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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1001.2230
|
Andr\'es Ace\~na
|
Andr\'es E. Ace\~na
|
Minimal data at a given point of space for solutions to certain
geometric systems
|
26 pages, no figures
| null |
10.1088/0264-9381/27/15/155006
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider a geometrical system of equations for a three dimensional
Riemannian manifold. This system of equations has been constructed as to
include several physically interesting systems of equations, such as the
stationary Einstein vacuum field equations or harmonic maps coupled to gravity
in three dimensions. We give a characterization of its solutions in a
neighbourhood of a given point through sequences of symmetric trace free
tensors (referred to as `null data'). We show that the null data determine a
formal expansion of the solution and we obtain necessary and sufficient growth
estimates on the null data for the formal expansion to be absolutely convergent
in a neighbourhood of the given point. This provides a complete
characterization of all the solutions to the given system of equations around
that point.
|
[
{
"created": "Wed, 13 Jan 2010 16:45:07 GMT",
"version": "v1"
}
] |
2015-05-18
|
[
[
"Aceña",
"Andrés E.",
""
]
] |
We consider a geometrical system of equations for a three dimensional Riemannian manifold. This system of equations has been constructed as to include several physically interesting systems of equations, such as the stationary Einstein vacuum field equations or harmonic maps coupled to gravity in three dimensions. We give a characterization of its solutions in a neighbourhood of a given point through sequences of symmetric trace free tensors (referred to as `null data'). We show that the null data determine a formal expansion of the solution and we obtain necessary and sufficient growth estimates on the null data for the formal expansion to be absolutely convergent in a neighbourhood of the given point. This provides a complete characterization of all the solutions to the given system of equations around that point.
|
2103.06516
|
Tatsuki Washimi Dr.
|
T. Washimi, T. Yokozawa, M. Nakano, T. Tanaka, K. Kaihotsu, Y. Mori,
T. Narita
|
Effects of lightning strokes on underground gravitational waves
observatories
| null |
JINST 16 P07033 (2021)
|
10.1088/1748-0221/16/07/P07033
|
JGW-P2112426
|
gr-qc astro-ph.IM
|
http://creativecommons.org/licenses/by-nc-sa/4.0/
|
For ground-based gravitational wave (GW) detectors, lightning strokes in the
atmosphere are sources of environmental noise. Some GW detectors are built or
planned in underground facilities, and knowledge of how lightning strokes
affect them is of interest. In this paper, the lightning detection system in
KAGRA is introduced, and the properties of the magnetic field measured inside
and outside the KAGRA tunnel are shown. One lightning-induced event in the GW
channel of the KAGRA main interferometer is also shown. Finally, possible
applications of lightning events for the GW experiments are discussed.
|
[
{
"created": "Thu, 11 Mar 2021 08:03:51 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Mar 2021 00:56:28 GMT",
"version": "v2"
},
{
"created": "Sun, 6 Jun 2021 07:42:30 GMT",
"version": "v3"
}
] |
2021-07-22
|
[
[
"Washimi",
"T.",
""
],
[
"Yokozawa",
"T.",
""
],
[
"Nakano",
"M.",
""
],
[
"Tanaka",
"T.",
""
],
[
"Kaihotsu",
"K.",
""
],
[
"Mori",
"Y.",
""
],
[
"Narita",
"T.",
""
]
] |
For ground-based gravitational wave (GW) detectors, lightning strokes in the atmosphere are sources of environmental noise. Some GW detectors are built or planned in underground facilities, and knowledge of how lightning strokes affect them is of interest. In this paper, the lightning detection system in KAGRA is introduced, and the properties of the magnetic field measured inside and outside the KAGRA tunnel are shown. One lightning-induced event in the GW channel of the KAGRA main interferometer is also shown. Finally, possible applications of lightning events for the GW experiments are discussed.
