id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2207.02106 | Rahul Kumar | Rahul Kumar Walia | Observational predictions of LQG motivated polymerized black holes and
constraints from Sgr A* and M87* | 46 pages, 20 figures and 5 tables. Matched with the published version | JCAP 03, 029 (2023) | 10.1088/1475-7516/2023/03/029 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Loop quantum gravity inspired partial polymer quantization in
four-dimensional spacetime leads to a globally regular black hole with a single
horizon. The polymerized black hole metric is characterized by the minimum
length parameter $k$, and mimics the Schwarzschild black hole in the weak-field
limit. We present an analytic and numerical investigation of the strong
gravitational lensing and shadow morphology to determine the observational
impacts of quantum effects. Interestingly, the light deflection angle, the
angular separation between the outermost relativistic image, and magnification
are significantly larger than those for the Schwarzschild black hole. Using the
ray-tracing technique, we simulate the black hole shadows under three distinct
optically thin accretion models: static spherical accretion, radially infalling
spherical accretion, and the thin accretion disk model. Polymerized black
holes' shadow morphology strongly depends on $k$. We derive constraints on $k$
from the M87* and Sgr A* black hole shadow observations from the Event Horizon
Telescope.
| [
{
"created": "Tue, 5 Jul 2022 15:20:27 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Mar 2023 01:11:04 GMT",
"version": "v2"
}
] | 2023-03-14 | [
[
"Walia",
"Rahul Kumar",
""
]
] | Loop quantum gravity inspired partial polymer quantization in four-dimensional spacetime leads to a globally regular black hole with a single horizon. The polymerized black hole metric is characterized by the minimum length parameter $k$, and mimics the Schwarzschild black hole in the weak-field limit. We present an analytic and numerical investigation of the strong gravitational lensing and shadow morphology to determine the observational impacts of quantum effects. Interestingly, the light deflection angle, the angular separation between the outermost relativistic image, and magnification are significantly larger than those for the Schwarzschild black hole. Using the ray-tracing technique, we simulate the black hole shadows under three distinct optically thin accretion models: static spherical accretion, radially infalling spherical accretion, and the thin accretion disk model. Polymerized black holes' shadow morphology strongly depends on $k$. We derive constraints on $k$ from the M87* and Sgr A* black hole shadow observations from the Event Horizon Telescope. |
gr-qc/0505134 | C\'edric Deffayet | Cedric Deffayet, Jan-Willem Rombouts | Ghosts, Strong Coupling and Accidental Symmetries in Massive Gravity | 21 pages | Phys.Rev.D72:044003,2005 | 10.1103/PhysRevD.72.044003 | null | gr-qc hep-ph hep-th | null | We show that the strong self-interaction of the scalar polarization of a
massive graviton can be understood in terms of the propagation of an extra
ghost-like degree of freedom, thus relating strong coupling to the sixth degree
of freedom discussed by Boulware and Deser in their Hamiltonian analysis of
massive gravity. This enables one to understand the Vainshtein recovery of
solutions of massless gravity as being due to the effect of the exchange of
this ghost which gets frozen at distances larger than the Vainshtein radius.
Inside this region, we can trust the two-field Lagrangian perturbatively, while
at larger distances one can use the higher derivative formulation. We also
compare massive gravity with other models, namely deconstructed theories of
gravity, as well as DGP model. In the latter case we argue that the Vainshtein
recovery process is of different nature, not involving a ghost degree of
freedom.
| [
{
"created": "Thu, 26 May 2005 17:18:13 GMT",
"version": "v1"
}
] | 2009-10-07 | [
[
"Deffayet",
"Cedric",
""
],
[
"Rombouts",
"Jan-Willem",
""
]
] | We show that the strong self-interaction of the scalar polarization of a massive graviton can be understood in terms of the propagation of an extra ghost-like degree of freedom, thus relating strong coupling to the sixth degree of freedom discussed by Boulware and Deser in their Hamiltonian analysis of massive gravity. This enables one to understand the Vainshtein recovery of solutions of massless gravity as being due to the effect of the exchange of this ghost which gets frozen at distances larger than the Vainshtein radius. Inside this region, we can trust the two-field Lagrangian perturbatively, while at larger distances one can use the higher derivative formulation. We also compare massive gravity with other models, namely deconstructed theories of gravity, as well as DGP model. In the latter case we argue that the Vainshtein recovery process is of different nature, not involving a ghost degree of freedom. |
gr-qc/0212029 | Sandro Silva e Costa | Sandro Silva e Costa (IAG-USP) | The harmonic oscillator, dimensional analysis and inflationary solutions | 6 pages, revtex4, no figures | null | null | null | gr-qc astro-ph | null | In this work, focused on the production of exact inflationary solutions using
dimensional analysis, it is shown how to explain inflation from a pragmatic and
basic point of view, in a step-by-step process, starting from the
one-dimensional harmonic oscillator.
| [
{
"created": "Fri, 6 Dec 2002 02:21:19 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Costa",
"Sandro Silva e",
"",
"IAG-USP"
]
] | In this work, focused on the production of exact inflationary solutions using dimensional analysis, it is shown how to explain inflation from a pragmatic and basic point of view, in a step-by-step process, starting from the one-dimensional harmonic oscillator. |
1803.02135 | Jian-dong Zhang | Changfu Shi, Jian-dong Zhang, Jianwei Mei | Hidden Conformal Symmetry for Vector Field on Various Black Hole
Backgrounds | 18 pages, no figure, matches the published version | JHEP04(2018)001 | 10.1007/JHEP04(2018)001 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hidden conformal symmetries of scalar field on various black hole backgrounds
have been investigated for years, but whether those features holds for other
fields are still open questions. Recently, with proper assumptions, Lunin
achieves to the separation of variables for Maxwell equations on Kerr
background. In this paper, with that equation, we find that hidden conformal
symmetry appears at near region under low frequency limit. We also extended
those results to vector field on Kerr-(A)dS and Kerr-NUT-(A)dS backgrounds,
then hidden conformal symmetry also appears if we focusing on the near-horizon
region at low frequency limit.
| [
{
"created": "Tue, 6 Mar 2018 12:15:44 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Apr 2018 05:20:22 GMT",
"version": "v2"
}
] | 2018-04-10 | [
[
"Shi",
"Changfu",
""
],
[
"Zhang",
"Jian-dong",
""
],
[
"Mei",
"Jianwei",
""
]
] | Hidden conformal symmetries of scalar field on various black hole backgrounds have been investigated for years, but whether those features holds for other fields are still open questions. Recently, with proper assumptions, Lunin achieves to the separation of variables for Maxwell equations on Kerr background. In this paper, with that equation, we find that hidden conformal symmetry appears at near region under low frequency limit. We also extended those results to vector field on Kerr-(A)dS and Kerr-NUT-(A)dS backgrounds, then hidden conformal symmetry also appears if we focusing on the near-horizon region at low frequency limit. |
1807.00180 | Orlando Luongo | Orlando Luongo, Marco Muccino | Speeding up the universe using dust with pressure | 11 pages, 2 figures, accepted for publication in Phys. Rev. D | Phys. Rev. D 98, 103520 (2018) | 10.1103/PhysRevD.98.103520 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revise the cosmological standard model presuming that matter, i.e. baryons
and cold dark matter, exhibits a non-vanishing pressure mimicking the
cosmological constant effects. In particular, we propose a scalar field
Lagrangian $\mathcal L_1$ for matter with the introduction of a Lagrange
multiplier as constraint. We also add a symmetry breaking effective potential
accounting for the classical cosmological constant problem, by adding a second
Lagrangian $\mathcal{L}_2$. Investigating the Noether current due to the shift
symmetry on the scalar field, $\varphi\rightarrow\varphi+c^0$, we show that
$\mathcal{L}_1$ turns out to be independent from the scalar field $\varphi$.
Further we find that a positive Helmotz free-energy naturally leads to a
negative pressure without introducing by hand any dark energy term. To face out
the fine-tuning problem, we investigate two phases: before and after transition
due to the symmetry breaking. We propose that during transition dark matter
cancels out the quantum field vacuum energy effects. This process leads to a
negative and constant pressure whose magnitude is determined by baryons only.
The numerical bounds over the pressure and matter densities are in agreement
with current observations, alleviating the coincidence problem. Finally
assuming a thermal equilibrium between the bath and our effective fluid, we
estimate the mass of the dark matter candidate. Our numerical outcomes seem to
be compatible with recent predictions on WIMP masses, for fixed spin and
temperature. In particular, we predict possible candidates whose masses span in
the range $0.5-1.7$ TeV.
| [
{
"created": "Sat, 30 Jun 2018 14:00:16 GMT",
"version": "v1"
},
{
"created": "Tue, 20 Nov 2018 11:04:45 GMT",
"version": "v2"
}
] | 2018-11-28 | [
[
"Luongo",
"Orlando",
""
],
[
"Muccino",
"Marco",
""
]
] | We revise the cosmological standard model presuming that matter, i.e. baryons and cold dark matter, exhibits a non-vanishing pressure mimicking the cosmological constant effects. In particular, we propose a scalar field Lagrangian $\mathcal L_1$ for matter with the introduction of a Lagrange multiplier as constraint. We also add a symmetry breaking effective potential accounting for the classical cosmological constant problem, by adding a second Lagrangian $\mathcal{L}_2$. Investigating the Noether current due to the shift symmetry on the scalar field, $\varphi\rightarrow\varphi+c^0$, we show that $\mathcal{L}_1$ turns out to be independent from the scalar field $\varphi$. Further we find that a positive Helmotz free-energy naturally leads to a negative pressure without introducing by hand any dark energy term. To face out the fine-tuning problem, we investigate two phases: before and after transition due to the symmetry breaking. We propose that during transition dark matter cancels out the quantum field vacuum energy effects. This process leads to a negative and constant pressure whose magnitude is determined by baryons only. The numerical bounds over the pressure and matter densities are in agreement with current observations, alleviating the coincidence problem. Finally assuming a thermal equilibrium between the bath and our effective fluid, we estimate the mass of the dark matter candidate. Our numerical outcomes seem to be compatible with recent predictions on WIMP masses, for fixed spin and temperature. In particular, we predict possible candidates whose masses span in the range $0.5-1.7$ TeV. |
2404.06509 | Yixuan Ma | Yixuan Ma and Luciano Rezzolla | Horizon-penetrating form of parametrized metrics for static and
stationary black holes | 15 pages, submitted to PRD, matching the accepted version | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Rezzolla-Zhidenko (RZ) and Konoplya-Rezzolla-Zhidenko (KRZ) frameworks
provide an efficient approach to characterize agnostically spherically
symmetric or stationary black-hole spacetimes in arbitrary metric theories. In
their original construction, these metrics were defined only in the spacetime
region outside of the event horizon, where they can reproduce any black-hole
metric with percent precision and a few parameters only. At the same time,
numerical simulations of accreting black holes often require metric functions
that are regular across the horizon, so that the inner boundary of the
computational domain can be placed in a region that is causally disconnected
from the exterior. We present a novel formulation of the RZ/KRZ parametrized
metrics in coordinate systems that are regular at the horizon and defined
everywhere in the interior. We compare the horizon-penetrating form of the KRZ
and RZ metrics with the corresponding forms of the Kerr metric in Kerr-Schild
coordinates and of the Schwarzschild metric in Eddington-Finkelstein
coordinates, remarking the similarities and differences. We expect the
horizon-penetrating formulations of the RZ/KRZ metrics to represent new tools
to study via simulations the physical processes that occur near the horizon of
an arbitrary black hole.
| [
{
"created": "Tue, 9 Apr 2024 17:59:04 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Apr 2024 18:00:21 GMT",
"version": "v2"
},
{
"created": "Mon, 17 Jun 2024 18:00:03 GMT",
"version": "v3"
}
] | 2024-06-19 | [
[
"Ma",
"Yixuan",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | The Rezzolla-Zhidenko (RZ) and Konoplya-Rezzolla-Zhidenko (KRZ) frameworks provide an efficient approach to characterize agnostically spherically symmetric or stationary black-hole spacetimes in arbitrary metric theories. In their original construction, these metrics were defined only in the spacetime region outside of the event horizon, where they can reproduce any black-hole metric with percent precision and a few parameters only. At the same time, numerical simulations of accreting black holes often require metric functions that are regular across the horizon, so that the inner boundary of the computational domain can be placed in a region that is causally disconnected from the exterior. We present a novel formulation of the RZ/KRZ parametrized metrics in coordinate systems that are regular at the horizon and defined everywhere in the interior. We compare the horizon-penetrating form of the KRZ and RZ metrics with the corresponding forms of the Kerr metric in Kerr-Schild coordinates and of the Schwarzschild metric in Eddington-Finkelstein coordinates, remarking the similarities and differences. We expect the horizon-penetrating formulations of the RZ/KRZ metrics to represent new tools to study via simulations the physical processes that occur near the horizon of an arbitrary black hole. |
0912.2920 | Sebastiano Bernuzzi | Sebastiano Bernuzzi and David Hilditch | Constraint violation in free evolution schemes: comparing BSSNOK with a
conformal decomposition of Z4 | Published in PRD | Phys.Rev.D81:084003,2010 | 10.1103/PhysRevD.81.084003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compare numerical evolutions performed with the BSSNOK formulation and a
conformal decomposition of a Z4-like formulation of General Relativity. The
important difference between the two formulations is that the Z4 formulation
has a propagating Hamiltonian constraint, whereas BSSNOK has a zero-speed
characteristic variable in the constraint subsystem. In spherical symmetry we
evolve both puncture and neutron star initial data. We demonstrate that the
propagating nature of the Z4 constraints leads to results that compare
favorably with BSSNOK evolutions, especially when matter is present in the
spacetime. From the point of view of implementation the new system is a simple
modification of BSSNOK.
| [
{
"created": "Tue, 15 Dec 2009 15:12:17 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Apr 2010 16:38:50 GMT",
"version": "v2"
}
] | 2010-04-29 | [
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Hilditch",
"David",
""
]
] | We compare numerical evolutions performed with the BSSNOK formulation and a conformal decomposition of a Z4-like formulation of General Relativity. The important difference between the two formulations is that the Z4 formulation has a propagating Hamiltonian constraint, whereas BSSNOK has a zero-speed characteristic variable in the constraint subsystem. In spherical symmetry we evolve both puncture and neutron star initial data. We demonstrate that the propagating nature of the Z4 constraints leads to results that compare favorably with BSSNOK evolutions, especially when matter is present in the spacetime. From the point of view of implementation the new system is a simple modification of BSSNOK. |
2202.08142 | Soumya Chakrabarti | Soumya Chakrabarti | On Generalized Theories of Varying Fine Structure Constant | 20 pages; 25 figures; manuscript in communication; comments are
welcome | null | 10.1093/mnras/stac979 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We work with a class of scalar extended theory of gravity that can drive the
present cosmic acceleration as well as accommodate a mild cosmic variation of
the fine structure constant $\alpha$. The motivation comes from a vintage
theory developed by Bekenstein, Sandvik, Barrow and Magueijo. The $\alpha$
variation is introduced by a real scalar field interacting with charged matter.
We execute a cosmological reconstruction based on a parametrization of the
present matter density of the Universe. Observational consistency is ensured by
comparing the theoretical estimates with JLA + OHD + BAO data sets, using a
Markov chain Monte Carlo simulation. An analysis of molecular absorption lines
from HIRES and UVES spectrographs is considered as a reference for the
variation of $\alpha$ at different redshifts. Two examples are discussed. The
first explores a field-dependent kinetic coupling of the scalar field
interacting with charged matter. The second example is a generalized
Brans-Dicke formalism where the varying $\alpha$ is fitted in as an effective
matter field. This generates a simultaneous variation of the Newtonian constant
$G$ and $\alpha$. The pattern of this variation can have a crucial role in
cosmic expansion history.
| [
{
"created": "Wed, 16 Feb 2022 15:33:07 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Feb 2022 06:42:48 GMT",
"version": "v2"
}
] | 2022-04-20 | [
[
"Chakrabarti",
"Soumya",
""
]
] | We work with a class of scalar extended theory of gravity that can drive the present cosmic acceleration as well as accommodate a mild cosmic variation of the fine structure constant $\alpha$. The motivation comes from a vintage theory developed by Bekenstein, Sandvik, Barrow and Magueijo. The $\alpha$ variation is introduced by a real scalar field interacting with charged matter. We execute a cosmological reconstruction based on a parametrization of the present matter density of the Universe. Observational consistency is ensured by comparing the theoretical estimates with JLA + OHD + BAO data sets, using a Markov chain Monte Carlo simulation. An analysis of molecular absorption lines from HIRES and UVES spectrographs is considered as a reference for the variation of $\alpha$ at different redshifts. Two examples are discussed. The first explores a field-dependent kinetic coupling of the scalar field interacting with charged matter. The second example is a generalized Brans-Dicke formalism where the varying $\alpha$ is fitted in as an effective matter field. This generates a simultaneous variation of the Newtonian constant $G$ and $\alpha$. The pattern of this variation can have a crucial role in cosmic expansion history. |
gr-qc/0403030 | Jiliang Jing | M. Giammatteo and Jiliang Jing | Dirac quasinormal frequencies in Schwarzschild-AdS space-time | 13 pages, 6 figures | Phys.Rev. D71 (2005) 024007 | 10.1103/PhysRevD.71.024007 | null | gr-qc astro-ph hep-th | null | We investigate the quasinormal mode frequencies for the massless Dirac field
in static four dimensional $AdS$ space-time. The separation of the Dirac
equation is achieved for the first time in $AdS$ space. Besides the relevance
that this calculation can have in the framework of the $AdS/CFT$ correspondence
between M-theory on $AdS_4\times S^7$ and SU(N) super Yang-Mills theory on
$M_3$, it also serves to fill in a gap in the literature, which has only been
concerned with particles of integral spin $0,1,2$.
| [
{
"created": "Sun, 7 Mar 2004 05:53:19 GMT",
"version": "v1"
},
{
"created": "Sat, 25 Dec 2004 08:08:22 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Giammatteo",
"M.",
""
],
[
"Jing",
"Jiliang",
""
]
] | We investigate the quasinormal mode frequencies for the massless Dirac field in static four dimensional $AdS$ space-time. The separation of the Dirac equation is achieved for the first time in $AdS$ space. Besides the relevance that this calculation can have in the framework of the $AdS/CFT$ correspondence between M-theory on $AdS_4\times S^7$ and SU(N) super Yang-Mills theory on $M_3$, it also serves to fill in a gap in the literature, which has only been concerned with particles of integral spin $0,1,2$. |
gr-qc/0006091 | Bela Szilagyi | Bela Szilagyi | Cauchy-Characteristic Matching In General Relativity | 16 LaTeX files, 1 bibliography (bbl) file, 1 style file, 68
PostScript figures | Ph.D. Thesis, University of Pittsburgh, 2000 | null | null | gr-qc | null | From Einstein's theory we know that besides the electromagnetic spectrum,
objects like quasars, active galactic nuclei, pulsars and black holes also
generate a physical signal of purely gravitational nature. The actual form of
the signal is impossible to determine analytically, which lead to use of
numerical methods.
Two major approaches emerged. The first one formulates the gravitational
radiation problem as a standard Cauchy initial value problem, while the other
approach uses a Characteristic Initial value formulation. In the strong field
region, where caustics in the wavefronts are likely to form, the Cauchy
formulation is more advantageous. On the other side, the Characteristic
formulation is uniquely suited to study radiation problems because it describes
space-time in terms of radiation wavefronts.
The fact that the advantages and disadvantages of these two systems are
complementary suggests that one may want to use the two of them together. In a
full nonlinear problem it would be advantageous to evolve the inner (strong
field) region using Cauchy evolution and the outer (radiation) region with the
Characteristic approach. Cauchy Characteristic Matching enables one to evolve
the whole space-time matching the boundaries of Cauchy and Characteristic
evolution. The methodology of Cauchy Characteristic Matching has been
successful in numerical evolution of the spherically symmetric
Klein-Gordon-Einstein field equations as well as for 3-D non-linear wave
equations. In this thesis the same methodology is studied in the context of the
Einstein equations.
| [
{
"created": "Mon, 26 Jun 2000 21:22:53 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Szilagyi",
"Bela",
""
]
] | From Einstein's theory we know that besides the electromagnetic spectrum, objects like quasars, active galactic nuclei, pulsars and black holes also generate a physical signal of purely gravitational nature. The actual form of the signal is impossible to determine analytically, which lead to use of numerical methods. Two major approaches emerged. The first one formulates the gravitational radiation problem as a standard Cauchy initial value problem, while the other approach uses a Characteristic Initial value formulation. In the strong field region, where caustics in the wavefronts are likely to form, the Cauchy formulation is more advantageous. On the other side, the Characteristic formulation is uniquely suited to study radiation problems because it describes space-time in terms of radiation wavefronts. The fact that the advantages and disadvantages of these two systems are complementary suggests that one may want to use the two of them together. In a full nonlinear problem it would be advantageous to evolve the inner (strong field) region using Cauchy evolution and the outer (radiation) region with the Characteristic approach. Cauchy Characteristic Matching enables one to evolve the whole space-time matching the boundaries of Cauchy and Characteristic evolution. The methodology of Cauchy Characteristic Matching has been successful in numerical evolution of the spherically symmetric Klein-Gordon-Einstein field equations as well as for 3-D non-linear wave equations. In this thesis the same methodology is studied in the context of the Einstein equations. |
0711.0332 | Gilles Esposito-Farese | Gilles Esposito-Farese | Summary of session A4 at the GRG18 conference: Alternative Theories of
Gravity | 9 pages, no figure; the GRG18 conference was held in Sydney,
Australia, 8-13 July 2007 | Class.Quant.Grav.25:114017,2008 | 10.1088/0264-9381/25/11/114017 | null | gr-qc | null | More than 50 abstracts were submitted to the A4 session on "Alternatives
Theories of Gravity" at the GRG18 conference. About 30 of them were scheduled
as oral presentations, that we summarize below. We do not intend to give a
critical review, but rather pointers to the corresponding papers. The main
topics were (i) brane models both from the mathematical and the
phenomenological viewpoints; (ii) Einstein-Gauss-Bonnet gravity in higher
dimensions or coupled to a scalar field; (iii) modified Newtonian dynamics
(MOND); (iv) scalar-tensor and f(R) theories; (v) alternative models involving
Lorentz violations, noncommutative spacetimes or Chern-Simons corrections.
| [
{
"created": "Fri, 2 Nov 2007 15:51:12 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Esposito-Farese",
"Gilles",
""
]
] | More than 50 abstracts were submitted to the A4 session on "Alternatives Theories of Gravity" at the GRG18 conference. About 30 of them were scheduled as oral presentations, that we summarize below. We do not intend to give a critical review, but rather pointers to the corresponding papers. The main topics were (i) brane models both from the mathematical and the phenomenological viewpoints; (ii) Einstein-Gauss-Bonnet gravity in higher dimensions or coupled to a scalar field; (iii) modified Newtonian dynamics (MOND); (iv) scalar-tensor and f(R) theories; (v) alternative models involving Lorentz violations, noncommutative spacetimes or Chern-Simons corrections. |
1501.07322 | Barry Wardell | Barry Wardell | Self-force: Computational Strategies | Synchronized with final published version. Review to appear in
"Equations of Motion in Relativistic Gravity", published as part of the
Springer "Fundamental Theories of Physics" series. D. Puetzfeld et al.
