expansion-free condition, which requires the existence of
vacuum cavity within the fluid distribution. We have discussed two family of
solutions which further provide two exact models in each family. Some of these
solutions satisfy Darmois junction condition while some show the presence of
thin shell on both boundary surfaces. We also formulate a relation between the
Weyl tensor and energy density.
| [
{
"created": "Wed, 30 Oct 2013 14:59:14 GMT",
"version": "v1"
}
] | 2013-11-13 | [
[
"Sharif",
"M.",
""
],
[
"Yousaf",
"Z.",
""
]
] | This paper investigates cylindrically symmetric distribution of an-isotropic fluid under the expansion-free condition, which requires the existence of vacuum cavity within the fluid distribution. We have discussed two family of solutions which further provide two exact models in each family. Some of these solutions satisfy Darmois junction condition while some show the presence of thin shell on both boundary surfaces. We also formulate a relation between the Weyl tensor and energy density. |
1503.01487 | Dejan Stojkovic | Anshul Saini and Dejan Stojkovic | Radiation from a collapsing object is manifestly unitary | typos corrected, difference between various frequencies (\omega_0,
\bar{\omega}, \Omega) explained, plots updated, discussion expanded | Phys.Rev.Lett. 114 (2015) 11, 111301 | 10.1103/PhysRevLett.114.111301 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The process of gravitational collapse excites the fields propagating in the
background geometry and gives rise to thermal radiation. We demonstrate by
explicit calculations that the density matrix corresponding to such radiation
actually describes a pure state. While Hawking's leading order density matrix
contains only the diagonal terms, we calculate the off-diagonal correlation
terms. These correlations start very small, but then grow in time. The
cumulative effect is that the correlations become comparable to the leading
order terms and significantly modify the density matrix. While the trace of the
Hawking's density matrix squared diverges from unity during the evolution, the
trace of the total density matrix squared remains unity at all times and all
frequencies. This implies that the process of radiation from a collapsing
object is unitary.
| [
{
"created": "Wed, 4 Mar 2015 22:34:58 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Mar 2015 00:05:00 GMT",
"version": "v2"
},
{
"created": "Wed, 8 Apr 2015 03:00:42 GMT",
"version": "v3"
},
{
"created": "Mon, 28 Sep 2015 22:33:28 GMT",
"version": "v4"
}
] | 2015-09-30 | [
[
"Saini",
"Anshul",
""
],
[
"Stojkovic",
"Dejan",
""
]
] | The process of gravitational collapse excites the fields propagating in the background geometry and gives rise to thermal radiation. We demonstrate by explicit calculations that the density matrix corresponding to such radiation actually describes a pure state. While Hawking's leading order density matrix contains only the diagonal terms, we calculate the off-diagonal correlation terms. These correlations start very small, but then grow in time. The cumulative effect is that the correlations become comparable to the leading order terms and significantly modify the density matrix. While the trace of the Hawking's density matrix squared diverges from unity during the evolution, the trace of the total density matrix squared remains unity at all times and all frequencies. This implies that the process of radiation from a collapsing object is unitary. |
1708.07694 | Kirill Krasnov | Kirill Krasnov | Field redefinitions and Plebanski formalism for GR | 15 pages, no figures | null | 10.1088/1361-6382/aac844 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We point out that there exists a family of transformations acting on BF-type
Lagrangians of gravity, with Lagrangians related by such a transformation
corresponding to classically equivalent theories. A transformation of this type
corresponds to a particular field redefinition. We discuss both the chiral and
non-chiral cases. In the chiral case there is a one-parameter, and in the
non-chiral case a two-parameter family of such transformations. In the chiral
setup, we use these transformations to give an alternative derivation of the
chiral BF plus potential formulation of General Relativity that was proposed
recently. In the non-chiral case, we show that there is a new BF plus potential
type formulation of GR. We also make some remarks on the non-chiral pure
connection formulation.
| [
{
"created": "Fri, 25 Aug 2017 11:35:18 GMT",
"version": "v1"
}
] | 2018-07-11 | [
[
"Krasnov",
"Kirill",
""
]
] | We point out that there exists a family of transformations acting on BF-type Lagrangians of gravity, with Lagrangians related by such a transformation corresponding to classically equivalent theories. A transformation of this type corresponds to a particular field redefinition. We discuss both the chiral and non-chiral cases. In the chiral case there is a one-parameter, and in the non-chiral case a two-parameter family of such transformations. In the chiral setup, we use these transformations to give an alternative derivation of the chiral BF plus potential formulation of General Relativity that was proposed recently. In the non-chiral case, we show that there is a new BF plus potential type formulation of GR. We also make some remarks on the non-chiral pure connection formulation. |
2408.04672 | Jo\~ao Pedro Da Cruz Bravo Ferreira | Jo\~ao Pedro Bravo | f(R) Gravitation: Equivalence of Frames Upon a Conformal Transformation | 78 pages, 18 figures, MSc thesis, supervisors: Sergio E. Jor\'{a}s,
Ribamar R. R. Reis | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate the behavior of the Ricci scalar in the Jordan (JF) and
Einstein (EF) frames, in the context of f(R) gravitation. We discuss the
physical equivalence of these two representations of the theory, which are
mathematically equivalent and whose metrics are connected by a conformal
transformation. We find that it is possible for this quantity to be singular in
the JF but finite in the EF, if the conformal transformation that connects the
frames is singular at the same point as the JF Ricci scalar. The absence of
this physical singularity in the EF could be used as an argument against the
physical equivalence of the frames. A plot of the EF potential as a function of
the associated conformal field shows that the absence of the singularity allows
the field to assume values associated to arbitrarily large values of the Ricci
curvature. A conjecture is then proposed: the dynamics of the conformal field
can be interpreted as a mechanism that can prevent the creation of
singularities in the JF.
| [
{
"created": "Wed, 7 Aug 2024 15:16:10 GMT",
"version": "v1"
}
] | 2024-08-12 | [
[
"Bravo",
"João Pedro",
""
]
] | We investigate the behavior of the Ricci scalar in the Jordan (JF) and Einstein (EF) frames, in the context of f(R) gravitation. We discuss the physical equivalence of these two representations of the theory, which are mathematically equivalent and whose metrics are connected by a conformal transformation. We find that it is possible for this quantity to be singular in the JF but finite in the EF, if the conformal transformation that connects the frames is singular at the same point as the JF Ricci scalar. The absence of this physical singularity in the EF could be used as an argument against the physical equivalence of the frames. A plot of the EF potential as a function of the associated conformal field shows that the absence of the singularity allows the field to assume values associated to arbitrarily large values of the Ricci curvature. A conjecture is then proposed: the dynamics of the conformal field can be interpreted as a mechanism that can prevent the creation of singularities in the JF. |
gr-qc/9907052 | M. B. Golubev | M.B.Golubev | Gravity Role in Classical Electrodynamics of Charged Point Source | 10 Russian Gravitational Conference, Report, 6 pages, LATEX | null | null | null | gr-qc | null | This paper deals with the problem of a point-like charged source under the
influence of the external electromagnetic field in terms of perturbation theory
for GR equations. It is obtained that GR, in contrast with the classical
electrodynamics, in linear perturbation theory predicts an unlimited growth of
the dipole perturbation. It is shown that the reason for this unlimited
perturbation growth might be related to the presence of the unstable rotational
perturbation mode. The analysis of the conditions under which this instability
may disappear is performed. The momentum value at which the stability is
reached is estimated. These estimations give the electron spin by the order of
magnitude (when charge value is equal to elementary one).
| [
{
"created": "Wed, 14 Jul 1999 11:33:55 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Golubev",
"M. B.",
""
]
] | This paper deals with the problem of a point-like charged source under the influence of the external electromagnetic field in terms of perturbation theory for GR equations. It is obtained that GR, in contrast with the classical electrodynamics, in linear perturbation theory predicts an unlimited growth of the dipole perturbation. It is shown that the reason for this unlimited perturbation growth might be related to the presence of the unstable rotational perturbation mode. The analysis of the conditions under which this instability may disappear is performed. The momentum value at which the stability is reached is estimated. These estimations give the electron spin by the order of magnitude (when charge value is equal to elementary one). |
gr-qc/0405077 | Thomas W. Baumgarte | Thomas W. Baumgarte, Monica L. Skoge and Stuart L. Shapiro | Black Hole-Neutron Star Binaries in General Relativity: Quasiequilibrium
Formulation | 17 pages, 7 figures; added discussion, tables; PRD in press | Phys.Rev. D70 (2004) 064040 | 10.1103/PhysRevD.70.064040 | null | gr-qc astro-ph | null | We present a new numerical method for the construction of quasiequilibrium
models of black hole-neutron star binaries. We solve the constraint equations
of general relativity, decomposed in the conformal thin-sandwich formalism,
together with the Euler equation for the neutron star matter. We take the
system to be stationary in a corotating frame and thereby assume the presence
of a helical Killing vector. We solve these coupled equations in the background
metric of a Kerr-Schild black hole, which accounts for the neutron star's black
hole companion. In this paper we adopt a polytropic equation of state for the
neutron star matter and assume large black hole--to--neutron star mass ratios.
These simplifications allow us to focus on the construction of quasiequilibrium
neutron star models in the presence of strong-field, black hole companions. We
summarize the results of several code tests, compare with Newtonian models, and
locate the onset of tidal disruption in a fully relativistic framework.
| [
{
"created": "Fri, 14 May 2004 20:00:39 GMT",
"version": "v1"
},
{
"created": "Tue, 20 Jul 2004 19:27:18 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Baumgarte",
"Thomas W.",
""
],
[
"Skoge",
"Monica L.",
""
],
[
"Shapiro",
"Stuart L.",
""
]
] | We present a new numerical method for the construction of quasiequilibrium models of black hole-neutron star binaries. We solve the constraint equations of general relativity, decomposed in the conformal thin-sandwich formalism, together with the Euler equation for the neutron star matter. We take the system to be stationary in a corotating frame and thereby assume the presence of a helical Killing vector. We solve these coupled equations in the background metric of a Kerr-Schild black hole, which accounts for the neutron star's black hole companion. In this paper we adopt a polytropic equation of state for the neutron star matter and assume large black hole--to--neutron star mass ratios. These simplifications allow us to focus on the construction of quasiequilibrium neutron star models in the presence of strong-field, black hole companions. We summarize the results of several code tests, compare with Newtonian models, and locate the onset of tidal disruption in a fully relativistic framework. |
1610.06690 | Sousuke Noda | Sousuke Noda, Yasusada Nambu, Masaaki Takahashi | Analog rotating black holes in a magnetohydrodynamic inflow | 17 pages, 5 figures, final version to match the published version | Phys. Rev. D 95, 104055 (2017) | 10.1103/PhysRevD.95.104055 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a model of the analog geometry in a magnetohydrodynamic (MHD)
flow. For the MHD flow with magnetic pressure-dominated and gas
pressure-dominated conditions, we obtain the magnetoacoustic metric for the
fast MHD mode. For the slow MHD mode, on the other hand, the wave is governed
by the advective-type equation without an isotropic dispersion term. Thus, the
"distance" perpendicular to the wave propagation is not defined and the
magnetoacoustic metric cannot be introduced. To investigate the properties of
the magnetoacoustic geometry for the fast mode, we prepare a two-dimensional
axisymmetric inflow and examine the behavior of magnetoacoustic rays which is a
counterpart of the MHD waves in the eikonal limit. We find that the
magnetoacoustic geometry is classified into three types depending on two
parameters characterizing the background flow:~analog spacetimes of rotating
black holes, ultra spinning stars with ergoregions, and spinning stars without
ergoregions. We address the effects of the magnetic pressure on the effective
geometries.
| [
{
"created": "Fri, 21 Oct 2016 07:39:14 GMT",
"version": "v1"
},
{
"created": "Mon, 31 Oct 2016 01:33:48 GMT",
"version": "v2"
},
{
"created": "Wed, 1 Mar 2017 07:22:26 GMT",
"version": "v3"
},
{
"created": "Tue, 6 Jun 2017 23:34:30 GMT",
"version": "v4"
}
] | 2017-06-08 | [
[
"Noda",
"Sousuke",
""
],
[
"Nambu",
"Yasusada",
""
],
[
"Takahashi",
"Masaaki",
""
]
] | We present a model of the analog geometry in a magnetohydrodynamic (MHD) flow. For the MHD flow with magnetic pressure-dominated and gas pressure-dominated conditions, we obtain the magnetoacoustic metric for the fast MHD mode. For the slow MHD mode, on the other hand, the wave is governed by the advective-type equation without an isotropic dispersion term. Thus, the "distance" perpendicular to the wave propagation is not defined and the magnetoacoustic metric cannot be introduced. To investigate the properties of the magnetoacoustic geometry for the fast mode, we prepare a two-dimensional axisymmetric inflow and examine the behavior of magnetoacoustic rays which is a counterpart of the MHD waves in the eikonal limit. We find that the magnetoacoustic geometry is classified into three types depending on two parameters characterizing the background flow:~analog spacetimes of rotating black holes, ultra spinning stars with ergoregions, and spinning stars without ergoregions. We address the effects of the magnetic pressure on the effective geometries. |
gr-qc/0007010 | Peter Dunsby | Stacey Hobbs and Peter K. S. Dunsby | Dynamical Systems Approach to Magnetised Cosmological Perturbations | 15 pages RevTeX, 5 figures. Accepted for publication in Physical
Review D | Phys.Rev. D62 (2000) 124007 | 10.1103/PhysRevD.62.124007 | uct-cosmology-00/05 | gr-qc astro-ph | null | Assuming a large-scale homogeneous magnetic field, we follow the covariant
and gauge-invariant approach used by Tsagas and Barrow to describe the
evolution of density and magnetic field inhomogeneities and curvature
perturbations in a matter-radiation universe. We use a two parameter
approximation scheme to linearize their exact non-linear general-relativistic
equations for magneto-hydrodynamic evolution. Using a two-fluid approach we set
up the governing equations as a fourth order autonomous dynamical system.
Analysis of the equilibrium points for the radiation dominated era lead to
solutions similar to the super-horizon modes found analytically by Tsagas and
Maartens. We find that a study of the dynamical system in the dust-dominated
era leads naturally to a magnetic critical length scale closely related to the
Jeans Length. Depending on the size of wavelengths relative to this scale,
these solutions show three distinct behaviours: large-scale stable growing
modes, intermediate decaying modes, and small-scale damped oscillatory
solutions.
| [
{
"created": "Fri, 7 Jul 2000 19:01:39 GMT",
"version": "v1"
},
{
"created": "Fri, 18 Aug 2000 14:59:39 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Hobbs",
"Stacey",
""
],
[
"Dunsby",
"Peter K. S.",
""
]
] | Assuming a large-scale homogeneous magnetic field, we follow the covariant and gauge-invariant approach used by Tsagas and Barrow to describe the evolution of density and magnetic field inhomogeneities and curvature perturbations in a matter-radiation universe. We use a two parameter approximation scheme to linearize their exact non-linear general-relativistic equations for magneto-hydrodynamic evolution. Using a two-fluid approach we set up the governing equations as a fourth order autonomous dynamical system. Analysis of the equilibrium points for the radiation dominated era lead to solutions similar to the super-horizon modes found analytically by Tsagas and Maartens. We find that a study of the dynamical system in the dust-dominated era leads naturally to a magnetic critical length scale closely related to the Jeans Length. Depending on the size of wavelengths relative to this scale, these solutions show three distinct behaviours: large-scale stable growing modes, intermediate decaying modes, and small-scale damped oscillatory solutions. |
1509.07976 | Shahram Jalalzadeh | M. Hashemi, S. Jalalzadeh and S. Vasheghani Farahani | The laws of thermodynamics and information for emergent cosmology | 10 pages, no figures, to appear in Gen. Rel. Grav | null | 10.1007/s10714-015-1971-8 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The aim here is to provide a set of equations for cosmology in terms of
information and thermodynamical parameters. The method we implement in order to
describe the universe is a development of Padmanabhan\rq{}s approach which is
based on the fact that emergence of the cosmic space is provided by the
evolution of the cosmic time. In this line we obtain the Friedmann equation or
its equivalent the conservation law in terms of information by the
implementation of Laundauer\rq{}s principle or in other words the information
loss/production rate. Hence, a self consistent description of the universe is
provided in terms of thermodynamical parameters. This is due to the fact that
in this work the role of information which is the most important actor of all
times, has stepped in to cosmology. We provide a picture of the emergent
cosmology merely based on the information theory. In addition, we introduce a
novel entropy on the horizon, which can also generalize Bekenstein-Hawking
entropy for the asymptotic holographic principle.
| [
{
"created": "Sat, 26 Sep 2015 13:25:31 GMT",
"version": "v1"
}
] | 2015-11-04 | [
[
"Hashemi",
"M.",
""
],
[
"Jalalzadeh",
"S.",
""
],
[
"Farahani",
"S. Vasheghani",
""
]
] | The aim here is to provide a set of equations for cosmology in terms of information and thermodynamical parameters. The method we implement in order to describe the universe is a development of Padmanabhan\rq{}s approach which is based on the fact that emergence of the cosmic space is provided by the evolution of the cosmic time. In this line we obtain the Friedmann equation or its equivalent the conservation law in terms of information by the implementation of Laundauer\rq{}s principle or in other words the information loss/production rate. Hence, a self consistent description of the universe is provided in terms of thermodynamical parameters. This is due to the fact that in this work the role of information which is the most important actor of all times, has stepped in to cosmology. We provide a picture of the emergent cosmology merely based on the information theory. In addition, we introduce a novel entropy on the horizon, which can also generalize Bekenstein-Hawking entropy for the asymptotic holographic principle. |
1609.06944 | Tao Jun | Xiaobo Guo, Bochen Lv, Jun Tao, Peng Wang | Quantum Tunneling In Deformed Quantum Mechanics with Minimal Length | 16 pages, 5 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the deformed quantum mechanics with a minimal length, one WKB connection
formula through a turning point is derived. We then use it to calculate
tunnelling rates through potential barriers under the WKB approximation.