|
1911.06520
|
Srijita Sinha
|
Srijita Sinha and Narayan Banerjee
|
Density perturbation in an interacting holographic dark energy model
|
17 pages, 11 figures, minor changes, references added; version
matches the accepted one
|
Eur. Phys. J. Plus 135, 779 (2020)
|
10.1140/epjp/s13360-020-00803-z
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The present work deals with the evolution of the density contrasts for a
cosmological model where along with the standard cold dark matter (CDM), the
present Universe also contains holographic dark energy (HDE). The
characteristic infra-red (IR) cut-off is taken as the future event horizon. The
HDE is allowed to interact with the CDM. The equations for the density
contrasts are integrated numerically. It is found that irrespective of the
presence of an interaction, the matter perturbation has growing modes. The HDE
is also found to have growth of perturbation, so very much like the CDM, thus
can also cluster. The interesting point to note is that the density contrast
corresponding to HDE has a peak at recent past and is decaying at the present
epoch. Another feature is that IR cut-off as the event horizon does not
naturally produce accelerated expansion of the Universe in the presence of an
interaction.
|
[
{
"created": "Fri, 15 Nov 2019 08:52:32 GMT",
"version": "v1"
},
{
"created": "Fri, 3 Jan 2020 09:51:51 GMT",
"version": "v2"
},
{
"created": "Fri, 9 Oct 2020 02:35:45 GMT",
"version": "v3"
}
] |
2020-12-07
|
[
[
"Sinha",
"Srijita",
""
],
[
"Banerjee",
"Narayan",
""
]
] |
The present work deals with the evolution of the density contrasts for a cosmological model where along with the standard cold dark matter (CDM), the present Universe also contains holographic dark energy (HDE). The characteristic infra-red (IR) cut-off is taken as the future event horizon. The HDE is allowed to interact with the CDM. The equations for the density contrasts are integrated numerically. It is found that irrespective of the presence of an interaction, the matter perturbation has growing modes. The HDE is also found to have growth of perturbation, so very much like the CDM, thus can also cluster. The interesting point to note is that the density contrast corresponding to HDE has a peak at recent past and is decaying at the present epoch. Another feature is that IR cut-off as the event horizon does not naturally produce accelerated expansion of the Universe in the presence of an interaction.
|
1601.03941
|
Massimo Tessarotto
|
Massimo Tessarotto (Department of Mathematics and Geosciences,
University of Trieste, Italy and Institute of Physics, Faculty of Philosophy
and Science, Silesian University in Opava, Bezru\v{c}ovo n\'am.13, CZ-74601
Opava, Czech Republic) and Claudio Cremaschini (Institute of Physics, Faculty
of Philosophy and Science, Silesian University in Opava, Bezru\v{c}ovo
n\'am.13, CZ-74601 Opava, Czech Republic)
|
Theory of non-local point transformations - Part 2: General form and
Gedanken experiment
| null | null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The problem is posed of further extending the axiomatic construction proposed
in Part 1 for non-local point transformations mapping in each other different
curved space times. The new transformations apply to curved space times when
expressed in arbitrary coordinate systems. It is shown that the solution
permits to achieve an ideal (Gedanken) experiment realizing a suitable kind of
phase-space transformation on point-particle classical dynamical systems.
Applications of the theory are discussed both for diagonal and non-diagonal
metric tensors.
|
[
{
"created": "Wed, 13 Jan 2016 08:07:05 GMT",
"version": "v1"
}
] |
2016-01-18
|
[
[
"Tessarotto",
"Massimo",
"",
"Department of Mathematics and Geosciences,\n University of Trieste, Italy and Institute of Physics, Faculty of Philosophy\n and Science, Silesian University in Opava, Bezručovo nám.13, CZ-74601\n Opava, Czech Republic"
],
[
"Cremaschini",
"Claudio",
"",
"Institute of Physics, Faculty\n of Philosophy and Science, Silesian University in Opava, Bezručovo\n nám.13, CZ-74601 Opava, Czech Republic"
]
] |
The problem is posed of further extending the axiomatic construction proposed in Part 1 for non-local point transformations mapping in each other different curved space times. The new transformations apply to curved space times when expressed in arbitrary coordinate systems. It is shown that the solution permits to achieve an ideal (Gedanken) experiment realizing a suitable kind of phase-space transformation on point-particle classical dynamical systems. Applications of the theory are discussed both for diagonal and non-diagonal metric tensors.
|
1411.0125
|
Bushra Majeed
|
Bushra Majeed, Mubasher Jamil and Azad A. Siddiqui
|
Holographic Dark Energy with Time Varying n^2 Parameter in Non-Flat
Universe
|
8 pages, 2 figures, Published in: International Journal of
Theoretical Physics
|
Int. J. Theor. Phys. (2015) 54:42-49
|
10.1007/s10773-014-2197-3
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider a holographic dark energy model, with a varying parameter, n,
which evolves slowly with time. We obtain the differential equation describing
evolution of the dark energy density parameter, $\Omega_d$, for the flat and
non-flat FRW universes. The equation of state parameter in this generalized
version of holographic dark energy depends on n.