(eds.), Equations of Motion in Relativistic Gravity, Fundamental Theories of
Physics 179, Springer, 2015 | null | 10.1007/978-3-319-18335-0_14 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Building on substantial foundational progress in understanding the effect of
a small body's self-field on its own motion, the past 15 years has seen the
emergence of several strategies for explicitly computing self-field corrections
to the equations of motion of a small, point-like charge. These approaches
broadly fall into three categories: (i) mode-sum regularization, (ii) effective
source approaches and (iii) worldline convolution methods. This paper reviews
the various approaches and gives details of how each one is implemented in
practice, highlighting some of the key features in each case.
| [
{
"created": "Thu, 29 Jan 2015 01:06:53 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Feb 2015 23:23:14 GMT",
"version": "v2"
},
{
"created": "Tue, 2 Jun 2015 11:53:32 GMT",
"version": "v3"
}
] | 2021-04-07 | [
[
"Wardell",
"Barry",
""
]
] | Building on substantial foundational progress in understanding the effect of a small body's self-field on its own motion, the past 15 years has seen the emergence of several strategies for explicitly computing self-field corrections to the equations of motion of a small, point-like charge. These approaches broadly fall into three categories: (i) mode-sum regularization, (ii) effective source approaches and (iii) worldline convolution methods. This paper reviews the various approaches and gives details of how each one is implemented in practice, highlighting some of the key features in each case. |
1801.08028 | Gao-Ming Deng | Gao-Ming Deng, Jinbo Fan, Xinfei Li, Yong-Chang Huang | Thermodynamics and phase transition of charged AdS black holes with a
global monopole | 13 pages, 9 figures, comments welcome | null | 10.1142/S0217751X18500227 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Thermodynamical properties of charged AdS black holes with a global monopole
still remain obscure. In this paper, we investigate the thermodynamics and
phase transition of the black holes in the extended phase space. It is shown
that thermodynamical quantities of the black holes exhibit an interesting
dependence on the internal global monopole, and they perfectly satisfy both the
first law of thermodynamics and Smarr relation. Furthermore, analysis of the
local and the global thermodynamical stability manifests that the charged AdS
black hole undergoes an elegant phase transition at critical point. Of special
interest, critical behaviors of the black holes resemble a Van der Waals
liquid-gas system. Our results not only reveal the effect of a global monopole
on thermodynamics of AdS black holes, but also further support that Van der
Waals-like behavior of the black holes is a universal phenomenon.
| [
{
"created": "Wed, 24 Jan 2018 15:37:58 GMT",
"version": "v1"
}
] | 2018-02-28 | [
[
"Deng",
"Gao-Ming",
""
],
[
"Fan",
"Jinbo",
""
],
[
"Li",
"Xinfei",
""
],
[
"Huang",
"Yong-Chang",
""
]
] | Thermodynamical properties of charged AdS black holes with a global monopole still remain obscure. In this paper, we investigate the thermodynamics and phase transition of the black holes in the extended phase space. It is shown that thermodynamical quantities of the black holes exhibit an interesting dependence on the internal global monopole, and they perfectly satisfy both the first law of thermodynamics and Smarr relation. Furthermore, analysis of the local and the global thermodynamical stability manifests that the charged AdS black hole undergoes an elegant phase transition at critical point. Of special interest, critical behaviors of the black holes resemble a Van der Waals liquid-gas system. Our results not only reveal the effect of a global monopole on thermodynamics of AdS black holes, but also further support that Van der Waals-like behavior of the black holes is a universal phenomenon. |
0812.1574 | Eyo Ita III | Eyo Eyo Ita III | Nonlinear gravitons in 4-D general relativity by expansion about the
Kodama state | 21 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we provide a possible realization of Penrose's idea of
nonlinear gravitons using a new description of nonmetric general relativity. In
the addressal of issues surrounding the normalizability of the Kodama state and
its reliability as a ground state for gravity, we expand the theory in
fluctuations about the Kodama state. This produces a theory of complex gravity
with a well-defined Hilbert space structure, whose quantization we carry out
both at the linearized level and in the full nonlinear theory. The results of
this paper demonstrate the preservation of the physical degrees of freedom of
the full nonlinear theory under linearization, as well provide a Hilbert space
of states of the former annihilated by the quantum Hamiltonian constraint.
| [
{
"created": "Mon, 8 Dec 2008 21:31:13 GMT",
"version": "v1"
},
{
"created": "Fri, 31 Jul 2009 09:06:04 GMT",
"version": "v2"
},
{
"created": "Sat, 4 Sep 2010 16:48:32 GMT",
"version": "v3"
}
] | 2010-09-07 | [
[
"Ita",
"Eyo Eyo",
"III"
]
] | In this paper we provide a possible realization of Penrose's idea of nonlinear gravitons using a new description of nonmetric general relativity. In the addressal of issues surrounding the normalizability of the Kodama state and its reliability as a ground state for gravity, we expand the theory in fluctuations about the Kodama state. This produces a theory of complex gravity with a well-defined Hilbert space structure, whose quantization we carry out both at the linearized level and in the full nonlinear theory. The results of this paper demonstrate the preservation of the physical degrees of freedom of the full nonlinear theory under linearization, as well provide a Hilbert space of states of the former annihilated by the quantum Hamiltonian constraint. |
0705.3475 | Mauricio Bellini | Mariano Anabitarte (Mar del Plata University - CONICET), Mauricio
Bellini (Mar del Plata University - CONICET) | Gauge invariant metric fluctuations in the early universe from STM
theory of gravity: nonperturbative formalism | version accepted in Physics Letters B | Phys.Lett.B652:233-237,2007 | 10.1016/j.physletb.2007.07.028 | null | gr-qc hep-th | null | We develop a nonperturbative quantum field formalism to describe scalar
gauge-invariant metric flucturations in the early universe from a 5D apparent
(Ricci flat) vacuum.
| [
{
"created": "Wed, 23 May 2007 22:04:08 GMT",
"version": "v1"
},
{
"created": "Wed, 30 May 2007 20:19:17 GMT",
"version": "v2"
},
{
"created": "Fri, 6 Jul 2007 17:27:25 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Anabitarte",
"Mariano",
"",
"Mar del Plata University - CONICET"
],
[
"Bellini",
"Mauricio",
"",
"Mar del Plata University - CONICET"
]
] | We develop a nonperturbative quantum field formalism to describe scalar gauge-invariant metric flucturations in the early universe from a 5D apparent (Ricci flat) vacuum. |
2203.11551 | Zheng-Wen Long | Yi Yang, Dong Liu, Ali \"Ovg\"un, Zheng-Wen Long, Zhaoyi Xu | Probing hairy black holes caused by gravitational decoupling using
quasinormal modes and greybody bounds | null | Phys. Rev. D 107, 064042 (2023) | 10.1103/PhysRevD.107.064042 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational decoupling can add hair to the black holes by adding extra
sources. The quasinormal modes of hairy black hole caused by gravitational
decoupling for the massless scalar field, electromagnetic field, and
gravitational perturbation are investigated. The equations of effective
potential for three perturbations are derived in hairy black hole spacetime. We
also study the time evolution corresponding to the three perturbations, and the
quasinormal mode frequencies are calculated using the Prony method through the
time-domain profiles. By analyzing the influence of the hairs ($\alpha$, $l_0$
and $Q$) for the black holes we studying on quasinormal mode, we find that the
hairs $\alpha$ and $l_0$ decrease the oscillation frequency of the
gravitational wave signal, and the hair $Q$ increase its oscillation
frequency.Furthermore, we have calculated the bounds of greybody factor and
high-energy absorption cross section with the Sinc approximation, which reveals
that the presence of charges ($\alpha$ and $l_0$) generating primary hair can
increase the probability of gravitational radiation arriving spatial infinity,
whereas the charge $Q$ from the extra sources does the opposite.
| [
{
"created": "Tue, 22 Mar 2022 09:11:56 GMT",
"version": "v1"
},
{
"created": "Tue, 5 Apr 2022 15:55:44 GMT",
"version": "v2"
},
{
"created": "Fri, 8 Apr 2022 15:15:56 GMT",
"version": "v3"
},
{
"created": "Tue, 21 Jun 2022 15:55:10 GMT",
"version": "v4"
},
{
"cre... | 2023-03-24 | [
[
"Yang",
"Yi",
""
],
[
"Liu",
"Dong",
""
],
[
"Övgün",
"Ali",
""
],
[
"Long",
"Zheng-Wen",
""
],
[
"Xu",
"Zhaoyi",
""
]
] | Gravitational decoupling can add hair to the black holes by adding extra sources. The quasinormal modes of hairy black hole caused by gravitational decoupling for the massless scalar field, electromagnetic field, and gravitational perturbation are investigated. The equations of effective potential for three perturbations are derived in hairy black hole spacetime. We also study the time evolution corresponding to the three perturbations, and the quasinormal mode frequencies are calculated using the Prony method through the time-domain profiles. By analyzing the influence of the hairs ($\alpha$, $l_0$ and $Q$) for the black holes we studying on quasinormal mode, we find that the hairs $\alpha$ and $l_0$ decrease the oscillation frequency of the gravitational wave signal, and the hair $Q$ increase its oscillation frequency.Furthermore, we have calculated the bounds of greybody factor and high-energy absorption cross section with the Sinc approximation, which reveals that the presence of charges ($\alpha$ and $l_0$) generating primary hair can increase the probability of gravitational radiation arriving spatial infinity, whereas the charge $Q$ from the extra sources does the opposite. |
1911.11054 | Dharm Veer Singh | Dharm Veer Singh, Sushant G. Ghosh and Sunil D. Maharaj | Bardeen-like regular black holes in $5D$ Einstein-Gauss-Bonnet gravity | 20 pages, 7 figures | Annals of Physics 412, 168025 (2020) | 10.1016/j.aop.2019.168025 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We find an exact spherically symmetric regular Bardeen-like solutions by
considering the coupling between Einstein-Gauss-Bonnet theory and nonlinear
electrodynamics (NED) in five-dimensional spacetime. These solutions, with an
additional parameter $g$ apart from the mass $M$, represent black holes with
Cauchy and event horizons, extremal black holes with degenerate horizons or no
black holes in the absence of the horizons, and encompasses as a special case
Boulware-Deser black holes which can be recovered in the absence of magnetic
charge ($g=0$). Owing to the NED corrected black hole, the thermodynamic
quantities have also been modified and we have obtained exact analytical
expressions for the thermodynamical quantities such the Hawking temperature
$T_+$, the entropy $S_+$, the specific heat $C_+$, and the Gibbs free energy
$F_+$. The heat capacity diverges at a critical radius $r=r_C$, where
incidentally the temperature has a maximum, and the Hawking-Page transitions
even in absence of the cosmological term. The thermal evaporation process leads
to eternal remnants for sufficiently small black holes and evaporates to a
thermodynamic stable extremel black hole remnants with vanishing temperature.
The heat capacity becomes positive $C_+ > 0$ for $r_+ < r_C$ allowing black
hole to become thermodynamically stable, in addition the smaller black holes
are globally stable with positive heat capacity $C_+ > 0$ and negative free
energy $F_+<0$. The entropy $ S $ of a 5D Bardeen black hole is not longer a
quarter of the horizon area $A$, i.e., $S \neq A/4$.
| [
{
"created": "Mon, 25 Nov 2019 17:09:17 GMT",
"version": "v1"
}
] | 2019-11-26 | [
[
"Singh",
"Dharm Veer",
""
],
[
"Ghosh",
"Sushant G.",
""
],
[
"Maharaj",
"Sunil D.",
""
]
] | We find an exact spherically symmetric regular Bardeen-like solutions by considering the coupling between Einstein-Gauss-Bonnet theory and nonlinear electrodynamics (NED) in five-dimensional spacetime. These solutions, with an additional parameter $g$ apart from the mass $M$, represent black holes with Cauchy and event horizons, extremal black holes with degenerate horizons or no black holes in the absence of the horizons, and encompasses as a special case Boulware-Deser black holes which can be recovered in the absence of magnetic charge ($g=0$). Owing to the NED corrected black hole, the thermodynamic quantities have also been modified and we have obtained exact analytical expressions for the thermodynamical quantities such the Hawking temperature $T_+$, the entropy $S_+$, the specific heat $C_+$, and the Gibbs free energy $F_+$. The heat capacity diverges at a critical radius $r=r_C$, where incidentally the temperature has a maximum, and the Hawking-Page transitions even in absence of the cosmological term. The thermal evaporation process leads to eternal remnants for sufficiently small black holes and evaporates to a thermodynamic stable extremel black hole remnants with vanishing temperature. The heat capacity becomes positive $C_+ > 0$ for $r_+ < r_C$ allowing black hole to become thermodynamically stable, in addition the smaller black holes are globally stable with positive heat capacity $C_+ > 0$ and negative free energy $F_+<0$. The entropy $ S $ of a 5D Bardeen black hole is not longer a quarter of the horizon area $A$, i.e., $S \neq A/4$. |
0802.3927 | Ivan Avramidi | Ivan G. Avramidi and Guglielmo Fucci | Kinematics in Matrix Gravity | 31 pages, no figures, discussion of Pioneer anomaly removed | Gen.Rel.Grav.41:1407-1435,2009 | 10.1007/s10714-008-0713-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop the kinematics in Matrix Gravity, which is a modified theory of
gravity obtained by a non-commutative deformation of General Relativity. In
this model the usual interpretation of gravity as Riemannian geometry is
replaced by a new kind of geometry, which is equivalent to a collection of
Finsler geometries with several Finsler metrics depending both on the position
and on the velocity. As a result the Riemannian geodesic flow is replaced by a
collection of Finsler flows. This naturally leads to a model in which a
particle is described by several mass parameters. If these mass parameters are
different then the equivalence principle is violated. In the non-relativistic
limit this also leads to corrections to the Newton's gravitational potential.
We find the first and second order corrections to the usual Riemannian geodesic
flow and evaluate the anomalous nongeodesic acceleration in a particular case
of static spherically symmetric background.
| [
{
"created": "Tue, 26 Feb 2008 22:31:11 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Nov 2008 22:40:02 GMT",
"version": "v2"
}
] | 2011-02-18 | [
[
"Avramidi",
"Ivan G.",
""
],
[
"Fucci",
"Guglielmo",
""
]
] | We develop the kinematics in Matrix Gravity, which is a modified theory of gravity obtained by a non-commutative deformation of General Relativity. In this model the usual interpretation of gravity as Riemannian geometry is replaced by a new kind of geometry, which is equivalent to a collection of Finsler geometries with several Finsler metrics depending both on the position and on the velocity. As a result the Riemannian geodesic flow is replaced by a collection of Finsler flows. This naturally leads to a model in which a particle is described by several mass parameters. If these mass parameters are different then the equivalence principle is violated. In the non-relativistic limit this also leads to corrections to the Newton's gravitational potential. We find the first and second order corrections to the usual Riemannian geodesic flow and evaluate the anomalous nongeodesic acceleration in a particular case of static spherically symmetric background. |
gr-qc/0510087 | Nakia Carlevaro | Nakia Carlevaro and Giovanni Montani | On the Gravitational Collapse of a Gas Cloud in Presence of Bulk
Viscosity | 13 pages, no figure | Class. Quant. Grav. 22, 4715-4728 (2005) | 10.1088/0264-9381/22/22/005 | null | gr-qc astro-ph | null | We analyze the effects induced by the bulk viscosity on the dynamics
associated to the extreme gravitational collapse. Aim of the work is to
investigate whether the presence of viscous corrections to the evolution of a
collapsing gas cloud influence the fragmentation process. To this end we study
the dynamics of a uniform and spherically symmetric cloud with corrections due
to the negative pressure contribution associated to the bulk viscosity
phenomenology. Within the framework of a Newtonian approach (whose range of
validity is outlined), we extend to the viscous case either the Lagrangian,
either the Eulerian motion of the system and we treat the asymptotic evolution
in correspondence to a viscosity coefficient of the form $\zeta=\zeta_0
\rho^{nu}$ ($\rho$ being the cloud density and $\zeta_0=const.$). We show how,
in the adiabatic-like behavior of the gas (i.e. when the politropic index takes
values $4/3<\gamma\leq5/3$), density contrasts acquire, asymptotically, a
vanishing behavior which prevents the formation of sub-structures. We can
conclude that in the adiabatic-like collapse the top down mechanism of
structures formation is suppressed as soon as enough strong viscous effects are
taken into account. Such a feature is not present in the isothermal-like (i.e.
$1\leq\gamma<4/3$) collapse because the sub-structures formation is yet present
and outlines the same behavior as in the non-viscous case. We emphasize that in
the adiabatic-like collapse the bulk viscosity is also responsible for the
appearance of a threshold scale beyond which perturbations begin to increase.
| [
{
"created": "Wed, 19 Oct 2005 11:02:33 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Jan 2007 17:11:09 GMT",
"version": "v2"
},
{
"created": "Thu, 12 Apr 2007 09:40:36 GMT",
"version": "v3"
},
{
"created": "Sat, 23 Jun 2007 15:58:12 GMT",
"version": "v4"
}
] | 2009-11-11 | [
[
"Carlevaro",
"Nakia",
""
],
[
"Montani",
"Giovanni",
""
]
] | We analyze the effects induced by the bulk viscosity on the dynamics associated to the extreme gravitational collapse. Aim of the work is to investigate whether the presence of viscous corrections to the evolution of a collapsing gas cloud influence the fragmentation process. To this end we study the dynamics of a uniform and spherically symmetric cloud with corrections due to the negative pressure contribution associated to the bulk viscosity phenomenology. Within the framework of a Newtonian approach (whose range of validity is outlined), we extend to the viscous case either the Lagrangian, either the Eulerian motion of the system and we treat the asymptotic evolution in correspondence to a viscosity coefficient of the form $\zeta=\zeta_0 \rho^{nu}$ ($\rho$ being the cloud density and $\zeta_0=const.$). We show how, in the adiabatic-like behavior of the gas (i.e. when the politropic index takes values $4/3<\gamma\leq5/3$), density contrasts acquire, asymptotically, a vanishing behavior which prevents the formation of sub-structures. We can conclude that in the adiabatic-like collapse the top down mechanism of structures formation is suppressed as soon as enough strong viscous effects are taken into account. Such a feature is not present in the isothermal-like (i.e. $1\leq\gamma<4/3$) collapse because the sub-structures formation is yet present and outlines the same behavior as in the non-viscous case. We emphasize that in the adiabatic-like collapse the bulk viscosity is also responsible for the appearance of a threshold scale beyond which perturbations begin to increase. |
2103.04369 | Minyong Guo | Yehui Hou, Minyong Guo and Bin Chen | Revisiting the shadow of braneworld black holes | 22 pages, 13 figures | Phys. Rev. D 104, 024001 (2021) | 10.1103/PhysRevD.104.024001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revisit the shadows of rotating braneworld black holes in the
Randall-Sundrum type II model, by considering not only the metric in the near
region of the black hole but also the linearized metric in the far region where
the observer stays. Our study is significantly different from previous studies,
which relies only on the metric in the near region. From the study, we identify
a critical angle $\theta_c$ which decides the shadow curve is open or closed:
the shadow curve would be open if the observational angle
$\theta_c<\theta_o\le\pi/2$, and the curve becomes closed when
$0<\theta_o\le\theta_c$. We study how various parameters affect the shape of
the shadow curve. We furthermore apply our analysis to the data of M87* from
the Event Horizon Telescope and obtain a new constraint on the parameters of
the braneworld black holes.
| [
{
"created": "Sun, 7 Mar 2021 14:58:29 GMT",
"version": "v1"
}
] | 2021-07-07 | [
[
"Hou",
"Yehui",
""
],
[
"Guo",
"Minyong",
""
],
[
"Chen",
"Bin",
""
]
] | We revisit the shadows of rotating braneworld black holes in the Randall-Sundrum type II model, by considering not only the metric in the near region of the black hole but also the linearized metric in the far region where the observer stays. Our study is significantly different from previous studies, which relies only on the metric in the near region. From the study, we identify a critical angle $\theta_c$ which decides the shadow curve is open or closed: the shadow curve would be open if the observational angle $\theta_c<\theta_o\le\pi/2$, and the curve becomes closed when $0<\theta_o\le\theta_c$. We study how various parameters affect the shape of the shadow curve. We furthermore apply our analysis to the data of M87* from the Event Horizon Telescope and obtain a new constraint on the parameters of the braneworld black holes. |
1608.00739 | Marcelo Schiffer | Marcelo Schiffer | Charge Fluctuations of an Uncharged Black Hole | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we calculate charge fluctuations of a Schwarzschild black-hole
of mass $M$ confined within a perfectly reflecting cavity of radius R in
thermal equilibrium with various species of radiation and fermions . Charge
conservation is constrained by a Lagrange multiplier (the chemical potential).
Black hole charge fluctuations are expected owing to continuous absorption and
emission of particles by the black hole. For black holes much more massive than
$10^{16} g$ , these fluctuations are exponentially suppressed. For black holes
lighter than this, the Schwarzschild black hole is unstable under charge
fluctuations for almost every possible size of the confining vessel. The
stability regime and the fluctuations are calculated through the second
derivative of the entropy with respect to the charge. The expression obtained
contains many puzzling terms besides the expected thermodynamical fluctuations:
terms corresponding to instabilities that do not depend on the specific value
of charge of the charge carriers and one of them depends on Newton's constant
instead. One of the contributions to the charge fluctuations $\hbar/4\pi$ does
not depend neither on number of species, nor on the the specific charge or even
the size of the confining vessel. As a matter of fact, this term emerges from
the second derivative of the black hole entropy alone, which means that it
corresponds to a genuine quantum mechanical property of the black hole itself.
Such a contribution would cause the event horizon to recede from $2M$ to
$2M-T_{BH}$ or equivalently, by $(4\pi)^{-1}$ of the black hole' s Compton wave
length. Similarly, a Cauchy horizon emerges at the same distance the event
horizon receded.
| [
{
"created": "Tue, 2 Aug 2016 08:58:58 GMT",
"version": "v1"
}
] | 2016-08-03 | [
[
"Schiffer",
"Marcelo",
""
]
] | In this paper we calculate charge fluctuations of a Schwarzschild black-hole of mass $M$ confined within a perfectly reflecting cavity of radius R in thermal equilibrium with various species of radiation and fermions . Charge conservation is constrained by a Lagrange multiplier (the chemical potential). Black hole charge fluctuations are expected owing to continuous absorption and emission of particles by the black hole. For black holes much more massive than $10^{16} g$ , these fluctuations are exponentially suppressed. For black holes lighter than this, the Schwarzschild black hole is unstable under charge fluctuations for almost every possible size of the confining vessel. The stability regime and the fluctuations are calculated through the second derivative of the entropy with respect to the charge. The expression obtained contains many puzzling terms besides the expected thermodynamical fluctuations: terms corresponding to instabilities that do not depend on the specific value of charge of the charge carriers and one of them depends on Newton's constant instead. One of the contributions to the charge fluctuations $\hbar/4\pi$ does not depend neither on number of species, nor on the the specific charge or even the size of the confining vessel. As a matter of fact, this term emerges from the second derivative of the black hole entropy alone, which means that it corresponds to a genuine quantum mechanical property of the black hole itself. Such a contribution would cause the event horizon to recede from $2M$ to $2M-T_{BH}$ or equivalently, by $(4\pi)^{-1}$ of the black hole' s Compton wave length. Similarly, a Cauchy horizon emerges at the same distance the event horizon receded. |
2302.03545 | Yumin Hu | Yu-Min Hu, Yaqi Zhao, Xin Ren, Bo Wang, Emmanuel N. Saridakis, Yi-Fu
Cai | The effective field theory approach to the strong coupling issue in
$f(T)$ gravity | 18 pages | JCAP 07 (2023) 060 | 10.1088/1475-7516/2023/07/060 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the scalar perturbations and the possible strong coupling
issues of $f(T)$ around a cosmological background, applying the effective field
theory (EFT) approach. We revisit the generalized EFT framework of modified
teleparallel gravity and apply it by considering both linear and second-order
perturbations for $f(T)$ theory. No new scalar mode is present in linear and
second-order perturbations in $f(T)$ gravity, which suggests a strong coupling
problem. However, based on the ratio of cubic to quadratic Lagrangians, we
provide a simple estimation of the strong coupling scale, a result which shows
that the strong coupling problem can be avoided at least for some modes. In
conclusion, perturbation behaviors that at first appear problematic may not
inevitably lead to a strong coupling problem, as long as the relevant scale is
comparable with the cutoff scale $M$ of the applicability of the theory.
| [
{
"created": "Tue, 7 Feb 2023 15:54:04 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Jul 2023 09:08:11 GMT",
"version": "v2"
}
] | 2023-11-22 | [
[
"Hu",
"Yu-Min",
""
],
[
"Zhao",
"Yaqi",
""
],
[
"Ren",
"Xin",
""
],
[
"Wang",
"Bo",
""
],
[
"Saridakis",
"Emmanuel N.",
""
],
[
"Cai",
"Yi-Fu",
""
]
] | We investigate the scalar perturbations and the possible strong coupling issues of $f(T)$ around a cosmological background, applying the effective field theory (EFT) approach. We revisit the generalized EFT framework of modified teleparallel gravity and apply it by considering both linear and second-order perturbations for $f(T)$ theory. No new scalar mode is present in linear and second-order perturbations in $f(T)$ gravity, which suggests a strong coupling problem. However, based on the ratio of cubic to quadratic Lagrangians, we provide a simple estimation of the strong coupling scale, a result which shows that the strong coupling problem can be avoided at least for some modes. In conclusion, perturbation behaviors that at first appear problematic may not inevitably lead to a strong coupling problem, as long as the relevant scale is comparable with the cutoff scale $M$ of the applicability of the theory. |
0811.2790 | Martin Bojowald | Martin Bojowald | Comment on "Quantum bounce and cosmic recall" [arXiv:0710.4543] | 1 page | Phys.Rev.Lett.101:209001,2008 | 10.1103/PhysRevLett.101.209001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A recently derived inequality on volume fluctuations of a bouncing cosmology,
valid for states which are semiclassical long after the bounce, does not
restrict pre-bounce fluctuations sufficiently strongly to conclude that the
pre-bounce state was semiclassical except in a very weak sense.
| [
{
"created": "Mon, 17 Nov 2008 20:47:28 GMT",
"version": "v1"
}
] | 2008-12-18 | [
[
"Bojowald",
"Martin",
""
]
] | A recently derived inequality on volume fluctuations of a bouncing cosmology, valid for states which are semiclassical long after the bounce, does not restrict pre-bounce fluctuations sufficiently strongly to conclude that the pre-bounce state was semiclassical except in a very weak sense. |
2212.06914 | Chris Stevens | Chris Stevens, Oliver Markwell | Toward fixing a framework for conformal cyclic cosmology | 14 Pages, 1 figure | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Conformal Cyclic Cosmology (CCC) is a cyclic model of the universe put
forward by Sir Roger Penrose. A conformal invariance assumption in the
neighbourhood of the crossover region between cycles (which Penrose calls
aeons) allows successive space-times to be related by a conformal rescaling. A
major open problem is how to choose the conformal factor in a unique way, and
is a fundamental hurdle to further study. Proposals have been put forward by
Newman, Tod and Nurowski, but they disagree in one way or another with
Penrose's original assumptions as well as each other. In this paper we compare
these different models in detail and rule out certain choices for the conformal
factor that have been put forward by Penrose. We extend the results of Newman
and fix inconsistencies that arose in his calculations. A new class of
solutions are put forward which agree with Penrose's assumptions exactly so
long as a certain additional relation is satisfied.
| [
{
"created": "Tue, 13 Dec 2022 21:36:19 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Dec 2022 05:55:37 GMT",
"version": "v2"
}
] | 2022-12-19 | [
[
"Stevens",
"Chris",
""
],
[
"Markwell",
"Oliver",
""
]
] | Conformal Cyclic Cosmology (CCC) is a cyclic model of the universe put forward by Sir Roger Penrose. A conformal invariance assumption in the neighbourhood of the crossover region between cycles (which Penrose calls aeons) allows successive space-times to be related by a conformal rescaling. A major open problem is how to choose the conformal factor in a unique way, and is a fundamental hurdle to further study. Proposals have been put forward by Newman, Tod and Nurowski, but they disagree in one way or another with Penrose's original assumptions as well as each other. In this paper we compare these different models in detail and rule out certain choices for the conformal factor that have been put forward by Penrose. We extend the results of Newman and fix inconsistencies that arose in his calculations. A new class of solutions are put forward which agree with Penrose's assumptions exactly so long as a certain additional relation is satisfied. |
0810.2264 | E Katsavounidis | J. Markowitz, M. Zanolin, L.Cadonati, and E. Katsavounidis | Gravitational Wave Burst Source Direction Estimation using Time and
Amplitude Information | 10 pages, 14 figures, submitted to PRD | Phys.Rev.D78:122003,2008 | 10.1103/PhysRevD.78.122003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we study two problems that arise when using timing and
amplitude estimates from a network of interferometers (IFOs) to evaluate the
direction of an incident gravitational wave burst (GWB). First, we discuss an
angular bias in the least squares timing-based approach that becomes
increasingly relevant for moderate to low signal-to-noise ratios. We show how
estimates of the arrival time uncertainties in each detector can be used to
correct this bias. We also introduce a stand alone parameter estimation
algorithm that can improve the arrival time estimation and provide
root-sum-squared strain amplitude (hrss) values for each site. In the second
part of the paper we discuss how to resolve the directional ambiguity that
arises from observations in three non co-located interferometers between the
true source location and its mirror image across the plane containing the
detectors. We introduce a new, exact relationship among the hrss values at the
three sites that, for sufficiently large signal amplitudes, determines the true
source direction regardless of whether or not the signal is linearly polarized.