Finally, the minimal length effects on two examples of quantum tunneling in
nuclear and atomic physics are discussed
| [
{
"created": "Thu, 22 Sep 2016 12:45:47 GMT",
"version": "v1"
}
] | 2016-09-23 | [
[
"Guo",
"Xiaobo",
""
],
[
"Lv",
"Bochen",
""
],
[
"Tao",
"Jun",
""
],
[
"Wang",
"Peng",
""
]
] | In the deformed quantum mechanics with a minimal length, one WKB connection formula through a turning point is derived. We then use it to calculate tunnelling rates through potential barriers under the WKB approximation. Finally, the minimal length effects on two examples of quantum tunneling in nuclear and atomic physics are discussed |
1703.06433 | Rafael A. Porto | Rafael A. Porto and Ira Z. Rothstein | On the Apparent Ambiguities in the Post-Newtonian Expansion for Binary
Systems | 12 pages. 1 figure. To appear in Phys. Rev. D | Phys. Rev. D 96, 024062 (2017) | 10.1103/PhysRevD.96.024062 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the source of the apparent ambiguities arising in the calculation
of the dynamics of binary black holes within the Post-Newtonian framework.
Divergences appear in both the near and far zone calculations, and may be of
either ultraviolet (UV) or infrared (IR) nature. The effective field theory
(EFT) formalism elucidates the origin of the singularities which may introduce
apparent ambiguities. In particular, the only (physical) 'ambiguity parameters'
that necessitate a matching calculation correspond to unknown finite size
effects, which first appear at fifth Post-Newtonian (5PN) order for
non-spinning bodies. We demonstrate that the ambiguities linked to IR
divergences in the near zone, that plague the recent derivations of the binding
energy at 4PN order, both in the ADM and 'Fokker-action' approach, can be
resolved by implementing the so-called 'zero-bin' subtraction in the EFT
framework. The procedure yields ambiguity-free results without the need of
additional information beyond the PN expansion.
| [
{
"created": "Sun, 19 Mar 2017 13:19:59 GMT",
"version": "v1"
},
{
"created": "Sun, 30 Jul 2017 14:52:53 GMT",
"version": "v2"
}
] | 2017-08-09 | [
[
"Porto",
"Rafael A.",
""
],
[
"Rothstein",
"Ira Z.",
""
]
] | We discuss the source of the apparent ambiguities arising in the calculation of the dynamics of binary black holes within the Post-Newtonian framework. Divergences appear in both the near and far zone calculations, and may be of either ultraviolet (UV) or infrared (IR) nature. The effective field theory (EFT) formalism elucidates the origin of the singularities which may introduce apparent ambiguities. In particular, the only (physical) 'ambiguity parameters' that necessitate a matching calculation correspond to unknown finite size effects, which first appear at fifth Post-Newtonian (5PN) order for non-spinning bodies. We demonstrate that the ambiguities linked to IR divergences in the near zone, that plague the recent derivations of the binding energy at 4PN order, both in the ADM and 'Fokker-action' approach, can be resolved by implementing the so-called 'zero-bin' subtraction in the EFT framework. The procedure yields ambiguity-free results without the need of additional information beyond the PN expansion. |
gr-qc/0012092 | Angelo Tartaglia | A. Tartaglia (Dip. Fisica, Politecnico, Torino and INFN Torino, Italy) | Gravitomagnetism, clocks and geometry | TCI Latex, 12 pages, 2 figures. To appear in European Journal of
Physics | null | 10.1088/0143-0807/22/2/301 | null | gr-qc | null | New techniques to evaluate the clock effect using light are described. These
are based on the flatness of the cylindrical surface containing the world lines
of the rays constrained to move on circular trajectories about a spinning mass.
The effect of the angular momentum of the source is manifested in the fact that
inertial observers must be replaced by local non rotating observers. Starting
from this an exact formula for circular trajectories is found. Numerical
estimates for the Earth environment show that light would be a better probe
than actual clocks to evidence the angular momentum influence. The advantages
of light in connection with some principle experiments are shortly reviewed.
| [
{
"created": "Fri, 22 Dec 2000 14:41:31 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Tartaglia",
"A.",
"",
"Dip. Fisica, Politecnico, Torino and INFN Torino, Italy"
]
] | New techniques to evaluate the clock effect using light are described. These are based on the flatness of the cylindrical surface containing the world lines of the rays constrained to move on circular trajectories about a spinning mass. The effect of the angular momentum of the source is manifested in the fact that inertial observers must be replaced by local non rotating observers. Starting from this an exact formula for circular trajectories is found. Numerical estimates for the Earth environment show that light would be a better probe than actual clocks to evidence the angular momentum influence. The advantages of light in connection with some principle experiments are shortly reviewed. |
gr-qc/9710051 | Robert Jantzen | Robert T Jantzen, Donato Bini, Paolo Carini | The Inertial Forces / Test Particle Motion Game | References corrected and updated, one equation (9) corrected, 22
pages, latex, 3 included pictex figures, needs World Scientific proceedings
style file mprocl.sty, and prepictex.tex, pictex.tex, postpictex.tex (all
available at http://xxx.lanl.gov), to appear in the Proceedings of the Eighth
Marcel Grossmann Meeting on General Relativity (Tsvi Piran, Ed.), World
Scientific, 1998 | Proceedings of the Eighth Marcel Grossmann Meeting on General
Relativity, Tsvi Piran, Editor, World Scientific, Singapore, 1998, Vol. A,
pp. 376-397 | null | null | gr-qc | null | The somewhat fragmented body of current literature analyzing the properties
of test particle motion in static and stationary spacetimes and in general
spacetimes is pulled together and clarified using the framework of
gravitoelectromagnetism.
| [
{
"created": "Wed, 8 Oct 1997 16:10:35 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Aug 1998 19:39:18 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Jantzen",
"Robert T",
""
],
[
"Bini",
"Donato",
""
],
[
"Carini",
"Paolo",
""
]
] | The somewhat fragmented body of current literature analyzing the properties of test particle motion in static and stationary spacetimes and in general spacetimes is pulled together and clarified using the framework of gravitoelectromagnetism. |
1208.1523 | Lorenzo Iorio | Lorenzo Iorio | Local cosmological effects of the order of H in the orbital motion of a
binary system | LaTex, 8 pages, no figures, 4 tables. Version matching the one at
press in Monthly Notices of the Royal Astronomical Society (MNRAS) | Mon.Not.Roy.Astron.Soc.429:915-922,2013 | 10.1093/mnras/sts396 | null | gr-qc astro-ph.CO astro-ph.EP physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A two-body system hypothetically affected by an additional radial
acceleration H v_r, where v_r is the radial velocity of the binary's proper
orbital motion, would experience long-term temporal changes of both its
semimajor axis a and the eccentricity e qualitatively different from any other
standard competing effect for them. Contrary to what one might reasonably
expect, the analytical expressions of such rates do not vanish in the limit
M--> 0, where M is the mass of the primary, being independent of it. This is a
general requirement that any potentially viable physical mechanism able to
provide such a putative acceleration should meet. Nonetheless, if H had the
same value H_0 of the Hubble parameter at present epoch, such rates of change
would have magnitude close to the present-day level of accuracy in determining
planetary orbital motions in our Solar System. A tension with recent
observations may even be present for Mercury and Mars. However, general
relativity, applied to a localized gravitationally bound binary system immersed
in an expanding Friedmann-Lemaitre-Robertson-Walker, does not predict the
existence of such a putative radial acceleration at Newtonian level. Instead,
it was recently shown in literature that an acceleration of order H and
directed along the velocity v of the test particle occurs at post-Newtonian
level. We worked out its orbital effects finding well-behaved secular rates of
change for both a and e proportional to the Schwarzschild radius r_s of the
primary. Their magnitude is quite small: the rate of change of a amounts to
just 20 microns per century in our Solar System. Finally, we discussed certain
basic criteria of viability that modified models of gravity should generally
meet when their observable effects are calculated.
| [
{
"created": "Tue, 7 Aug 2012 20:53:33 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Aug 2012 13:32:16 GMT",
"version": "v2"
},
{
"created": "Mon, 12 Nov 2012 14:21:30 GMT",
"version": "v3"
},
{
"created": "Wed, 28 Nov 2012 15:51:00 GMT",
"version": "v4"
}
] | 2013-01-15 | [
[
"Iorio",
"Lorenzo",
""
]
] | A two-body system hypothetically affected by an additional radial acceleration H v_r, where v_r is the radial velocity of the binary's proper orbital motion, would experience long-term temporal changes of both its semimajor axis a and the eccentricity e qualitatively different from any other standard competing effect for them. Contrary to what one might reasonably expect, the analytical expressions of such rates do not vanish in the limit M--> 0, where M is the mass of the primary, being independent of it. This is a general requirement that any potentially viable physical mechanism able to provide such a putative acceleration should meet. Nonetheless, if H had the same value H_0 of the Hubble parameter at present epoch, such rates of change would have magnitude close to the present-day level of accuracy in determining planetary orbital motions in our Solar System. A tension with recent observations may even be present for Mercury and Mars. However, general relativity, applied to a localized gravitationally bound binary system immersed in an expanding Friedmann-Lemaitre-Robertson-Walker, does not predict the existence of such a putative radial acceleration at Newtonian level. Instead, it was recently shown in literature that an acceleration of order H and directed along the velocity v of the test particle occurs at post-Newtonian level. We worked out its orbital effects finding well-behaved secular rates of change for both a and e proportional to the Schwarzschild radius r_s of the primary. Their magnitude is quite small: the rate of change of a amounts to just 20 microns per century in our Solar System. Finally, we discussed certain basic criteria of viability that modified models of gravity should generally meet when their observable effects are calculated. |
1605.03567 | Carsten van de Bruck | Carsten van de Bruck, Clare Burrage and Jack Morrice | Vacuum Cherenkov radiation and bremsstrahlung from disformal couplings | 17 pages, 3 figures; slight reordering of material and references
added | null | 10.1088/1475-7516/2016/08/003 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The simplest way to modify gravity is to extend the gravitational sector to
include an additional scalar degree of freedom. The most general metric that
can be built in such a theory includes disformal terms, so that standard model
fields move on a metric which is the sum of the space time metric and a tensor
constructed from first derivatives of the scalar. In such a theory
gravitational waves and photons can propagate at different speeds, and these
can in turn be different from the maximum speed limit for matter particles. In
this work we show that disformal couplings can cause charged particles to emit
Cherenkov radiation and bremsstrahlung apparently in vacuum, depending on the
background evolution of the scalar field. We discuss the implications of this
for observations of cosmic rays, and the constraints that arise for models of
dark energy with disformal couplings.
| [
{
"created": "Wed, 11 May 2016 18:09:36 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Jun 2016 14:25:31 GMT",
"version": "v2"
}
] | 2016-08-17 | [
[
"van de Bruck",
"Carsten",
""
],
[
"Burrage",
"Clare",
""
],
[
"Morrice",
"Jack",
""
]
] | The simplest way to modify gravity is to extend the gravitational sector to include an additional scalar degree of freedom. The most general metric that can be built in such a theory includes disformal terms, so that standard model fields move on a metric which is the sum of the space time metric and a tensor constructed from first derivatives of the scalar. In such a theory gravitational waves and photons can propagate at different speeds, and these can in turn be different from the maximum speed limit for matter particles. In this work we show that disformal couplings can cause charged particles to emit Cherenkov radiation and bremsstrahlung apparently in vacuum, depending on the background evolution of the scalar field. We discuss the implications of this for observations of cosmic rays, and the constraints that arise for models of dark energy with disformal couplings. |
0812.4430 | Roberto A. Sussman | Roberto A Sussman | Shear viscosity, relaxation and collision times in spherically symmetric
spacetimes | Invited contribution in "Casimir effect and Cosmology", special
volume on the occasion of 70th birthday of Prof. I. Brevik, collection of
articles, Odintsov, S. D., E.Elizalde and O.G. Gorbunova, -Scientific
Editors, TSPU Publishing Company, TSPU, Tomsk, single book, 2008. IOP LaTeX
style, 15 pages, 3 pdf figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We interpret as shear viscosity the anisotropic pressure that emerges in
inhomogeneous spherically symmetric spacetimes described by the
Lemaitre-Tolman-Bondi (LTB) metric in a comoving frame. By assuming that local
isotropic pressure and energy density satisfy a generic ideal gas equation of
state, we reduce the field equations to a set of evolution equations based on
auxiliary quasi-local variables. We examine the transport equation of shear
viscosity from Extended Irreversible Thermodynamics and use a numerical
solution of the evolution equations to obtain the relaxation times for the full
and "truncated" versions. Considering a gas of cold dark matter WIMPS after its
decoupling from the cosmic fluid, we show that the relaxation times for the
general equation are qualitatively analogous to collision times, while the
truncated version is inadequate to describe transient phenomena of transition
to equilibrium.
| [
{
"created": "Tue, 23 Dec 2008 17:17:27 GMT",
"version": "v1"
}
] | 2008-12-24 | [
[
"Sussman",
"Roberto A",
""
]
] | We interpret as shear viscosity the anisotropic pressure that emerges in inhomogeneous spherically symmetric spacetimes described by the Lemaitre-Tolman-Bondi (LTB) metric in a comoving frame. By assuming that local isotropic pressure and energy density satisfy a generic ideal gas equation of state, we reduce the field equations to a set of evolution equations based on auxiliary quasi-local variables. We examine the transport equation of shear viscosity from Extended Irreversible Thermodynamics and use a numerical solution of the evolution equations to obtain the relaxation times for the full and "truncated" versions. Considering a gas of cold dark matter WIMPS after its decoupling from the cosmic fluid, we show that the relaxation times for the general equation are qualitatively analogous to collision times, while the truncated version is inadequate to describe transient phenomena of transition to equilibrium. |
2212.05542 | Tiberiu Harko | Jin-Zhao Yang, Shahab Shahidi, Tiberiu Harko | Black hole solutions in the quadratic Weyl conformal geometric theory of
gravity | 29 pages, 13 figures, accepted for publication in EPJC | null | 10.1140/epjc/s10052-022-11131-0 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider numerical black hole solutions in the Weyl conformal geometry,
and its associated conformally invariant Weyl quadratic gravity. In this model
Einstein gravity (with a positive cosmological constant) is recovered in the
spontaneously broken phase of Weyl gravity, after the Weyl gauge field ($\omega
_{\mu}$) becomes massive through a Stueckelberg mechanism, and it decouples. As
a first step in our investigations we write down the conformally invariant
gravitational action, containing a scalar degree of freedom, and the Weyl
vector. The field equations are derived from the variational principle in the
absence of matter. By adopting a static spherically symmetric geometry, the
vacuum field equations for the gravitational, scalar, and Weyl fields are
obtained. After reformulating the field equations in a dimensionless form, and
by introducing a suitable independent radial coordinate, we obtain their
solutions numerically. We detect the formation of a black hole from the
presence of a Killing horizon for the timelike Killing vector in the metric
tensor components, indicating the existence of the singularity in the metric.