|
[
{
"created": "Sat, 1 Nov 2014 14:56:50 GMT",
"version": "v1"
}
] |
2015-01-28
|
[
[
"Majeed",
"Bushra",
""
],
[
"Jamil",
"Mubasher",
""
],
[
"Siddiqui",
"Azad A.",
""
]
] |
We consider a holographic dark energy model, with a varying parameter, n, which evolves slowly with time. We obtain the differential equation describing evolution of the dark energy density parameter, $\Omega_d$, for the flat and non-flat FRW universes. The equation of state parameter in this generalized version of holographic dark energy depends on n.
|
2404.16093
|
Prashant Kocherlakota
|
Prashant Kocherlakota and Ramesh Narayan
|
Self-Gravitating Matter in Stationary and Axisymmetric Black Hole
Spacetimes
|
25 pages, 9 figures, 2 tables
| null | null | null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
All black holes (BHs) in nature are expected to be described by the Kerr
vacuum solution of general relativity. However, the Kerr solution comes with
several difficulties such as the existence of Cauchy horizons, curvature
singularities, and causality-violating regions. Attempts to resolve some of
these issues include phenomenological BH models, which typically contain
nontrivial matter content. We introduce a simple framework here to examine the
properties of matter in such phenomenological models for a broad class of
stationary and axisymmetric spinning BH spacetimes, generated from nonspinning
seed solutions via a metric ansatz. We apply this framework to a representative
set of spinning BH spacetimes and the non-spinning seeds from which they are
derived. The models span different types of matter - fluids, scalar fields,
electromagnetic fields. For each model, we calculate the timelike four-velocity
of the matter and thereby identify the rest frame of the matter, both outside
and inside the horizon. We then examine the spatial distribution of the matter
rest-frame energy density $\epsilon$ and the principal pressures. This provides
a complete picture of how the matter moves, what its material properties are,
and whether it obeys the classical energy conditions. Notably, at a horizon,
the normal component of the pressure always satisfies $p_n = -\epsilon$. We
also investigate the expansions of the principal null congruences and explore
the Hawking mass profiles of these spacetimes. These provide glimpses into the
geometry of the stationary BH exterior as well as the nonstationary interior
cosmology. The axisymmetric metric ansatz we work with can be used to generate
new spinning solutions from a variety of nonspinning seeds. The matter in these
models often satisfies the weak energy condition, at least in the BH exterior,
and some models exhibit non-rigid, differential rotation.
|
[
{
"created": "Wed, 24 Apr 2024 18:00:01 GMT",
"version": "v1"
}
] |
2024-04-26
|
[
[
"Kocherlakota",
"Prashant",
""
],
[
"Narayan",
"Ramesh",
""
]
] |
All black holes (BHs) in nature are expected to be described by the Kerr vacuum solution of general relativity. However, the Kerr solution comes with several difficulties such as the existence of Cauchy horizons, curvature singularities, and causality-violating regions. Attempts to resolve some of these issues include phenomenological BH models, which typically contain nontrivial matter content. We introduce a simple framework here to examine the properties of matter in such phenomenological models for a broad class of stationary and axisymmetric spinning BH spacetimes, generated from nonspinning seed solutions via a metric ansatz. We apply this framework to a representative set of spinning BH spacetimes and the non-spinning seeds from which they are derived. The models span different types of matter - fluids, scalar fields, electromagnetic fields. For each model, we calculate the timelike four-velocity of the matter and thereby identify the rest frame of the matter, both outside and inside the horizon. We then examine the spatial distribution of the matter rest-frame energy density $\epsilon$ and the principal pressures. This provides a complete picture of how the matter moves, what its material properties are, and whether it obeys the classical energy conditions. Notably, at a horizon, the normal component of the pressure always satisfies $p_n = -\epsilon$. We also investigate the expansions of the principal null congruences and explore the Hawking mass profiles of these spacetimes. These provide glimpses into the geometry of the stationary BH exterior as well as the nonstationary interior cosmology. The axisymmetric metric ansatz we work with can be used to generate new spinning solutions from a variety of nonspinning seeds. The matter in these models often satisfies the weak energy condition, at least in the BH exterior, and some models exhibit non-rigid, differential rotation.
|
2407.14122
|
Gamal G.L. Nashed
|
Waleed El Hanafy, Mahmoud Hashim, and G.G.L. Nashed
|
Revisiting Flat Rotation Curves in Chern-Simons Modified Gravity
|
13 pages, 2 figures, match the version that will appear in Phys.