Both the algorithm estimating arrival times, arrival time uncertainties, and
hrss values and the directional follow-up can be applied to any set of
gravitational wave candidates observed in a network of three non co-located
interferometers. As a case study we test the methods on simulated waveforms
embedded in simulations of the noise of the LIGO and Virgo detectors at design
sensitivity.
| [
{
"created": "Mon, 13 Oct 2008 19:01:38 GMT",
"version": "v1"
}
] | 2009-01-08 | [
[
"Markowitz",
"J.",
""
],
[
"Zanolin",
"M.",
""
],
[
"Cadonati",
"L.",
""
],
[
"Katsavounidis",
"E.",
""
]
] | In this article we study two problems that arise when using timing and amplitude estimates from a network of interferometers (IFOs) to evaluate the direction of an incident gravitational wave burst (GWB). First, we discuss an angular bias in the least squares timing-based approach that becomes increasingly relevant for moderate to low signal-to-noise ratios. We show how estimates of the arrival time uncertainties in each detector can be used to correct this bias. We also introduce a stand alone parameter estimation algorithm that can improve the arrival time estimation and provide root-sum-squared strain amplitude (hrss) values for each site. In the second part of the paper we discuss how to resolve the directional ambiguity that arises from observations in three non co-located interferometers between the true source location and its mirror image across the plane containing the detectors. We introduce a new, exact relationship among the hrss values at the three sites that, for sufficiently large signal amplitudes, determines the true source direction regardless of whether or not the signal is linearly polarized. Both the algorithm estimating arrival times, arrival time uncertainties, and hrss values and the directional follow-up can be applied to any set of gravitational wave candidates observed in a network of three non co-located interferometers. As a case study we test the methods on simulated waveforms embedded in simulations of the noise of the LIGO and Virgo detectors at design sensitivity. |
2301.07019 | Phongpichit Channuie | Phongpichit Channuie (Walailak U.), Khamphee Karwan (Naresuan U.),
Jakkrit Sangtawee (Naresuan U.) | Observational Constraints and Preheating in Cuscuton Inflation | v2: 16 pages, no figure, version accepted for publication in European
Physical Journal C | Eur.Phys.J.C 83 (2023) 421 | 10.1140/epjc/s10052-023-11566-z | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study cuscuton inflation for the models where the potential of the
cuscuton takes quadratic and exponential forms. We find that for the quadratic
potential, a scalar spectral index $n_s$ is not affected by cuscuton at the
leading order in the slow-roll inflation models. However, a tensor-to-scalar
ratio $r$ can be suppressed. For the exponential potential of cuscuton, we find
the condition for which the inflation has a graceful exit. Under this
condition, the observational predictions in this model differ by a few percent
from those found in standard inflation. We also examine the particle production
due to parametric resonances in both models. We find that in Minkowski space
the stage of parametric resonances can be described by the Mathieu equation.
For the case where the cuscuton has quadratic potential, the amplitude of the
driving force in the Mathieu equation has a similar form as that in standard
inflation. Nevertheless, in the case of exponential potential, the amplitude of
the driving force decreases faster than that in the standard case. However,
parametric resonances in our models can be sufficiently broad possible for the
exponential growth of the number of particles. We briefly discuss the case in
which the expansion of space is taken into account.
| [
{
"created": "Tue, 17 Jan 2023 17:08:54 GMT",
"version": "v1"
},
{
"created": "Mon, 1 May 2023 15:25:34 GMT",
"version": "v2"
}
] | 2023-05-23 | [
[
"Channuie",
"Phongpichit",
"",
"Walailak U."
],
[
"Karwan",
"Khamphee",
"",
"Naresuan U."
],
[
"Sangtawee",
"Jakkrit",
"",
"Naresuan U."
]
] | We study cuscuton inflation for the models where the potential of the cuscuton takes quadratic and exponential forms. We find that for the quadratic potential, a scalar spectral index $n_s$ is not affected by cuscuton at the leading order in the slow-roll inflation models. However, a tensor-to-scalar ratio $r$ can be suppressed. For the exponential potential of cuscuton, we find the condition for which the inflation has a graceful exit. Under this condition, the observational predictions in this model differ by a few percent from those found in standard inflation. We also examine the particle production due to parametric resonances in both models. We find that in Minkowski space the stage of parametric resonances can be described by the Mathieu equation. For the case where the cuscuton has quadratic potential, the amplitude of the driving force in the Mathieu equation has a similar form as that in standard inflation. Nevertheless, in the case of exponential potential, the amplitude of the driving force decreases faster than that in the standard case. However, parametric resonances in our models can be sufficiently broad possible for the exponential growth of the number of particles. We briefly discuss the case in which the expansion of space is taken into account. |
0802.0658 | Enric Verdaguer | B.L. Hu and E. Verdaguer | Stochastic Gravity: Theory and Applications | 100 pages, no figures; an update of the 2003 review in Living Reviews
in Relativity gr-qc/0307032 ; it includes new sections on the Validity of
Semiclassical Gravity, the Stability of Minkowski Spacetime, and the Metric
Fluctuations of an Evaporating Black Hole | Living Rev. Relativity, 11 (2008) 3 | 10.12942/lrr-2008-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Whereas semiclassical gravity is based on the semiclassical Einstein equation
with sources given by the expectation value of the stress-energy tensor of
quantum fields, stochastic semiclassical gravity is based on the
Einstein-Langevin equation, which has in addition sources due to the noise
kernel. In the first part, we describe the fundamentals of this new theory via
two approaches: the axiomatic and the functional. In the second part, we
describe three applications of stochastic gravity theory. First, we consider
metric perturbations in a Minkowski spacetime, compute the two-point
correlation functions of these perturbations and prove that Minkowski spacetime
is a stable solution of semiclassical gravity. Second, we discuss structure
formation from the stochastic gravity viewpoint. Third, we discuss the
backreaction of Hawking radiation in the gravitational background of a black
hole and describe the metric fluctuations near the event horizon of an
evaporating black hole
| [
{
"created": "Tue, 5 Feb 2008 16:23:28 GMT",
"version": "v1"
}
] | 2015-05-13 | [
[
"Hu",
"B. L.",
""
],
[
"Verdaguer",
"E.",
""
]
] | Whereas semiclassical gravity is based on the semiclassical Einstein equation with sources given by the expectation value of the stress-energy tensor of quantum fields, stochastic semiclassical gravity is based on the Einstein-Langevin equation, which has in addition sources due to the noise kernel. In the first part, we describe the fundamentals of this new theory via two approaches: the axiomatic and the functional. In the second part, we describe three applications of stochastic gravity theory. First, we consider metric perturbations in a Minkowski spacetime, compute the two-point correlation functions of these perturbations and prove that Minkowski spacetime is a stable solution of semiclassical gravity. Second, we discuss structure formation from the stochastic gravity viewpoint. Third, we discuss the backreaction of Hawking radiation in the gravitational background of a black hole and describe the metric fluctuations near the event horizon of an evaporating black hole |
gr-qc/0004045 | Roberto De Pietri | Roberto De Pietri and Carlo Petronio | Feynman Diagrams of Generalized Matrix Models and the Associated
Manifolds in Dimension 4 | 25 pages, 10 figures. Minor canges | J.Math.Phys. 41 (2000) 6671-6688 | 10.1063/1.1290053 | null | gr-qc hep-lat hep-th | null | The problem of constructing a quantum theory of gravity has been tackled with
very different strategies, most of which relying on the interplay between ideas
from physics and from advanced mathematics. On the mathematical side, a central
role is played by combinatorial topology, often used to recover the space-time
manifold from the other structures involved. An extremely attractive
possibility is that of encoding all possible space-times as specific Feynman
diagrams of a suitable field theory. In this work we analyze how exactly one
can associate combinatorial 4-manifolds to the Feynman diagrams of certain
tensor theories.
| [
{
"created": "Fri, 14 Apr 2000 10:33:59 GMT",
"version": "v1"
},
{
"created": "Sat, 24 Jun 2000 08:44:25 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"De Pietri",
"Roberto",
""
],
[
"Petronio",
"Carlo",
""
]
] | The problem of constructing a quantum theory of gravity has been tackled with very different strategies, most of which relying on the interplay between ideas from physics and from advanced mathematics. On the mathematical side, a central role is played by combinatorial topology, often used to recover the space-time manifold from the other structures involved. An extremely attractive possibility is that of encoding all possible space-times as specific Feynman diagrams of a suitable field theory. In this work we analyze how exactly one can associate combinatorial 4-manifolds to the Feynman diagrams of certain tensor theories. |
1701.02731 | Uri Ben-Ya'acov | Uri Ben-Ya'acov | The 'twin paradox' in relativistic rigid motion | 16 pages, 6 figures | U. Ben-Ya'acov Euro.J.Phys. {\bf37} 055601, 069401 (2016) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Relativistic rigid motion suggests a new version for the so-called `twin
paradox', comparing the ages of two astronauts on a very long spaceship.
Although there is always an instantaneous inertial frame in which the whole
spaceship, being rigid, is simultaneously at rest, the twins' ages, measured as
the proper-times along their individual world lines, are different when they
are located at remote parts of the spaceship. The age, or proper-time,
difference depends on the distance at rest between the astronauts and the
rapidity difference between start to end. The relation of the age difference
with the relative Doppler shift of light signals transmitted between the
astronauts, and implications for the possibility to assign common age
(proper-time) to complex, spatially extended, relativistic systems, are also
discussed. The condition for simultaneous arrival of light signals emitted
simultaneously from the opposite ends of a rigidly accelerating spaceship is
resolved.
| [
{
"created": "Mon, 9 Jan 2017 23:18:58 GMT",
"version": "v1"
}
] | 2017-01-12 | [
[
"Ben-Ya'acov",
"Uri",
""
]
] | Relativistic rigid motion suggests a new version for the so-called `twin paradox', comparing the ages of two astronauts on a very long spaceship. Although there is always an instantaneous inertial frame in which the whole spaceship, being rigid, is simultaneously at rest, the twins' ages, measured as the proper-times along their individual world lines, are different when they are located at remote parts of the spaceship. The age, or proper-time, difference depends on the distance at rest between the astronauts and the rapidity difference between start to end. The relation of the age difference with the relative Doppler shift of light signals transmitted between the astronauts, and implications for the possibility to assign common age (proper-time) to complex, spatially extended, relativistic systems, are also discussed. The condition for simultaneous arrival of light signals emitted simultaneously from the opposite ends of a rigidly accelerating spaceship is resolved. |
gr-qc/0402030 | Kirill Bronnikov | Kirill A. Bronnikov and Boris E. Meierovich | A general thick brane supported by a scalar field | 6 pages, gc style | Grav.Cosmol.9:313-318,2003 | null | null | gr-qc | null | A thick Z_2-symmetric domain wall supported by a scalar field with an
arbitrary potential V(\phi) in 5D general relativity is considered as a
candidate brane world. We show that, under the global regularity requirement,
such a configuration (i) has always an AdS asymptotic far from the brane, (ii)
is only possible if V(\phi) has an alternating sign and (iii) V(\phi) satisfies
a certain fine-tuning type equality. The thin brane limit is well defined and
conforms to the Randall-Sundrum (RS2) brane world model if the asymptotic value
of V(\phi) (related to \Lambda, the effective cosmological constant) is kept
thickness-independent. Universality of such a transition is demonstrated using
as an example exact solutions for stepwise potentials of different shapes.
Also, due to scale invariance of the Einstein-scalar equations, any given
regular solution creates a one-parameter family of solutions with different
potentials. In such families, a thin brane limit does not exist while the ratio
\Lambda/(brane tension)^2 is thickness-independent and is in general different
from its value in the RS2 model.
| [
{
"created": "Thu, 5 Feb 2004 05:49:33 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Bronnikov",
"Kirill A.",
""
],
[
"Meierovich",
"Boris E.",
""
]
] | A thick Z_2-symmetric domain wall supported by a scalar field with an arbitrary potential V(\phi) in 5D general relativity is considered as a candidate brane world. We show that, under the global regularity requirement, such a configuration (i) has always an AdS asymptotic far from the brane, (ii) is only possible if V(\phi) has an alternating sign and (iii) V(\phi) satisfies a certain fine-tuning type equality. The thin brane limit is well defined and conforms to the Randall-Sundrum (RS2) brane world model if the asymptotic value of V(\phi) (related to \Lambda, the effective cosmological constant) is kept thickness-independent. Universality of such a transition is demonstrated using as an example exact solutions for stepwise potentials of different shapes. Also, due to scale invariance of the Einstein-scalar equations, any given regular solution creates a one-parameter family of solutions with different potentials. In such families, a thin brane limit does not exist while the ratio \Lambda/(brane tension)^2 is thickness-independent and is in general different from its value in the RS2 model. |
1805.11340 | Romualdo Tresguerres | Romualdo Tresguerres | Matter sources of gauge thermodynamics | 26 Revtex pages, no figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A unified gauge approach to both, dynamics and thermodynamics involving
gravity, is developed from the local realization of the Poincar\'e group as a
particular instance of a spacetime group including translations. The formalism
is applied to study the physical features of the spherical non-rotating matter
source of an inner Schwarzschild metric.
| [
{
"created": "Tue, 29 May 2018 10:12:06 GMT",
"version": "v1"
}
] | 2018-05-30 | [
[
"Tresguerres",
"Romualdo",
""
]
] | A unified gauge approach to both, dynamics and thermodynamics involving gravity, is developed from the local realization of the Poincar\'e group as a particular instance of a spacetime group including translations. The formalism is applied to study the physical features of the spherical non-rotating matter source of an inner Schwarzschild metric. |
1907.09676 | Yun Soo Myung | Yun Soo Myung, De-Cheng Zou | Black holes in new massive conformal gravity | 17 pages, 3 figures, title changed, version to appear in PRD | Phys. Rev. D 100, 064057 (2019) | 10.1103/PhysRevD.100.064057 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the black holes in the new massive conformal gravity which is
not invariant under conformal transformations because of the presence of the
Einstein-Hilbert term. First, we show that the small Schwarzschild black hole
is unstable against the $s$-mode of linearized Ricci tensor by solving the
Lichnerowicz-Ricci tensor equation. This instability induces the appearance of
the non-BBMB (Bocharova-Bronnikov-Melnikov-Bekenstein) black hole that has both
Ricci tensor and conformal scalar hair.
| [
{
"created": "Tue, 23 Jul 2019 03:32:12 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Sep 2019 22:50:31 GMT",
"version": "v2"
}
] | 2019-10-02 | [
[
"Myung",
"Yun Soo",
""
],
[
"Zou",
"De-Cheng",
""
]
] | We investigate the black holes in the new massive conformal gravity which is not invariant under conformal transformations because of the presence of the Einstein-Hilbert term. First, we show that the small Schwarzschild black hole is unstable against the $s$-mode of linearized Ricci tensor by solving the Lichnerowicz-Ricci tensor equation. This instability induces the appearance of the non-BBMB (Bocharova-Bronnikov-Melnikov-Bekenstein) black hole that has both Ricci tensor and conformal scalar hair. |
1105.0345 | Recai Erdem | Recai Erdem | A simple toy model for a unified picture of dark energy, dark matter,
and inflation | 25 pages. The model is given in 3 pages. The rest is compatibility
check with observations and supplementary material | null | null | IZTECH-P2011-03 | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A specific scale factor in Robertson-Walker metric with the prospect of
giving the overall cosmic history in a unified picture roughly is considered.
The corresponding energy-momentum tensor is identified as that of two scalar
fields where one plays the roles of both inflaton and dark matter while the
other accounts for dark energy. A preliminary phenomenological analysis gives
an order of magnitude agreement with observational data. The resulting picture
may be considered as a first step towards a single model for all epochs of
cosmic evolution.
| [
{
"created": "Mon, 2 May 2011 14:41:04 GMT",
"version": "v1"
}
] | 2011-05-05 | [
[
"Erdem",
"Recai",
""
]
] | A specific scale factor in Robertson-Walker metric with the prospect of giving the overall cosmic history in a unified picture roughly is considered. The corresponding energy-momentum tensor is identified as that of two scalar fields where one plays the roles of both inflaton and dark matter while the other accounts for dark energy. A preliminary phenomenological analysis gives an order of magnitude agreement with observational data. The resulting picture may be considered as a first step towards a single model for all epochs of cosmic evolution. |
1609.07125 | Abhishek Majhi | Abhishek Majhi | Proof of Bekenstein-Mukhanov ansatz in loop quantum gravity | 5 pages, close to published version | Mod. Phys. Lett. A, Vol. 31, No. 31 (2016) 1650171 | 10.1142/S0217732316501716 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A simple proof of Bekenstein-Mukhanov(BM) ansatz is given within the loop
quantum gravity(LQG) framework. The macroscopic area of an equilibrium black
hole horizon indeed manifests a linear quantization. The quantum number
responsible for this discreteness of the macroscopic area has a physical
meaning in the LQG framework, unlike the ad hoc one that remained unexplained
in BM ansatz.
| [
{
"created": "Thu, 22 Sep 2016 19:39:13 GMT",
"version": "v1"
}
] | 2016-09-23 | [
[
"Majhi",
"Abhishek",
""
]
] | A simple proof of Bekenstein-Mukhanov(BM) ansatz is given within the loop quantum gravity(LQG) framework. The macroscopic area of an equilibrium black hole horizon indeed manifests a linear quantization. The quantum number responsible for this discreteness of the macroscopic area has a physical meaning in the LQG framework, unlike the ad hoc one that remained unexplained in BM ansatz. |
2403.18752 | Leonardo Mastrototaro | A. Campitelli, L. Mastrototaro | Neutron Stars Mass-Radius relations analysis in the Quintessence
scenario | 5 pages, 2 figures | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we explore the effects of General Relativity modification on
the Mass-Radius relations of Neutron Stars induced by the presence of the
Quintessence field. We consider, in particular, the Kiselev model, according to
which the Quintessence field, being present in the entire Universe, might also
be present around massive objects. Considering the Equation of State (EoS) for
Baryonic matter BSk22 derived by A. Y. Potekhin et al., we infer the upper
limit for NS masses in the presence of Quintessence. The presence of
Quintessence generates a peculiar effect for which the Mass-Radius relation is
unvaried and therefore the presence of Quintessence is indistinguishable from
ordinary matter, at least for the Kiselev model studied in this paper.
| [
{
"created": "Wed, 27 Mar 2024 16:52:53 GMT",
"version": "v1"
}
] | 2024-03-28 | [
[
"Campitelli",
"A.",
""
],
[
"Mastrototaro",
"L.",
""
]
] | In this paper, we explore the effects of General Relativity modification on the Mass-Radius relations of Neutron Stars induced by the presence of the Quintessence field. We consider, in particular, the Kiselev model, according to which the Quintessence field, being present in the entire Universe, might also be present around massive objects. Considering the Equation of State (EoS) for Baryonic matter BSk22 derived by A. Y. Potekhin et al., we infer the upper limit for NS masses in the presence of Quintessence. The presence of Quintessence generates a peculiar effect for which the Mass-Radius relation is unvaried and therefore the presence of Quintessence is indistinguishable from ordinary matter, at least for the Kiselev model studied in this paper. |
gr-qc/0002033 | Esposito Giampiero | Giampiero Esposito | A Theory of Quantum Gravity from First Principles | 15 pages, plain Tex. In the revised version, the part after Eq. (38)
is completely new | null | null | DSF preprint 2000/3 | gr-qc | null | When quantum fields are studied on manifolds with boundary, the corresponding
one-loop quantum theory for bosonic gauge fields with linear covariant gauges
needs the assignment of suitable boundary conditions for elliptic differential
operators of Laplace type. There are however deep reasons to modify such a
scheme and allow for pseudo-differential boundary-value problems. When the
boundary operator is allowed to be pseudo-differential while remaining a
projector, the conditions on its kernel leading to strong ellipticity of the
boundary-value problem are studied in detail. This makes it possible to develop
a theory of one-loop quantum gravity from first principles only, i.e. the
physical principle of invariance under infinitesimal diffeomorphisms and the
mathematical requirement of a strongly elliptic theory.
| [
{
"created": "Tue, 8 Feb 2000 06:43:02 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Apr 2000 08:22:47 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Esposito",
"Giampiero",
""
]
] | When quantum fields are studied on manifolds with boundary, the corresponding one-loop quantum theory for bosonic gauge fields with linear covariant gauges needs the assignment of suitable boundary conditions for elliptic differential operators of Laplace type. There are however deep reasons to modify such a scheme and allow for pseudo-differential boundary-value problems. When the boundary operator is allowed to be pseudo-differential while remaining a projector, the conditions on its kernel leading to strong ellipticity of the boundary-value problem are studied in detail. This makes it possible to develop a theory of one-loop quantum gravity from first principles only, i.e. the physical principle of invariance under infinitesimal diffeomorphisms and the mathematical requirement of a strongly elliptic theory. |
1705.01597 | Aurelien Barrau | Aur\'elien Barrau | Testing different approaches to quantum gravity with cosmology: An
overview | Invited introductory article for a special issue of Comptes Rendus
Physique | null | 10.1016/j.crhy.2017.05.001 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Among the available quantum gravity proposals, string theory, loop quantum
gravity, non-commutative geometry, group field theory, causal sets, asymptotic
safety, causal dynamical triangulation, emergent gravity are among the best
motivated models. As an introductory summary to this special issue of Comptes
Rendus Physique, I explain how those different theories can be tested or
constrained by cosmological observations.