Several models, corresponding to different functional forms of the Weyl vector,
are considered. An exact black hole model, corresponding to a Weyl vector
having only a radial spacelike component, is also obtained. The thermodynamic
properties of the Weyl geometric type black holes (horizon temperature,
specific heat, entropy and evaporation time due to Hawking luminosity) are also
analyzed in detail.
| [
{
"created": "Sun, 11 Dec 2022 16:52:01 GMT",
"version": "v1"
}
] | 2023-01-18 | [
[
"Yang",
"Jin-Zhao",
""
],
[
"Shahidi",
"Shahab",
""
],
[
"Harko",
"Tiberiu",
""
]
] | We consider numerical black hole solutions in the Weyl conformal geometry, and its associated conformally invariant Weyl quadratic gravity. In this model Einstein gravity (with a positive cosmological constant) is recovered in the spontaneously broken phase of Weyl gravity, after the Weyl gauge field ($\omega _{\mu}$) becomes massive through a Stueckelberg mechanism, and it decouples. As a first step in our investigations we write down the conformally invariant gravitational action, containing a scalar degree of freedom, and the Weyl vector. The field equations are derived from the variational principle in the absence of matter. By adopting a static spherically symmetric geometry, the vacuum field equations for the gravitational, scalar, and Weyl fields are obtained. After reformulating the field equations in a dimensionless form, and by introducing a suitable independent radial coordinate, we obtain their solutions numerically. We detect the formation of a black hole from the presence of a Killing horizon for the timelike Killing vector in the metric tensor components, indicating the existence of the singularity in the metric. Several models, corresponding to different functional forms of the Weyl vector, are considered. An exact black hole model, corresponding to a Weyl vector having only a radial spacelike component, is also obtained. The thermodynamic properties of the Weyl geometric type black holes (horizon temperature, specific heat, entropy and evaporation time due to Hawking luminosity) are also analyzed in detail. |
1510.04656 | Alessio Belenchia | Alessio Belenchia, Dionigi M.T. Benincasa, Fay Dowker | The continuum limit of a 4-dimensional causal set scalar d'Alembertian | 31 pages, 2 figures. Slightly revised version, accepted for
publication in Classical and Quantum Gravity | null | 10.1088/0264-9381/33/24/245018 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The continuum limit of a 4-dimensional, discrete d'Alembertian operator for
scalar fields on causal sets is studied. The continuum limit of the mean of
this operator in the Poisson point process in 4-dimensional Minkowski spacetime
is shown to be the usual continuum scalar d'Alembertian $\Box$. It is shown
that the mean is close to the limit when there exists a frame in which the
scalar field is slowly varying on a scale set by the density of the Poisson
process. The continuum limit of the mean of the causal set d'Alembertian in
4-dimensional curved spacetime is shown to equal $\Box - \frac{1}{2}R$, where
$R$ is the Ricci scalar, under certain conditions on the spacetime and the
scalar field.
| [
{
"created": "Thu, 15 Oct 2015 18:30:53 GMT",
"version": "v1"
},
{
"created": "Sun, 30 Oct 2016 13:37:57 GMT",
"version": "v2"
}
] | 2016-12-14 | [
[
"Belenchia",
"Alessio",
""
],
[
"Benincasa",
"Dionigi M. T.",
""
],
[
"Dowker",
"Fay",
""
]
] | The continuum limit of a 4-dimensional, discrete d'Alembertian operator for scalar fields on causal sets is studied. The continuum limit of the mean of this operator in the Poisson point process in 4-dimensional Minkowski spacetime is shown to be the usual continuum scalar d'Alembertian $\Box$. It is shown that the mean is close to the limit when there exists a frame in which the scalar field is slowly varying on a scale set by the density of the Poisson process. The continuum limit of the mean of the causal set d'Alembertian in 4-dimensional curved spacetime is shown to equal $\Box - \frac{1}{2}R$, where $R$ is the Ricci scalar, under certain conditions on the spacetime and the scalar field. |
gr-qc/0703020 | arXiv Admin | G. Felici | The meaning of systematic errors, a comment to "Reply to On the
Systematic Errors in the Detection of the Lense-Thirring Effect with a Mars
Orbiter", by Lorenzo Iorio | This submission has been removed because 'G. Felici' is an apparent
pseudonym, in violation of arXiv policies | null | null | null | gr-qc | null | This submission has been removed because 'G. Felici' is an apparent
pseudonym, in violation of arXiv policies.
| [
{
"created": "Sat, 3 Mar 2007 20:06:32 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Mar 2007 13:53:40 GMT",
"version": "v2"
},
{
"created": "Fri, 14 Feb 2014 15:43:57 GMT",
"version": "v3"
}
] | 2014-02-17 | [
[
"Felici",
"G.",
""
]
] | This submission has been removed because 'G. Felici' is an apparent pseudonym, in violation of arXiv policies. |
2304.02118 | Mykhailo Tataryn | Mykhailo Tataryn and Mykola Stetsko | Three-dimensional static black hole with $\Lambda$ and nonlinear
electromagnetic fields and its thermodynamics | null | International Journal of Modern Physics D. Vol. 28, 1950160 (2019) | 10.1142/S0218271819501608 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Static black hole with the Power Maxwell invariant (PMI), Born-Infeld (BI),
logarithmic (LN), exponential (EN) electromagnetic fields in three-dimensional
spacetime with cosmological constant was studied. It was shown that the LN and
EN fields represent the Born-Infeld type of nonlinear electrodynamics. It the
framework of General Relativity the exact solutions of the field equations were
obtained, corresponding thermodynamic functions were calculated and the P-V
criticality of the black holes in the extended phase space thermodynamics was
investigated.
| [
{
"created": "Tue, 4 Apr 2023 20:57:02 GMT",
"version": "v1"
}
] | 2023-04-06 | [
[
"Tataryn",
"Mykhailo",
""
],
[
"Stetsko",
"Mykola",
""
]
] | Static black hole with the Power Maxwell invariant (PMI), Born-Infeld (BI), logarithmic (LN), exponential (EN) electromagnetic fields in three-dimensional spacetime with cosmological constant was studied. It was shown that the LN and EN fields represent the Born-Infeld type of nonlinear electrodynamics. It the framework of General Relativity the exact solutions of the field equations were obtained, corresponding thermodynamic functions were calculated and the P-V criticality of the black holes in the extended phase space thermodynamics was investigated. |
2010.13958 | Yacine Ali-Ha\"imoud | Yacine Ali-Ha\"imoud, Tristan L. Smith and Chiara M. F. Mingarelli | Insights into searches for anisotropies in the nanohertz
gravitational-wave background | 21 pages, 14 figures. Version accepted for publication in PRD after
minor changes | Phys. Rev. D 103, 042009 (2021) | 10.1103/PhysRevD.103.042009 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Within the next several years pulsar timing arrays (PTAs) are positioned to
detect the stochastic gravitational-wave background (GWB) likely produced by
the collection of inspiralling super-massive black holes binaries, and
potentially constrain some exotic physics. So far most of the pulsar timing
data analysis has focused on the monopole of the GWB, assuming it is perfectly
isotropic. The natural next step is to search for anisotropies in the GWB. In
this paper, we use the recently developed PTA Fisher matrix to gain insights
into optimal search strategies for GWB anisotropies. For concreteness, we apply
our results to EPTA data, using realistic noise characteristics of its pulsars.
We project the detectability of a GWB whose angular dependence is assumed to be
a linear combination of predetermined maps, such as spherical harmonics or
coarse pixels. We find that the GWB monopole is always statistically correlated
with these maps, implying a loss of sensitivity to the monopole when searching
simultaneously for anisotropies. We then derive the angular distributions of
the GWB intensity to which a PTA is most sensitive, and illustrate how one may
use these "principal maps" to approximately reconstruct the angular dependence
of the GWB. Since the principal maps are neither perfectly anisotropic nor
uncorrelated with the monopole, we also develop a frequentist criterion to
specifically search for anisotropies in the GWB without any prior knowledge
about their angular distribution. Lastly, we show how to recover existing EPTA
results with our Fisher formalism, and clarify their meaning. The tools
presented here will be valuable in guiding and optimizing the computationally
demanding analyses of pulsar timing data.
| [
{
"created": "Mon, 26 Oct 2020 23:51:50 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Feb 2021 23:12:56 GMT",
"version": "v2"
}
] | 2021-02-24 | [
[
"Ali-Haïmoud",
"Yacine",
""
],
[
"Smith",
"Tristan L.",
""
],
[
"Mingarelli",
"Chiara M. F.",
""
]
] | Within the next several years pulsar timing arrays (PTAs) are positioned to detect the stochastic gravitational-wave background (GWB) likely produced by the collection of inspiralling super-massive black holes binaries, and potentially constrain some exotic physics. So far most of the pulsar timing data analysis has focused on the monopole of the GWB, assuming it is perfectly isotropic. The natural next step is to search for anisotropies in the GWB. In this paper, we use the recently developed PTA Fisher matrix to gain insights into optimal search strategies for GWB anisotropies. For concreteness, we apply our results to EPTA data, using realistic noise characteristics of its pulsars. We project the detectability of a GWB whose angular dependence is assumed to be a linear combination of predetermined maps, such as spherical harmonics or coarse pixels. We find that the GWB monopole is always statistically correlated with these maps, implying a loss of sensitivity to the monopole when searching simultaneously for anisotropies. We then derive the angular distributions of the GWB intensity to which a PTA is most sensitive, and illustrate how one may use these "principal maps" to approximately reconstruct the angular dependence of the GWB. Since the principal maps are neither perfectly anisotropic nor uncorrelated with the monopole, we also develop a frequentist criterion to specifically search for anisotropies in the GWB without any prior knowledge about their angular distribution. Lastly, we show how to recover existing EPTA results with our Fisher formalism, and clarify their meaning. The tools presented here will be valuable in guiding and optimizing the computationally demanding analyses of pulsar timing data. |
1411.1843 | Farhad Ali Khan | Farhad Ali, Tooba Feroze | Approximate Noether Symmetries from Lagrangian for Plane Symmetric
Spacetimes | null | null | 10.1142/S0219887815501248 | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/3.0/ | Noether symmetries from geodetic Lagrangian for time-conformal plane
symmetric spacetime are presented. Here, time conformal factor is used to find
the approximate Noether symmetries. This is a generalization of the idea
discussed by I. Hussain and A. Noether symmetries from geodetic Lagrangian for
time-conformal plane symmetric spacetime are presented. Here, time conformal
factor is used to find the approximate Noether symmetries. This is a
generalization of the idea discussed by I. Hussain and A. Qadir [3,4], where
they obtained approximate Noether symmetries from Lagrangian for a particular
plane symmetric static spacetime. In the present article, the most general
plane symmetric static spacetime is considered and perturb it by introducing a
general time conformal factor $e^{\epsilon f(t)}$, where $\epsilon$ is very
small which causes the perturbation in the spacetime. Taking the perturbation
up to the first order, we find all Lagrangian for plane symmetric spactimes
from which approximate Noether symmetries exist. PACS 11.30.-j-Symmetries and
conservation laws PACS 04.20.-q-Classical general Relativity
| [
{
"created": "Fri, 7 Nov 2014 06:33:12 GMT",
"version": "v1"
}
] | 2015-11-04 | [
[
"Ali",
"Farhad",
""
],
[
"Feroze",
"Tooba",
""
]
] | Noether symmetries from geodetic Lagrangian for time-conformal plane symmetric spacetime are presented. Here, time conformal factor is used to find the approximate Noether symmetries. This is a generalization of the idea discussed by I. Hussain and A. Noether symmetries from geodetic Lagrangian for time-conformal plane symmetric spacetime are presented. Here, time conformal factor is used to find the approximate Noether symmetries. This is a generalization of the idea discussed by I. Hussain and A. Qadir [3,4], where they obtained approximate Noether symmetries from Lagrangian for a particular plane symmetric static spacetime. In the present article, the most general plane symmetric static spacetime is considered and perturb it by introducing a general time conformal factor $e^{\epsilon f(t)}$, where $\epsilon$ is very small which causes the perturbation in the spacetime. Taking the perturbation up to the first order, we find all Lagrangian for plane symmetric spactimes from which approximate Noether symmetries exist. PACS 11.30.-j-Symmetries and conservation laws PACS 04.20.-q-Classical general Relativity |
2108.05006 | Chi-Yong Lin | Tien Hsieh, Da-Shin Lee, and Chi-Yong Lin | Gravitational time delay effects by Kerr and Kerr-Newman black holes in
strong field limits | 33 pages, 5 figures. Revised version to appear in Physical Review D.
arXiv admin note: text overlap with arXiv:2101.09008 | null | 10.1103/PhysRevD.104.104013 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study the time delay between two relativistic images due to strong
gravitational lensing of the light rays caused by the Kerr and Kerr-Newman
black holes. The trajectories of the light rays are restricted on the
equatorial plane. Using the known form of the deflection angle in the strong
deflection limit (SDL) allows us to analytically develop the formalism for the
travel time of the light from the distant source winding around the black hole
several times and reaching the observer. We find that the black hole with
higher mass or with spin of the extreme black hole potentially have higher time
delay. The effect of the charge of the black hole enhances the time delay
between the images lying on the opposite side of the optical axis resulting
from the light rays when one light ray is in the direct orbit and the other is
in the retrograde orbit. In contrary, when both light rays travel along either
direct or retrograde orbits giving the images on the same side of the optical
axis, the charge effect reduces the time delay between them. We then examine
the time delay observations due to the galactic and supermassive black holes
respectively
| [
{
"created": "Wed, 11 Aug 2021 03:21:31 GMT",
"version": "v1"
},
{
"created": "Sun, 26 Sep 2021 01:44:29 GMT",
"version": "v2"
}
] | 2021-11-17 | [
[
"Hsieh",
"Tien",
""
],
[
"Lee",
"Da-Shin",
""
],
[
"Lin",
"Chi-Yong",
""
]
] | We study the time delay between two relativistic images due to strong gravitational lensing of the light rays caused by the Kerr and Kerr-Newman black holes. The trajectories of the light rays are restricted on the equatorial plane. Using the known form of the deflection angle in the strong deflection limit (SDL) allows us to analytically develop the formalism for the travel time of the light from the distant source winding around the black hole several times and reaching the observer. We find that the black hole with higher mass or with spin of the extreme black hole potentially have higher time delay. The effect of the charge of the black hole enhances the time delay between the images lying on the opposite side of the optical axis resulting from the light rays when one light ray is in the direct orbit and the other is in the retrograde orbit. In contrary, when both light rays travel along either direct or retrograde orbits giving the images on the same side of the optical axis, the charge effect reduces the time delay between them. We then examine the time delay observations due to the galactic and supermassive black holes respectively |
1604.06668 | Molin Liu | Molin Liu, Zonghua Zhao, Xiaohe You, Jianbo Lu, Lixin Xu | Test of the Weak Equivalence Principle using LIGO observations of
GW150914 and Fermi observations of GBM transient 150914 | 9 pages, 4 figures, accepted for publication in Physics Letters B | Physics Letters B 770 (2017) 8-15 | 10.1016/j.physletb.2017.04.033 | null | gr-qc astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | About 0.4s after the Laser Interferometer Gravitational-Wave Observatory
(LIGO) detected a transient gravitational-wave (GW) signal GW150914, the Fermi
Gamma-ray Burst Monitor (GBM) also found a weak electromagnetic transient (GBM
transient 150914). Time and location coincidences favor a possible association
between GW150904 and GBM transient 150914. Under this possible association, we
adopt Fermi's electromagnetic (EM) localization and derive constraints on
possible violations of the Weak Equivalence Principle (WEP) from the
observations of two events. Our calculations are based on four comparisons:
(1)The first is the comparison of the initial GWs detected at the two LIGO
sites. From the different polarizations of these initial GWs, we obtain a limit
on any difference in the parametrized post-Newtonian (PPN) parameter
$\Delta\gamma\lesssim 10^{-10}$. (2) The second is a comparison of GWs and
possible EM waves. Using a traditional super-Eddington accretion model for GBM
transient 150914, we again obtain an upper limit $\Delta\gamma\lesssim
10^{-10}$. Compared with previous results for photons and neutrinos, our limits
are five orders of magnitude stronger than those from PeV neutrinos in blazar
flares, and seven orders stronger than those from MeV neutrinos in SN1987A. (3)
The third is a comparison of GWs with different frequencies in the range [35
Hz, 250 Hz]. (4) The fourth is a comparison of EM waves with different energies
in the range [1 keV, 10 MeV]. These last two comparisons lead to an even
stronger limit, $\Delta\gamma\lesssim 10^{-8}$. Our results highlight the
potential of multi-messenger signals exploiting different emission channels to
strengthen existing tests of the WEP.