Lett. B
| null |
10.1016/j.physletb.2024.138882
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
We revisit slow rotating black hole (BH) solutions in Chern-Simons modified
gravity (CSMG) by considering perturbative solution about Schwarzschild BH. In
particular, the case when nondynamical CSMG with noncanonical CS scalar is
considered. We provide a new solution different from the previously obtained
one \cite{Konno:2007ze} which we refer to as KMT model. The present solution
accounts for frame dragging effect which includes not only radial dependence as
in the KMT. Nevertheless, it reduces to KMT as a particular case. We show that
the tidal gravitational force (Kretschmann invariant) associated to the present
solution contains a term of order $1/r^3$ additional to Schwarzschild but
absent from directional divergence, unlike KMT model which diverges along the
axis of symmetry. We derive the corresponding circular velocity of a massive
test particle in which the KMT velocity is recovered in addition to an extra
term $\propto r$. We investigate possible constraints on KMT and the present
solutions from the observed rotation curve of UGC11455 galaxy as an example. We
show that perturbation solutions cannot physically explain the flattening of
galactic rotation curves.
|
[
{
"created": "Fri, 19 Jul 2024 08:41:58 GMT",
"version": "v1"
}
] |
2024-07-22
|
[
[
"Hanafy",
"Waleed El",
""
],
[
"Hashim",
"Mahmoud",
""
],
[
"Nashed",
"G. G. L.",
""
]
] |
We revisit slow rotating black hole (BH) solutions in Chern-Simons modified gravity (CSMG) by considering perturbative solution about Schwarzschild BH. In particular, the case when nondynamical CSMG with noncanonical CS scalar is considered. We provide a new solution different from the previously obtained one \cite{Konno:2007ze} which we refer to as KMT model. The present solution accounts for frame dragging effect which includes not only radial dependence as in the KMT. Nevertheless, it reduces to KMT as a particular case. We show that the tidal gravitational force (Kretschmann invariant) associated to the present solution contains a term of order $1/r^3$ additional to Schwarzschild but absent from directional divergence, unlike KMT model which diverges along the axis of symmetry. We derive the corresponding circular velocity of a massive test particle in which the KMT velocity is recovered in addition to an extra term $\propto r$. We investigate possible constraints on KMT and the present solutions from the observed rotation curve of UGC11455 galaxy as an example. We show that perturbation solutions cannot physically explain the flattening of galactic rotation curves.
|
1909.07803
|
Subhajit Saha
|
Subhajit Saha
|
How to obtain a class of emergent universes with a general form of
dissipation?
|
5 pages; Under Review
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper, we have assumed a flat Friedmann-Lemaitr\'e-Robertson-Walker
universe endowed with a general form of dissipation. The source of dissipation
is considered to be a bulk viscous pressure $\Pi$ which leads to an adiabatic
creation of particles induced by the gravitational field. Further, the cosmic
substratum is assumed to satisfy the equation of state $p=(\gamma -1)\rho$ and
$\Pi$ is considered to be proportional to $H^{2k+1}$, where $H$ is the Hubble
parameter and $k$ is the index of dissipation. This choice of dissipation is
consistent with the pioneering works by Barrow and Clifton. Finally, by
assuming an exponential form for $H$ given by $H=e^{m(t-t_0)}$, where $m$ is a
positive real parameter and which bears all the signatures of an emergent
universe, we have been able to establish that the sufficiency of the inequality
$\gamma k \leq 0$ can produce a class of emergent universes. However, this
condition is by no means necessary for the existence of an emergent universe.