| [
{
"created": "Wed, 3 May 2017 19:50:08 GMT",
"version": "v1"
}
] | 2017-06-28 | [
[
"Barrau",
"Aurélien",
""
]
] | Among the available quantum gravity proposals, string theory, loop quantum gravity, non-commutative geometry, group field theory, causal sets, asymptotic safety, causal dynamical triangulation, emergent gravity are among the best motivated models. As an introductory summary to this special issue of Comptes Rendus Physique, I explain how those different theories can be tested or constrained by cosmological observations. |
gr-qc/0003055 | Benedetti Riccardo | Riccardo Benedetti and Enore Guadagnini | Cosmological Time in (2+1) - Gravity | Totally new version with strongly improved exposition. Clarifying
examples and figures have been included. 21 pages, Latex, 9 figures | Nucl.Phys. B613 (2001) 330-352 | 10.1016/S0550-3213(01)00386-8 | null | gr-qc | null | We consider maximal globally hyperbolic flat (2+1) spacetimes with compact
space S of genus g>1. For any spacetime M of this type, the length of time that
the events have been in existence is M defines a global time, called the
cosmological time CT of M, which reveals deep intrinsic properties of
spacetime. In particular, the past/future asymptotic states of the cosmological
time recover and decouple the linear and the translational parts of the
ISO(2,1)-valued holonomy of the flat spacetime. The initial singularity can be
interpreted as an isometric action of the fundamental group of S on a suitable
real tree. The initial singularity faithfully manifests itself as a lack of
smoothness of the embedding of the CT level surfaces into the spacetime M. The
cosmological time determines a real analytic curve in the Teichmuller space of
Riemann surfaces of genus g, which connects an interior point (associated to
the linear part of the holonomy) with a point on Thurston's natural boundary
(associated to the initial singularity).
| [
{
"created": "Tue, 14 Mar 2000 13:30:03 GMT",
"version": "v1"
},
{
"created": "Mon, 30 Apr 2001 09:14:52 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Benedetti",
"Riccardo",
""
],
[
"Guadagnini",
"Enore",
""
]
] | We consider maximal globally hyperbolic flat (2+1) spacetimes with compact space S of genus g>1. For any spacetime M of this type, the length of time that the events have been in existence is M defines a global time, called the cosmological time CT of M, which reveals deep intrinsic properties of spacetime. In particular, the past/future asymptotic states of the cosmological time recover and decouple the linear and the translational parts of the ISO(2,1)-valued holonomy of the flat spacetime. The initial singularity can be interpreted as an isometric action of the fundamental group of S on a suitable real tree. The initial singularity faithfully manifests itself as a lack of smoothness of the embedding of the CT level surfaces into the spacetime M. The cosmological time determines a real analytic curve in the Teichmuller space of Riemann surfaces of genus g, which connects an interior point (associated to the linear part of the holonomy) with a point on Thurston's natural boundary (associated to the initial singularity). |
2408.05576 | Cosimo Bambi | Bakhtiyor Narzilloev, Ahmadjon Abdujabbarov, Bobomurat Ahmedov, Cosimo
Bambi | Observed jet power and radiative efficiency of black hole candidates in
Kerr + PFDM model | 13 pages, 9 figures. Accepted in EPJC. arXiv admin note: text overlap
with arXiv:2310.10554 | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this research, we explore the electromagnetic energy emitted by
astrophysical black holes within the Kerr+PFDM spacetime, a model encompassing
rotating black holes surrounded by dark matter. Our investigation focuses on
black holes within X-ray binary systems, namely GRS 1915+105, GRO J1655-40, XTE
J1550-564, A0620-00, H1743-322, and GRS 1124-683. Our findings indicate that
the Kerr+PFDM spacetime can account for the radiative efficiency of these
sources as determined through the continuum fitting method (CFM). Additionally,
employing the Blandford-Znajeck mechanism, we demonstrate the ability to
replicate the observed jet power. By combining the outcomes of both analyses
for the selected objects, we establish more rigorous constraints on the
spacetime parameters. Notably, our results reveal that similar to the Kerr
spacetime, the Kerr+PFDM spacetime cannot simultaneously account for the
observed jet power and radiative efficiency of GRS 1915+105.
| [
{
"created": "Sat, 10 Aug 2024 14:59:54 GMT",
"version": "v1"
}
] | 2024-08-13 | [
[
"Narzilloev",
"Bakhtiyor",
""
],
[
"Abdujabbarov",
"Ahmadjon",
""
],
[
"Ahmedov",
"Bobomurat",
""
],
[
"Bambi",
"Cosimo",
""
]
] | In this research, we explore the electromagnetic energy emitted by astrophysical black holes within the Kerr+PFDM spacetime, a model encompassing rotating black holes surrounded by dark matter. Our investigation focuses on black holes within X-ray binary systems, namely GRS 1915+105, GRO J1655-40, XTE J1550-564, A0620-00, H1743-322, and GRS 1124-683. Our findings indicate that the Kerr+PFDM spacetime can account for the radiative efficiency of these sources as determined through the continuum fitting method (CFM). Additionally, employing the Blandford-Znajeck mechanism, we demonstrate the ability to replicate the observed jet power. By combining the outcomes of both analyses for the selected objects, we establish more rigorous constraints on the spacetime parameters. Notably, our results reveal that similar to the Kerr spacetime, the Kerr+PFDM spacetime cannot simultaneously account for the observed jet power and radiative efficiency of GRS 1915+105. |
1212.4730 | Richard Price | Richard H. Price, John W. Belcher, David A. Nichols | Comparison of electromagnetic and gravitational radiation; what we can
learn about each from the other | 22 pages, 7 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compare the nature of electromagnetic fields and of gravitational fields
in linearized general relativity. We carry out this comparison both
mathematically and visually. In particular the "lines of force" visualizations
of electromagnetism are contrasted with the recently introduced tendex/vortex
eigenline technique for visualizing gravitational fields. Specific solutions,
visualizations, and comparisons are given for an oscillating point quadrupole
source. Among the similarities illustrated are the quasistatic nature of the
near fields, the transverse 1/r nature of the far fields, and the interesting
intermediate field structures connecting these two limiting forms. Among the
differences illustrated are the meaning of field line motion, and of the flow
of energy.
| [
{
"created": "Wed, 19 Dec 2012 16:43:15 GMT",
"version": "v1"
}
] | 2012-12-20 | [
[
"Price",
"Richard H.",
""
],
[
"Belcher",
"John W.",
""
],
[
"Nichols",
"David A.",
""
]
] | We compare the nature of electromagnetic fields and of gravitational fields in linearized general relativity. We carry out this comparison both mathematically and visually. In particular the "lines of force" visualizations of electromagnetism are contrasted with the recently introduced tendex/vortex eigenline technique for visualizing gravitational fields. Specific solutions, visualizations, and comparisons are given for an oscillating point quadrupole source. Among the similarities illustrated are the quasistatic nature of the near fields, the transverse 1/r nature of the far fields, and the interesting intermediate field structures connecting these two limiting forms. Among the differences illustrated are the meaning of field line motion, and of the flow of energy. |
2103.05802 | Wan Cong Ms | Wan Cong, Jiri Bicak, David Kubiznak and Robert Mann | Quantum Detection of Conicity | 5+1 pages, 4 figures | Physics Letters B 820, 136482 (2021) | 10.1016/j.physletb.2021.136482 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the sensitivity of an Unruh-DeWitt detector to the global
features of a deficit angle that are otherwise classically inaccessible.
Specifically, we consider a detector placed inside an infinite thin hollow
cylinder whose spacetime is everywhere flat but outside of which the spacetime
has a deficit angle and study its response to a scalar field to which it
couples. We find that the response of the detector is sensitive to the deficit
angle, despite the fact that it does not interact with the cylinder.
| [
{
"created": "Wed, 10 Mar 2021 01:13:25 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Jul 2021 18:52:18 GMT",
"version": "v2"
}
] | 2021-07-06 | [
[
"Cong",
"Wan",
""
],
[
"Bicak",
"Jiri",
""
],
[
"Kubiznak",
"David",
""
],
[
"Mann",
"Robert",
""
]
] | We investigate the sensitivity of an Unruh-DeWitt detector to the global features of a deficit angle that are otherwise classically inaccessible. Specifically, we consider a detector placed inside an infinite thin hollow cylinder whose spacetime is everywhere flat but outside of which the spacetime has a deficit angle and study its response to a scalar field to which it couples. We find that the response of the detector is sensitive to the deficit angle, despite the fact that it does not interact with the cylinder. |
gr-qc/0403057 | Y. Jack Ng | Y. Jack Ng and H. van Dam | Spacetime Foam, Holographic Principle, and Black Hole Quantum Computers | 8 pages, LaTeX; Talk given by Jack Ng, in celebration of Paul
Frampton's 60th birthday, at the Coral Gables Conference (in Fort Lauderdale,
Florida on December 17, 2003). To appear in the Proceedings of the 2003 Coral
Gables Conference | Int.J.Mod.Phys. A20 (2005) 1328-1335 | 10.1142/S0217751X05024237 | null | gr-qc hep-th quant-ph | null | Spacetime foam, also known as quantum foam, has its origin in quantum
fluctuations of spacetime. Arguably it is the source of the holographic
principle, which severely limits how densely information can be packed in
space. Its physics is also intimately linked to that of black holes and
computation. In particular, the same underlying physics is shown to govern the
computational power of black hole quantum computers.
| [
{
"created": "Sat, 13 Mar 2004 21:14:46 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Ng",
"Y. Jack",
""
],
[
"van Dam",
"H.",
""
]
] | Spacetime foam, also known as quantum foam, has its origin in quantum fluctuations of spacetime. Arguably it is the source of the holographic principle, which severely limits how densely information can be packed in space. Its physics is also intimately linked to that of black holes and computation. In particular, the same underlying physics is shown to govern the computational power of black hole quantum computers. |
gr-qc/0401127 | Simone Mercuri | Simone Mercuri, Giovanni Montani | On the Frame Fixing in Quantum Gravity | 3 pages, no figures, proceeding of the X Marcel Grossmann meeting,
Rio de Janeiro, Brazil, July 20-26, 2003 | null | 10.1142/9789812704030_0301 | null | gr-qc | null | We provide a discussion about the necessity to fix the reference frame before
quantizing the gravitational field. Our presentation is based on stressing how
the 3+1-slicing of the space time becomes an ambiguous procedure as referred to
a quantum 4-metric.
| [
{
"created": "Fri, 30 Jan 2004 15:20:37 GMT",
"version": "v1"
}
] | 2016-11-09 | [
[
"Mercuri",
"Simone",
""
],
[
"Montani",
"Giovanni",
""
]
] | We provide a discussion about the necessity to fix the reference frame before quantizing the gravitational field. Our presentation is based on stressing how the 3+1-slicing of the space time becomes an ambiguous procedure as referred to a quantum 4-metric. |
1501.03921 | Nahid Ahmadi | Nahid Ahmadi and Zainab Sedaghatmanesh | Deflection of light by the field of a binary system | 9 pages, 4 figures | Class. Quantum Grav. 32 (2015) 235015 (20pp) | 10.1088/0264-9381/32/23/235015 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the motion of a photon in the gravitational field of a binary
system. The equations of motion are geodesic equations in a Schwarzchild
background with a tidal force. We specialize the equations to that of an
edge-on binary and use the method of osculating elements to integrate them.
This work helps to identify a binary system through the gravitational light
deflection of one member in the gravitational field of the other member. It is
found that the effects of the companion body on a photon passing the edge of
the star can be potentially detected by astrometric satellites with $\mu$as
precision, if the ratio of the Schwarzchid radius to the star radius,
$\frac{Gm}{c^2 R}\geq 10^{-5}$. Two different cumulative effects on the photon
path are identified.
| [
{
"created": "Fri, 16 Jan 2015 09:10:53 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Apr 2015 14:54:15 GMT",
"version": "v2"
}
] | 2021-08-31 | [
[
"Ahmadi",
"Nahid",
""
],
[
"Sedaghatmanesh",
"Zainab",
""
]
] | We examine the motion of a photon in the gravitational field of a binary system. The equations of motion are geodesic equations in a Schwarzchild background with a tidal force. We specialize the equations to that of an edge-on binary and use the method of osculating elements to integrate them. This work helps to identify a binary system through the gravitational light deflection of one member in the gravitational field of the other member. It is found that the effects of the companion body on a photon passing the edge of the star can be potentially detected by astrometric satellites with $\mu$as precision, if the ratio of the Schwarzchid radius to the star radius, $\frac{Gm}{c^2 R}\geq 10^{-5}$. Two different cumulative effects on the photon path are identified. |
2101.03167 | Ellery Ames | Ellery Ames, Florian Beyer, James Isenberg and Todd Oliynyk | Stability of AVTD Behavior within the Polarized $T^2$-symmetric vacuum
spacetimes | 28 pages. Fixed minor typos and made several clarifications. Agrees
with published version | Ann. Henri Poincar\'e (2022) | 10.1007/s00023-021-01142-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We prove stability of the family of Kasner solutions within the class of
polarized $T^2$-symmetric solutions of the vacuum Einstein equations in the
contracting time direction with respect to an areal time foliation. All Kasner
solutions for which the asymptotic velocity parameter $K$ satisfies $|K-1|>2$
are non-linearly stable, and all sufficiently small perturbations exhibit
asymptotically velocity term dominated (AVTD) behavior and blow-up of the
Kretschmann scalar.
| [
{
"created": "Fri, 8 Jan 2021 18:57:19 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Feb 2021 03:27:45 GMT",
"version": "v2"
},
{
"created": "Tue, 25 Jan 2022 21:59:38 GMT",
"version": "v3"
}
] | 2022-05-20 | [
[
"Ames",
"Ellery",
""
],
[
"Beyer",
"Florian",
""
],
[
"Isenberg",
"James",
""
],
[
"Oliynyk",
"Todd",
""
]
] | We prove stability of the family of Kasner solutions within the class of polarized $T^2$-symmetric solutions of the vacuum Einstein equations in the contracting time direction with respect to an areal time foliation. All Kasner solutions for which the asymptotic velocity parameter $K$ satisfies $|K-1|>2$ are non-linearly stable, and all sufficiently small perturbations exhibit asymptotically velocity term dominated (AVTD) behavior and blow-up of the Kretschmann scalar. |
2404.08732 | Jose Natario | Lu\'is Machado, Jos\'e Nat\'ario, Jorge Drumond Silva | Free-falling motion of an elastic rigid rod towards a Schwarzschild
black hole | 10 pages, 5 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study the motion of an elastic rigid rod which is radially free-falling
towards a Schwarzschild black hole. This is accomplished by reducing the
corresponding free-boundary PDE problem to a sequence of ODEs, which we
integrate numerically. Starting with a rod at rest, we show that it is possible
to choose its initial compression profile so that its midpoint falls
substantially faster, or slower, than a free-falling particle with the same
initial conditions. This seems to be a purely kinematic effect, since on
average there is no net transfer of elastic to mechanical energy.
| [
{
"created": "Fri, 12 Apr 2024 18:00:02 GMT",
"version": "v1"
}
] | 2024-04-16 | [
[
"Machado",
"Luís",
""
],
[
"Natário",
"José",
""
],
[
"Silva",
"Jorge Drumond",
""
]
] | We study the motion of an elastic rigid rod which is radially free-falling towards a Schwarzschild black hole. This is accomplished by reducing the corresponding free-boundary PDE problem to a sequence of ODEs, which we integrate numerically. Starting with a rod at rest, we show that it is possible to choose its initial compression profile so that its midpoint falls substantially faster, or slower, than a free-falling particle with the same initial conditions. This seems to be a purely kinematic effect, since on average there is no net transfer of elastic to mechanical energy. |
2308.03192 | Yurii Ignat'ev | Yu. G. Ignat'ev | Formation of supermassive nuclei of Black holes in the early Universe by
the mechanism of scalar-gravitational instability. I. Local picture | 19 pages,18 figures, 34 references | Gravit. Cosmol. 2023, 29, 327 | 10.1134/S0202289323040102 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Based on the formulated and proven similarity properties of cosmological
models based on a statistical system of degenerate scalarly charged fermions,
as well as the previously identified mechanism of scalar-gravitational
instability of cosmological models, a numerical-analytical study of the
formation of supermassive black hole nuclei in the early Universe was carried
out. A mathematical model of the evolution of spherical perturbations is
constructed, on the basis of which the main regularities of the process of
evolution of collapsing masses and the dependence of the parameters of forming
black holes on the fundamental parameters of the cosmological model and the
wavelength of gravitational perturbations are revealed. In this case, the mass
loss of the black hole due to quantum evaporation is taken into account. A
stable tendency for the early formation of supermassive black hole nuclei in
the class of cosmological models under study is shown, and a close connection
between the growth of masses of spherical perturbations and the nature of the
singular points of these models is shown. Keywords: scalarly charged plasma,
cosmological model, Higgs scalar field, gravitational stability, spherical
perturbations, black hole formation, evaporation.
| [
{
"created": "Sun, 6 Aug 2023 18:55:07 GMT",
"version": "v1"
}
] | 2023-12-04 | [
[
"Ignat'ev",
"Yu. G.",
""
]
] | Based on the formulated and proven similarity properties of cosmological models based on a statistical system of degenerate scalarly charged fermions, as well as the previously identified mechanism of scalar-gravitational instability of cosmological models, a numerical-analytical study of the formation of supermassive black hole nuclei in the early Universe was carried out. A mathematical model of the evolution of spherical perturbations is constructed, on the basis of which the main regularities of the process of evolution of collapsing masses and the dependence of the parameters of forming black holes on the fundamental parameters of the cosmological model and the wavelength of gravitational perturbations are revealed. In this case, the mass loss of the black hole due to quantum evaporation is taken into account. A stable tendency for the early formation of supermassive black hole nuclei in the class of cosmological models under study is shown, and a close connection between the growth of masses of spherical perturbations and the nature of the singular points of these models is shown. Keywords: scalarly charged plasma, cosmological model, Higgs scalar field, gravitational stability, spherical perturbations, black hole formation, evaporation. |
1407.8545 | Charles Suggs | R. Jackiw and So-Young Pi | Fake Conformal Symmetry in Conformal Cosmological Models | References updated, errors corrected, published in Phys. Rev. D. 4
pages, RevTeX, no figures | Phys. Rev. D 91, 067501 (2015) | 10.1103/PhysRevD.91.067501 | MIT-CTP/4570 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the local conformal invariance (Weyl invariance) in tensor-scalar
theories used in recently proposed conformal cosmological models. We show that
the Noether currents associated with Weyl invariance in these theories vanish.
We assert that the corresponding Weyl symmetry does not have any dynamical
role.
| [
{
"created": "Thu, 31 Jul 2014 19:49:33 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Oct 2014 18:33:03 GMT",
"version": "v2"
},
{
"created": "Tue, 24 Feb 2015 17:52:31 GMT",
"version": "v3"
}
] | 2015-03-18 | [
[
"Jackiw",
"R.",
""
],
[
"Pi",
"So-Young",
""
]
] | We examine the local conformal invariance (Weyl invariance) in tensor-scalar theories used in recently proposed conformal cosmological models. We show that the Noether currents associated with Weyl invariance in these theories vanish. We assert that the corresponding Weyl symmetry does not have any dynamical role. |
0805.4046 | HongSheng Zhao | HongSheng Zhao (U. of St Andrews) | Reinterpreting MOND: coupling of Einsteinian gravity and spin of cosmic
neutrinos? | 8p, some changes of notations, references added | null | null | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Several rare coincidences of scales in standard particle physics are needed
to explain (i) why neutrinos have mass, (ii) why the negative pressure of the
cosmological dark energy (DE) coincides with the positive pressure of random
motion of dark matter (DM) in bright galaxies, (iii) why Dark Matter in
galaxies seems to have a finite phase-space density, and to follow the
Tully-Fisher-Milgrom relation of galaxy rotation curves. The old idea of
self-interacting DM is given a new spin: we propose that the neutrino
spin-gravity coupling could lead to a cosmic neutrino dark fluid with a an
internal energy density varying as function of the local acceleration of the
neutrino fluid with respect the CMB background. We link the
Tully-Fisher-Milgrom relation of spiral galaxies (or MOND) with the
relativistic pressure of the neutrino dark fluid without modifying Einsteinian
gravity.
| [
{
"created": "Tue, 27 May 2008 03:44:40 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Jun 2008 16:50:33 GMT",
"version": "v2"
}
] | 2008-06-11 | [
[
"Zhao",
"HongSheng",
"",
"U. of St Andrews"
]
] | Several rare coincidences of scales in standard particle physics are needed to explain (i) why neutrinos have mass, (ii) why the negative pressure of the cosmological dark energy (DE) coincides with the positive pressure of random motion of dark matter (DM) in bright galaxies, (iii) why Dark Matter in galaxies seems to have a finite phase-space density, and to follow the Tully-Fisher-Milgrom relation of galaxy rotation curves. The old idea of self-interacting DM is given a new spin: we propose that the neutrino spin-gravity coupling could lead to a cosmic neutrino dark fluid with a an internal energy density varying as function of the local acceleration of the neutrino fluid with respect the CMB background. We link the Tully-Fisher-Milgrom relation of spiral galaxies (or MOND) with the relativistic pressure of the neutrino dark fluid without modifying Einsteinian gravity. |
2012.05178 | Burkhard Kleihaus | Rustam Ibadov, Burkhard Kleihaus, Jutta Kunz, Sardor Murodov | Scalarized nutty wormholes | 14 pages, 4 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct scalarized wormholes with a NUT charge in higher curvature
theories. We consider both Einstein-scalar-Gauss-Bonnet and
Einstein-scalar-Chern-Simons theories, following a recent paper by Brihaye et
al. [1], where spontaneously scalarised Schwarzschild-NUT solutions were
studied. By varying the coupling parameter and the scalar charge we determine
the domain of existence of the scalarized nutty wormholes, and their dependence
on the NUT charge. In the Gauss-Bonnet case the known set of scalarized
wormholes [2] is reached in the limit of vanishing NUT charge. In the
Chern-Simons case, however, the limit is peculiar, since with vanishing NUT
charge the coupling constant diverges. We focus on scalarized nutty wormholes
with a single throat and study their properties. All these scalarized nutty
wormholes feature a critical polar angle, beyond which closed timelike curves
are present.
| [
{
"created": "Wed, 9 Dec 2020 17:06:19 GMT",
"version": "v1"
}
] | 2020-12-10 | [
[
"Ibadov",
"Rustam",
""
],
[
"Kleihaus",
"Burkhard",
""
],
[
"Kunz",
"Jutta",
""
],
[
"Murodov",
"Sardor",
""
]
] | We construct scalarized wormholes with a NUT charge in higher curvature theories. We consider both Einstein-scalar-Gauss-Bonnet and Einstein-scalar-Chern-Simons theories, following a recent paper by Brihaye et al. [1], where spontaneously scalarised Schwarzschild-NUT solutions were studied. By varying the coupling parameter and the scalar charge we determine the domain of existence of the scalarized nutty wormholes, and their dependence on the NUT charge. In the Gauss-Bonnet case the known set of scalarized wormholes [2] is reached in the limit of vanishing NUT charge. In the Chern-Simons case, however, the limit is peculiar, since with vanishing NUT charge the coupling constant diverges. We focus on scalarized nutty wormholes with a single throat and study their properties. All these scalarized nutty wormholes feature a critical polar angle, beyond which closed timelike curves are present. |
2309.13931 | Conghua Liu | Conghua Liu, Ran Li, Kun Zhang and Jin Wang | Generalized free energy and dynamical state transition of the dyonic AdS
black hole in the grand canonical ensemble | null | JHEP11(2023)068 | 10.1007/JHEP11(2023)068 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the generalized free energy of the dyonic AdS black hole in an
ensemble with varying electric charge $q_E$ and fixed magnetic charge $q_M$.