| [
{
"created": "Fri, 22 Apr 2016 14:08:15 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Apr 2016 06:16:08 GMT",
"version": "v2"
},
{
"created": "Wed, 19 Apr 2017 10:27:24 GMT",
"version": "v3"
}
] | 2017-04-25 | [
[
"Liu",
"Molin",
""
],
[
"Zhao",
"Zonghua",
""
],
[
"You",
"Xiaohe",
""
],
[
"Lu",
"Jianbo",
""
],
[
"Xu",
"Lixin",
""
]
] | About 0.4s after the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected a transient gravitational-wave (GW) signal GW150914, the Fermi Gamma-ray Burst Monitor (GBM) also found a weak electromagnetic transient (GBM transient 150914). Time and location coincidences favor a possible association between GW150904 and GBM transient 150914. Under this possible association, we adopt Fermi's electromagnetic (EM) localization and derive constraints on possible violations of the Weak Equivalence Principle (WEP) from the observations of two events. Our calculations are based on four comparisons: (1)The first is the comparison of the initial GWs detected at the two LIGO sites. From the different polarizations of these initial GWs, we obtain a limit on any difference in the parametrized post-Newtonian (PPN) parameter $\Delta\gamma\lesssim 10^{-10}$. (2) The second is a comparison of GWs and possible EM waves. Using a traditional super-Eddington accretion model for GBM transient 150914, we again obtain an upper limit $\Delta\gamma\lesssim 10^{-10}$. Compared with previous results for photons and neutrinos, our limits are five orders of magnitude stronger than those from PeV neutrinos in blazar flares, and seven orders stronger than those from MeV neutrinos in SN1987A. (3) The third is a comparison of GWs with different frequencies in the range [35 Hz, 250 Hz]. (4) The fourth is a comparison of EM waves with different energies in the range [1 keV, 10 MeV]. These last two comparisons lead to an even stronger limit, $\Delta\gamma\lesssim 10^{-8}$. Our results highlight the potential of multi-messenger signals exploiting different emission channels to strengthen existing tests of the WEP. |
1009.3292 | Valerio Ferroni | Valerio Ferroni and Alexander Silbergleit | Electrostatic Patch Effect in Cylindrical Geometry. I. Potential and
Energy between Slightly Non-Coaxial Cylinders | 26 pages, 1 Figure. Submitted to Classical and Quantum Gravity | Class.Quant.Grav.28:145001,2011 | 10.1088/0264-9381/28/14/145001 | null | gr-qc physics.class-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the effect of any uneven voltage distribution on two close
cylindrical conductors with parallel axes that are slightly shifted in the
radial and by any length in the axial direction. The investigation is
especially motivated by certain precision measurements, such as the Satellite
Test of the Equivalence Principle (STEP). By energy conservation, the force can
be found as the energy gradient in the vector of the shift, which requires
determining potential distribution and energy in the gap. The boundary value
problem for the potential is solved, and energy is thus found to the second
order in the small transverse shift, and to lowest order in the gap to cylinder
radius ratio. The energy consists of three parts: the usual capacitor part due
to the uniform potential difference, the one coming from the interaction
between the voltage patches and the uniform voltage difference, and the energy
of patch interaction, entirely independent of the uniform voltage. Patch effect
forces and torques in the cylindrical configuration are derived and analyzed in
the next two parts of this work.
| [
{
"created": "Thu, 16 Sep 2010 22:00:40 GMT",
"version": "v1"
}
] | 2011-06-07 | [
[
"Ferroni",
"Valerio",
""
],
[
"Silbergleit",
"Alexander",
""
]
] | We study the effect of any uneven voltage distribution on two close cylindrical conductors with parallel axes that are slightly shifted in the radial and by any length in the axial direction. The investigation is especially motivated by certain precision measurements, such as the Satellite Test of the Equivalence Principle (STEP). By energy conservation, the force can be found as the energy gradient in the vector of the shift, which requires determining potential distribution and energy in the gap. The boundary value problem for the potential is solved, and energy is thus found to the second order in the small transverse shift, and to lowest order in the gap to cylinder radius ratio. The energy consists of three parts: the usual capacitor part due to the uniform potential difference, the one coming from the interaction between the voltage patches and the uniform voltage difference, and the energy of patch interaction, entirely independent of the uniform voltage. Patch effect forces and torques in the cylindrical configuration are derived and analyzed in the next two parts of this work. |
2003.04303 | Daniel Sobral Blanco | Daniel Sobral-Blanco and Lucas Lombriser | A local self-tuning mechanism for the cosmological constant | 14 pages | Phys. Rev. D 102, 043506 (2020) | 10.1103/PhysRevD.102.043506 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently the global variation of the Planck mass in the General Relativistic
Einstein-Hilbert action was proposed as a self-tuning mechanism of the
cosmological constant preventing vacuum energy from freely gravitating. We show
that this global mechanism emerges for generic local scalar-tensor theories
with additional coupling of the scalar field to the field strength of a
three-form gauge field that turns the scalar field constant on the domain of
the action. Evaluation of the resulting integral constraint equation over the
observable Universe yields a self-consistent framework with General
Relativistic field equations and arbitrary radiatively stable residual
cosmological constant. We argue that the expectation value for this residual is
in good agreement with the magnitude of the observed cosmic acceleration.
| [
{
"created": "Mon, 9 Mar 2020 17:59:09 GMT",
"version": "v1"
}
] | 2020-08-12 | [
[
"Sobral-Blanco",
"Daniel",
""
],
[
"Lombriser",
"Lucas",
""
]
] | Recently the global variation of the Planck mass in the General Relativistic Einstein-Hilbert action was proposed as a self-tuning mechanism of the cosmological constant preventing vacuum energy from freely gravitating. We show that this global mechanism emerges for generic local scalar-tensor theories with additional coupling of the scalar field to the field strength of a three-form gauge field that turns the scalar field constant on the domain of the action. Evaluation of the resulting integral constraint equation over the observable Universe yields a self-consistent framework with General Relativistic field equations and arbitrary radiatively stable residual cosmological constant. We argue that the expectation value for this residual is in good agreement with the magnitude of the observed cosmic acceleration. |
2308.03084 | Sarath Nelleri | Naseeba.K.M, Sarath Nelleri, Navaneeth Poonthottathil | Testing the dynamical stability and validity of generalized second law
within the phantom dynamical dark energy model | 18 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hubble constant($H_0$) tension and tension in the matter fluctuation
amplitude ($s_8$) are fascinating puzzles in cosmology nowadays. Phantom
dynamical dark energy model (PDDE), also known as little sibling of the big rip
is an abrupt event that can happen in the far future evolution of the universe.
Recent analysis of PDDE model based on CMBR data shows that the model is a
potential candidate to alleviate these tension problems. In this work, we study
the background evolution of the universe within the PDDE model. Analysis based
on the SNIa+BAO+OHD data shows that the model is successful in explaining the
late phase acceleration of the universe. Also, the values of the cosmological
parameters predicted by PDDE model are consistent with the values predicted by
the $\Lambda$CDM model. However, most of the phanton dark energy models doesn't
give stable solution in the asymptotic future. In this regard, we address the
dynamical stability of the PDDE model and also test the validity of the
generalized second law (GSL) of thermodynamics. We show that the model is
dynamically unstable and violates the GSL. The model doesn't satisfy the
convexity condition and hence the universe doesn't behave like an ordinary
macroscopic system within the PDDE model.
| [
{
"created": "Sun, 6 Aug 2023 10:37:03 GMT",
"version": "v1"
}
] | 2023-08-08 | [
[
"M",
"Naseeba. K.",
""
],
[
"Nelleri",
"Sarath",
""
],
[
"Poonthottathil",
"Navaneeth",
""
]
] | Hubble constant($H_0$) tension and tension in the matter fluctuation amplitude ($s_8$) are fascinating puzzles in cosmology nowadays. Phantom dynamical dark energy model (PDDE), also known as little sibling of the big rip is an abrupt event that can happen in the far future evolution of the universe. Recent analysis of PDDE model based on CMBR data shows that the model is a potential candidate to alleviate these tension problems. In this work, we study the background evolution of the universe within the PDDE model. Analysis based on the SNIa+BAO+OHD data shows that the model is successful in explaining the late phase acceleration of the universe. Also, the values of the cosmological parameters predicted by PDDE model are consistent with the values predicted by the $\Lambda$CDM model. However, most of the phanton dark energy models doesn't give stable solution in the asymptotic future. In this regard, we address the dynamical stability of the PDDE model and also test the validity of the generalized second law (GSL) of thermodynamics. We show that the model is dynamically unstable and violates the GSL. The model doesn't satisfy the convexity condition and hence the universe doesn't behave like an ordinary macroscopic system within the PDDE model. |
1610.03281 | G\'abor Zsolt T\'oth | Gabor Zsolt Toth | Noether's theorems and conserved currents in gauge theories in the
presence of fixed fields | 28 pages, LaTeX, minor changes, journal reference added | Phys. Rev. D 96, 025018 (2017) | 10.1103/PhysRevD.96.025018 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We extend the standard construction of conserved currents for matter fields
in general relativity to general gauge theories. In the original construction
the conserved current associated with a spacetime symmetry generated by a
Killing field $h^\mu$ is given by $\sqrt{-g}\,T^{\mu\nu}h_\nu$, where
$T^{\mu\nu}$ is the energy-momentum tensor of the matter. We show that if in a
Lagrangian field theory that has gauge symmetry in the general Noetherian sense
some of the elementary fields are fixed and are invariant under a particular
infinitesimal gauge transformation, then there is a current $\mathcal{B}^\mu$
that is analogous to $\sqrt{-g}\,T^{\mu\nu}h_\nu$ and is conserved if the
non-fixed fields satisfy their Euler-Lagrange equations. The conservation of
$\mathcal{B}^\mu$ can be seen as a consequence of an identity that is a
generalization of $\nabla_\mu T^{\mu\nu}=0$ and is a consequence of the gauge
symmetry of the Lagrangian. This identity holds in any configuration of the
fixed fields if the non-fixed fields satisfy their Euler-Lagrange equations. We
also show that $\mathcal{B}^\mu$ differs from the relevant canonical Noether
current by the sum of an identically conserved current and a term that vanishes
if the non-fixed fields are on-shell. As example we discuss the case of
general, possibly fermionic, matter fields propagating in fixed gravitational
and Yang-Mills background. We find that in this case the generalization of
$\nabla_\mu T^{\mu\nu}=0$ is the Lorentz law $\nabla_\mu T^{\mu\nu} -
F^{a\nu\lambda}\mathcal{J}_{a\lambda} = 0$, which holds as a consequence of the
diffeomorphism, local Lorentz and Yang-Mills gauge symmetry of the matter
Lagrangian. As a second simple example we consider the case of general fields
propagating in a background that consists of a gravitational and a real scalar
field.
| [
{
"created": "Tue, 11 Oct 2016 11:37:19 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Oct 2016 08:37:00 GMT",
"version": "v2"
},
{
"created": "Thu, 27 Oct 2016 16:35:19 GMT",
"version": "v3"
},
{
"created": "Tue, 28 Mar 2017 16:20:54 GMT",
"version": "v4"
},
{
"created": "Sun, 18 Jun 2017 19:47:14 GMT",
"version": "v5"
},
{
"created": "Tue, 25 Jul 2017 09:41:53 GMT",
"version": "v6"
}
] | 2018-02-12 | [
[
"Toth",
"Gabor Zsolt",
""
]
] | We extend the standard construction of conserved currents for matter fields in general relativity to general gauge theories. In the original construction the conserved current associated with a spacetime symmetry generated by a Killing field $h^\mu$ is given by $\sqrt{-g}\,T^{\mu\nu}h_\nu$, where $T^{\mu\nu}$ is the energy-momentum tensor of the matter. We show that if in a Lagrangian field theory that has gauge symmetry in the general Noetherian sense some of the elementary fields are fixed and are invariant under a particular infinitesimal gauge transformation, then there is a current $\mathcal{B}^\mu$ that is analogous to $\sqrt{-g}\,T^{\mu\nu}h_\nu$ and is conserved if the non-fixed fields satisfy their Euler-Lagrange equations. The conservation of $\mathcal{B}^\mu$ can be seen as a consequence of an identity that is a generalization of $\nabla_\mu T^{\mu\nu}=0$ and is a consequence of the gauge symmetry of the Lagrangian. This identity holds in any configuration of the fixed fields if the non-fixed fields satisfy their Euler-Lagrange equations. We also show that $\mathcal{B}^\mu$ differs from the relevant canonical Noether current by the sum of an identically conserved current and a term that vanishes if the non-fixed fields are on-shell. As example we discuss the case of general, possibly fermionic, matter fields propagating in fixed gravitational and Yang-Mills background. We find that in this case the generalization of $\nabla_\mu T^{\mu\nu}=0$ is the Lorentz law $\nabla_\mu T^{\mu\nu} - F^{a\nu\lambda}\mathcal{J}_{a\lambda} = 0$, which holds as a consequence of the diffeomorphism, local Lorentz and Yang-Mills gauge symmetry of the matter Lagrangian. As a second simple example we consider the case of general fields propagating in a background that consists of a gravitational and a real scalar field. |
1606.04361 | Jose Beltran Jimenez | Jose Beltran Jimenez | Cosmology with vector distortion | 4 pages, Contribution to the proceedings of the Cosmology session of
Moriond 2016 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider an extension of Weyl geometry with the most general connection
linearly determined by a vector field. We discuss some of the geometrical
properties within this framework and then we construct gravitational theories
leading to an interesting class of vector-tensor theories with cosmological
applications.
| [
{
"created": "Fri, 10 Jun 2016 09:00:15 GMT",
"version": "v1"
}
] | 2016-06-15 | [
[
"Jimenez",
"Jose Beltran",
""
]
] | We consider an extension of Weyl geometry with the most general connection linearly determined by a vector field. We discuss some of the geometrical properties within this framework and then we construct gravitational theories leading to an interesting class of vector-tensor theories with cosmological applications. |
1704.04426 | Cosimo Bambi | Hao Zhang, Menglei Zhou, Cosimo Bambi, Burkhard Kleihaus, Jutta Kunz,
Eugen Radu | Testing Einstein-dilaton-Gauss-Bonnet gravity from the reflection
spectrum of accreting black holes | 10 pages, 6 figures. v2: fixed some typos | Phys. Rev. D 95, 104043 (2017) | 10.1103/PhysRevD.95.104043 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Einstein-dilaton-Gauss-Bonnet gravity is a theoretically well-motivated
alternative theory of gravity emerging as a low-energy 4-dimensional model from
heterotic string theory. Its rotating black hole solutions are known
numerically and can have macroscopic deviations from the Kerr black holes of
Einstein's gravity. Einstein-dilaton-Gauss-Bonnet gravity can thus be tested
with observations of astrophysical black holes. In the present paper, we
simulate observations of the reflection spectrum of thin accretion disks with
present and future X-ray facilities to understand whether X-ray reflection
spectroscopy can distinguish the black holes in Einstein-dilaton-Gauss-Bonnet
gravity from those in Einstein's gravity. We find that this is definitively out
of reach for present X-ray missions, but it may be achieved with the next
generation of facilities.
| [
{
"created": "Fri, 14 Apr 2017 14:10:01 GMT",
"version": "v1"
},
{
"created": "Tue, 30 May 2017 19:40:35 GMT",
"version": "v2"
}
] | 2017-06-01 | [
[
"Zhang",
"Hao",
""
],
[
"Zhou",
"Menglei",
""
],
[
"Bambi",
"Cosimo",
""
],
[
"Kleihaus",
"Burkhard",
""
],
[
"Kunz",
"Jutta",
""
],
[
"Radu",
"Eugen",
""
]
] | Einstein-dilaton-Gauss-Bonnet gravity is a theoretically well-motivated alternative theory of gravity emerging as a low-energy 4-dimensional model from heterotic string theory. Its rotating black hole solutions are known numerically and can have macroscopic deviations from the Kerr black holes of Einstein's gravity. Einstein-dilaton-Gauss-Bonnet gravity can thus be tested with observations of astrophysical black holes. In the present paper, we simulate observations of the reflection spectrum of thin accretion disks with present and future X-ray facilities to understand whether X-ray reflection spectroscopy can distinguish the black holes in Einstein-dilaton-Gauss-Bonnet gravity from those in Einstein's gravity. We find that this is definitively out of reach for present X-ray missions, but it may be achieved with the next generation of facilities. |
2109.01075 | Ren Tsuda | Ren Tsuda and Takanori Fujiwara | Higher Dimensional Polytopal Universe in Regge Calculus | 29 pages, 12 figures | Prog Theor Exp Phys (2022) | 10.1093/ptep/ptac009 | null | gr-qc hep-lat hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Higher dimensional closed Friedmann-Lema\^itre-Robertson-Walker (FLRW)
universe with positive cosmological constant is investigated by Regge calculus.