|
[
{
"created": "Sun, 15 Sep 2019 10:07:14 GMT",
"version": "v1"
}
] |
2019-09-18
|
[
[
"Saha",
"Subhajit",
""
]
] |
In this paper, we have assumed a flat Friedmann-Lemaitr\'e-Robertson-Walker universe endowed with a general form of dissipation. The source of dissipation is considered to be a bulk viscous pressure $\Pi$ which leads to an adiabatic creation of particles induced by the gravitational field. Further, the cosmic substratum is assumed to satisfy the equation of state $p=(\gamma -1)\rho$ and $\Pi$ is considered to be proportional to $H^{2k+1}$, where $H$ is the Hubble parameter and $k$ is the index of dissipation. This choice of dissipation is consistent with the pioneering works by Barrow and Clifton. Finally, by assuming an exponential form for $H$ given by $H=e^{m(t-t_0)}$, where $m$ is a positive real parameter and which bears all the signatures of an emergent universe, we have been able to establish that the sufficiency of the inequality $\gamma k \leq 0$ can produce a class of emergent universes. However, this condition is by no means necessary for the existence of an emergent universe.
|
gr-qc/0702075
|
Salvatore Capozziello
|
S. Capozziello, R. Garattini
|
The cosmological constant as an eigenvalue of f(R)-gravity Hamiltonian
constraint
|
16 pages, to appear in Class. Quant. Grav
|
Class.Quant.Grav.24:1627-1646,2007
|
10.1088/0264-9381/24/6/016
| null |
gr-qc astro-ph hep-th
| null |
In the framework of ADM formalism, it is possible to find out eigenvalues of
the WDW equation with the meaning of vacuum states, i.e. cosmological
constants, for f(R) theories of gravity, where f(R) is a generic analytic
function of the Ricci curvature scalar R. The explicit calculation is performed
for a Schwarzschild metric where one-loop energy is derived by the zeta
function regularization method and a renormalized running Lambda constant is
obtained.
|
[
{
"created": "Wed, 14 Feb 2007 08:43:19 GMT",
"version": "v1"
}
] |
2008-11-26
|
[
[
"Capozziello",
"S.",
""
],
[
"Garattini",
"R.",
""
]
] |
In the framework of ADM formalism, it is possible to find out eigenvalues of the WDW equation with the meaning of vacuum states, i.e. cosmological constants, for f(R) theories of gravity, where f(R) is a generic analytic function of the Ricci curvature scalar R. The explicit calculation is performed for a Schwarzschild metric where one-loop energy is derived by the zeta function regularization method and a renormalized running Lambda constant is obtained.
|
1702.05246
|
Tao Wang
|
Shao-Jun Wang, Xin-Xuan Guo, Towe Wang
|
Maximal volume behind horizons without curvature singularity
|
11 pages, 4 figures, Sect III improved
|
Phys. Rev. D 97, 024039 (2018)
|
10.1103/PhysRevD.97.024039
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The black hole information paradox is related to the area of event horizon,
and potentially to the volume and singularity behind it. One example is the
complexity/volume duality conjectured by Stanford and Susskind. Accepting the
proposal of Christodoulou and Rovelli, we calculate the maximal volume inside
regular black holes, which are free of curvature singularity, in asymptotically
flat and anti-de Sitter spacetimes respectively. The complexity/volume duality
is then applied to anti-de Sitter regular black holes. We also present an
analytical expression for the maximal volume outside the de Sitter horizon.
|
[
{
"created": "Fri, 17 Feb 2017 07:51:33 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Jan 2018 09:52:01 GMT",
"version": "v2"
}
] |
2018-01-31
|
[
[
"Wang",
"Shao-Jun",
""
],
[
"Guo",
"Xin-Xuan",
""
],
[
"Wang",
"Towe",
""
]
] |
The black hole information paradox is related to the area of event horizon, and potentially to the volume and singularity behind it. One example is the complexity/volume duality conjectured by Stanford and Susskind. Accepting the proposal of Christodoulou and Rovelli, we calculate the maximal volume inside regular black holes, which are free of curvature singularity, in asymptotically flat and anti-de Sitter spacetimes respectively. The complexity/volume duality is then applied to anti-de Sitter regular black holes. We also present an analytical expression for the maximal volume outside the de Sitter horizon.
|
gr-qc/0002003
|
Leonid Ya. Kobelev
|
L.Ya.Kobelev
|
Maxwell equation, Shroedinger equation, Dirac equation, Einstein
equation defined on the multifractal sets of the time and the space
|
RevTeX
| null | null | null |
gr-qc
| null |
What forms will have an equations of modern physics if the dimensions of our
time and space are fractional? The generalized equations enumerated by title
are presented by help the generalized fractional derivatives of
Riemann-Liouville.