When we adjust the temperature $T$ and the electric potential $\Phi_E$ of the
ensemble, the Ricci scalar curvature $R$ and electromagnetic potential $A_u$
usually diverge at the horizon. We regularize them and incorporate the
off-shell corrections into the Einstein-Hilbert action. Alternatively, we find
that the off-shell corrections can also be obtained by adding a boundary near
the horizon to exclude the singularities. Ultimately, we derive the generalized
free energy which is consistent with the definition of the thermodynamic
relations. Based on the generalized free energy landscape, we can describe the
dynamics of state transition as a stochastic process quantified by the Langevin
equation. The path integral framework can be formulated to derive the
time-dependent trajectory of the order parameter and the time evolution of the
transition probability. By comparing the probability with the result of the
classical master equation, we attribute the contribution to the probability of
one pseudomolecule or antipseudomolecule (the instanton and anti-instanton
pair) to the rate of state transition. These results are consistent with the
qualitative analysis of the free energy landscape.
| [
{
"created": "Mon, 25 Sep 2023 08:01:23 GMT",
"version": "v1"
},
{
"created": "Wed, 1 Nov 2023 07:39:43 GMT",
"version": "v2"
}
] | 2023-11-15 | [
[
"Liu",
"Conghua",
""
],
[
"Li",
"Ran",
""
],
[
"Zhang",
"Kun",
""
],
[
"Wang",
"Jin",
""
]
] | We study the generalized free energy of the dyonic AdS black hole in an ensemble with varying electric charge $q_E$ and fixed magnetic charge $q_M$. When we adjust the temperature $T$ and the electric potential $\Phi_E$ of the ensemble, the Ricci scalar curvature $R$ and electromagnetic potential $A_u$ usually diverge at the horizon. We regularize them and incorporate the off-shell corrections into the Einstein-Hilbert action. Alternatively, we find that the off-shell corrections can also be obtained by adding a boundary near the horizon to exclude the singularities. Ultimately, we derive the generalized free energy which is consistent with the definition of the thermodynamic relations. Based on the generalized free energy landscape, we can describe the dynamics of state transition as a stochastic process quantified by the Langevin equation. The path integral framework can be formulated to derive the time-dependent trajectory of the order parameter and the time evolution of the transition probability. By comparing the probability with the result of the classical master equation, we attribute the contribution to the probability of one pseudomolecule or antipseudomolecule (the instanton and anti-instanton pair) to the rate of state transition. These results are consistent with the qualitative analysis of the free energy landscape. |
2006.01883 | Javier Olmedo | Ivan Agullo, Javier Olmedo and V. Sreenath | Observational consequences of Bianchi I spacetimes in loop quantum
cosmology | 37 pages, 12 figures, version matching published manuscript | Phys. Rev. D 102, 043523 (2020) | 10.1103/PhysRevD.102.043523 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Anisotropies generically dominate the earliest stages of expansion of a
homogeneous universe. They are particularly relevant in bouncing models, since
shears grow in the contracting phase of the cosmos, making the isotropic
situation unstable. This paper extends the study of cosmological perturbations
in loop quantum cosmology (LQC) to anisotropic Bianchi I models that contain a
bounce followed by a phase of slow-roll inflation. We show that, although the
shear tensor dilutes and the universe isotropizes soon after the bounce, cosmic
perturbations retain memory of this short anisotropic phase. We develop the
formalism needed to describe perturbations in anisotropic, effective LQC, and
apply it to make predictions for the cosmic microwave background (CMB), while
respecting current observational constraints. We show that the anisotropic
bounce induces: (i) anisotropic features in all angular correlation functions
in the CMB, and in particular a quadrupolar modulation that can account for a
similar feature observed in the temperature map by the Planck satellite, and
(ii) quantum entanglement between scalar and tensor modes, that manifests
itself in temperature-polarization (T-B and E-B) correlations in the CMB.
| [
{
"created": "Tue, 2 Jun 2020 19:02:28 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Sep 2020 08:09:42 GMT",
"version": "v2"
}
] | 2020-09-04 | [
[
"Agullo",
"Ivan",
""
],
[
"Olmedo",
"Javier",
""
],
[
"Sreenath",
"V.",
""
]
] | Anisotropies generically dominate the earliest stages of expansion of a homogeneous universe. They are particularly relevant in bouncing models, since shears grow in the contracting phase of the cosmos, making the isotropic situation unstable. This paper extends the study of cosmological perturbations in loop quantum cosmology (LQC) to anisotropic Bianchi I models that contain a bounce followed by a phase of slow-roll inflation. We show that, although the shear tensor dilutes and the universe isotropizes soon after the bounce, cosmic perturbations retain memory of this short anisotropic phase. We develop the formalism needed to describe perturbations in anisotropic, effective LQC, and apply it to make predictions for the cosmic microwave background (CMB), while respecting current observational constraints. We show that the anisotropic bounce induces: (i) anisotropic features in all angular correlation functions in the CMB, and in particular a quadrupolar modulation that can account for a similar feature observed in the temperature map by the Planck satellite, and (ii) quantum entanglement between scalar and tensor modes, that manifests itself in temperature-polarization (T-B and E-B) correlations in the CMB. |
1310.2957 | Sebastian Steinhaus | Wojciech Kaminski and Sebastian Steinhaus | The Barrett-Crane model: asymptotic measure factor | 12 pages, clarifications and references added, version accepted in
Class. Quant. Grav | Class. Quantum Grav. 31 (2014) 075014 | 10.1088/0264-9381/31/7/075014 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The original spin foam model construction for 4D gravity by Barrett and Crane
suffers from a few troubling issues. In the simple examples of the vertex
amplitude they can be summarized as the existence of contributions to the
asymptotics from non geometric configurations. Even restricted to geometric
contributions the amplitude is not completely worked out. While the phase is
known to be the Regge action, the so called measure factor has remained
mysterious for a decade. In the toy model case of the 6j symbol this measure
factor has a nice geometric interpretation of $V^{-1/2}$ leading to
speculations that a similar interpretation should be possible also in the 4D
case. In this paper we provide the first geometric interpretation of the
geometric part of the asymptotic for the spin foam consisting of two glued
4-simplices (decomposition of the 4-sphere) in the Barrett-Crane model in the
large internal spin regime.
| [
{
"created": "Thu, 10 Oct 2013 20:28:06 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Oct 2013 22:36:41 GMT",
"version": "v2"
},
{
"created": "Sun, 23 Feb 2014 18:48:48 GMT",
"version": "v3"
}
] | 2014-03-12 | [
[
"Kaminski",
"Wojciech",
""
],
[
"Steinhaus",
"Sebastian",
""
]
] | The original spin foam model construction for 4D gravity by Barrett and Crane suffers from a few troubling issues. In the simple examples of the vertex amplitude they can be summarized as the existence of contributions to the asymptotics from non geometric configurations. Even restricted to geometric contributions the amplitude is not completely worked out. While the phase is known to be the Regge action, the so called measure factor has remained mysterious for a decade. In the toy model case of the 6j symbol this measure factor has a nice geometric interpretation of $V^{-1/2}$ leading to speculations that a similar interpretation should be possible also in the 4D case. In this paper we provide the first geometric interpretation of the geometric part of the asymptotic for the spin foam consisting of two glued 4-simplices (decomposition of the 4-sphere) in the Barrett-Crane model in the large internal spin regime. |
2308.01233 | Martiros Khurshudyan | Martiros Khurshudyan | Swampland criteria and neutrino generation in a non-cold dark matter
universe | accepted in Astrophysics (Astrofizika) | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | In this paper, the implications of string Swampland criteria for a dark
energy-dominated universe, where we have a deviation from the cold dark matter
model, will be discussed. In particular, we have considered two models. One of
them is one parameter model, while the second one has been crafted to reveal
the dynamics in the deviation. The analysis has been obtained through the use
of Gaussian processes (GPs) and $H(z)$ expansion rate data (a $30$-point sample
deduced from a differential age method and a $10$-point sample obtained from
the radial BAO method). We learned that the tension with the Swampland criteria
still will survive as in the cases of the models where dark matter is cold. In
the analysis besides mentioned $40$-point $H(z)$ data, we used the latest
values of $H_{0}$ reported by the Planck and Hubble missions to reveal possible
solutions for the $H_{0}$ tension problem. Finally, the constraints on the
neutrino generation number have been obtained revealing interesting results to
be discussed yet. This and various related questions have been left to be
discussed in forthcoming papers.
| [
{
"created": "Wed, 2 Aug 2023 15:40:29 GMT",
"version": "v1"
}
] | 2023-08-03 | [
[
"Khurshudyan",
"Martiros",
""
]
] | In this paper, the implications of string Swampland criteria for a dark energy-dominated universe, where we have a deviation from the cold dark matter model, will be discussed. In particular, we have considered two models. One of them is one parameter model, while the second one has been crafted to reveal the dynamics in the deviation. The analysis has been obtained through the use of Gaussian processes (GPs) and $H(z)$ expansion rate data (a $30$-point sample deduced from a differential age method and a $10$-point sample obtained from the radial BAO method). We learned that the tension with the Swampland criteria still will survive as in the cases of the models where dark matter is cold. In the analysis besides mentioned $40$-point $H(z)$ data, we used the latest values of $H_{0}$ reported by the Planck and Hubble missions to reveal possible solutions for the $H_{0}$ tension problem. Finally, the constraints on the neutrino generation number have been obtained revealing interesting results to be discussed yet. This and various related questions have been left to be discussed in forthcoming papers. |
1910.03933 | David Benisty | Shreya Banerjee, David Benisty and Eduardo I. Guendelman | Running Dark Energy and Dark Matter from Dynamical Spacetime | 6 pages, 4 figures, modified version | Bulg.J.Phys. 48 (2021) no.2, 117-137 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Running Dark Energy and Dark Matter models are candidates to resolve the
Hubble constant tension. However the model does not consider a Lagrangian
formulation directly. In this paper we formulate an action principle where the
Running Vacuum Model (RVM) is obtained from an action principle, with a scalar
field model for the whole dark components. The Dynamical Spacetime vector field
$\chi_\mu$ is a Lagrange multiplier that forces the kinetic term of the scalar
field to behave as the modified dark matter. When we replace the vector field
by a derivative of a scalar the model predicts diffusion interactions between
the dark components with a different correspondence to the RVM. We test the
models with the Cosmic Chronometers, Type Ia Supernova, Quasars, Gamma ray
Bursts and the Baryon Acoustic Oscillations data sets. We find that
$\Lambda$CDM is still the best model. However this formulation suggests an
action principle for the $\Lambda$CDM, the RVM model and other extensions.
| [
{
"created": "Tue, 8 Oct 2019 06:08:17 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Apr 2020 18:39:38 GMT",
"version": "v2"
},
{
"created": "Fri, 23 Apr 2021 14:44:14 GMT",
"version": "v3"
}
] | 2021-04-26 | [
[
"Banerjee",
"Shreya",
""
],
[
"Benisty",
"David",
""
],
[
"Guendelman",
"Eduardo I.",
""
]
] | Running Dark Energy and Dark Matter models are candidates to resolve the Hubble constant tension. However the model does not consider a Lagrangian formulation directly. In this paper we formulate an action principle where the Running Vacuum Model (RVM) is obtained from an action principle, with a scalar field model for the whole dark components. The Dynamical Spacetime vector field $\chi_\mu$ is a Lagrange multiplier that forces the kinetic term of the scalar field to behave as the modified dark matter. When we replace the vector field by a derivative of a scalar the model predicts diffusion interactions between the dark components with a different correspondence to the RVM. We test the models with the Cosmic Chronometers, Type Ia Supernova, Quasars, Gamma ray Bursts and the Baryon Acoustic Oscillations data sets. We find that $\Lambda$CDM is still the best model. However this formulation suggests an action principle for the $\Lambda$CDM, the RVM model and other extensions. |
gr-qc/0104049 | Roy Maartens | Roy Maartens (Portsmouth), Bahram Mashhoon (Missouri-Columbia), David
Matravers (Portsmouth) | Holonomy and gravitomagnetism | 6 pages Latex (IOP style); new results covering stationary
axisymmetric spacetimes; version accepted for Class. Quant. Grav | Class.Quant.Grav. 19 (2002) 195-202 | 10.1088/0264-9381/19/2/301 | null | gr-qc | null | We analyze parallel transport of a vector field around an equatorial orbit in
Kerr and stationary axisymmetric spacetimes that are reflection symmetric about
their equatorial planes. As in Schwarzschild spacetime, there is a band
structure of holonomy invariance. The new feature introduced by rotation is a
shift in the timelike component of the vector, which is the holonomic
manifestation of the gravitomagnetic clock effect.
| [
{
"created": "Tue, 17 Apr 2001 08:15:23 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Nov 2001 11:01:34 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Maartens",
"Roy",
"",
"Portsmouth"
],
[
"Mashhoon",
"Bahram",
"",
"Missouri-Columbia"
],
[
"Matravers",
"David",
"",
"Portsmouth"
]
] | We analyze parallel transport of a vector field around an equatorial orbit in Kerr and stationary axisymmetric spacetimes that are reflection symmetric about their equatorial planes. As in Schwarzschild spacetime, there is a band structure of holonomy invariance. The new feature introduced by rotation is a shift in the timelike component of the vector, which is the holonomic manifestation of the gravitomagnetic clock effect. |
gr-qc/9712006 | Michele Maggiore | Stefano Foffa and Michele Maggiore | Anisotropic String Cosmology at Large Curvatures | 16 pages, Latex, 2 figures | Phys.Rev. D58 (1998) 023505 | 10.1103/PhysRevD.58.023505 | IFUP-TH/53-97 | gr-qc | null | We study the effect of the antisymmetric tensor field $B_{\mu\nu}$ on the
large curvature phase of string cosmology. It is well-known that a
non-vanishing value of $H=dB$ leads to an anisotropic expansion of the spatial
dimensions. Correspondingly, in the string phase of the model, including
$\alpha '$ corrections, we find anisotropic fixed points of the evolution,
which act as regularizing attractors of the lowest order solutions. The
attraction basin can also include isotropic initial conditions for the scale
factors. We present explicit examples at order $\alpha '$ for different values
of the number of spatial dimensions and for different ans\"{a}tze for $H$.
| [
{
"created": "Mon, 1 Dec 1997 12:14:12 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Foffa",
"Stefano",
""
],
[
"Maggiore",
"Michele",
""
]
] | We study the effect of the antisymmetric tensor field $B_{\mu\nu}$ on the large curvature phase of string cosmology. It is well-known that a non-vanishing value of $H=dB$ leads to an anisotropic expansion of the spatial dimensions. Correspondingly, in the string phase of the model, including $\alpha '$ corrections, we find anisotropic fixed points of the evolution, which act as regularizing attractors of the lowest order solutions. The attraction basin can also include isotropic initial conditions for the scale factors. We present explicit examples at order $\alpha '$ for different values of the number of spatial dimensions and for different ans\"{a}tze for $H$. |
2201.12210 | Surajit Kalita | Surajit Kalita and Lupamudra Sarmah | Weak-field limit of $f(R)$ gravity to unify peculiar white dwarfs | 10 pages with 1 figure; accepted for publication in Physics Letters B | PLB 827 (2022) 136942 | 10.1016/j.physletb.2022.136942 | null | gr-qc astro-ph.HE astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In recent years, the idea of sub- and super-Chandrasekhar limiting mass white
dwarfs (WDs), which are potential candidates to produce under- and
over-luminous type Ia supernovae, respectively, has been a key interest in the
scientific community. Although researchers have proposed different models to
explain these peculiar objects, modified theories of Einstein's gravity,
particularly $f(R)$ gravity with $R$ being the scalar curvature, seems to be
one of the finest choices to explain both the regimes of these peculiar WDs. It
was already shown that considering higher-order corrections to the Starobinsky
model with two parameters, the structure of sub- and super-Chandrasekhar
progenitor WDs can be explained self consistently. It is also well-known that
WDs can be considered Newtonian objects because of their large size. In this
paper, we derive the weak-field limit of $f(R)$ gravity, which turns out to be
the higher-order correction to the Poisson equation. Later, we use this
equation to obtain the structures of sub- and super-Chandrasekhar limiting mass
WDs at various central densities incorporating just one model parameter.
| [
{
"created": "Fri, 28 Jan 2022 16:08:52 GMT",
"version": "v1"
}
] | 2022-02-04 | [
[
"Kalita",
"Surajit",
""
],
[
"Sarmah",
"Lupamudra",
""
]
] | In recent years, the idea of sub- and super-Chandrasekhar limiting mass white dwarfs (WDs), which are potential candidates to produce under- and over-luminous type Ia supernovae, respectively, has been a key interest in the scientific community. Although researchers have proposed different models to explain these peculiar objects, modified theories of Einstein's gravity, particularly $f(R)$ gravity with $R$ being the scalar curvature, seems to be one of the finest choices to explain both the regimes of these peculiar WDs. It was already shown that considering higher-order corrections to the Starobinsky model with two parameters, the structure of sub- and super-Chandrasekhar progenitor WDs can be explained self consistently. It is also well-known that WDs can be considered Newtonian objects because of their large size. In this paper, we derive the weak-field limit of $f(R)$ gravity, which turns out to be the higher-order correction to the Poisson equation. Later, we use this equation to obtain the structures of sub- and super-Chandrasekhar limiting mass WDs at various central densities incorporating just one model parameter. |
2103.13203 | Shibendu Gupta Choudhury | Shibendu Gupta Choudhury, Ananda Dasgupta and Narayan Banerjee | The Raychaudhuri equation for a quantized timelike geodesic congruence | 14 pages, major changes, version accepted for publication in EPJC | Eur. Phys. J. C 81, 906 (2021) | 10.1140/epjc/s10052-021-09714-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A recent attempt to arrive at a quantum version of Raychaudhuri's equation is
looked at critically. It is shown that the method, and even the idea, has some
inherent problems. The issues are pointed out here. We have also shown that it
is possible to salvage the method in some limited domain of applicability.
Although no generality can be claimed, a quantum version of the equation should
be useful in the context of ascertaining the existence of a singularity in the
quantum regime. The equation presented in the present work holds for arbitrary
$n + 1$ dimensions. An important feature of the Hamiltonian in the operator
form is that it admits a self-adjoint extension quite generally. Thus, the
conservation of probability is ensured.
| [
{
"created": "Wed, 24 Mar 2021 14:04:00 GMT",
"version": "v1"
},
{
"created": "Tue, 5 Oct 2021 13:22:53 GMT",
"version": "v2"
}
] | 2021-10-19 | [
[
"Choudhury",
"Shibendu Gupta",
""
],
[
"Dasgupta",
"Ananda",
""
],
[
"Banerjee",
"Narayan",
""
]
] | A recent attempt to arrive at a quantum version of Raychaudhuri's equation is looked at critically. It is shown that the method, and even the idea, has some inherent problems. The issues are pointed out here. We have also shown that it is possible to salvage the method in some limited domain of applicability. Although no generality can be claimed, a quantum version of the equation should be useful in the context of ascertaining the existence of a singularity in the quantum regime. The equation presented in the present work holds for arbitrary $n + 1$ dimensions. An important feature of the Hamiltonian in the operator form is that it admits a self-adjoint extension quite generally. Thus, the conservation of probability is ensured. |
0911.4417 | Sergio Zerbini | S. A. Hayward, R. Di Criscienzo, M. Nadalini, L. Vanzo, S. Zerbini | Comment on "On the tunneling through the black hole horizon"
[arXiv:0910.3934] | latex file, 1 figure | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The arguments of the above article [arXiv:0910.3934] do not apply to the
papers which it criticizes, and contain several key errors, including a
fundamental misunderstanding about the equivalence principle.
| [
{
"created": "Mon, 23 Nov 2009 14:38:10 GMT",
"version": "v1"
}
] | 2009-11-24 | [
[
"Hayward",
"S. A.",
""
],
[
"Di Criscienzo",
"R.",
""
],
[
"Nadalini",
"M.",
""
],
[
"Vanzo",
"L.",
""
],
[
"Zerbini",
"S.",
""
]
] | The arguments of the above article [arXiv:0910.3934] do not apply to the papers which it criticizes, and contain several key errors, including a fundamental misunderstanding about the equivalence principle. |
2308.00371 | Chopin Soo | Chopin Soo | Cosmic time and the initial state of the universe | 17 pages, 2 appendices | Universe, 2023, Volume 9, Issue 12, 489 | 10.3390/universe9120489 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The exact solution of the Hamiltonian constraint in canonical gravity and the
resultant reduction of Einstein's theory reveal the synergy between gravitation
and the intrinsic cosmic clock of our expanding universe. Intrinsic Time
Geometrodynamics advocates a paradigm shift from four covariances to just
spatial diffeomorphism invariance. Consequently, causal time-ordering and
quantum Schrodinger-Heisenberg evolution in cosmic time become meaningful. The
natural addition of a Cotton-York term to the physical Hamiltonian changes the
initial data problem radically. In the classical context, this is studied with
the Lichnerowicz-York equation; quantum mechanically, it lends weight to the
origin of the universe as an exact Chern-Simons Hartle-Hawking state, which
features Euclidean-Lorentzian instanton tunneling. At the level of expectation
values, this quantum state yields a low-entropy hot smooth Robertson-Walker
beginning in accord with Penrose's Weyl Curvature Hypothesis. The Chern-Simons
Hartle-Hawking state also manifests transverse traceless quantum metric
fluctuations, with, at the lowest approximation, scale-invariant two-point
correlations as one of its defining characteristics.
| [
{
"created": "Tue, 1 Aug 2023 08:27:02 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Nov 2023 07:25:45 GMT",
"version": "v2"
}
] | 2023-11-27 | [
[
"Soo",
"Chopin",
""
]
] | The exact solution of the Hamiltonian constraint in canonical gravity and the resultant reduction of Einstein's theory reveal the synergy between gravitation and the intrinsic cosmic clock of our expanding universe. Intrinsic Time Geometrodynamics advocates a paradigm shift from four covariances to just spatial diffeomorphism invariance. Consequently, causal time-ordering and quantum Schrodinger-Heisenberg evolution in cosmic time become meaningful. The natural addition of a Cotton-York term to the physical Hamiltonian changes the initial data problem radically. In the classical context, this is studied with the Lichnerowicz-York equation; quantum mechanically, it lends weight to the origin of the universe as an exact Chern-Simons Hartle-Hawking state, which features Euclidean-Lorentzian instanton tunneling. At the level of expectation values, this quantum state yields a low-entropy hot smooth Robertson-Walker beginning in accord with Penrose's Weyl Curvature Hypothesis. The Chern-Simons Hartle-Hawking state also manifests transverse traceless quantum metric fluctuations, with, at the lowest approximation, scale-invariant two-point correlations as one of its defining characteristics. |
gr-qc/0007065 | Pedro Gonzalez | Pedro F. Gonzalez-Diaz (IMAFF, Csic) | Kinks, energy conditions and closed timelike curves | 11 pages, LaTex, 1 figure, to appear in IJMPD | Int.J.Mod.Phys. D9 (2000) 531-541 | 10.1142/S0218271800000475 | IMAFF-RCA-00-07 | gr-qc | null | A link between the possibility of extending a geodessically incomplete kinked
spacetime to a spacetime which is geodesically complete and the energy
conditions is discussed for the case of a cylindrically-symmetric spacetime
kink. It is concluded that neither the strong nor the weak energy condition can
be satisfied in the four-dimensional example, though the latter condition may
survive on the transversal sections of such a spacetime. It is also shown that
the matter which propagates quantum-mechanically in a kinked spacetime can
always be trapped by closed timelike curves, but signaling connections between
that matter and any possible observer can only be made of totally incoherent
radiation, so preventing observation of causality violation.
| [
{
"created": "Mon, 24 Jul 2000 15:27:11 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Gonzalez-Diaz",
"Pedro F.",
"",
"IMAFF, Csic"
]
] | A link between the possibility of extending a geodessically incomplete kinked spacetime to a spacetime which is geodesically complete and the energy conditions is discussed for the case of a cylindrically-symmetric spacetime kink. It is concluded that neither the strong nor the weak energy condition can be satisfied in the four-dimensional example, though the latter condition may survive on the transversal sections of such a spacetime. It is also shown that the matter which propagates quantum-mechanically in a kinked spacetime can always be trapped by closed timelike curves, but signaling connections between that matter and any possible observer can only be made of totally incoherent radiation, so preventing observation of causality violation. |
gr-qc/0009044 | Pedro Marronetti | Pedro Marronetti and Richard A. Matzner | Solving the Initial Value Problem of two Black Holes | 4 pages, 3 figures. Minor corrections, some points clarified, and one
reference added. To appear in Phys. Rev. Lett | Phys.Rev.Lett.85:5500-5503,2000 | 10.1103/PhysRevLett.85.5500 | null | gr-qc astro-ph | null | We solve the elliptic equations associated with the Hamiltonian and momentum
constraints, corresponding to a system composed of two black holes with
arbitrary linear and angular momentum. These new solutions are based on a
Kerr-Schild spacetime slicing which provides more physically realistic
solutions than the initial data based on conformally flat metric/maximal
slicing methods. The singularity/inner boundary problems are circumvented by a
new technique that allows the use of an elliptic solver on a Cartesian grid
where no points are excised, simplifying enormously the numerical problem.
| [
{
"created": "Wed, 13 Sep 2000 17:17:38 GMT",
"version": "v1"
},
{
"created": "Mon, 6 Nov 2000 14:39:49 GMT",
"version": "v2"
},
{
"created": "Thu, 30 Nov 2000 22:56:26 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Marronetti",
"Pedro",
""
],
[
"Matzner",
"Richard A.",
""
]
] | We solve the elliptic equations associated with the Hamiltonian and momentum constraints, corresponding to a system composed of two black holes with arbitrary linear and angular momentum. These new solutions are based on a Kerr-Schild spacetime slicing which provides more physically realistic solutions than the initial data based on conformally flat metric/maximal slicing methods. The singularity/inner boundary problems are circumvented by a new technique that allows the use of an elliptic solver on a Cartesian grid where no points are excised, simplifying enormously the numerical problem. |
2402.16250 | Xinliang An | Xinliang An, Hong Kiat Tan | A Proof of Weak Cosmic Censorship Conjecture for the Spherically
Symmetric Einstein-Maxwell-Charged Scalar Field System | 148 pages | null | null | null | gr-qc math-ph math.AP math.DG math.MP | http://creativecommons.org/licenses/by-sa/4.0/ | Under spherical symmetry, we show that the weak cosmic censorship holds for
the gravitational collapse of the Einstein-Maxwell-charged scalar field system.