A Cauchy surface of discretized FLRW universe is replaced by a regular polytope
in accordance with the Collins-Williams (CW) formalism. Polytopes in an
arbitrary dimensions can be systematically dealt with by a set of five integers
integrating the Schl\"afli symbol of the polytope. Regge action in continuum
time limit is given. It possesses reparameterization invariance of the time
variable. Variational principle for edge lengths and struts yields Hamiltonian
constraint and evolution equation. They describe oscillating universe in
dimensions larger than three. To go beyond the approximation by regular
polytopes, we propose pseudo-regular polytopes with fractional Schl\"afli
symbols as a substitute for geodesic domes in higher dimensions. We examine the
pseudo-regular polytope model as an effective theory of Regge calculus for the
geodesic domes. In the infinite frequency limit, the pseudo-regular polytope
model reduces to the continuum FLRW universe.
| [
{
"created": "Thu, 2 Sep 2021 16:42:24 GMT",
"version": "v1"
}
] | 2022-03-09 | [
[
"Tsuda",
"Ren",
""
],
[
"Fujiwara",
"Takanori",
""
]
] | Higher dimensional closed Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe with positive cosmological constant is investigated by Regge calculus. A Cauchy surface of discretized FLRW universe is replaced by a regular polytope in accordance with the Collins-Williams (CW) formalism. Polytopes in an arbitrary dimensions can be systematically dealt with by a set of five integers integrating the Schl\"afli symbol of the polytope. Regge action in continuum time limit is given. It possesses reparameterization invariance of the time variable. Variational principle for edge lengths and struts yields Hamiltonian constraint and evolution equation. They describe oscillating universe in dimensions larger than three. To go beyond the approximation by regular polytopes, we propose pseudo-regular polytopes with fractional Schl\"afli symbols as a substitute for geodesic domes in higher dimensions. We examine the pseudo-regular polytope model as an effective theory of Regge calculus for the geodesic domes. In the infinite frequency limit, the pseudo-regular polytope model reduces to the continuum FLRW universe. |
1602.03880 | Felipe J. Llanes-Estrada | Miguel Aparicio Resco, Alvaro de la Cruz-Dombriz, Felipe J.
Llanes-Estrada and Victor Zapatero Castrillo | On neutron stars in f(R) theories: small radii, large masses and large
energy emitted in a merger | 19 pages, 23 plots. Irrelevant paragraph deleted | Phys.Dark Univ. 13 (2016) 147-161 | 10.1016/j.dark.2016.07.001 | null | gr-qc astro-ph.CO nucl-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the context of f(R) gravity theories, we show that the apparent mass of a
neutron star as seen from an observer at infinity is numerically calculable but
requires careful matching, first at the star's edge, between interior and
exterior solutions, none of them being totally Schwarzschild-like but
presenting instead small oscillations of the curvature scalar R; and second at
large radii, where the Newtonian potential is used to identify the mass of the
neutron star. We find that for the same equation of state, this mass definition
is always larger than its general relativistic counterpart. We exemplify this
with quadratic $R^2$ and Hu-Sawicki-like modifications of the standard General
Relativity action. Therefore, the finding of two-solar mass neutron stars
basically imposes no constraint on stable f(R) theories. However, star radii
are in general smaller than in General Relativity, which can give an
observational handle on such classes of models at the astrophysical level. Both
larger masses and smaller matter radii are due to much of the apparent
effective energy residing in the outer metric for scalar-tensor theories.
Finally, because the f(R) neutron star masses can be much larger than General
Relativity counterparts, the total energy available for radiating gravitational
waves could be of order several solar masses, and thus a merger of these stars
constitutes an interesting wave source.
| [
{
"created": "Thu, 11 Feb 2016 20:51:11 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Feb 2016 17:12:45 GMT",
"version": "v2"
},
{
"created": "Wed, 20 Jul 2016 15:36:27 GMT",
"version": "v3"
},
{
"created": "Tue, 13 Sep 2016 08:06:55 GMT",
"version": "v4"
}
] | 2016-09-14 | [
[
"Resco",
"Miguel Aparicio",
""
],
[
"de la Cruz-Dombriz",
"Alvaro",
""
],
[
"Llanes-Estrada",
"Felipe J.",
""
],
[
"Castrillo",
"Victor Zapatero",
""
]
] | In the context of f(R) gravity theories, we show that the apparent mass of a neutron star as seen from an observer at infinity is numerically calculable but requires careful matching, first at the star's edge, between interior and exterior solutions, none of them being totally Schwarzschild-like but presenting instead small oscillations of the curvature scalar R; and second at large radii, where the Newtonian potential is used to identify the mass of the neutron star. We find that for the same equation of state, this mass definition is always larger than its general relativistic counterpart. We exemplify this with quadratic $R^2$ and Hu-Sawicki-like modifications of the standard General Relativity action. Therefore, the finding of two-solar mass neutron stars basically imposes no constraint on stable f(R) theories. However, star radii are in general smaller than in General Relativity, which can give an observational handle on such classes of models at the astrophysical level. Both larger masses and smaller matter radii are due to much of the apparent effective energy residing in the outer metric for scalar-tensor theories. Finally, because the f(R) neutron star masses can be much larger than General Relativity counterparts, the total energy available for radiating gravitational waves could be of order several solar masses, and thus a merger of these stars constitutes an interesting wave source. |
1509.05174 | Ozay Gurtug | O. Gurtug and M. Halilsoy | Wavy way to the Kerr metric and the quantum nature of its ring
singularity | 18 pages, 2 figures, Title has been changed and explanations have
been improved | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | From inherent non-linearity two gravitational waves, unless they are
unidirectional, fail to satisfy a superposition law. They collide to develop a
new spacetime carrying the imprints of the incoming waves. Same behaviour is
valid also for any massless lightlike field. As a result of the violent
collision process either a naked singularity or a Cauchy horizon (CH) develops.
It was shown by Chandrasekhar and Xanthopoulos (CX) that a particular class of
colliding gravitational waves (CGW) spacetime is locally isometric to the Kerr
metric for rotating black holes. This relation came to be known as the CX
duality. Such a duality can be exploited as an alternative derivation for the
Kerr metric as we do herein. Not each case gives rise to a CH but those which
do are transient to a black hole state provided stability requirements are met.
These classical considerations can be borrowed to shed light on black hole
formation in high energy collisions. Their questionable stability and many
other sophisticated agenda, we admit that await for a full - fledged quantum
gravity. Yet, to add an element of novelty, a quantum probe is sent in the
plane $\theta =\pi /2$ to the naked ring singularity of Kerr which develops for
the overspinning case $(a>M)$ to test it from a quantum picture. We show that
the spatial operator of the reduced Klein-Gordon equation has a unique
self-adjoint extension. As a result, the classical Kerr`s ring singularity is
healed and becomes quantum regular. Our poetic message of the paper is
summarized as
Let there be light
that collide with might
to disperse the night
and create holes that are white
| [
{
"created": "Thu, 17 Sep 2015 09:09:03 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Mar 2016 09:50:06 GMT",
"version": "v2"
}
] | 2016-03-17 | [
[
"Gurtug",
"O.",
""
],
[
"Halilsoy",
"M.",
""
]
] | From inherent non-linearity two gravitational waves, unless they are unidirectional, fail to satisfy a superposition law. They collide to develop a new spacetime carrying the imprints of the incoming waves. Same behaviour is valid also for any massless lightlike field. As a result of the violent collision process either a naked singularity or a Cauchy horizon (CH) develops. It was shown by Chandrasekhar and Xanthopoulos (CX) that a particular class of colliding gravitational waves (CGW) spacetime is locally isometric to the Kerr metric for rotating black holes. This relation came to be known as the CX duality. Such a duality can be exploited as an alternative derivation for the Kerr metric as we do herein. Not each case gives rise to a CH but those which do are transient to a black hole state provided stability requirements are met. These classical considerations can be borrowed to shed light on black hole formation in high energy collisions. Their questionable stability and many other sophisticated agenda, we admit that await for a full - fledged quantum gravity. Yet, to add an element of novelty, a quantum probe is sent in the plane $\theta =\pi /2$ to the naked ring singularity of Kerr which develops for the overspinning case $(a>M)$ to test it from a quantum picture. We show that the spatial operator of the reduced Klein-Gordon equation has a unique self-adjoint extension. As a result, the classical Kerr`s ring singularity is healed and becomes quantum regular. Our poetic message of the paper is summarized as Let there be light that collide with might to disperse the night and create holes that are white |
gr-qc/0105088 | Mikhail Sheftel B. | Y. Nutku (deceased) and M. B. Sheftel | A family of heavenly metrics | minor changes, correction to formula (29), 16 pages | null | null | null | gr-qc math-ph math.MP nlin.SI | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is a corrected and essentially extended version of the previous preprint
arXiv:gr-qc/0105088 v4 (2002) by Y. Nutku and M. Sheftel containing new
results. It is being published now in honor of Y. Nutku's memory. All
responsibility for the additions and changes must be attributed to M. Sheftel.
We present new anti-self-dual exact solutions of the Einstein field equations
with Euclidean and neutral (ultra-hyperbolic) signatures that admit only one
rotational Killing vector. Such solutions of the Einstein field equations are
determined by non-invariant solutions of Boyer-Finley ($BF$) equation. For the
case of Euclidean signature such a solution of the $BF$ equation was first
constructed by Calderbank and Tod. Two years later, Martina, Sheftel and
Winternitz applied the method of group foliation to the Boyer-Finley equation
and reproduced the Calderbank-Tod solution together with new solutions for the
neutral signature. In the case of Euclidean signature we obtain new metrics
which asymptotically locally look like a flat space and have a non-removable
singular point at the origin. In the case of ultra-hyperbolic signature there
exist three inequivalent forms of metric. Only one of these can be obtained by
analytic continuation from the Calderbank-Tod solution whereas the other two
are new.
| [
{
"created": "Thu, 24 May 2001 14:35:38 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Jun 2001 12:13:29 GMT",
"version": "v2"
},
{
"created": "Tue, 8 Oct 2002 13:42:41 GMT",
"version": "v3"
},
{
"created": "Wed, 9 Oct 2002 11:03:03 GMT",
"version": "v4"
},
{
"created": "Tue, 4 Jun 2013 09:24:57 GMT",
"version": "v5"
},
{
"created": "Tue, 11 Jun 2013 18:15:23 GMT",
"version": "v6"
},
{
"created": "Mon, 21 Oct 2013 17:21:14 GMT",
"version": "v7"
},
{
"created": "Tue, 10 Dec 2013 10:04:38 GMT",
"version": "v8"
}
] | 2013-12-11 | [
[
"Nutku",
"Y.",
"",
"deceased"
],
[
"Sheftel",
"M. B.",
""
]
] | This is a corrected and essentially extended version of the previous preprint arXiv:gr-qc/0105088 v4 (2002) by Y. Nutku and M. Sheftel containing new results. It is being published now in honor of Y. Nutku's memory. All responsibility for the additions and changes must be attributed to M. Sheftel. We present new anti-self-dual exact solutions of the Einstein field equations with Euclidean and neutral (ultra-hyperbolic) signatures that admit only one rotational Killing vector. Such solutions of the Einstein field equations are determined by non-invariant solutions of Boyer-Finley ($BF$) equation. For the case of Euclidean signature such a solution of the $BF$ equation was first constructed by Calderbank and Tod. Two years later, Martina, Sheftel and Winternitz applied the method of group foliation to the Boyer-Finley equation and reproduced the Calderbank-Tod solution together with new solutions for the neutral signature. In the case of Euclidean signature we obtain new metrics which asymptotically locally look like a flat space and have a non-removable singular point at the origin. In the case of ultra-hyperbolic signature there exist three inequivalent forms of metric. Only one of these can be obtained by analytic continuation from the Calderbank-Tod solution whereas the other two are new. |
1712.09353 | Seokcheon Lee | Young-Hwan Hyun, Yoonbai Kim, and Seokcheon Lee | Conformal Frame dependence on Cosmological Observations in Scalar-Tensor
Theories of Gravity | 14 pages, 5 figures | J. Korean Phys. Soc. (2019) 74 : 1101 | 10.3938/jkps.74.1101 | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cosmological observations provide more accurate values both for background
evolution of the Universe and for the structure formation. These values are
given by the so-called dark energy equation of state, $\omega$ and the growth
index parameter, $\gamma$. From these observed parameters, one can reconstruct
the model functions in scalar tensor gravity theories. However, there is a long
standing debate about the (in)equality between conformally transformed frames
in scalar tensor gravity models. We show that cosmological observables are
frame dependent when they are described by frame independent parameter,
redshift. Thus, if the cosmological observables are interpreted in one frame,
then all of the observables should also be interpreted in that frame. This
explicitly shows the conformal inequality of cosmological observables. Also,
our method provides the model independent analysis for STG models about various
observables in both frames.
| [
{
"created": "Tue, 26 Dec 2017 07:36:51 GMT",
"version": "v1"
}
] | 2019-07-01 | [
[
"Hyun",
"Young-Hwan",
""
],
[
"Kim",
"Yoonbai",
""
],
[
"Lee",
"Seokcheon",
""
]
] | Cosmological observations provide more accurate values both for background evolution of the Universe and for the structure formation. These values are given by the so-called dark energy equation of state, $\omega$ and the growth index parameter, $\gamma$. From these observed parameters, one can reconstruct the model functions in scalar tensor gravity theories. However, there is a long standing debate about the (in)equality between conformally transformed frames in scalar tensor gravity models. We show that cosmological observables are frame dependent when they are described by frame independent parameter, redshift. Thus, if the cosmological observables are interpreted in one frame, then all of the observables should also be interpreted in that frame. This explicitly shows the conformal inequality of cosmological observables. Also, our method provides the model independent analysis for STG models about various observables in both frames. |
2403.00883 | Rahul Mapari Dr. | V. R. Patil, J. L. Pawde, R. V. Mapari, and S. K. Waghmare | Energy Conditions in f(R, T) Gravity with an Anisotropic Background | 19 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In our study, we explored the properties of a spatially homogeneous and
anisotropic Bianchi type V I0 Universe. Our investigation centered on
integrating cosmic domain walls into the f(R, T) theory of gravitation,
initially proposed by Harko et al. in 2011. To tackle the field equations, we
employed the relationship between the expansion scalar ({\theta}) and the shear
scalar ({\sigma}). Our analysis encompassed both the dynamic and cosmological
aspects of the Universe. By comparing our findings to the {\Lambda}CDM model,
specifically focusing on the evolution of the jerk parameter, we found a
striking agreement between the two models. A noteworthy discovery was the
verification of accelerated expansion in our described model, consistent with
the prevailing observational data. Finally, we examine the energy condition
criteria and determine that the violation of the Strong Energy Condition (SEC),
while the Null Energy Condition (NEC), Weak Energy Condition (WEC) and Dominant
Energy Condition (DEC) continue to meet the requirements for positivity.
| [
{
"created": "Fri, 1 Mar 2024 09:37:07 GMT",
"version": "v1"
}
] | 2024-03-05 | [
[
"Patil",
"V. R.",
""
],
[
"Pawde",
"J. L.",
""
],
[
"Mapari",
"R. V.",
""
],
[
"Waghmare",
"S. K.",
""
]
] | In our study, we explored the properties of a spatially homogeneous and anisotropic Bianchi type V I0 Universe. Our investigation centered on integrating cosmic domain walls into the f(R, T) theory of gravitation, initially proposed by Harko et al. in 2011. To tackle the field equations, we employed the relationship between the expansion scalar ({\theta}) and the shear scalar ({\sigma}). Our analysis encompassed both the dynamic and cosmological aspects of the Universe. By comparing our findings to the {\Lambda}CDM model, specifically focusing on the evolution of the jerk parameter, we found a striking agreement between the two models. A noteworthy discovery was the verification of accelerated expansion in our described model, consistent with the prevailing observational data. Finally, we examine the energy condition criteria and determine that the violation of the Strong Energy Condition (SEC), while the Null Energy Condition (NEC), Weak Energy Condition (WEC) and Dominant Energy Condition (DEC) continue to meet the requirements for positivity. |
0806.2966 | Jiri Podolsky | Jiri Podolsky | Photon rockets in (anti-)de Sitter universe | 8 pages. To appear in Phys. Rev. D | Phys.Rev.D78:044029,2008 | 10.1103/PhysRevD.78.044029 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A class of exact solutions of Einstein's equations is presented which
describes accelerating photon rockets in de Sitter and anti-de Sitter universe.