|
[
{
"created": "Tue, 1 Feb 2000 10:23:15 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Kobelev",
"L. Ya.",
""
]
] |
What forms will have an equations of modern physics if the dimensions of our time and space are fractional? The generalized equations enumerated by title are presented by help the generalized fractional derivatives of Riemann-Liouville.
|
1712.09878
|
Kristina Giesel
|
Kristina Giesel, Adrian Herzog
|
Gauge invariant canonical cosmological perturbation theory with
geometrical clocks in extended phase space - a review and applications
|
Added some references, corrected typos
|
Int. J. Mod. Phys. D 27, 1830005 (2018)
|
10.1142/S0218271818300057
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The theory of cosmological perturbations is a well elaborated field. To deal
with the diffeomorphism invariance of general relativity one generally
introduces combinations of the metric and matter perturbations which are gauge
invariant up to the considered order in the perturbations. For linear
cosmological perturbations one works with the so-called Bardeen potentials
widely used in this context. However, there exists no common procedure to
construct gauge invariant quantities also for higher order perturbations.
Usually, one has to find new gauge invariant quantities independently for each
order in perturbation theory. With the relational formalism introduced by
Rovelli and further developed by Dittrich and Thiemann, it is in principle
possible to calculate manifestly gauge invariant quantities, that is quantities
that are gauge invariant up to arbitrary order once one has chosen a set of
so-called reference fields, often also called clock fields. This article
contains a review of the relational formalism and its application to canonical
general relativity following the work of Garcia, Pons, Sundermeyer and
Salisbury. As the starting point for our application of this formalism to
cosmological perturbation theory, we also review the Hamiltonian formulation of
the linearized theory for perturbations around FLRW spacetimes. The main aim of
our work will be to identify clock fields in the context of the relational
formalism that can be used to reconstruct quantities like the Bardeen potential
as well as the Mukhanov-Sasaki variable. This requires a careful analysis of
the canonical formulation in the extended ADM-phase space where lapse and shift
are treated as dynamical variables. The actual construction of such observables
and further investigations thereof will be carried out in our companion paper.
|
[
{
"created": "Thu, 28 Dec 2017 14:51:27 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Mar 2018 14:19:27 GMT",
"version": "v2"
}
] |
2018-05-31
|
[
[
"Giesel",
"Kristina",
""
],
[
"Herzog",
"Adrian",
""
]
] |
The theory of cosmological perturbations is a well elaborated field. To deal with the diffeomorphism invariance of general relativity one generally introduces combinations of the metric and matter perturbations which are gauge invariant up to the considered order in the perturbations. For linear cosmological perturbations one works with the so-called Bardeen potentials widely used in this context. However, there exists no common procedure to construct gauge invariant quantities also for higher order perturbations. Usually, one has to find new gauge invariant quantities independently for each order in perturbation theory. With the relational formalism introduced by Rovelli and further developed by Dittrich and Thiemann, it is in principle possible to calculate manifestly gauge invariant quantities, that is quantities that are gauge invariant up to arbitrary order once one has chosen a set of so-called reference fields, often also called clock fields. This article contains a review of the relational formalism and its application to canonical general relativity following the work of Garcia, Pons, Sundermeyer and Salisbury. As the starting point for our application of this formalism to cosmological perturbation theory, we also review the Hamiltonian formulation of the linearized theory for perturbations around FLRW spacetimes. The main aim of our work will be to identify clock fields in the context of the relational formalism that can be used to reconstruct quantities like the Bardeen potential as well as the Mukhanov-Sasaki variable. This requires a careful analysis of the canonical formulation in the extended ADM-phase space where lapse and shift are treated as dynamical variables. The actual construction of such observables and further investigations thereof will be carried out in our companion paper.