Namely, for this system, with generic initial data, the formed spacetime
singularities are concealed inside black-hole regions. This generalizes
Christodoulou's celebrated results to the charged case. Due to the presence of
charge $Q$ and the complexification of the scalar field $\phi$, multiple
delicate features and miraculous monotonic properties of the Einstein-(real)
scalar field system are not present. We develop a systematical approach to
incorporate $Q$ and the complex-valued $\phi$ into the integrated arguments.
For instance, we discover a new path, employing the reduced mass ratio, to
establish the sharp trapped surface formation criterion for the charged case.
Due to the complex structure and the absence of translational symmetry of
$\phi$, we also carry out detailed modified scale-critical BV area estimates
with renormalized quantities to deal with $Q$ and $\phi$. We present a new
$C^1$ extension criterion by utilizing the Doppler exponent to elucidate the
blueshift effect, analogous to the role of integrating vorticity in the
Beale-Kato-Madja breakdown criterion for incompressible fluids. Furthermore, by
utilizing only double-null foliations, we establish the desired first and
second instability theorems for the charged scenarios and identify generic
initial conditions for the non-appearance of naked singularities. Our
instability argument requires intricate generalizations of the treatment for
the uncharged case via analyzing the precise contribution of the charged terms
and its connection to the reduced mass ratio.
| [
{
"created": "Mon, 26 Feb 2024 02:28:36 GMT",
"version": "v1"
}
] | 2024-02-27 | [
[
"An",
"Xinliang",
""
],
[
"Tan",
"Hong Kiat",
""
]
] | Under spherical symmetry, we show that the weak cosmic censorship holds for the gravitational collapse of the Einstein-Maxwell-charged scalar field system. Namely, for this system, with generic initial data, the formed spacetime singularities are concealed inside black-hole regions. This generalizes Christodoulou's celebrated results to the charged case. Due to the presence of charge $Q$ and the complexification of the scalar field $\phi$, multiple delicate features and miraculous monotonic properties of the Einstein-(real) scalar field system are not present. We develop a systematical approach to incorporate $Q$ and the complex-valued $\phi$ into the integrated arguments. For instance, we discover a new path, employing the reduced mass ratio, to establish the sharp trapped surface formation criterion for the charged case. Due to the complex structure and the absence of translational symmetry of $\phi$, we also carry out detailed modified scale-critical BV area estimates with renormalized quantities to deal with $Q$ and $\phi$. We present a new $C^1$ extension criterion by utilizing the Doppler exponent to elucidate the blueshift effect, analogous to the role of integrating vorticity in the Beale-Kato-Madja breakdown criterion for incompressible fluids. Furthermore, by utilizing only double-null foliations, we establish the desired first and second instability theorems for the charged scenarios and identify generic initial conditions for the non-appearance of naked singularities. Our instability argument requires intricate generalizations of the treatment for the uncharged case via analyzing the precise contribution of the charged terms and its connection to the reduced mass ratio. |
0710.3880 | Jorge P\'aramos | J. Paramos and O. Bertolami | Galileo satellite constellation and extensions to General Relativity | Based on talk presented by one of us (J.P.) at the 1st. Colloquium
"Scientific and Fundamental Aspects of the Galileo Programme", Toulouse,
France, 1-4 October 2007. To be published in the Proceedings of the
Colloquium | null | null | null | gr-qc | null | We consider the impact of some known extensions of General Relativity in
observables that will be available with the Galileo positioning systems, and
draw conclusions as to the possibility of measuring them. We specifically
address the effects of the presence of a cosmological constant, a Yukawa-like
addition to the Newtonian potential, and the existence of an extra, constant
acceleration. We also consider the phenomenological impact of a broad class of
metric theories, which can be classified through the parameterized
Post-Newtonian formalism.
| [
{
"created": "Sat, 20 Oct 2007 22:07:06 GMT",
"version": "v1"
}
] | 2007-10-23 | [
[
"Paramos",
"J.",
""
],
[
"Bertolami",
"O.",
""
]
] | We consider the impact of some known extensions of General Relativity in observables that will be available with the Galileo positioning systems, and draw conclusions as to the possibility of measuring them. We specifically address the effects of the presence of a cosmological constant, a Yukawa-like addition to the Newtonian potential, and the existence of an extra, constant acceleration. We also consider the phenomenological impact of a broad class of metric theories, which can be classified through the parameterized Post-Newtonian formalism. |
2307.03011 | Robie Hennigar | Masaya Amo, Antonia M. Frassino, Robie A. Hennigar | Entropy Bounds for Rotating AdS Black Holes | 14 pages, 1 figure; v2: updated to match published version | null | 10.1103/PhysRevLett.131.241401 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose novel thermodynamic inequalities that apply to stationary
asymptotically Anti-de Sitter (AdS) black holes. These inequalities incorporate
the thermodynamic volume and refine the reverse isoperimetric inequality. To
assess the validity of our conjectures, we apply them to a wide range of
analytical black hole solutions, observing compelling evidence in their favour.
Intriguingly, our findings indicate that these inequalities may also apply for
black holes of non-spherical horizon topology, as we show their validity as
well for thin black rings in AdS.
| [
{
"created": "Thu, 6 Jul 2023 14:20:31 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Dec 2023 14:28:24 GMT",
"version": "v2"
}
] | 2023-12-13 | [
[
"Amo",
"Masaya",
""
],
[
"Frassino",
"Antonia M.",
""
],
[
"Hennigar",
"Robie A.",
""
]
] | We propose novel thermodynamic inequalities that apply to stationary asymptotically Anti-de Sitter (AdS) black holes. These inequalities incorporate the thermodynamic volume and refine the reverse isoperimetric inequality. To assess the validity of our conjectures, we apply them to a wide range of analytical black hole solutions, observing compelling evidence in their favour. Intriguingly, our findings indicate that these inequalities may also apply for black holes of non-spherical horizon topology, as we show their validity as well for thin black rings in AdS. |
1806.07134 | Jean-Luc Lehners | Alice Di Tucci and Jean-Luc Lehners | Unstable no-boundary fluctuations from sums over regular metrics | 22 pages, 8 figures | Phys. Rev. D 98, 103506 (2018) | 10.1103/PhysRevD.98.103506 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It was recently shown by Feldbrugge et al. that the no-boundary proposal,
defined via a Lorentzian path integral and in minisuperspace, leads to unstable
fluctuations, in disagreement with early universe observations. In these
calculations many off-shell geometries summed over in the path integral in fact
contain singularities, and the question arose whether the instability might
ultimately be caused by these off-shell singularities. We address this question
here by considering a sum over purely regular geometries, by extending a
calculation pioneered by Halliwell and Louko. We confirm that the fluctuations
are unstable, even in this restricted context which, arguably, is closer in
spirit to the original proposal of Hartle and Hawking. Elucidating the reasons
for the instability of the no-boundary proposal will hopefully show how to
overcome these difficulties, or pave the way to new theories of initial
conditions for the universe.
| [
{
"created": "Tue, 19 Jun 2018 09:51:30 GMT",
"version": "v1"
}
] | 2018-11-14 | [
[
"Di Tucci",
"Alice",
""
],
[
"Lehners",
"Jean-Luc",
""
]
] | It was recently shown by Feldbrugge et al. that the no-boundary proposal, defined via a Lorentzian path integral and in minisuperspace, leads to unstable fluctuations, in disagreement with early universe observations. In these calculations many off-shell geometries summed over in the path integral in fact contain singularities, and the question arose whether the instability might ultimately be caused by these off-shell singularities. We address this question here by considering a sum over purely regular geometries, by extending a calculation pioneered by Halliwell and Louko. We confirm that the fluctuations are unstable, even in this restricted context which, arguably, is closer in spirit to the original proposal of Hartle and Hawking. Elucidating the reasons for the instability of the no-boundary proposal will hopefully show how to overcome these difficulties, or pave the way to new theories of initial conditions for the universe. |
0711.1868 | Nicolas Yunes | Daniel Grumiller (MIT), Nicolas Yunes (Penn State) | How do Black Holes Spin in Chern-Simons Modified Gravity? | 20 pages, 1 figure. Submitted to PRD | Phys.Rev.D77:044015,2008 | 10.1103/PhysRevD.77.044015 | IGC-07/11-1, MIT-CTP 3908 | gr-qc hep-th | null | No Kerr-like exact solution has yet been found in Chern-Simons modified
gravity. Intrigued by this absence, we study stationary and axisymmetric
metrics that could represent the exterior field of spinning black holes. For
the standard choice of the background scalar, the modified field equations
decouple into the Einstein equations and additional constraints. These
constraints eliminate essentially all solutions except for Schwarzschild. For
non-canonical choices of the background scalar, we find several exact solutions
of the modified field equations, including mathematical black holes and
pp-waves. We show that the ultrarelativistically boosted Kerr metric can
satisfy the modified field equations, and we argue that physical spinning black
holes may exist in Chern-Simons modified gravity only if the metric breaks
stationarity, axisymmetry or energy-momentum conservation.
| [
{
"created": "Tue, 13 Nov 2007 16:05:48 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Grumiller",
"Daniel",
"",
"MIT"
],
[
"Yunes",
"Nicolas",
"",
"Penn State"
]
] | No Kerr-like exact solution has yet been found in Chern-Simons modified gravity. Intrigued by this absence, we study stationary and axisymmetric metrics that could represent the exterior field of spinning black holes. For the standard choice of the background scalar, the modified field equations decouple into the Einstein equations and additional constraints. These constraints eliminate essentially all solutions except for Schwarzschild. For non-canonical choices of the background scalar, we find several exact solutions of the modified field equations, including mathematical black holes and pp-waves. We show that the ultrarelativistically boosted Kerr metric can satisfy the modified field equations, and we argue that physical spinning black holes may exist in Chern-Simons modified gravity only if the metric breaks stationarity, axisymmetry or energy-momentum conservation. |
1907.03897 | Zack Carson | Zack Carson, Brian C. Seymour, Kent Yagi | Future Prospects for Probing Scalar-Tensor Theories with Gravitational
Waves from Mixed Binaries | 8 pages, 8 figures; updated to match with the version published in
CQG | null | 10.1088/1361-6382/ab6a1f | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The extreme-gravity collisions of binaries with one black hole and one
neutron star provide for excellent tests of general relativity. We here study
how well one can constrain theories beyond general relativity with additional
scalar fields that allow for spontaneous scalarization of neutron stars, and
those motivated from string theory. We find that existing bounds can be
improved with current gravitational-wave detectors if the black hole mass is
sufficiently small. Bounds will further improve by many orders of magnitude
with future detections, especially by combining multiple events.
| [
{
"created": "Mon, 8 Jul 2019 22:33:02 GMT",
"version": "v1"
},
{
"created": "Sat, 11 Jan 2020 03:07:07 GMT",
"version": "v2"
},
{
"created": "Fri, 17 Jan 2020 17:10:49 GMT",
"version": "v3"
},
{
"created": "Mon, 20 Jan 2020 16:39:53 GMT",
"version": "v4"
}
] | 2020-04-08 | [
[
"Carson",
"Zack",
""
],
[
"Seymour",
"Brian C.",
""
],
[
"Yagi",
"Kent",
""
]
] | The extreme-gravity collisions of binaries with one black hole and one neutron star provide for excellent tests of general relativity. We here study how well one can constrain theories beyond general relativity with additional scalar fields that allow for spontaneous scalarization of neutron stars, and those motivated from string theory. We find that existing bounds can be improved with current gravitational-wave detectors if the black hole mass is sufficiently small. Bounds will further improve by many orders of magnitude with future detections, especially by combining multiple events. |
2308.11886 | Shao-Wen Wei | Shao-Wen Wei, Yu-Xiao Liu | Thermodynamic Nature of Black Holes in Coexistence Region | 5 pages, 5 figures | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Studying the system state of coexistence regions has important applications
in revealing detailed microscopic interactions between different phases.
However, the thermodynamic nature in the coexistence black hole regions has
been neglected in previous studies. In this work, we introduce two new ratio
parameters to investigate these coexistence states. The first parameter
measures the ratio of the horizon radii of the statured coexistence small and
large black holes. Of particular interest, we demonstrate that it can serve as
an order parameter to characterize the first-order phase transition.
Furthermore, combining with the ratio of the ratio of the small black hole
molecule number to the total molecule number, each black hole state in the
coexistence region is uniquely determined via these two introduced parameters
bounded between 0 and 1. These results are quite significant in analytical
study of black hole phase transition and uncover the thermodynamical
microscopic nature of black hole in the coexistence regions.
| [
{
"created": "Wed, 23 Aug 2023 03:19:43 GMT",
"version": "v1"
}
] | 2023-08-24 | [
[
"Wei",
"Shao-Wen",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] | Studying the system state of coexistence regions has important applications in revealing detailed microscopic interactions between different phases. However, the thermodynamic nature in the coexistence black hole regions has been neglected in previous studies. In this work, we introduce two new ratio parameters to investigate these coexistence states. The first parameter measures the ratio of the horizon radii of the statured coexistence small and large black holes. Of particular interest, we demonstrate that it can serve as an order parameter to characterize the first-order phase transition. Furthermore, combining with the ratio of the ratio of the small black hole molecule number to the total molecule number, each black hole state in the coexistence region is uniquely determined via these two introduced parameters bounded between 0 and 1. These results are quite significant in analytical study of black hole phase transition and uncover the thermodynamical microscopic nature of black hole in the coexistence regions. |
2107.12776 | Gamal G.L. Nashed | G.G.L. Nashed and K. Bamba | Black holes solutions in power-law Maxwell-$f(T)$ gravity in diverse
dimensions | 17 pages, 6 figures, Accepted for publication in Physics of the Dark
Universe | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We investigate the solutions of black holes in $f(T)$ gravity with nonlinear
power-law Maxwell field, where $T$ is the torsion scalar in teleparalelism. In
particular, we introduce the Langranian with diverse dimensions in which the
quadratic polynomial form of $f(T)$ couples with the nonlinear power-law
Maxwell field. We explore the leverage of the nonlinear electrodynamics on the
space-time behavior. It is found that these new black hole solutions tend
towards those in general relativity without any limit. Furthermore, it is
demonstrated that the singularity of the curvature invariant and the torsion
scalar is softer than the quadratic form of the charged field equations in
$f(T)$ gravity and much milder than that in the classical general relativity
because of the nonlinearity of the Maxwell field. In addition, from the
analyses of physical and thermodynamic quantities of the mass, charge and the
Hawking temperature of black holes, it is shown that the power-law parameter
affects the asymptotic behavior of the radial coordinate of the charged terms,
and that a higher-order nonlinear power-law Maxwell field imparts the black
holes with the local stability.
| [
{
"created": "Sun, 25 Jul 2021 08:57:33 GMT",
"version": "v1"
}
] | 2021-07-28 | [
[
"Nashed",
"G. G. L.",
""
],
[
"Bamba",
"K.",
""
]
] | We investigate the solutions of black holes in $f(T)$ gravity with nonlinear power-law Maxwell field, where $T$ is the torsion scalar in teleparalelism. In particular, we introduce the Langranian with diverse dimensions in which the quadratic polynomial form of $f(T)$ couples with the nonlinear power-law Maxwell field. We explore the leverage of the nonlinear electrodynamics on the space-time behavior. It is found that these new black hole solutions tend towards those in general relativity without any limit. Furthermore, it is demonstrated that the singularity of the curvature invariant and the torsion scalar is softer than the quadratic form of the charged field equations in $f(T)$ gravity and much milder than that in the classical general relativity because of the nonlinearity of the Maxwell field. In addition, from the analyses of physical and thermodynamic quantities of the mass, charge and the Hawking temperature of black holes, it is shown that the power-law parameter affects the asymptotic behavior of the radial coordinate of the charged terms, and that a higher-order nonlinear power-law Maxwell field imparts the black holes with the local stability. |
2003.11095 | Marc Schneider | Cecilia Giavoni and Marc Schneider | Quantum effects across dynamical horizons | 24 pages, journal version | Class. Quantum Grav. 37 (2020) 215020 | 10.1088/1361-6382/abb576 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a generalization of the Hawking effect for dynamical trapping
horizons by calculating the tunneling rate in the Hamilton-Jacobi formalism. It
turns out that all horizons classified by Hayward are subjected to thermal
quantum effects. While the Hawking effect for future outer and past inner
trapping horizons is given as a particle emission, we show that the Hawking
effect for future inner and past outer trapping horizons translates to an
absorption. The universality of the treatment allows a natural transfer to the
static case.
| [
{
"created": "Tue, 24 Mar 2020 20:00:01 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Oct 2020 10:24:27 GMT",
"version": "v2"
}
] | 2020-10-19 | [
[
"Giavoni",
"Cecilia",
""
],
[
"Schneider",
"Marc",
""
]
] | We present a generalization of the Hawking effect for dynamical trapping horizons by calculating the tunneling rate in the Hamilton-Jacobi formalism. It turns out that all horizons classified by Hayward are subjected to thermal quantum effects. While the Hawking effect for future outer and past inner trapping horizons is given as a particle emission, we show that the Hawking effect for future inner and past outer trapping horizons translates to an absorption. The universality of the treatment allows a natural transfer to the static case. |
gr-qc/0505018 | Xiaoning Wu | Xiaoning Wu, Chiang-Mei Chen and James M. Nester | Quasi-local energy-momentum and energy flux at null infinity | 14 pages, accepted by Phys.Rev.D | Phys.Rev. D71 (2005) 124010 | 10.1103/PhysRevD.71.124010 | null | gr-qc | null | The null infinity limit of the gravitational energy-momentum and energy flux
determined by the covariant Hamiltonian quasi-local expressions is evaluated
using the NP spin coefficients. The reference contribution is considered by
three different embedding approaches. All of them give the expected Bondi
energy and energy flux.
| [
{
"created": "Wed, 4 May 2005 14:01:22 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Jun 2005 05:44:02 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Wu",
"Xiaoning",
""
],
[
"Chen",
"Chiang-Mei",
""
],
[
"Nester",
"James M.",
""
]
] | The null infinity limit of the gravitational energy-momentum and energy flux determined by the covariant Hamiltonian quasi-local expressions is evaluated using the NP spin coefficients. The reference contribution is considered by three different embedding approaches. All of them give the expected Bondi energy and energy flux. |
gr-qc/0006094 | hamid Reza Sepangi | S. S. Gousheh and H. R. Sepangi | Wave packets and initial conditions in quantum cosmology | 12 pages, 12 eps figures, to appear in Phys. Lett. A | Phys.Lett. A272 (2000) 304-312 | 10.1016/S0375-9601(00)00443-6 | null | gr-qc hep-th | null | We discuss the construction of wave packets resulting from the solutions of a
class of Wheeler-DeWitt equations in Robertson-Walker type cosmologies. We
present an ansatz for the initial conditions which leads to a unique
determination of the expansion coefficients in the construction of the wave
packets with probability distributions which, in an interesting contrast to
some of the earlier works, agree well with all possible classical paths. The
possible relationship between these initial conditions and signature transition
in the context of classical cosmology is also discussed.
| [
{
"created": "Tue, 27 Jun 2000 11:07:14 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Gousheh",
"S. S.",
""
],
[
"Sepangi",
"H. R.",
""
]
] | We discuss the construction of wave packets resulting from the solutions of a class of Wheeler-DeWitt equations in Robertson-Walker type cosmologies. We present an ansatz for the initial conditions which leads to a unique determination of the expansion coefficients in the construction of the wave packets with probability distributions which, in an interesting contrast to some of the earlier works, agree well with all possible classical paths. The possible relationship between these initial conditions and signature transition in the context of classical cosmology is also discussed. |
1603.05839 | Jose M. M. Senovilla | Marc Mars, Tim-Torben Paetz, Jos\'e M. M. Senovilla, Walter Simon | Characterization of (asymptotically) Kerr-de Sitter-like spacetimes at
null infinity | 49 pages. v2: Revised version with some changes with respect to the
published paper in order to amend a mistake in the statements of theorems 4
and 6 in arXiv:1307.5018v2 (corrected in v3). The validity of all results
remains unaltered | null | 10.1088/0264-9381/33/15/155001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate solutions $(\mathcal{M}, g)$ to Einstein's vacuum field
equations with positive cosmological constant $\Lambda$ which admit a smooth
past null infinity $\mathcal{J}^-$ \`a la Penrose and a Killing vector field
whose associated Mars-Simon tensor (MST) vanishes. The main purpose of this
work is to provide a characterization of these spacetimes in terms of their
Cauchy data on $\mathcal{J}^-$.