These are particular members of the Robinson-Trautman family of axially
symmetric spacetimes with pure radiation. In particular, generalizations of
(type D) Kinnersley's rockets and (type II) Bonnor's rockets to the case of a
non-vanishing cosmological constant are given. Some of the main physical
properties of these solutions are investigated, and their relation to the
C-metric solution which describes uniformly accelerated black holes is also
given.
| [
{
"created": "Wed, 18 Jun 2008 11:22:49 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Podolsky",
"Jiri",
""
]
] | A class of exact solutions of Einstein's equations is presented which describes accelerating photon rockets in de Sitter and anti-de Sitter universe. These are particular members of the Robinson-Trautman family of axially symmetric spacetimes with pure radiation. In particular, generalizations of (type D) Kinnersley's rockets and (type II) Bonnor's rockets to the case of a non-vanishing cosmological constant are given. Some of the main physical properties of these solutions are investigated, and their relation to the C-metric solution which describes uniformly accelerated black holes is also given. |
2310.08667 | Andrea Calcinari | Andrea Calcinari and Steffen Gielen | Generalised Gaussian states in group field theory and
$\mathfrak{su(1,1)}$ quantum cosmology | 27 pages, 3 figures; v2: title, abstract and other minor changes to
match published version | Phys. Rev. D 109 (2024), 066022 | 10.1103/PhysRevD.109.066022 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We define generalised Gaussian states for quantum cosmological models based
on the $\mathfrak{su(1,1)}$ algebra, with particular emphasis on its
realisation in group field theory for a single field mode, and study their
semiclassical properties. These states are generalisations of coherent,
squeezed and thermal states considered previously. As two possible
characterisations of semiclassicality, we contrast the requirement of small
relative fluctuations in volume and energy with the saturation of the
Robertson--Schr\"odinger uncertainty principle. We find that for the most
general class of states the appearance of small relative fluctuations, which we
take as the main criterion relevant for the emergence of cosmology, is mostly
determined by the amount of displacement used to define the state. We also
observe that defining such generalised Gaussian states is less straightforward
in the algebraic approach to canonical quantisation of group field theory, and
discuss special cases.
| [
{
"created": "Thu, 12 Oct 2023 18:59:03 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Mar 2024 12:30:28 GMT",
"version": "v2"
}
] | 2024-03-26 | [
[
"Calcinari",
"Andrea",
""
],
[
"Gielen",
"Steffen",
""
]
] | We define generalised Gaussian states for quantum cosmological models based on the $\mathfrak{su(1,1)}$ algebra, with particular emphasis on its realisation in group field theory for a single field mode, and study their semiclassical properties. These states are generalisations of coherent, squeezed and thermal states considered previously. As two possible characterisations of semiclassicality, we contrast the requirement of small relative fluctuations in volume and energy with the saturation of the Robertson--Schr\"odinger uncertainty principle. We find that for the most general class of states the appearance of small relative fluctuations, which we take as the main criterion relevant for the emergence of cosmology, is mostly determined by the amount of displacement used to define the state. We also observe that defining such generalised Gaussian states is less straightforward in the algebraic approach to canonical quantisation of group field theory, and discuss special cases. |
2204.02244 | Michael Bradley | Philip Semr\'en, Michael Bradley | General Perturbations of Homogeneous and Orthogonal Locally Rotationally
Symmetric Class II Cosmologies with Applications to Dissipative Fluids | 27 pages, 1 figure | null | 10.1088/1361-6382/ac9bc7 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | First order perturbations of homogeneous and hypersurface orthogonal LRS
(Locally Rotationally Symmetric) class II cosmologies with a cosmological
constant are considered in the framework of the 1+1+2 covariant decomposition
of spacetime. The perturbations, which are for a general energy-momentum
tensor, include scalar, vector and tensor modes and extend some previous works
where matter was assumed to be a perfect fluid. Through a harmonic
decomposition, the system of equations is then transformed to evolution
equations in time and algebraic constraints. This result is then applied to
dissipative one-component fluids, and on using the simplified acausal Eckart
theory the system is reduced to two closed subsystems governed by four and
eight harmonic coefficients for the odd and even sectors respectively. The
system is also seen to close in a simplified causal theory. It is then
demonstrated, within the Eckart theory, how vorticity can be generated from
viscosity.
| [
{
"created": "Tue, 5 Apr 2022 14:32:15 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Apr 2022 14:55:43 GMT",
"version": "v2"
}
] | 2022-11-23 | [
[
"Semrén",
"Philip",
""
],
[
"Bradley",
"Michael",
""
]
] | First order perturbations of homogeneous and hypersurface orthogonal LRS (Locally Rotationally Symmetric) class II cosmologies with a cosmological constant are considered in the framework of the 1+1+2 covariant decomposition of spacetime. The perturbations, which are for a general energy-momentum tensor, include scalar, vector and tensor modes and extend some previous works where matter was assumed to be a perfect fluid. Through a harmonic decomposition, the system of equations is then transformed to evolution equations in time and algebraic constraints. This result is then applied to dissipative one-component fluids, and on using the simplified acausal Eckart theory the system is reduced to two closed subsystems governed by four and eight harmonic coefficients for the odd and even sectors respectively. The system is also seen to close in a simplified causal theory. It is then demonstrated, within the Eckart theory, how vorticity can be generated from viscosity. |
2206.06756 | Avijit Chowdhury | Avijit Chowdhury, Semin Xavier and S. Shankaranarayanan (IIT Bombay) | The dominating mode of two competing massive modes of quadratic gravity | To appear in Nature Scientific Reports | Sci Rep 13, 8547 (2023) | 10.1038/s41598-023-34802-8 | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | Over the last two decades, motivations for modified gravity have emerged from
both theoretical and observational levels. $f(R)$ and Chern-Simons gravity have
received more attention as they are the simplest generalization. However,
$f(R)$ and Chern-Simons gravity contain only an additional scalar (spin-0)
degree of freedom and, as a result, do not include other modes of modified
theories of gravity. In contrast, quadratic gravity (also referred to as Stelle
gravity) is the most general second-order modification to 4-D general
relativity and contains a massive spin-2 mode that is not present in $f(R)$ and
Chern-Simons gravity. Using two different physical settings $-$ the
gravitational wave energy-flux measured by the detectors and the backreaction
of the emitted gravitational radiation on the spacetime of the remnant black
hole $-$ we demonstrate that massive spin-2 mode carries more energy than the
spin-0 mode. Our analysis shows that the effects are pronounced for
intermediate-mass black holes, which are prime targets for LISA.
| [
{
"created": "Tue, 14 Jun 2022 11:08:41 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Dec 2022 14:54:02 GMT",
"version": "v2"
},
{
"created": "Wed, 24 May 2023 17:46:51 GMT",
"version": "v3"
}
] | 2023-05-29 | [
[
"Chowdhury",
"Avijit",
"",
"IIT Bombay"
],
[
"Xavier",
"Semin",
"",
"IIT Bombay"
],
[
"Shankaranarayanan",
"S.",
"",
"IIT Bombay"
]
] | Over the last two decades, motivations for modified gravity have emerged from both theoretical and observational levels. $f(R)$ and Chern-Simons gravity have received more attention as they are the simplest generalization. However, $f(R)$ and Chern-Simons gravity contain only an additional scalar (spin-0) degree of freedom and, as a result, do not include other modes of modified theories of gravity. In contrast, quadratic gravity (also referred to as Stelle gravity) is the most general second-order modification to 4-D general relativity and contains a massive spin-2 mode that is not present in $f(R)$ and Chern-Simons gravity. Using two different physical settings $-$ the gravitational wave energy-flux measured by the detectors and the backreaction of the emitted gravitational radiation on the spacetime of the remnant black hole $-$ we demonstrate that massive spin-2 mode carries more energy than the spin-0 mode. Our analysis shows that the effects are pronounced for intermediate-mass black holes, which are prime targets for LISA. |
2309.00319 | Vittorio De Falco Dr | Vittorio De Falco, Emmanuele Battista | Analytical results for binary dynamics at the first post-Newtonian order
in Einstein-Cartan theory with the Weyssenhoff fluid | 13 pages, 2 figures, accepted for pubblication on Phys. Rev. D | null | 10.1103/PhysRevD.108.064032 | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | The quantum spin effects inside matter can be modeled via the Weyssenhoff
fluid, which permits to unearth a formal analogy between general relativity and
Einstein-Cartan theory at the first post-Newtonian order. In this framework, we
provide some analytical formulas pertaining to the dynamics of binary systems
having the spins aligned perpendicular to the orbital plane. We derive the
expressions of the relative orbit and the coordinate time, which in turn allow
to determine the gravitational waveform, and the energy and angular momentum
fluxes. The potentialities of our results are presented in two astrophysical
applications, where we compute: ($i$) the quantum spin contributions to the
energy flux and gravitational waveform during the inspiral phase; ($ii$) the
macroscopic angular momentum of one of the bodies starting from the
time-averaged energy flux and the knowledge of few timing parameters.
| [
{
"created": "Fri, 1 Sep 2023 08:07:27 GMT",
"version": "v1"
}
] | 2023-09-20 | [
[
"De Falco",
"Vittorio",
""
],
[
"Battista",
"Emmanuele",
""
]
] | The quantum spin effects inside matter can be modeled via the Weyssenhoff fluid, which permits to unearth a formal analogy between general relativity and Einstein-Cartan theory at the first post-Newtonian order. In this framework, we provide some analytical formulas pertaining to the dynamics of binary systems having the spins aligned perpendicular to the orbital plane. We derive the expressions of the relative orbit and the coordinate time, which in turn allow to determine the gravitational waveform, and the energy and angular momentum fluxes. The potentialities of our results are presented in two astrophysical applications, where we compute: ($i$) the quantum spin contributions to the energy flux and gravitational waveform during the inspiral phase; ($ii$) the macroscopic angular momentum of one of the bodies starting from the time-averaged energy flux and the knowledge of few timing parameters. |
1805.07692 | Chiang-Mei Chen | Chiang-Mei Chen, Jian-Liang Liu, James M. Nester | Gravitational energy is well defined | 7 pages, Honorable Mention in the 2018 Essay Competition of the
Gravity Research Foundation | Int. J. Mod. Phys. D27 (2018) 1847017 | 10.1142/S021827181847017X | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The energy of gravitating systems has been an issue since Einstein proposed
general relativity: considered to be ill defined, having no proper local
density. Energy-momentum is now regarded as \emph{quasi-local} (associated with
a closed 2-surface). We consider the pseudotensor and quasi-local proposals in
the Lagrangian-Noether-Hamiltonian formulations. There are two ambiguities: (i)
many expressions, (ii) each depends on some non-dynamical structure, e.g., a
reference frame. The Hamiltonian approach gives a handle on both problems. Our
remarkable discovery is that with a 4D isometric Minkowski reference a large
class of expressions---those that agree with the Einstein pseudotensor's Freud
superpotential to linear order---give a common quasi-local energy value. With a
best-matched reference on the boundary this value is the non-negative Wang-Yau
mass.
| [
{
"created": "Sun, 20 May 2018 02:22:44 GMT",
"version": "v1"
}
] | 2018-11-15 | [
[
"Chen",
"Chiang-Mei",
""
],
[
"Liu",
"Jian-Liang",
""
],
[
"Nester",
"James M.",
""
]
] | The energy of gravitating systems has been an issue since Einstein proposed general relativity: considered to be ill defined, having no proper local density. Energy-momentum is now regarded as \emph{quasi-local} (associated with a closed 2-surface). We consider the pseudotensor and quasi-local proposals in the Lagrangian-Noether-Hamiltonian formulations. There are two ambiguities: (i) many expressions, (ii) each depends on some non-dynamical structure, e.g., a reference frame. The Hamiltonian approach gives a handle on both problems. Our remarkable discovery is that with a 4D isometric Minkowski reference a large class of expressions---those that agree with the Einstein pseudotensor's Freud superpotential to linear order---give a common quasi-local energy value. With a best-matched reference on the boundary this value is the non-negative Wang-Yau mass. |
gr-qc/0301013 | L. C. Garcia de Andrade | L.C. Garcia de Andrade | On non-Riemannian geometry of superfluids | Latex file | null | null | null | gr-qc | null | The Gross-Pitaevski (GP) equation describing helium superfluids is extended
to non-Riemannian spacetime background where torsion is shown to induce the
splitting in the potential energy of the flow. A cylindrically symmetric
solution for Minkowski background with constant torsion is obtained which shows
that torsion induces a damping on the superfluid flow velocity. The Sagnac
phase shift is computed from the superfluid flow velocity obtained from the
solution of GP equations.
| [
{
"created": "Sun, 5 Jan 2003 22:32:34 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
""
]
] | The Gross-Pitaevski (GP) equation describing helium superfluids is extended to non-Riemannian spacetime background where torsion is shown to induce the splitting in the potential energy of the flow. A cylindrically symmetric solution for Minkowski background with constant torsion is obtained which shows that torsion induces a damping on the superfluid flow velocity. The Sagnac phase shift is computed from the superfluid flow velocity obtained from the solution of GP equations. |
gr-qc/0203078 | Brien C. Nolan | Brien C. Nolan and Filipe C. Mena | Geometry and topology of singularities in spherical dust collapse | 12 pages. To appear in Classical and Quantum Gravity | Class.Quant.Grav.19:2587-2606,2002 | 10.1088/0264-9381/19/10/305 | null | gr-qc | null | We derive some more results on the nature of the singularities arising in the
collapse of inhomogeneous dust spheres. (i) It is shown that there are
future-pointing radial and non-radial time-like geodesics emerging from the
singularity if and only if there are future-pointing radial null geodesics
emerging from the singularity. (ii) Limits of various space-time invariants and
other useful quantities (relating to Thorne's point-cigar-barrel-pancake
classification and to isotropy/entropy measures) are studied in the approach to
the singularity. (iii) The topology of the singularity is studied from the
point of view of ideal boundary structure. In each case, the different nature
of the visible and censored region of the singularity is emphasized.
| [
{
"created": "Fri, 22 Mar 2002 17:22:42 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Nolan",
"Brien C.",
""
],
[
"Mena",
"Filipe C.",
""
]
] | We derive some more results on the nature of the singularities arising in the collapse of inhomogeneous dust spheres. (i) It is shown that there are future-pointing radial and non-radial time-like geodesics emerging from the singularity if and only if there are future-pointing radial null geodesics emerging from the singularity. (ii) Limits of various space-time invariants and other useful quantities (relating to Thorne's point-cigar-barrel-pancake classification and to isotropy/entropy measures) are studied in the approach to the singularity. (iii) The topology of the singularity is studied from the point of view of ideal boundary structure. In each case, the different nature of the visible and censored region of the singularity is emphasized. |
1404.0663 | Xihao Deng | Xihao Deng | Searching for Gravitational Wave Bursts via Bayesian Nonparametric Data
Analysis with Pulsar Timing Arrays | 30 pages, 9 figures, submitted to Physical Review D. arXiv admin
note: text overlap with arXiv:1004.3499 by other authors | Physical Review D, 90, 024020, 2014 | 10.1103/PhysRevD.90.024020 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational wave burst is a catch-all category for signals whose durations
are shorter than the observation period. We apply a method new to gravitational
wave data analysis --- Bayesian non-parameterics --- to the problem of
gravitational wave detection, with an emphasis on pulsar timing array
observations. In Bayesian non-parametrics, constraints are set on the function
space that may be reasonably thought to characterize the range of
gravitational-wave signals. This differs from the approaches currently employed
or proposed, which focus on introducing parametric signal models or looking for
excess power as evidence of the presence of a gravitational wave signal. Our
Bayesian nonparametrics analysis method addresses two issues: (1) investigate
if a gravitational wave burst is present in the data; (2) infer the sky
location of the source and the duration of the burst. Compared with the popular
method proposed by Finn \& Lommen, our method improves in two aspects: (1) we
can estimate the burst duration by adding the prior that the gravitational wave
signals are smooth, while Finn \& Lommen ignored this important point; (2) we
perform a full Bayesian analysis by marginalizing over all possible parameters
and provide robust inference on the presence of gravitational waves, while Finn
\& Lommen chose to optimize over parameters, which would increase false alarm
risk and also underestimate the parameter uncertainties.