|
gr-qc/0006063
|
Manfred Requardt
|
Manfred Requardt
|
Let's call it Nonlocal Quantum Physics
|
47 pages, Latex, no figures
| null | null | null |
gr-qc hep-th quant-ph
| null |
In the following we undertake to derive quantum theory as a stochastic
low-energy and coarse-grained theory from a more primordial discrete and
basically geometric theory living on the Planck scale and which (as we argue)
possibly underlies also \tit{string theory}. We isolate the so-called
\tit{ideal elements} which represent at the same time the cornerstones of the
framework of ordinary quantum theory and show how and why they encode the
\tit{non-local} aspects, being ubiquituous in the quantum realm, in a, on the
surface, local way. We show that the quantum non-locality emerges in our
approach as a natural consequence of the underlying \tit{two-storey} nature of
space-time or the physical vacuum, that is, quantum theory turns out to be a
residual effect of the geometric depth structure of space-time on the Planck
scale. We indicate how the \tit{measurement problem} and the emergence of the
\tit{macroscopic sub-regime} can be understood in this framework.
|
[
{
"created": "Mon, 19 Jun 2000 08:56:17 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Requardt",
"Manfred",
""
]
] |
In the following we undertake to derive quantum theory as a stochastic low-energy and coarse-grained theory from a more primordial discrete and basically geometric theory living on the Planck scale and which (as we argue) possibly underlies also \tit{string theory}. We isolate the so-called \tit{ideal elements} which represent at the same time the cornerstones of the framework of ordinary quantum theory and show how and why they encode the \tit{non-local} aspects, being ubiquituous in the quantum realm, in a, on the surface, local way. We show that the quantum non-locality emerges in our approach as a natural consequence of the underlying \tit{two-storey} nature of space-time or the physical vacuum, that is, quantum theory turns out to be a residual effect of the geometric depth structure of space-time on the Planck scale. We indicate how the \tit{measurement problem} and the emergence of the \tit{macroscopic sub-regime} can be understood in this framework.
|
2402.18237
|
Houri Ziaeepour
|
Houri Ziaeepour
|
Quantum state of fields in $SU(\infty)$ Quantum Gravity
($SU(\infty)$-QGR)
|
18+12 pages, 1 figure. v2: citation extended
| null | null | null |
gr-qc hep-th quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Our Universe is ruled by quantum mechanics and should be treated as a quantum
system. {$SU(\infty)$-QGR is a recently proposed quantum model for the
Universe, in which gravity is associated to $SU(\infty)$ symmetry of its
Hilbert space. Clustering/blockization of its infinite dimensional state due to
random quantum fluctuations divides the Universe to approximately isolated
subsystems. In addition to parameters of their {\it internal} finite rank
symmetries, states and dynamics of subsystems are characterized by 4 continuous
parameters, and the perceived classical spacetime is their effective
representation, reflecting quantum states of subsystems and their relative
evolution. At lowest order the effective Lagrangian of {$SU(\infty)$-QGR has
the form of Yang-Mills gauge theories for both $SU(\infty)$ - gravity - and
internal symmetries defined on the aforementioned 4D parameter space. In the
present work we study more thoroughly some of the fundamental aspects of
{$SU(\infty)$-QGR. Specifically, we clarify impact of the degeneracy of
$\mathcal{SU}(\infty)$; describe mixed states of subsystems and their
purification; calculate measures of their entanglement to the rest of the
Universe; and discuss their role in the emergence of local gauge symmetries. We
also describe the relationship between what is called {\it internal space} of
$SU(\infty)$ Yang-Mills with the 4D parameter space, and analytically
demonstrate irrelevance of the geometry of parameter space for physical
observables. Along with these topics, we demonstrate the equivalence of two
sets of criteria for compositeness of a quantum system, and show uniqueness of
the limit of various algebras leading to $\mathcal{SU}(\infty)$.