Along the way, we also study spacetimes for which the MST does not vanish. In
that case there is an ambiguity in its definition which is captured by a scalar
function $Q$. We analyze properties of the MST for different choices of $Q$. In
doing so, we are led to a definition of "asymptotically Kerr-de Sitter-like
spacetimes", which we also characterize in terms of their asymptotic data on
$\mathcal{J}^-$.
| [
{
"created": "Fri, 18 Mar 2016 11:09:37 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Dec 2016 12:20:40 GMT",
"version": "v2"
}
] | 2016-12-20 | [
[
"Mars",
"Marc",
""
],
[
"Paetz",
"Tim-Torben",
""
],
[
"Senovilla",
"José M. M.",
""
],
[
"Simon",
"Walter",
""
]
] | We investigate solutions $(\mathcal{M}, g)$ to Einstein's vacuum field equations with positive cosmological constant $\Lambda$ which admit a smooth past null infinity $\mathcal{J}^-$ \`a la Penrose and a Killing vector field whose associated Mars-Simon tensor (MST) vanishes. The main purpose of this work is to provide a characterization of these spacetimes in terms of their Cauchy data on $\mathcal{J}^-$. Along the way, we also study spacetimes for which the MST does not vanish. In that case there is an ambiguity in its definition which is captured by a scalar function $Q$. We analyze properties of the MST for different choices of $Q$. In doing so, we are led to a definition of "asymptotically Kerr-de Sitter-like spacetimes", which we also characterize in terms of their asymptotic data on $\mathcal{J}^-$. |
2005.03028 | Kyriakos Destounis Dr. | Kyriakos Destounis, Rodrigo D. B. Fontana and Filipe C. Mena | Accelerating black holes: quasinormal modes and late-time tails | 15 pages, 8 figures, matches published version | Phys. Rev. D 102, 044005 (2020) | 10.1103/PhysRevD.102.044005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black holes found in binaries move at very high velocities relative to our
own reference frame and can accelerate due to the emission of gravitational
radiation. Here, we investigate the numerical stability and late-time behavior
of linear scalar perturbations in accelerating black holes described by the
$C-$metric. We identify a family of quasinormal modes associated with the
photon surface and a brand new family of purely imaginary modes associated with
the boost parameter of the accelerating black hole spacetime. When the
accelerating black hole is charged, we find a third family of modes which
dominates the ringdown waveform near extremality. Our frequency and time domain
analysis indicate that such spacetimes are stable under scalar fluctuations,
while the late-time behavior follows an exponential decay law, dominated by
quasinormal modes. This result is in contrast with the common belief that such
perturbations, for black holes without a cosmological constant, always have a
power-law cutoff. In this sense, our results suggest that the asymptotic
structure of black hole backgrounds does not always dictate how radiative
fields behave at late times.
| [
{
"created": "Wed, 6 May 2020 18:00:01 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Aug 2020 19:13:39 GMT",
"version": "v2"
}
] | 2020-08-06 | [
[
"Destounis",
"Kyriakos",
""
],
[
"Fontana",
"Rodrigo D. B.",
""
],
[
"Mena",
"Filipe C.",
""
]
] | Black holes found in binaries move at very high velocities relative to our own reference frame and can accelerate due to the emission of gravitational radiation. Here, we investigate the numerical stability and late-time behavior of linear scalar perturbations in accelerating black holes described by the $C-$metric. We identify a family of quasinormal modes associated with the photon surface and a brand new family of purely imaginary modes associated with the boost parameter of the accelerating black hole spacetime. When the accelerating black hole is charged, we find a third family of modes which dominates the ringdown waveform near extremality. Our frequency and time domain analysis indicate that such spacetimes are stable under scalar fluctuations, while the late-time behavior follows an exponential decay law, dominated by quasinormal modes. This result is in contrast with the common belief that such perturbations, for black holes without a cosmological constant, always have a power-law cutoff. In this sense, our results suggest that the asymptotic structure of black hole backgrounds does not always dictate how radiative fields behave at late times. |
2307.11463 | Vahideh Memari Rishakani | Mustafa Halilsoy and Vahideh Memari | General Relativistic Fall on a Thick-Plate | 11 pages, 1 figure | Int. J. Theor. Phys.,62, 219 (2023) | 10.1007/s10773-023-05474-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As an extension of a thin-shell, we adopt a single parametric plane-symmetric
Kasner-type spacetime to represent an exact thick-plate. This naturally extends
the domain wall spacetime to a domain thick-wall case. Physical properties of
such a plate with symmetry axis $z$ and thickness $0\leq z\leq z_{0}$ are
investigated. Geodesic analysis determines the possibility of a Newtonian-like
fall, namely with constant negative acceleration as it is near the Earth's
surface. This restricts the Kasner-like exponents to a finely-tuned set, which
together with the thickness and energy parameter determine the G-force of the
plate. In contrast to the inverse square law, the escape velocity of the
thick-shell is unbounded. The metric is regular everywhere but expectedly the
energy-momentum of the thick-plate remains problematic.
| [
{
"created": "Fri, 21 Jul 2023 09:58:15 GMT",
"version": "v1"
}
] | 2023-10-13 | [
[
"Halilsoy",
"Mustafa",
""
],
[
"Memari",
"Vahideh",
""
]
] | As an extension of a thin-shell, we adopt a single parametric plane-symmetric Kasner-type spacetime to represent an exact thick-plate. This naturally extends the domain wall spacetime to a domain thick-wall case. Physical properties of such a plate with symmetry axis $z$ and thickness $0\leq z\leq z_{0}$ are investigated. Geodesic analysis determines the possibility of a Newtonian-like fall, namely with constant negative acceleration as it is near the Earth's surface. This restricts the Kasner-like exponents to a finely-tuned set, which together with the thickness and energy parameter determine the G-force of the plate. In contrast to the inverse square law, the escape velocity of the thick-shell is unbounded. The metric is regular everywhere but expectedly the energy-momentum of the thick-plate remains problematic. |
2010.14918 | Rodrigo Ferreira Sobreiro | Amanda Guerrieri and Rodrigo F. Sobreiro | Non-relativistic limit of gravity theories in the first order formalism | 27 pages. No figures. V2 - Section 5 rewritten. Final version
accepted for publication at JHEP | JHEP 03 (2021) 104 | 10.1007/JHEP03(2021)104 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the non-relativistic limit of gravity in four dimensions in the
first order formalism. First, we revisit the case of the Einstein-Hilbert
action and formally discuss some geometrical configurations in vacuum and in
the presence of matter at leading order. Second, we consider the more general
Mardones-Zanelli action and its non-relativistic limit. The field equations and
some interesting geometries, in vacuum and in the presence of matter, are
formally obtained. Remarkably, in contrast to the Einstein-Hilbert limit, the
set of field equations is fully determined because the boost connection appears
in the action and field equations. It is found that the cosmological constant
must disappear in the non-relativistic Mardones-Zanelli action at leading
order. The conditions for Newtonian absolute time be acceptable are also
discussed. It turns out that Newtonian absolute time can be safely implemented
with reasonable conditions.
| [
{
"created": "Wed, 28 Oct 2020 12:28:11 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Jan 2021 12:01:44 GMT",
"version": "v2"
}
] | 2021-03-15 | [
[
"Guerrieri",
"Amanda",
""
],
[
"Sobreiro",
"Rodrigo F.",
""
]
] | We consider the non-relativistic limit of gravity in four dimensions in the first order formalism. First, we revisit the case of the Einstein-Hilbert action and formally discuss some geometrical configurations in vacuum and in the presence of matter at leading order. Second, we consider the more general Mardones-Zanelli action and its non-relativistic limit. The field equations and some interesting geometries, in vacuum and in the presence of matter, are formally obtained. Remarkably, in contrast to the Einstein-Hilbert limit, the set of field equations is fully determined because the boost connection appears in the action and field equations. It is found that the cosmological constant must disappear in the non-relativistic Mardones-Zanelli action at leading order. The conditions for Newtonian absolute time be acceptable are also discussed. It turns out that Newtonian absolute time can be safely implemented with reasonable conditions. |
2203.06506 | Reinoud Slagter | Reinoud Jan Slagter | The Dilaton Black Hole on a Conformal Invariant Five Dimensional Warped
Spacetime: Paradoxes Possibly Resolved? | V4 preliminary version. Some typos were corrected and the layout
improved. Any comment is welcome! 19 pictures | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | A thorough investigation is presented of the exact black hole solution on a
warped five-dimensional spacetime in conformal dilaton gravity (CDG), found in
earlier work. Summarized, we will prove: The black hole solution in the CDG
model on a warped 5D spacetime: 1. It is an exact solution for the metric
components as well as for the dilaton field. 2.The quintic polynomial
describing the zero's of the model, has no essential singularities. 3.If we
write $^{(5)}g_{\mu\nu}=\omega^{4/3}{^{(5)}}{\tilde g_{\mu\nu}}, ^{(5)}\tilde
g_{\mu\nu}=^{(4)}\tilde g_{\mu\nu}+n_\mu n_\nu, ^{(4)}\tilde
g_{\mu\nu}=\bar\omega^2 {^{(4)}}\bar g{\mu\nu}$ then ${^{(4)}}\bar g{\mu\nu}$
is conformally flat and with $n_\mu$ the normal to the brane. 4. It fits the
antipodal boundary condition, i.e., antipodal points in the projected space are
identified using the embedding of a Klein surface in $\mathbb{C}^4$. 5. One can
apply 't Hooft's back reaction method in constructing the unitary S-matrix and
there is no "inside" of the black hole. 6. The contribution from the bulk
determines the poles on the effective 4D spacetime. 7. The zeros of the quintic
resolvent can analytically described by the icosahedral equation, i.e., in
terms of hypergeometric functions and elliptic modular functions. 8. The Hopf
fibration of the Klein bottle can be applied.
| [
{
"created": "Sat, 12 Mar 2022 19:52:13 GMT",
"version": "v1"
},
{
"created": "Sun, 3 Apr 2022 20:22:06 GMT",
"version": "v2"
},
{
"created": "Sat, 9 Apr 2022 09:15:54 GMT",
"version": "v3"
},
{
"created": "Mon, 18 Apr 2022 18:28:30 GMT",
"version": "v4"
}
] | 2022-04-20 | [
[
"Slagter",
"Reinoud Jan",
""
]
] | A thorough investigation is presented of the exact black hole solution on a warped five-dimensional spacetime in conformal dilaton gravity (CDG), found in earlier work. Summarized, we will prove: The black hole solution in the CDG model on a warped 5D spacetime: 1. It is an exact solution for the metric components as well as for the dilaton field. 2.The quintic polynomial describing the zero's of the model, has no essential singularities. 3.If we write $^{(5)}g_{\mu\nu}=\omega^{4/3}{^{(5)}}{\tilde g_{\mu\nu}}, ^{(5)}\tilde g_{\mu\nu}=^{(4)}\tilde g_{\mu\nu}+n_\mu n_\nu, ^{(4)}\tilde g_{\mu\nu}=\bar\omega^2 {^{(4)}}\bar g{\mu\nu}$ then ${^{(4)}}\bar g{\mu\nu}$ is conformally flat and with $n_\mu$ the normal to the brane. 4. It fits the antipodal boundary condition, i.e., antipodal points in the projected space are identified using the embedding of a Klein surface in $\mathbb{C}^4$. 5. One can apply 't Hooft's back reaction method in constructing the unitary S-matrix and there is no "inside" of the black hole. 6. The contribution from the bulk determines the poles on the effective 4D spacetime. 7. The zeros of the quintic resolvent can analytically described by the icosahedral equation, i.e., in terms of hypergeometric functions and elliptic modular functions. 8. The Hopf fibration of the Klein bottle can be applied. |
2301.07326 | Tao Wang | Zhi-Shuo Qu, Towe Wang, Chao-Jun Feng | Images of nonsingular nonrotating black holes in conformal gravity | 10 pages, 6 figures, footnotes and references added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The accretion disk around a black hole and its emissions play an essential
role in theoretical analysis of the black hole image. In the literature, two
analytical toy models of accretions are widely adopted: the spherical model and
the thin disk model. They are different geometrically but both thin optically.
We polish them for free-falling accretions around static spherical black holes.
As an application, we investigate the image of a class of nonsingular black
holes conformally related to the Schwarzschild black hole, which are the vacuum
solution of a family of conformal gravity theories. Results are compared with
the Schwarzschild black hole of the same mass. Our results indicate that the
conformal factor does not affect the shadow radius seen by distant observers,
but it leaves an imprint on the intensity image of black hole.
| [
{
"created": "Wed, 18 Jan 2023 06:19:47 GMT",
"version": "v1"
},
{
"created": "Sun, 26 Feb 2023 19:41:27 GMT",
"version": "v2"
}
] | 2023-02-28 | [
[
"Qu",
"Zhi-Shuo",
""
],
[
"Wang",
"Towe",
""
],
[
"Feng",
"Chao-Jun",
""
]
] | The accretion disk around a black hole and its emissions play an essential role in theoretical analysis of the black hole image. In the literature, two analytical toy models of accretions are widely adopted: the spherical model and the thin disk model. They are different geometrically but both thin optically. We polish them for free-falling accretions around static spherical black holes. As an application, we investigate the image of a class of nonsingular black holes conformally related to the Schwarzschild black hole, which are the vacuum solution of a family of conformal gravity theories. Results are compared with the Schwarzschild black hole of the same mass. Our results indicate that the conformal factor does not affect the shadow radius seen by distant observers, but it leaves an imprint on the intensity image of black hole. |
gr-qc/0004051 | Michael C. Ashworth | Michael C. Ashworth Sean A. Hayward | Noether Currents of Charged Spherical Black Holes | 4 pages | Phys.Rev. D62 (2000) 064024 | 10.1103/PhysRevD.62.064024 | null | gr-qc | null | We calculate the Noether currents and charges for Einstein-Maxwell theory
using a version of the Wald approach. In spherical symmetry, the choice of time
can be taken as the Kodama vector. For the static case, the resulting combined
Einstein-Maxwell charge is just the mass of the black hole. Using either a
classically defined entropy or the Iyer-Wald selection rules, the entropy is
found to be just a quarter of the area of the trapping horizon. We propose
identifying the combined Noether charge as an energy associated with the Kodama
time. For the extremal black hole case, we discuss the problem of Wald's
rescaling of the surface gravity to define the entropy.
| [
{
"created": "Mon, 17 Apr 2000 08:37:59 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Hayward",
"Michael C. Ashworth Sean A.",
""
]
] | We calculate the Noether currents and charges for Einstein-Maxwell theory using a version of the Wald approach. In spherical symmetry, the choice of time can be taken as the Kodama vector. For the static case, the resulting combined Einstein-Maxwell charge is just the mass of the black hole. Using either a classically defined entropy or the Iyer-Wald selection rules, the entropy is found to be just a quarter of the area of the trapping horizon. We propose identifying the combined Noether charge as an energy associated with the Kodama time. For the extremal black hole case, we discuss the problem of Wald's rescaling of the surface gravity to define the entropy. |
1201.4160 | Frans Klinkhamer | F. R. Klinkhamer | Entropic-gravity derivation of MOND | 6 pages; v5: published version | Mod. Phys. Lett. A 27, 1250056 (2012) | 10.1142/S0217732312500563 | KA-TP-02-2012 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A heuristic entropic-gravity derivation has previously been given of the
gravitational two-body force of modified Newtonian dynamics (MOND). Here, it is
shown that also another characteristic of MOND can be recovered, namely, the
external field effect (implying a violation of the Strong Equivalence
Principle). In fact, the derivation gives precisely the modified Poisson
equation which Bekenstein and Milgrom proposed as a consistent nonrelativistic
theory of MOND.
| [
{
"created": "Thu, 19 Jan 2012 19:53:58 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Jan 2012 19:07:54 GMT",
"version": "v2"
},
{
"created": "Wed, 25 Jan 2012 19:02:15 GMT",
"version": "v3"
},
{
"created": "Tue, 14 Feb 2012 18:43:46 GMT",
"version": "v4"
},
{
"c... | 2012-04-05 | [
[
"Klinkhamer",
"F. R.",
""
]
] | A heuristic entropic-gravity derivation has previously been given of the gravitational two-body force of modified Newtonian dynamics (MOND). Here, it is shown that also another characteristic of MOND can be recovered, namely, the external field effect (implying a violation of the Strong Equivalence Principle). In fact, the derivation gives precisely the modified Poisson equation which Bekenstein and Milgrom proposed as a consistent nonrelativistic theory of MOND. |
1706.07446 | Daniel George | Daniel George, Hongyu Shen, E. A. Huerta | Deep Transfer Learning: A new deep learning glitch classification method
for advanced LIGO | null | null | 10.1103/PhysRevD.97.101501 | null | gr-qc astro-ph.IM cs.CV cs.LG cs.NE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The exquisite sensitivity of the advanced LIGO detectors has enabled the
detection of multiple gravitational wave signals. The sophisticated design of
these detectors mitigates the effect of most types of noise. However, advanced
LIGO data streams are contaminated by numerous artifacts known as glitches:
non-Gaussian noise transients with complex morphologies. Given their high rate
of occurrence, glitches can lead to false coincident detections, obscure and
even mimic gravitational wave signals. Therefore, successfully characterizing
and removing glitches from advanced LIGO data is of utmost importance. Here, we
present the first application of Deep Transfer Learning for glitch
classification, showing that knowledge from deep learning algorithms trained
for real-world object recognition can be transferred for classifying glitches
in time-series based on their spectrogram images. Using the Gravity Spy
dataset, containing hand-labeled, multi-duration spectrograms obtained from
real LIGO data, we demonstrate that this method enables optimal use of very
deep convolutional neural networks for classification given small training
datasets, significantly reduces the time for training the networks, and
achieves state-of-the-art accuracy above 98.8%, with perfect precision-recall
on 8 out of 22 classes. Furthermore, new types of glitches can be classified
accurately given few labeled examples with this technique. Once trained via
transfer learning, we show that the convolutional neural networks can be
truncated and used as excellent feature extractors for unsupervised clustering
methods to identify new classes based on their morphology, without any labeled
examples. Therefore, this provides a new framework for dynamic glitch
classification for gravitational wave detectors, which are expected to
encounter new types of noise as they undergo gradual improvements to attain
design sensitivity.
| [
{
"created": "Thu, 22 Jun 2017 18:11:13 GMT",
"version": "v1"
}
] | 2018-07-15 | [
[
"George",
"Daniel",
""
],
[
"Shen",
"Hongyu",
""
],
[
"Huerta",
"E. A.",
""
]
] | The exquisite sensitivity of the advanced LIGO detectors has enabled the detection of multiple gravitational wave signals. The sophisticated design of these detectors mitigates the effect of most types of noise. However, advanced LIGO data streams are contaminated by numerous artifacts known as glitches: non-Gaussian noise transients with complex morphologies. Given their high rate of occurrence, glitches can lead to false coincident detections, obscure and even mimic gravitational wave signals. Therefore, successfully characterizing and removing glitches from advanced LIGO data is of utmost importance. Here, we present the first application of Deep Transfer Learning for glitch classification, showing that knowledge from deep learning algorithms trained for real-world object recognition can be transferred for classifying glitches in time-series based on their spectrogram images. Using the Gravity Spy dataset, containing hand-labeled, multi-duration spectrograms obtained from real LIGO data, we demonstrate that this method enables optimal use of very deep convolutional neural networks for classification given small training datasets, significantly reduces the time for training the networks, and achieves state-of-the-art accuracy above 98.8%, with perfect precision-recall on 8 out of 22 classes. Furthermore, new types of glitches can be classified accurately given few labeled examples with this technique. Once trained via transfer learning, we show that the convolutional neural networks can be truncated and used as excellent feature extractors for unsupervised clustering methods to identify new classes based on their morphology, without any labeled examples. Therefore, this provides a new framework for dynamic glitch classification for gravitational wave detectors, which are expected to encounter new types of noise as they undergo gradual improvements to attain design sensitivity. |
2306.13010 | Thanasis Giannakopoulos | Thanasis Giannakopoulos, Nigel T. Bishop, David Hilditch, Denis
Pollney, Miguel Zilh\~ao | Numerical convergence of model Cauchy-characteristic extraction and
matching | 20 pages, 11 figures, 2 tables, data and code can be found at
http://dx.doi.org/10.5281/zenodo.7981429 and
https://github.com/ThanasisGiannakopoulos/model_CCE_CCM_public, updated to
match published version | null | 10.1103/PhysRevD.108.104033 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves provide a powerful enhancement to our understanding of
fundamental physics. To make the most of their detection we need to accurately
model the entire process of their emission and propagation toward
interferometers. Cauchy-characteristic extraction and matching are methods to
compute gravitational waves at null infinity, a mathematical idealization of
detector location, from numerical relativity simulations. Both methods can in
principle contribute to modeling by providing highly accurate gravitational
waveforms. An underappreciated subtlety in realizing this potential is posed by
the (mere) weak hyperbolicity of the particular PDE systems solved in the
characteristic formulation of the Einstein field equations. This shortcoming
results from the popular choice of Bondi-like coordinates. So motivated, we
construct toy models that capture that PDE structure and study
Cauchy-characteristic extraction and matching with them. Where possible we
provide energy estimates for their solutions and perform careful numerical norm
convergence tests to demonstrate the effect of weak hyperbolicity on
Cauchy-characteristic extraction and matching. Our findings strongly indicate
that, as currently formulated, Cauchy-characteristic matching for the Einstein
field equations would provide solutions that are, at best, convergent at an
order lower than expected for the numerical method, and may be unstable. In
contrast, under certain conditions, the extraction method can provide properly
convergent solutions. Establishing however that these conditions hold for the
aforementioned characteristic formulations is still an open problem.
| [
{
"created": "Thu, 22 Jun 2023 16:19:00 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Nov 2023 22:00:03 GMT",
"version": "v2"
}
] | 2023-11-22 | [
[
"Giannakopoulos",
"Thanasis",
""
],
[
"Bishop",
"Nigel T.",
""
],
[
"Hilditch",
"David",
""
],
[
"Pollney",
"Denis",
""
],
[
"Zilhão",
"Miguel",
""
]
] | Gravitational waves provide a powerful enhancement to our understanding of fundamental physics. To make the most of their detection we need to accurately model the entire process of their emission and propagation toward interferometers. Cauchy-characteristic extraction and matching are methods to compute gravitational waves at null infinity, a mathematical idealization of detector location, from numerical relativity simulations. Both methods can in principle contribute to modeling by providing highly accurate gravitational waveforms. An underappreciated subtlety in realizing this potential is posed by the (mere) weak hyperbolicity of the particular PDE systems solved in the characteristic formulation of the Einstein field equations. This shortcoming results from the popular choice of Bondi-like coordinates. So motivated, we construct toy models that capture that PDE structure and study Cauchy-characteristic extraction and matching with them. Where possible we provide energy estimates for their solutions and perform careful numerical norm convergence tests to demonstrate the effect of weak hyperbolicity on Cauchy-characteristic extraction and matching. Our findings strongly indicate that, as currently formulated, Cauchy-characteristic matching for the Einstein field equations would provide solutions that are, at best, convergent at an order lower than expected for the numerical method, and may be unstable. In contrast, under certain conditions, the extraction method can provide properly convergent solutions. Establishing however that these conditions hold for the aforementioned characteristic formulations is still an open problem. |
1405.5232 | Shamaila Rani | M. Sharif and Shamaila Rani | Viscous Dark Energy in $f(T)$ Gravity | 17 pages, 12 figures | Mod. Phys. Lett. A 28(2013)1350118 | 10.1142/S0217732313501186 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the bulk viscosity taking dust matter in the generalized
teleparallel gravity. We consider different dark energy models in this scenario
along with a time dependent viscous model to construct the viscous equation of
state parameter for these dark energy models. We discuss the graphical
representation of this parameter to investigate the viscosity effects on the
accelerating expansion of the universe. It is mentioned here that the behavior
of the universe depends upon the viscous coefficients showing the transition
from decelerating to accelerating phase. It leads to the crossing of phantom
divide line and becomes phantom dominated for specific ranges of these
coefficients.
| [
{
"created": "Sun, 18 May 2014 15:45:52 GMT",
"version": "v1"
}
] | 2015-06-19 | [
[
"Sharif",
"M.",
""
],
[
"Rani",
"Shamaila",
""
]
] | We study the bulk viscosity taking dust matter in the generalized teleparallel gravity. We consider different dark energy models in this scenario along with a time dependent viscous model to construct the viscous equation of state parameter for these dark energy models. We discuss the graphical representation of this parameter to investigate the viscosity effects on the accelerating expansion of the universe. It is mentioned here that the behavior of the universe depends upon the viscous coefficients showing the transition from decelerating to accelerating phase. It leads to the crossing of phantom divide line and becomes phantom dominated for specific ranges of these coefficients. |
1407.7243 | George F. R. Ellis | George F R Ellis | The Evolving Block Universe and the Meshing Together of Times | 23 pages,4 figures | Ann N Y Acad Sci. (2014) Oct;1326:26-41 | 10.1111/nyas.12559 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is proposed that spacetime should be regarded as an evolving block
universe, bounded to the future by the present time, which continually extends
to the future. This future boundary is defined at each time by measuring proper
time along Ricci eigenlines from the start of the universe. A key point is that
physical reality can be represented at many different scales: hence the passage
of times may be seen as different at different scales, with quantum gravity
determining the evolution of space time itself but quantum field theory
determining the evolution of events within spacetime .The fundamental issue
then arises as to how the effective times at different scales mesh together,
leading to the concept so global and local times.
| [
{
"created": "Sun, 27 Jul 2014 15:02:58 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Ellis",
"George F R",
""
]
] | It is proposed that spacetime should be regarded as an evolving block universe, bounded to the future by the present time, which continually extends to the future. This future boundary is defined at each time by measuring proper time along Ricci eigenlines from the start of the universe. A key point is that physical reality can be represented at many different scales: hence the passage of times may be seen as different at different scales, with quantum gravity determining the evolution of space time itself but quantum field theory determining the evolution of events within spacetime .The fundamental issue then arises as to how the effective times at different scales mesh together, leading to the concept so global and local times. |
2401.09502 | Omar Mustafa | Omar Mustafa, Adriano R. Soares, Carlos F. S. Pereira, Ricardo L. L.