| [
{
"created": "Wed, 2 Apr 2014 19:41:22 GMT",
"version": "v1"
},
{
"created": "Fri, 30 May 2014 01:17:21 GMT",
"version": "v2"
}
] | 2015-06-19 | [
[
"Deng",
"Xihao",
""
]
] | Gravitational wave burst is a catch-all category for signals whose durations are shorter than the observation period. We apply a method new to gravitational wave data analysis --- Bayesian non-parameterics --- to the problem of gravitational wave detection, with an emphasis on pulsar timing array observations. In Bayesian non-parametrics, constraints are set on the function space that may be reasonably thought to characterize the range of gravitational-wave signals. This differs from the approaches currently employed or proposed, which focus on introducing parametric signal models or looking for excess power as evidence of the presence of a gravitational wave signal. Our Bayesian nonparametrics analysis method addresses two issues: (1) investigate if a gravitational wave burst is present in the data; (2) infer the sky location of the source and the duration of the burst. Compared with the popular method proposed by Finn \& Lommen, our method improves in two aspects: (1) we can estimate the burst duration by adding the prior that the gravitational wave signals are smooth, while Finn \& Lommen ignored this important point; (2) we perform a full Bayesian analysis by marginalizing over all possible parameters and provide robust inference on the presence of gravitational waves, while Finn \& Lommen chose to optimize over parameters, which would increase false alarm risk and also underestimate the parameter uncertainties. |
1901.04486 | David Garfinkle | David Garfinkle | On "the'' electric field of a uniformly accelerating charge | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The problem of the electric field of a uniformly accelerating charge is a
longstanding one that has led to several issues. We resolve these issues using
techniques from linguistics, cognitive psychology, and the mathematics of
partial differential equations.
| [
{
"created": "Mon, 14 Jan 2019 18:30:23 GMT",
"version": "v1"
}
] | 2019-01-16 | [
[
"Garfinkle",
"David",
""
]
] | The problem of the electric field of a uniformly accelerating charge is a longstanding one that has led to several issues. We resolve these issues using techniques from linguistics, cognitive psychology, and the mathematics of partial differential equations. |
gr-qc/0501054 | Frank L\"offler | Ian Hawke, Frank L\"offler, Andrea Nerozzi | Excision methods for high resolution shock capturing schemes applied to
general relativistic hydrodynamics | 13 pages, 6 figures | Phys.Rev. D71 (2005) 104006 | 10.1103/PhysRevD.71.104006 | AEI-2005-002 | gr-qc | null | We present a simple method for applying excision boundary conditions for the
relativistic Euler equations. This method depends on the use of
Reconstruction-Evolution methods, a standard class of HRSC methods. We test
three different reconstruction schemes, namely TVD, PPM and ENO. The method
does not require that the coordinate system is adapted to the excision
boundary. We demonstrate the effectiveness of our method using tests containing
discontinuites, static test-fluid solutions with black holes, and full
dynamical collapse of a neutron star to a black hole. A modified PPM scheme is
introduced because of problems arisen when matching excision with the original
PPM reconstruction scheme.
| [
{
"created": "Tue, 18 Jan 2005 12:45:21 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Hawke",
"Ian",
""
],
[
"Löffler",
"Frank",
""
],
[
"Nerozzi",
"Andrea",
""
]
] | We present a simple method for applying excision boundary conditions for the relativistic Euler equations. This method depends on the use of Reconstruction-Evolution methods, a standard class of HRSC methods. We test three different reconstruction schemes, namely TVD, PPM and ENO. The method does not require that the coordinate system is adapted to the excision boundary. We demonstrate the effectiveness of our method using tests containing discontinuites, static test-fluid solutions with black holes, and full dynamical collapse of a neutron star to a black hole. A modified PPM scheme is introduced because of problems arisen when matching excision with the original PPM reconstruction scheme. |
0906.5568 | Charmousis | C. Charmousis, T. Kolyvaris and E. Papantonopoulos | Charged C-metric with conformally coupled scalar field | regular article, no figures, typos corrected, to appear in Classical
and Quantum Gravity | Class.Quant.Grav.26:175012,2009 | 10.1088/0264-9381/26/17/175012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a generalisation of the charged C-metric conformally coupled with
a scalar field in the presence of a cosmological constant. The solution is
asymptotically flat or a constant curvature spacetime. The spacetime metric has
the geometry of a usual charged C-metric with cosmological constant, where the
mass and charge are equal. When the cosmological constant is absent it is found
that the scalar field only blows up at the angular pole of the event horizon.
The presence of the cosmological constant can generically render the scalar
field regular where the metric is regular, pushing the singularity beyond the
event horizon. For certain cases of enhanced acceleration with a negative
cosmological constant, the conical singularity disappears all together and the
scalar field is everywhere regular. The black hole is then rather a black
string with its event horizon extending all the way to asymptotic infinity and
providing itself the necessary acceleration.
| [
{
"created": "Tue, 30 Jun 2009 19:29:15 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Aug 2009 19:24:03 GMT",
"version": "v2"
}
] | 2009-09-29 | [
[
"Charmousis",
"C.",
""
],
[
"Kolyvaris",
"T.",
""
],
[
"Papantonopoulos",
"E.",
""
]
] | We present a generalisation of the charged C-metric conformally coupled with a scalar field in the presence of a cosmological constant. The solution is asymptotically flat or a constant curvature spacetime. The spacetime metric has the geometry of a usual charged C-metric with cosmological constant, where the mass and charge are equal. When the cosmological constant is absent it is found that the scalar field only blows up at the angular pole of the event horizon. The presence of the cosmological constant can generically render the scalar field regular where the metric is regular, pushing the singularity beyond the event horizon. For certain cases of enhanced acceleration with a negative cosmological constant, the conical singularity disappears all together and the scalar field is everywhere regular. The black hole is then rather a black string with its event horizon extending all the way to asymptotic infinity and providing itself the necessary acceleration. |
1505.03647 | Jing-Bo Wang | Jingbo Wang and Chao-Guang Huang | BF theory explanation of the entropy for rotating isolated horizons | 8 pages, no figures | Int. J. Mod. Phys.D 25,1650100 (2016) | 10.1142/S0218271816501005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, the isolated horizons with rotation are considered. It is
shown that the symplectic form is the same as that in the nonrotating case. As
a result, the boundary degrees of freedom can be also described by an SO$(1,1)$
BF theory. The entropy satisfies the Bekenstein-Hawking area law with the same
Barbero-Immirzi parameter.
| [
{
"created": "Thu, 14 May 2015 08:25:09 GMT",
"version": "v1"
},
{
"created": "Tue, 5 Jul 2016 00:36:33 GMT",
"version": "v2"
}
] | 2016-07-06 | [
[
"Wang",
"Jingbo",
""
],
[
"Huang",
"Chao-Guang",
""
]
] | In this paper, the isolated horizons with rotation are considered. It is shown that the symplectic form is the same as that in the nonrotating case. As a result, the boundary degrees of freedom can be also described by an SO$(1,1)$ BF theory. The entropy satisfies the Bekenstein-Hawking area law with the same Barbero-Immirzi parameter. |
gr-qc/0309068 | Takashi Tamaki | Takashi Tamaki (Kyoto University), Nobuyuki Sakai (Yamagata
University) | Properties of global monopoles with an event horizon | 5 pages, 7 figures | Phys.Rev. D69 (2004) 044018 | 10.1103/PhysRevD.69.044018 | null | gr-qc astro-ph hep-ph | null | We investigate the properties of global monopoles with an event horizon. We
find that there is an unstable circular orbit even if a particle does not have
an angular momentum when the core mass is negative. We also obtain the
asymptotic form of solutions when the event horizon is much larger than the
core radius of the monopole, and discuss if they could be a model of galactic
halos.
| [
{
"created": "Sun, 14 Sep 2003 05:34:40 GMT",
"version": "v1"
},
{
"created": "Thu, 18 Sep 2003 05:09:24 GMT",
"version": "v2"
}
] | 2016-08-31 | [
[
"Tamaki",
"Takashi",
"",
"Kyoto University"
],
[
"Sakai",
"Nobuyuki",
"",
"Yamagata\n University"
]
] | We investigate the properties of global monopoles with an event horizon. We find that there is an unstable circular orbit even if a particle does not have an angular momentum when the core mass is negative. We also obtain the asymptotic form of solutions when the event horizon is much larger than the core radius of the monopole, and discuss if they could be a model of galactic halos. |
1809.06841 | Sohyun Park | Sohyun Park, R. P. Woodard | Do the Spirits Rise? | 20 pages, 7 figures, v2: revised for publication | Phys. Rev. D 99, 024014 (2019) | 10.1103/PhysRevD.99.024014 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A nonlocal gravity model based on $\frac1{\square} R$ achieves the
phenomenological goals of generating cosmic acceleration without dark energy
and of suppressing the growth of perturbations compared to the $\Lambda$CDM
model. Although the localized version of this model possesses a scalar ghost,
the nonlocal version does not suffer from any obvious problem with ghosts. Here
we study the possibility that the scalar ghost mode might be excited through
time evolution, even though it is initially absent. We present strong evidence
that this does not happen.
| [
{
"created": "Tue, 18 Sep 2018 17:43:15 GMT",
"version": "v1"
},
{
"created": "Sun, 13 Jan 2019 16:14:05 GMT",
"version": "v2"
}
] | 2019-01-16 | [
[
"Park",
"Sohyun",
""
],
[
"Woodard",
"R. P.",
""
]
] | A nonlocal gravity model based on $\frac1{\square} R$ achieves the phenomenological goals of generating cosmic acceleration without dark energy and of suppressing the growth of perturbations compared to the $\Lambda$CDM model. Although the localized version of this model possesses a scalar ghost, the nonlocal version does not suffer from any obvious problem with ghosts. Here we study the possibility that the scalar ghost mode might be excited through time evolution, even though it is initially absent. We present strong evidence that this does not happen. |
1902.09769 | Andreas Finke | Andreas Finke | The perturbed FLRW metric on all scales: Newtonian limit and top-hat
collapse | couple of useful clarifications; agrees with published version | Monthly Notices of the Royal Astronomical Society, Volume 491,
Issue 2, January 2020 | 10.1093/mnras/stz3145 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The applicability of a linearized perturbed FLRW metric to the late, lumpy
universe has been subject to debate. We consider in an elementary way the
Newtonian limit of the Einstein equations with this ansatz for the case of
structure formation in late-time cosmology, on small and large scales, and
argue that linearizing the Einstein tensor produces only a small error down to
arbitrarily small, decoupled scales (e.g. Solar system scales). On subhorizon
patches, the metric scale factor becomes a coordinate choice equivalent to
choosing the spatial curvature, and not a sign that the FLRW metric cannot
perturbatively accommodate very different local physical expansion rates of
matter; we distinguish these concepts, and show that they merge on large scales
for the Newtonian limit to be globally valid. Furthermore, on subhorizon
scales, a perturbed FLRW metric ansatz does not already imply assumptions on
isotropy, and effects beyond an FLRW background, including those potentially
caused by non-linearities of general relativity (GR), may be encoded into
non-trivial boundary conditions. The corresponding cosmologies have already
been developed in a Newtonian setting by Heckmann and Sch\"ucking and none of
these boundary conditions can explain the accelerated expansion of the
universe. Our analysis of the field equations is confirmed on the level of
solutions by an example of pedagogical value, comparing a collapsing top-hat
overdensity (embedded into a cosmological background) treated in such
perturbative manner to the corresponding exact solution of GR, where we find
good agreement even in the regimes of strong density contrast.
| [
{
"created": "Tue, 26 Feb 2019 07:18:22 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Jul 2019 12:17:01 GMT",
"version": "v2"
},
{
"created": "Tue, 17 Dec 2019 10:29:38 GMT",
"version": "v3"
}
] | 2019-12-18 | [
[
"Finke",
"Andreas",
""
]
] | The applicability of a linearized perturbed FLRW metric to the late, lumpy universe has been subject to debate. We consider in an elementary way the Newtonian limit of the Einstein equations with this ansatz for the case of structure formation in late-time cosmology, on small and large scales, and argue that linearizing the Einstein tensor produces only a small error down to arbitrarily small, decoupled scales (e.g. Solar system scales). On subhorizon patches, the metric scale factor becomes a coordinate choice equivalent to choosing the spatial curvature, and not a sign that the FLRW metric cannot perturbatively accommodate very different local physical expansion rates of matter; we distinguish these concepts, and show that they merge on large scales for the Newtonian limit to be globally valid. Furthermore, on subhorizon scales, a perturbed FLRW metric ansatz does not already imply assumptions on isotropy, and effects beyond an FLRW background, including those potentially caused by non-linearities of general relativity (GR), may be encoded into non-trivial boundary conditions. The corresponding cosmologies have already been developed in a Newtonian setting by Heckmann and Sch\"ucking and none of these boundary conditions can explain the accelerated expansion of the universe. Our analysis of the field equations is confirmed on the level of solutions by an example of pedagogical value, comparing a collapsing top-hat overdensity (embedded into a cosmological background) treated in such perturbative manner to the corresponding exact solution of GR, where we find good agreement even in the regimes of strong density contrast. |
1506.00989 | Barun Kumar Pal Dr. | Barun Kumar Pal | Theoretical and observational aspects of cosmological inflation | PHD thesis defended on 20/11/2014 at Jadavpur University, 124 Pages
and 22 Figures. arXiv admin note: text overlap with arXiv:0906.0664,
arXiv:hep-ph/0210162 by other authors | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This thesis piles up the results of five works in the field of cosmological
inflation, inflationary cosmological perturbations, cosmic microwave
background(CMB) and weak gravitational lensing of cosmic microwave background.
| [
{
"created": "Tue, 2 Jun 2015 19:09:19 GMT",
"version": "v1"
}
] | 2015-06-03 | [
[
"Pal",
"Barun Kumar",
""
]
] | This thesis piles up the results of five works in the field of cosmological inflation, inflationary cosmological perturbations, cosmic microwave background(CMB) and weak gravitational lensing of cosmic microwave background. |
2404.18288 | Wei-Liang Qian | Shui-Fa Shen, Wei-Liang Qian, Jie Zhang, Yu Pan, Yu-Peng Yan,
Cheng-Gang Shao | Matrix method and the suppression of Runge's phenomenon | 17 pages, 4 figures and 4 tables | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Higher-degree polynomial interpolations carried out on uniformly distributed
nodes are often plagued by {\it overfitting}, known as Runge's phenomenon. This
work investigates Runge's phenomenon and its suppression in various versions of
the matrix method for black hole quasinormal modes. It is shown that an
appropriate choice of boundary conditions gives rise to desirable suppression
of oscillations associated with the increasing Lebesgue constant. For the case
of discontinuous effective potentials, where the application of the above
boundary condition is not feasible, the recently proposed scheme with delimited
expansion domain also leads to satisfactory results. The onset of Runge's
phenomenon and its effective suppression are demonstrated by evaluating the
relevant waveforms. Furthermore, we argue that both scenarios are either
closely related to or practical imitations of the Chebyshev grid. The
implications of the present study are also addressed.
| [
{
"created": "Sun, 28 Apr 2024 19:28:55 GMT",
"version": "v1"
}
] | 2024-04-30 | [
[
"Shen",
"Shui-Fa",
""
],
[
"Qian",
"Wei-Liang",
""
],
[
"Zhang",
"Jie",
""
],
[
"Pan",
"Yu",
""
],
[
"Yan",
"Yu-Peng",
""
],
[
"Shao",
"Cheng-Gang",
""
]
] | Higher-degree polynomial interpolations carried out on uniformly distributed nodes are often plagued by {\it overfitting}, known as Runge's phenomenon. This work investigates Runge's phenomenon and its suppression in various versions of the matrix method for black hole quasinormal modes. It is shown that an appropriate choice of boundary conditions gives rise to desirable suppression of oscillations associated with the increasing Lebesgue constant. For the case of discontinuous effective potentials, where the application of the above boundary condition is not feasible, the recently proposed scheme with delimited expansion domain also leads to satisfactory results. The onset of Runge's phenomenon and its effective suppression are demonstrated by evaluating the relevant waveforms. Furthermore, we argue that both scenarios are either closely related to or practical imitations of the Chebyshev grid. The implications of the present study are also addressed. |
2107.11497 | Raphael Wittkowski | Michael te Vrugt, Sabine Hossenfelder, Raphael Wittkowski | Mori-Zwanzig formalism for general relativity: a new approach to the
averaging problem | 7 pages, 1 figure | Physical Review Letters 127, 231101 (2021) | 10.1103/PhysRevLett.127.231101 | null | gr-qc astro-ph.CO cond-mat.stat-mech hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cosmology relies on a coarse-grained description of the universe, assumed to
be valid on large length scales. However, the nonlinearity of general
relativity makes coarse-graining extremely difficult. We here address this
problem by extending the Mori-Zwanzig projection operator formalism, a highly
successful coarse-graining method from statistical mechanics, towards general
relativity. Using the Buchert equations, we derive a new dynamic equation for
the Hubble parameter which captures the effects of averaging through a memory
function. This gives an empirical prediction for the cosmic jerk.
| [
{
"created": "Sat, 24 Jul 2021 00:51:00 GMT",
"version": "v1"
}
] | 2021-12-07 | [
[
"Vrugt",
"Michael te",
""
],
[
"Hossenfelder",
"Sabine",
""
],
[
"Wittkowski",
"Raphael",
""
]
] | Cosmology relies on a coarse-grained description of the universe, assumed to be valid on large length scales. However, the nonlinearity of general relativity makes coarse-graining extremely difficult. We here address this problem by extending the Mori-Zwanzig projection operator formalism, a highly successful coarse-graining method from statistical mechanics, towards general relativity. Using the Buchert equations, we derive a new dynamic equation for the Hubble parameter which captures the effects of averaging through a memory function. This gives an empirical prediction for the cosmic jerk. |
1512.06497 | Ryotaro Kase | Ryotaro Kase, Shinji Tsujikawa and Antonio De Felice | Conical singularities and the Vainshtein screening in full GLPV theories | 25 pages, 1 figure | JCAP03(2016)003 | 10.1088/1475-7516/2016/03/003 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, it is known that the
conical singularity arises at the center of a spherically symmetric body
($r=0$) in the case where the parameter $\alpha_{{\rm H}4}$ characterizing the
deviation from the Horndeski Lagrangian $L_4$ approaches a non-zero constant as
$r \to 0$. We derive spherically symmetric solutions around the center in full
GLPV theories and show that the GLPV Lagrangian $L_5$ does not modify the
divergent property of the Ricci scalar $R$ induced by the non-zero
$\alpha_{{\rm H}4}$. Provided that $\alpha_{{\rm H}4}=0$, curvature scalar
quantities can remain finite at $r=0$ even in the presence of $L_5$ beyond the
Horndeski domain. For the theories in which the scalar field $\phi$ is directly
coupled to $R$, we also obtain spherically symmetric solutions inside/outside
the body to study whether the fifth force mediated by $\phi$ can be screened by
non-linear field self-interactions. We find that there is one specific model of
GLPV theories in which the effect of $L_5$ vanishes in the equations of motion.
We also show that, depending on the sign of a $L_5$-dependent term in the field
equation, the model can be compatible with solar-system constraints under the
Vainshtein mechanism or it is plagued by the problem of a divergence of the
field derivative in high-density regions.
| [
{
"created": "Mon, 21 Dec 2015 05:17:16 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Mar 2016 05:34:49 GMT",
"version": "v2"
}
] | 2016-03-03 | [
[
"Kase",
"Ryotaro",
""
],
[
"Tsujikawa",
"Shinji",
""
],
[
"De Felice",
"Antonio",
""
]
] | In Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, it is known that the conical singularity arises at the center of a spherically symmetric body ($r=0$) in the case where the parameter $\alpha_{{\rm H}4}$ characterizing the deviation from the Horndeski Lagrangian $L_4$ approaches a non-zero constant as $r \to 0$. We derive spherically symmetric solutions around the center in full GLPV theories and show that the GLPV Lagrangian $L_5$ does not modify the divergent property of the Ricci scalar $R$ induced by the non-zero $\alpha_{{\rm H}4}$. Provided that $\alpha_{{\rm H}4}=0$, curvature scalar quantities can remain finite at $r=0$ even in the presence of $L_5$ beyond the Horndeski domain. For the theories in which the scalar field $\phi$ is directly coupled to $R$, we also obtain spherically symmetric solutions inside/outside the body to study whether the fifth force mediated by $\phi$ can be screened by non-linear field self-interactions. We find that there is one specific model of GLPV theories in which the effect of $L_5$ vanishes in the equations of motion. We also show that, depending on the sign of a $L_5$-dependent term in the field equation, the model can be compatible with solar-system constraints under the Vainshtein mechanism or it is plagued by the problem of a divergence of the field derivative in high-density regions. |
gr-qc/0511045 | Ignacio Navarro | Ignacio Navarro and Karel Van Acoleyen | Consistent long distance modification of gravity from inverse powers of
the curvature | 27 pages, 1 figure, v2. references added, improved discussion | JCAP 0603 (2006) 008 | 10.1088/1475-7516/2006/03/008 | DAMTP-2005-105, DCPT/05/142, IPPP/05/71 | gr-qc astro-ph hep-th | null | In this paper we study long distance modifications of gravity obtained by
considering actions that are singular in the limit of vanishing curvature. In
particular, we showed in a previous publication that models that include
inverse powers of curvature invariants that diverge for r->0 in the
Schwarzschild geometry, recover an acceptable weak field limit at short
distances from sources. We study then the linearisation of generic actions of
the form L=F[R,P,Q] where P=R_{ab}R^{ab} and Q=R_{abcd}R^{abcd}. We show that
for the case in which F[R,P,Q]=F[R,Q-4P], the theory is ghost free. Assuming
this is the case, in the models that can explain the acceleration of the
Universe without recourse to Dark Energy there is still an extra scalar field
in the spectrum besides the massless spin two graviton. The mass of this extra
excitation is of the order of the Hubble scale in vacuum. We nevertheless
recover Einstein gravity at short distances because the mass of this scalar
field depends on the background in such a way that it effectively decouples
when one gets close to any source. Remarkably, for the values of the parameters
necessary to explain the cosmic acceleration the induced modifications of
gravity are suppressed at the Solar System level but can be important for
systems like a galaxy.
| [
{
"created": "Wed, 9 Nov 2005 19:16:35 GMT",
"version": "v1"
},
{
"created": "Fri, 9 Dec 2005 20:02:21 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Navarro",
"Ignacio",
""
],
[
"Van Acoleyen",
"Karel",
""
]
] | In this paper we study long distance modifications of gravity obtained by considering actions that are singular in the limit of vanishing curvature. In particular, we showed in a previous publication that models that include inverse powers of curvature invariants that diverge for r->0 in the Schwarzschild geometry, recover an acceptable weak field limit at short distances from sources. We study then the linearisation of generic actions of the form L=F[R,P,Q] where P=R_{ab}R^{ab} and Q=R_{abcd}R^{abcd}. We show that for the case in which F[R,P,Q]=F[R,Q-4P], the theory is ghost free. Assuming this is the case, in the models that can explain the acceleration of the Universe without recourse to Dark Energy there is still an extra scalar field in the spectrum besides the massless spin two graviton. The mass of this extra excitation is of the order of the Hubble scale in vacuum. We nevertheless recover Einstein gravity at short distances because the mass of this scalar field depends on the background in such a way that it effectively decouples when one gets close to any source. Remarkably, for the values of the parameters necessary to explain the cosmic acceleration the induced modifications of gravity are suppressed at the Solar System level but can be important for systems like a galaxy. |
1306.3164 | Mehrdad Farhoudi Prof. | Hamid Shabani and Mehrdad Farhoudi | f(R,T) Cosmological Models in Phase Space | 30 pages, many figures, some corrections made, Refs. added | Phys. Rev. D 88, 044048 (2013) | 10.1103/PhysRevD.88.044048 | null | gr-qc astro-ph.CO hep-th math-ph math.MP physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate cosmological solutions of f(R,T) modified theories of gravity
for perfect fluid in spatially FLRW metric through phase space analysis, where
R is Ricci scalar and T denotes the trace of energy-momentum tensor of matter
content. We explore and analyze three general theories with Lagrangians of
minimal $g(R)+h(T)$, pure non--minimal g(R)h(T) and non-minimal $g(R)(1+h(T))$
couplings through dynamical systems approach. We introduce a few variables and
dimensionless parameters to simplify the equations in more concise forms. The
conservation of energy-momentum tensor leads to a constraint equation that, in
the minimal gravity, confines functionality of h(T) to a particular form,
hence, relates the dynamical variables. In this case, acceptable cosmological
solutions that contain a long enough matter dominated era followed by a
late-time accelerated expansion are found. To support theoretical results, we
also obtain numerical solutions for a few functions of g(R), and results of the
corresponding models confirm the predictions. We classify solutions into six
classes which demonstrate more acceptable solutions and there is more freedom
to have the matter dominated era than in the f(R) gravity. In particular, there
is a new fixed point which can represent late-time acceleration. We draw
different diagrams of the matter densities (consistent with the present
values), the related scale factors and effective equation of state. The
corresponding diagrams of parameters illustrate that there is a saddle
acceleration era which is a middle era before final stable acceleration de
Sitter era for some models. All presented diagrams determine radiation, matter
and late-time acceleration eras very well.
| [
{
"created": "Thu, 13 Jun 2013 16:55:24 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jun 2013 17:53:48 GMT",
"version": "v2"
},
{
"created": "Sat, 3 Aug 2013 13:30:50 GMT",
"version": "v3"
},
{
"created": "Mon, 19 Aug 2013 13:15:53 GMT",
"version": "v4"
}
] | 2017-05-23 | [
[
"Shabani",
"Hamid",
""
],
[
"Farhoudi",
"Mehrdad",
""
]
] | We investigate cosmological solutions of f(R,T) modified theories of gravity for perfect fluid in spatially FLRW metric through phase space analysis, where R is Ricci scalar and T denotes the trace of energy-momentum tensor of matter content. We explore and analyze three general theories with Lagrangians of minimal $g(R)+h(T)$, pure non--minimal g(R)h(T) and non-minimal $g(R)(1+h(T))$ couplings through dynamical systems approach. We introduce a few variables and dimensionless parameters to simplify the equations in more concise forms. The conservation of energy-momentum tensor leads to a constraint equation that, in the minimal gravity, confines functionality of h(T) to a particular form, hence, relates the dynamical variables. In this case, acceptable cosmological solutions that contain a long enough matter dominated era followed by a late-time accelerated expansion are found. To support theoretical results, we also obtain numerical solutions for a few functions of g(R), and results of the corresponding models confirm the predictions. We classify solutions into six classes which demonstrate more acceptable solutions and there is more freedom to have the matter dominated era than in the f(R) gravity. In particular, there is a new fixed point which can represent late-time acceleration. We draw different diagrams of the matter densities (consistent with the present values), the related scale factors and effective equation of state. The corresponding diagrams of parameters illustrate that there is a saddle acceleration era which is a middle era before final stable acceleration de Sitter era for some models. All presented diagrams determine radiation, matter and late-time acceleration eras very well. |
1509.06316 | Andrzej Krasi\'nski | Andrzej Krasi\'nski | Cosmological blueshifting may explain the gamma ray bursts | 23 pages, 18 figures. Typos corrected, title and two sentences in the
abstract modified, bibliography updated. The present text matches the
published version | Phys. Rev. D 93, 043525 (2016) | 10.1103/PhysRevD.93.043525 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that the basic observed properties of the gamma-ray bursts (GRBs)
are accounted for if one assumes that the GRBs arise by blueshifting the
emission radiation of hydrogen and helium generated during the last scattering
epoch. The blueshift generator for a single GRB is a region with a nonconstant
bang-time function $t_B(r)$ (described by a Lema\^{\i}tre -- Tolman (L--T)
exact solution of Einstein's equations) matched into a homogeneous and
isotropic (Friedmann) background. Blueshift visible to the present observer
arises \textit{only on those rays that are emitted radially in an L--T region}.
The paper presents three L--T models with different Big Bang profiles, adapted
for the highest and the lowest end of the GRB frequency range. The models
account for: (1) The observed frequency range of the GRBs; (2) Their limited
duration; (3) The afterglows; (4) Their hypothetical collimation into narrow
jets; (5) The large distances to their sources; (6) The multitude of the
observed GRBs. Properties (2), (3) and (6) are accounted for only
qualitatively. With a small correction of the parameters of the model, the
implied perturbations of the CMB radiation will be consistent with those
actually caused by the GRBs. A complete model of the Universe would consist of
many L--T regions with different $t_B(r)$ profiles, matched into the same
Friedmann background. This paper is meant to be an initial exploration of the
possibilities offered by models of this kind; the actual fitting of all
parameters to observational results requires fine-tuning of several
interconnected variables and is left for a separate study.
| [
{
"created": "Mon, 21 Sep 2015 17:28:36 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Feb 2016 15:01:24 GMT",
"version": "v2"
}
] | 2016-02-24 | [
[
"Krasiński",
"Andrzej",
""
]
] | It is shown that the basic observed properties of the gamma-ray bursts (GRBs) are accounted for if one assumes that the GRBs arise by blueshifting the emission radiation of hydrogen and helium generated during the last scattering epoch. The blueshift generator for a single GRB is a region with a nonconstant bang-time function $t_B(r)$ (described by a Lema\^{\i}tre -- Tolman (L--T) exact solution of Einstein's equations) matched into a homogeneous and isotropic (Friedmann) background. Blueshift visible to the present observer arises \textit{only on those rays that are emitted radially in an L--T region}. The paper presents three L--T models with different Big Bang profiles, adapted for the highest and the lowest end of the GRB frequency range. The models account for: (1) The observed frequency range of the GRBs; (2) Their limited duration; (3) The afterglows; (4) Their hypothetical collimation into narrow jets; (5) The large distances to their sources; (6) The multitude of the observed GRBs. Properties (2), (3) and (6) are accounted for only qualitatively. With a small correction of the parameters of the model, the implied perturbations of the CMB radiation will be consistent with those actually caused by the GRBs. A complete model of the Universe would consist of many L--T regions with different $t_B(r)$ profiles, matched into the same Friedmann background. This paper is meant to be an initial exploration of the possibilities offered by models of this kind; the actual fitting of all parameters to observational results requires fine-tuning of several interconnected variables and is left for a separate study. |
gr-qc/0611123 | Sayan Kar | Sayan Kar (IIT Kharagpur, India) and Soumitra SenGupta (IACS, Kolkata,
India) | The Raychaudhuri equations: a brief review | 35 pages, two figures, to appear in the special issue of Pramana
dedicated to the memory of A. K. Raychaudhuri | Pramana69:49,2007 | 10.1007/s12043-007-0110-9 | null | gr-qc | null | We present a brief review on the Raychaudhuri equations. Beginning with a
summary of the essential features of the original article by Raychaudhuri and
subsequent work of numerous authors, we move on to a discussion of the
equations in the context of alternate non--Riemannian spacetimes as well as
other theories of gravity, with a special mention on the equations in
spacetimes with torsion (Einstein--Cartan--Sciama--Kibble theory). Finally, we
give an overview of some recent applications of these equations in General
Relativity, Quantum Field Theory, String Theory and the theory of relativisitic
membranes. We conclude with a summary and provide our own perspectives on
directions of future research.
| [
{
"created": "Thu, 23 Nov 2006 10:55:07 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Kar",
"Sayan",
"",
"IIT Kharagpur, India"
],
[
"SenGupta",
"Soumitra",
"",
"IACS, Kolkata,\n India"
]
] | We present a brief review on the Raychaudhuri equations. Beginning with a summary of the essential features of the original article by Raychaudhuri and subsequent work of numerous authors, we move on to a discussion of the equations in the context of alternate non--Riemannian spacetimes as well as other theories of gravity, with a special mention on the equations in spacetimes with torsion (Einstein--Cartan--Sciama--Kibble theory). Finally, we give an overview of some recent applications of these equations in General Relativity, Quantum Field Theory, String Theory and the theory of relativisitic membranes. We conclude with a summary and provide our own perspectives on directions of future research. |
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