Vit\'oria | On the Klein-Gordon oscillators in Eddington-inspired Born-Infeld
gravity global monopole spacetime and a Wu-Yang magnetic monopole | 17 pages, 8 figures | Eur. Phys. J. C 84 (2024) 405 | 10.1140/epjc/s10052-024-12781-y | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We consider Klein-Gordon (KG) particles in a global monopole (GM) spacetime
within Eddington-inspired Born-Infeld gravity (EiBI-gravity) and in a Wu-Yang
magnetic monopole (WYMM). We discuss a set of KG-oscillators in such spacetime
settings. We propose a textbook power series expansion for the KG radial wave
function that allows us to retrieve the exact energy levels for KG-oscillators
in a GM spacetime and a WYMM without EiBI-gravity. We, moreover, report some
\textit{conditionally exact}, closed form, energy levels (through some
parametric correlations) for KG-oscillators in a GM spacetime and a WYMM within
EiBI-gravity, and for massless KG-oscillators in a GM spacetime and a WYMM
within EiBI-gravity under the influence of a Coulomb plus linear Lorentz scalar
potential. We study and discuss the effects of the Eddington parameter
$\kappa$, GM-parameter $\alpha$, WYMM strength $\sigma$, KG-oscillators'
frequency $\Omega$, and the coupling parameters of the Coulomb plus linear
Lorentz scalar potential, on the spectroscopic structure of the KG-oscillators
at hand. Such effects are studied over a vast range of the radial quantum
number $n_r\geq 0$ and include energy levels clustering at $\kappa>>1$ (i.e.,
extreme EiBI-gravity), and at $|\sigma|>>1$ (i.e., extreme WYMM strength).
| [
{
"created": "Wed, 17 Jan 2024 09:34:05 GMT",
"version": "v1"
}
] | 2024-04-24 | [
[
"Mustafa",
"Omar",
""
],
[
"Soares",
"Adriano R.",
""
],
[
"Pereira",
"Carlos F. S.",
""
],
[
"Vitória",
"Ricardo L. L.",
""
]
] | We consider Klein-Gordon (KG) particles in a global monopole (GM) spacetime within Eddington-inspired Born-Infeld gravity (EiBI-gravity) and in a Wu-Yang magnetic monopole (WYMM). We discuss a set of KG-oscillators in such spacetime settings. We propose a textbook power series expansion for the KG radial wave function that allows us to retrieve the exact energy levels for KG-oscillators in a GM spacetime and a WYMM without EiBI-gravity. We, moreover, report some \textit{conditionally exact}, closed form, energy levels (through some parametric correlations) for KG-oscillators in a GM spacetime and a WYMM within EiBI-gravity, and for massless KG-oscillators in a GM spacetime and a WYMM within EiBI-gravity under the influence of a Coulomb plus linear Lorentz scalar potential. We study and discuss the effects of the Eddington parameter $\kappa$, GM-parameter $\alpha$, WYMM strength $\sigma$, KG-oscillators' frequency $\Omega$, and the coupling parameters of the Coulomb plus linear Lorentz scalar potential, on the spectroscopic structure of the KG-oscillators at hand. Such effects are studied over a vast range of the radial quantum number $n_r\geq 0$ and include energy levels clustering at $\kappa>>1$ (i.e., extreme EiBI-gravity), and at $|\sigma|>>1$ (i.e., extreme WYMM strength). |
0808.1967 | Yuri Obukhov | Yuri N. Obukhov | Electromagnetic energy and momentum in moving media | 22 pages, Latex AdP-style, to appear in Minkowski's centenary issue
of Annalen der Physik | null | 10.1002/andp.200810313 | null | gr-qc hep-th physics.class-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The problem of the electromagnetic energy-momentum tensor is among the oldest
and the most controversial in macroscopic electrodynamics. In the center of the
issue is a dispute about the Minkowski and the Abraham tensors for moving
media. An overview of the current situation is presented. After putting the
discussion into a general Lagrange-Noether framework, the Minkowski tensor is
recovered as a canonical energy-momentum. It is shown that the balance
equations of energy, momentum, and angular momentum are always satisfied for an
open electromagnetic system despite the lack of the symmetry of the canonical
tensor. On the other hand, although the Abraham tensor is not defined from
first principles, one can formulate a general symmetrization prescription
provided a timelike vector is available. We analyze in detail the variational
model of a relativistic ideal fluid with isotropic electric and magnetic
properties interacting with the electromagnetic field. The relation between the
Minkowski energy-momentum tensor, the canonical energy-momentum of the medium
and the Abraham tensor is clarified. It is demonstrated that the Abraham
energy-momentum is relevant when the 4-velocity of matter is the only covariant
variable that enters the constitutive tensor.
| [
{
"created": "Thu, 14 Aug 2008 09:41:17 GMT",
"version": "v1"
}
] | 2008-08-15 | [
[
"Obukhov",
"Yuri N.",
""
]
] | The problem of the electromagnetic energy-momentum tensor is among the oldest and the most controversial in macroscopic electrodynamics. In the center of the issue is a dispute about the Minkowski and the Abraham tensors for moving media. An overview of the current situation is presented. After putting the discussion into a general Lagrange-Noether framework, the Minkowski tensor is recovered as a canonical energy-momentum. It is shown that the balance equations of energy, momentum, and angular momentum are always satisfied for an open electromagnetic system despite the lack of the symmetry of the canonical tensor. On the other hand, although the Abraham tensor is not defined from first principles, one can formulate a general symmetrization prescription provided a timelike vector is available. We analyze in detail the variational model of a relativistic ideal fluid with isotropic electric and magnetic properties interacting with the electromagnetic field. The relation between the Minkowski energy-momentum tensor, the canonical energy-momentum of the medium and the Abraham tensor is clarified. It is demonstrated that the Abraham energy-momentum is relevant when the 4-velocity of matter is the only covariant variable that enters the constitutive tensor. |
2210.01909 | Michael Gammon | Michael Gammon, Robert Mann | Slowly Rotating Black Holes in 4D Einstein Gauss-Bonnet Gravity | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Since the recent derivation of a well-defined $D\rightarrow 4$ limit for
regularized 4D Einstein Gauss-Bonnet (4DEGB) gravity, there has been
considerable interest in testing it as an alternative to Einstein's general
theory of relativity. In this paper we construct slowly rotating black hole
solutions for 4DEGB gravity in asymptotically flat, de Sitter, and anti-de
Sitter spacetimes. At leading order in the rotation parameter, exact solutions
of the metric functions are derived and studied for all three of these cases.
We compare how physical properties (innermost stable circular orbits, photon
rings, black hole shadow, etc.) of the solutions are modified by varying
coupling strengths of the 4DEGB theory relative to standard Einstein gravity
results. We find that a vanishing or negative cosmological constant in 4DEGB
gravity enforces a minimum mass on the black hole solutions, whereas a positive
cosmological constant enforces both a minimum \textit{and} maximum mass with a
horizon root structure directly analogous to the Reissner-Nordstr\"om de Sitter
spacetime. Besides this, many of the physical properties are qualitatively
similar to general relativity, with the greatest deviations typically being
found in the low (near-minimal) mass regime.
| [
{
"created": "Tue, 4 Oct 2022 21:09:30 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Nov 2022 22:02:22 GMT",
"version": "v2"
},
{
"created": "Sat, 30 Mar 2024 19:53:19 GMT",
"version": "v3"
}
] | 2024-04-02 | [
[
"Gammon",
"Michael",
""
],
[
"Mann",
"Robert",
""
]
] | Since the recent derivation of a well-defined $D\rightarrow 4$ limit for regularized 4D Einstein Gauss-Bonnet (4DEGB) gravity, there has been considerable interest in testing it as an alternative to Einstein's general theory of relativity. In this paper we construct slowly rotating black hole solutions for 4DEGB gravity in asymptotically flat, de Sitter, and anti-de Sitter spacetimes. At leading order in the rotation parameter, exact solutions of the metric functions are derived and studied for all three of these cases. We compare how physical properties (innermost stable circular orbits, photon rings, black hole shadow, etc.) of the solutions are modified by varying coupling strengths of the 4DEGB theory relative to standard Einstein gravity results. We find that a vanishing or negative cosmological constant in 4DEGB gravity enforces a minimum mass on the black hole solutions, whereas a positive cosmological constant enforces both a minimum \textit{and} maximum mass with a horizon root structure directly analogous to the Reissner-Nordstr\"om de Sitter spacetime. Besides this, many of the physical properties are qualitatively similar to general relativity, with the greatest deviations typically being found in the low (near-minimal) mass regime. |
gr-qc/0507085 | Ugur Camci | Ugur Camci | Dirac Analysis and Integrability of Geodesic Equations for Cylindrically
Symmetric Spacetimes | 12 Pages, Latex, no figures | Int.J.Mod.Phys. D12 (2003) 1431 | 10.1142/S0218271803003621 | null | gr-qc | null | Dirac's constraint analysis and the symplectic structure of geodesic
equations are obtained for the general cylindrically symmetric stationary
spacetime. For this metric, using the obtained first order Lagrangian, the
geodesic equations of motion are integrated, and found some solutions for
Lewis, Levi-Civita, and Van Stockum spacetimes.
| [
{
"created": "Tue, 19 Jul 2005 08:06:47 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Camci",
"Ugur",
""
]
] | Dirac's constraint analysis and the symplectic structure of geodesic equations are obtained for the general cylindrically symmetric stationary spacetime. For this metric, using the obtained first order Lagrangian, the geodesic equations of motion are integrated, and found some solutions for Lewis, Levi-Civita, and Van Stockum spacetimes. |
2211.08027 | Fethi M. Ramazanoglu | Andrew Coates and Fethi M. Ramazano\u{g}lu | Coordinate singularities of self-interacting vector field theories | 5 pages, 2 figures. Minor changes to bring into line with published
version in PRL | Phys. Rev. Lett. 130, 021401 (2023) | 10.1103/PhysRevLett.130.021401 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Self-interacting vectors are seeing a burst of interest where various groups
demonstrated that the field evolution ends in finite time. Two nonequivalent
criteria have been offered to identify this breakdown: (i) the vector
constraint equation cannot be satisfied beyond a point where the breakdown
occurs, (ii) the dynamics is governed by an effective metric that becomes
singular at the breakdown. We show that (i) identifies a coordinate
singularity, and can be removed by a change of coordinates. Hence, it does not
signify a physical problem, and cannot determine the validity of a theory.
| [
{
"created": "Tue, 15 Nov 2022 10:19:08 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Jan 2023 19:19:35 GMT",
"version": "v2"
}
] | 2023-01-19 | [
[
"Coates",
"Andrew",
""
],
[
"Ramazanoğlu",
"Fethi M.",
""
]
] | Self-interacting vectors are seeing a burst of interest where various groups demonstrated that the field evolution ends in finite time. Two nonequivalent criteria have been offered to identify this breakdown: (i) the vector constraint equation cannot be satisfied beyond a point where the breakdown occurs, (ii) the dynamics is governed by an effective metric that becomes singular at the breakdown. We show that (i) identifies a coordinate singularity, and can be removed by a change of coordinates. Hence, it does not signify a physical problem, and cannot determine the validity of a theory. |
1406.2571 | Ivan Arraut | Ivan Arraut | The Komar mass function in the de-Rham-Gabadadze-Tolley non-linear
theory of massive gravity | Version to appear in Physical Review D | Phys.Rev.D90, (2014) 124082 | 10.1103/PhysRevD.90.124082 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I derive the Komar mass/function for the Schwarszchild de-Sitter (S-dS)
black-hole inside the dRGT non-linear theory of massive gravity by taking the
usual notion of time-like Killing vector in unitary gauge. The dRGT Komar
function depends on the dynamics of the St\"uckelberg fields through the gauge
transformation function. It goes to the standard value obtained in General
Relativity (GR) if the spatial derivative of the gauge function vanishes. In
such a case, the (gauge) function corresponds to the usual notion of time as in
GR.
| [
{
"created": "Mon, 9 Jun 2014 15:48:19 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Dec 2014 15:00:30 GMT",
"version": "v2"
}
] | 2014-12-31 | [
[
"Arraut",
"Ivan",
""
]
] | I derive the Komar mass/function for the Schwarszchild de-Sitter (S-dS) black-hole inside the dRGT non-linear theory of massive gravity by taking the usual notion of time-like Killing vector in unitary gauge. The dRGT Komar function depends on the dynamics of the St\"uckelberg fields through the gauge transformation function. It goes to the standard value obtained in General Relativity (GR) if the spatial derivative of the gauge function vanishes. In such a case, the (gauge) function corresponds to the usual notion of time as in GR. |
0902.0217 | Ahmadjon Abdujabbarov | B.V. Turimov, B.J. Ahmedov, A.A. Abdujabbarov | Electromagnetic Fields of Slowly Rotating Magnetized Gravastars | 5 pages, 2 figures, accepted for publication to Mod. Phys. Lett. A | Mod.Phys.Lett.A24:733-737,2009 | 10.1142/S0217732309030497 | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the dipolar magnetic field configuration and present solutions of
Maxwell equations in the internal background spacetime of a a slowly rotating
gravastar. The shell of gravastar where magnetic field penetrated is modeled as
sphere consisting of perfect highly magnetized fluid with infinite
conductivity. Dipolar magnetic field of the gravastar is produced by a circular
current loop symmetrically placed at radius $a$ at the equatorial plane.
| [
{
"created": "Mon, 2 Feb 2009 07:55:08 GMT",
"version": "v1"
}
] | 2010-04-20 | [
[
"Turimov",
"B. V.",
""
],
[
"Ahmedov",
"B. J.",
""
],
[
"Abdujabbarov",
"A. A.",
""
]
] | We study the dipolar magnetic field configuration and present solutions of Maxwell equations in the internal background spacetime of a a slowly rotating gravastar. The shell of gravastar where magnetic field penetrated is modeled as sphere consisting of perfect highly magnetized fluid with infinite conductivity. Dipolar magnetic field of the gravastar is produced by a circular current loop symmetrically placed at radius $a$ at the equatorial plane. |
1409.8534 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | On the stability of thin-shell wormholes | 5 pages, no figures | Fundamental J. Mod. Phys., vol. 7, 111-119 (2014) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A thin-shell wormhole is theoretically constructible by surgically grafting
together two Schwarzschild spacetimes using the so-called cut-and-paste
technique. By describing such a wormhole as the limiting case of a spherical
shell, it is shown that the structure must be unstable to linearized radial
perturbations. Some earlier studies by the author et al. have shown, however,
that under certain conditions, thin-shell wormholes can be stable.
| [
{
"created": "Tue, 30 Sep 2014 13:16:34 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Nov 2014 18:11:41 GMT",
"version": "v2"
},
{
"created": "Thu, 18 Dec 2014 18:20:00 GMT",
"version": "v3"
},
{
"created": "Sun, 30 Aug 2015 13:32:57 GMT",
"version": "v4"
},
{
"cr... | 2016-03-07 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | A thin-shell wormhole is theoretically constructible by surgically grafting together two Schwarzschild spacetimes using the so-called cut-and-paste technique. By describing such a wormhole as the limiting case of a spherical shell, it is shown that the structure must be unstable to linearized radial perturbations. Some earlier studies by the author et al. have shown, however, that under certain conditions, thin-shell wormholes can be stable. |
gr-qc/0103033 | Edward Malec | Edward Malec and Gerhard Schaefer | Can Schwarzschildean gravitational fields suppress gravitational waves? | 18 pages, Revtex. Added three references; a new comment in Sec. 7;
several misprints corrected. To appear in the Phys. Rev. D | Phys.Rev.D64:044012,2001 | 10.1103/PhysRevD.64.044012 | null | gr-qc astro-ph | null | Gravitational waves in the linear approximation propagate in the
Schwarzschild spacetime similarly as electromagnetic waves. A fraction of the
radiation scatters off the curvature of the geometry. The energy of the
backscattered part of an initially outgoing pulse of the quadrupole
gravitational radiation is estimated by compact formulas depending on the
initial energy, the Schwarzschild radius, and the location and width of the
pulse. The backscatter becomes negligible in the short wavelength regime.
| [
{
"created": "Fri, 9 Mar 2001 21:04:45 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Jun 2001 08:06:41 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Malec",
"Edward",
""
],
[
"Schaefer",
"Gerhard",
""
]
] | Gravitational waves in the linear approximation propagate in the Schwarzschild spacetime similarly as electromagnetic waves. A fraction of the radiation scatters off the curvature of the geometry. The energy of the backscattered part of an initially outgoing pulse of the quadrupole gravitational radiation is estimated by compact formulas depending on the initial energy, the Schwarzschild radius, and the location and width of the pulse. The backscatter becomes negligible in the short wavelength regime. |
gr-qc/9903070 | S. M. Kopeikin | Sergei M. Kopeikin | Timing Effects of Gravitational Waves from Localized Sources | 6 pages, 2 figures, a talk given at the XXXIVth Rencontres de Moriond
on "Gravitational Waves and Experimental Gravity", Les Arcs, 23-30 January
1999 | null | null | null | gr-qc astro-ph | null | Localized astronomical sources like a double stellar system, rotating neutron
star, or a massive black hole at the center of the Milky Way emit periodic
gravitational waves. For a long time only a far-zone contribution of
gravitational fields of the localized sources (plane-wave-front approximation)
were a matter of theoretical analysis. We demonstrate how this analysis can be
extended to take into account near-zone and intermediate-zone contributions as
well. The formalism is used to calculate gravitational-wave corrections to the
Shapiro time delay in binary pulsars and low-frequency (LF) pulsar timing noise
produced by an ensemble of double stars in our galaxy.
| [
{
"created": "Thu, 18 Mar 1999 22:38:37 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kopeikin",
"Sergei M.",
""
]
] | Localized astronomical sources like a double stellar system, rotating neutron star, or a massive black hole at the center of the Milky Way emit periodic gravitational waves. For a long time only a far-zone contribution of gravitational fields of the localized sources (plane-wave-front approximation) were a matter of theoretical analysis. We demonstrate how this analysis can be extended to take into account near-zone and intermediate-zone contributions as well. The formalism is used to calculate gravitational-wave corrections to the Shapiro time delay in binary pulsars and low-frequency (LF) pulsar timing noise produced by an ensemble of double stars in our galaxy. |
2403.19458 | Vinod Kumar Bhardwaj Dr. | Bhojraj Singh Jayas and Vinod Kumar Bhardwaj | Evaluation of Transit cosmological model in $f(R,T^{\phi})$ theory of
gravity | 18 pages, 13 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | We have explored a transitioning cosmic model, depicting late-time
accelerated expansion in $f(R,T^{\phi})$ theory of gravity for an isotropic and
homogeneous universe, where the trace of energy-momentum tensor $T^{\phi}$ is
the function of the self-interacting scalar field $\phi$. We have proposed an
explicit solution to the derived model by utilizing a scale factor of the
hybrid form $a(t) = t^{\alpha} e^{\beta t}$, where $\alpha$ and $\beta$ are
constants. To evaluate the best-fit values of free parameters of the suggested
model, the statistical analysis based on the Markov Chain Monte Carlo (MCMC)
method has been employed on 57 OHD points. We have described the dynamical
features of the model like energy density, cosmic pressure, and equation of
state parameter in the context of scalar field $\phi$. We have also described
the potential and behavior of the scalar field for quintessence and phantom
scenarios. The deceleration parameter depicts a transitioning universe with
signature flipping at $z_t = 0.82$ with the present value of deceleration
parameter $q_0=-0.41$. The violation of SEC for the derived model indicates the
cosmic expansion at a faster rate. We have used statefinders to diagnose the
model. The findings for our theoretical model indicate that the derived model
agrees with observed findings within a particular range of limitations.
| [
{
"created": "Thu, 28 Mar 2024 14:30:40 GMT",
"version": "v1"
}
] | 2024-03-29 | [
[
"Jayas",
"Bhojraj Singh",
""
],
[
"Bhardwaj",
"Vinod Kumar",
""
]
] | We have explored a transitioning cosmic model, depicting late-time accelerated expansion in $f(R,T^{\phi})$ theory of gravity for an isotropic and homogeneous universe, where the trace of energy-momentum tensor $T^{\phi}$ is the function of the self-interacting scalar field $\phi$. We have proposed an explicit solution to the derived model by utilizing a scale factor of the hybrid form $a(t) = t^{\alpha} e^{\beta t}$, where $\alpha$ and $\beta$ are constants. To evaluate the best-fit values of free parameters of the suggested model, the statistical analysis based on the Markov Chain Monte Carlo (MCMC) method has been employed on 57 OHD points. We have described the dynamical features of the model like energy density, cosmic pressure, and equation of state parameter in the context of scalar field $\phi$. We have also described the potential and behavior of the scalar field for quintessence and phantom scenarios. The deceleration parameter depicts a transitioning universe with signature flipping at $z_t = 0.82$ with the present value of deceleration parameter $q_0=-0.41$. The violation of SEC for the derived model indicates the cosmic expansion at a faster rate. We have used statefinders to diagnose the model. The findings for our theoretical model indicate that the derived model agrees with observed findings within a particular range of limitations. |
2008.12327 | Parthapratim Pradhan | Parthapratim Pradhan | Black Hole versus Naked Singularity via Axial Perturbation | 19 pages, 56 figures | null | null | null | gr-qc astro-ph.GA | http://creativecommons.org/licenses/by/4.0/ | We differentiate non-extremal black hole, \emph{extremal} black hole and
\emph{naked singularity} via metric perturbations for Reissner-Nordstr\"{o}m
spacetime. First we study the axial perturbations for \emph{extremal}
Reissner-Nordstr\"{o}m black hole and compute the effective potential due to
these perturbations. Then we study the axial perturbations for the naked
singularity case and compute the effective potential. We show that for the
non-extremal black hole, \emph{the effective potential outside the event
horizon~($r_{+}$) is real and positive. While in between Cauchy
horizon~($r_{-}$) and event horizon~($r_{-}<r<r_{+}$) the effective potential
is negative.} For the \emph{extremal black hole, the effective potential is
always positive}. Also for \emph{naked singularity, the effective potential is
positive.} From the effective potential diagram, we show that the structure of
effective potentials for extremal BH looks like a potential barrier outside the
horizon. While for non-extremal BH, the structure of the effective potentials
look like a \emph{potential well} rather than a potential barrier. For NS the
structure of the effective potentials is \emph{neither a potential barrier nor
a potential well. Preferably it looks like an exponential decay function}. We
observe that the geometric construction of an effective potential barrier due
to axial perturbations could allow us to distinguish between the non-extremal
black hole, extremal black hole, and naked singularity. Stability of extremal
BH has been discussed.
| [
{
"created": "Thu, 27 Aug 2020 18:35:59 GMT",
"version": "v1"
}
] | 2020-08-31 | [
[
"Pradhan",
"Parthapratim",
""
]
] | We differentiate non-extremal black hole, \emph{extremal} black hole and \emph{naked singularity} via metric perturbations for Reissner-Nordstr\"{o}m spacetime. First we study the axial perturbations for \emph{extremal} Reissner-Nordstr\"{o}m black hole and compute the effective potential due to these perturbations. Then we study the axial perturbations for the naked singularity case and compute the effective potential. We show that for the non-extremal black hole, \emph{the effective potential outside the event horizon~($r_{+}$) is real and positive. While in between Cauchy horizon~($r_{-}$) and event horizon~($r_{-}<r<r_{+}$) the effective potential is negative.} For the \emph{extremal black hole, the effective potential is always positive}. Also for \emph{naked singularity, the effective potential is positive.} From the effective potential diagram, we show that the structure of effective potentials for extremal BH looks like a potential barrier outside the horizon. While for non-extremal BH, the structure of the effective potentials look like a \emph{potential well} rather than a potential barrier. For NS the structure of the effective potentials is \emph{neither a potential barrier nor a potential well. Preferably it looks like an exponential decay function}. We observe that the geometric construction of an effective potential barrier due to axial perturbations could allow us to distinguish between the non-extremal black hole, extremal black hole, and naked singularity. Stability of extremal BH has been discussed. |
1011.4988 | Aron Wall | Sudipta Sarkar, Aron C. Wall | Second Law Violations in Lovelock Gravity for Black Hole Mergers | 15 pages, 1 figure, v2 Title change & minor revisions to match
published version, v3 fixed accidental deletion of author names | Phys.Rev.D83:124048,2011 | 10.1103/PhysRevD.83.124048 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the classical second law of black hole thermodynamics, for Lovelock
theories (other than General Relativity), in arbitrary dimensions. Using the
standard formula for black hole entropy, we construct scenarios involving the
merger of two black holes in which the entropy instantaneously decreases. Our
construction involves a Kaluza-Klein compactification down to a dimension in
which one of the Lovelock terms is topological. We discuss some open issues in
the definition of the second law which might be used to compensate this entropy
decrease.
| [
{
"created": "Tue, 23 Nov 2010 01:56:27 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Sep 2011 17:11:43 GMT",
"version": "v2"
},
{
"created": "Fri, 2 Oct 2015 21:34:28 GMT",
"version": "v3"
}
] | 2015-10-06 | [
[
"Sarkar",
"Sudipta",
""
],
[
"Wall",
"Aron C.",
""
]
] | We study the classical second law of black hole thermodynamics, for Lovelock theories (other than General Relativity), in arbitrary dimensions. Using the standard formula for black hole entropy, we construct scenarios involving the merger of two black holes in which the entropy instantaneously decreases. Our construction involves a Kaluza-Klein compactification down to a dimension in which one of the Lovelock terms is topological. We discuss some open issues in the definition of the second law which might be used to compensate this entropy decrease. |
2105.07750 | Yonadav Barry Ginat | Yonadav Barry Ginat | The Equivalence Principle and The Cosmological Constant Problem | The essay received an Honorable Mention in the Gravity Research
Foundation essay competition 2021 | null | null | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this essay I point out that, in the context of semi-classical gravity, the
equivalence principle can mitigate the cosmological constant problem. On a
Minkowski space-time background with the usual $\mathbb{R}^4$ topology, the
vacuum self-energy is removed by normal ordering; this is allowed because it is
not observable; I argue that, in a freely-falling frame of reference, the same
must hold true, up to contributions from modes whose wavelength is of the order
of the background radius of curvature. Thus, the equivalence principle implies
that ultra-violet modes do not contribute to the effective energy-momentum
tensor.
| [
{
"created": "Mon, 17 May 2021 11:52:54 GMT",
"version": "v1"
}
] | 2021-05-18 | [
[
"Ginat",
"Yonadav Barry",
""
]
] | In this essay I point out that, in the context of semi-classical gravity, the equivalence principle can mitigate the cosmological constant problem. On a Minkowski space-time background with the usual $\mathbb{R}^4$ topology, the vacuum self-energy is removed by normal ordering; this is allowed because it is not observable; I argue that, in a freely-falling frame of reference, the same must hold true, up to contributions from modes whose wavelength is of the order of the background radius of curvature. Thus, the equivalence principle implies that ultra-violet modes do not contribute to the effective energy-momentum tensor. |
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