|
[
{
"created": "Wed, 28 Feb 2024 11:06:45 GMT",
"version": "v1"
},
{
"created": "Sun, 7 Jul 2024 09:20:29 GMT",
"version": "v2"
}
] |
2024-07-09
|
[
[
"Ziaeepour",
"Houri",
""
]
] |
Our Universe is ruled by quantum mechanics and should be treated as a quantum system. {$SU(\infty)$-QGR is a recently proposed quantum model for the Universe, in which gravity is associated to $SU(\infty)$ symmetry of its Hilbert space. Clustering/blockization of its infinite dimensional state due to random quantum fluctuations divides the Universe to approximately isolated subsystems. In addition to parameters of their {\it internal} finite rank symmetries, states and dynamics of subsystems are characterized by 4 continuous parameters, and the perceived classical spacetime is their effective representation, reflecting quantum states of subsystems and their relative evolution. At lowest order the effective Lagrangian of {$SU(\infty)$-QGR has the form of Yang-Mills gauge theories for both $SU(\infty)$ - gravity - and internal symmetries defined on the aforementioned 4D parameter space. In the present work we study more thoroughly some of the fundamental aspects of {$SU(\infty)$-QGR. Specifically, we clarify impact of the degeneracy of $\mathcal{SU}(\infty)$; describe mixed states of subsystems and their purification; calculate measures of their entanglement to the rest of the Universe; and discuss their role in the emergence of local gauge symmetries. We also describe the relationship between what is called {\it internal space} of $SU(\infty)$ Yang-Mills with the 4D parameter space, and analytically demonstrate irrelevance of the geometry of parameter space for physical observables. Along with these topics, we demonstrate the equivalence of two sets of criteria for compositeness of a quantum system, and show uniqueness of the limit of various algebras leading to $\mathcal{SU}(\infty)$.
|
1802.02334
|
Tuhina Manna
|
Tuhina Manna, Farook Rahaman, Sabiruddin Molla, Jhumpa Bhadra and
Hasrat Hussain Shah
|
Strong Lensing of a Regular Black Hole with an Electrodynamics Source
|
Accepted in General Relativity and Gravitation
|
Gen.Rel.Grav. 50 (2018) 5, 54
|
10.1007/s10714-018-2375-3
|
GERG-D-18-00048
|
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper we have investigated the gravitational lensing phenomenon in
the strong field regime for a regular, charged, static, non-linear black hole
having a electrodynamics source. We have obtained the angle of deflection and
compared it to a Schwarzschild black hole and Reissner Nordstrom black hole
with similar properties. We have also done a graphical study of the
relativistic image positions and magnifications. We hope that this method may
be useful in the detection of non-luminous bodies like this current black hole.
|
[
{
"created": "Wed, 7 Feb 2018 08:01:26 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Mar 2018 17:11:36 GMT",
"version": "v2"
},
{
"created": "Wed, 8 Nov 2023 15:29:54 GMT",
"version": "v3"
}
] |
2023-11-09
|
[
[
"Manna",
"Tuhina",
""
],
[
"Rahaman",
"Farook",
""
],
[
"Molla",
"Sabiruddin",
""
],
[
"Bhadra",
"Jhumpa",
""
],
[
"Shah",
"Hasrat Hussain",
""
]
] |
In this paper we have investigated the gravitational lensing phenomenon in the strong field regime for a regular, charged, static, non-linear black hole having a electrodynamics source. We have obtained the angle of deflection and compared it to a Schwarzschild black hole and Reissner Nordstrom black hole with similar properties. We have also done a graphical study of the relativistic image positions and magnifications. We hope that this method may be useful in the detection of non-luminous bodies like this current black hole.
|
gr-qc/9801077
|
Alfio Bonanno
|
Alfio Bonanno (Istituto di Astronomia, Catania)
|
The Cauchy Horizon in Higher-derivative Gravity Theories
|
REVTex, 13 pages, to appear on the proceedings of the workshop on "
The Internal Structure of Black Holes and Spacetime Singularities", held at
Technion -Israel Institute of Technology-, Haifa,Israel,June 29-July 3, 1997
| null | null |
Istituto di Astronomia, preprint 2-1998
|
gr-qc
| null |
A class of exact solutions of the field equations with higher derivative
terms is presented when the matter field is a pressureless null fluid plus a
Maxwellian static electric component. It is found that the stable solutions are
black holes in anti de Sitter background. The issue of the stability of the
Cauchy horizon is discussed.
|
[
{
"created": "Thu, 22 Jan 1998 12:35:38 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Bonanno",
"Alfio",
"",
"Istituto di Astronomia, Catania"
]
] |
A class of exact solutions of the field equations with higher derivative terms is presented when the matter field is a pressureless null fluid plus a Maxwellian static electric component. It is found that the stable solutions are black holes in anti de Sitter background. The issue of the stability of the Cauchy horizon is discussed.
|
1801.03426
|
Vasilis Oikonomou
|
V.K. Oikonomou
|
Exponential Inflation with $F(R)$ Gravity
|
PRD Accepted
|
Phys. Rev. D 97, 064001 (2018)
|
10.1103/PhysRevD.97.064001
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper we shall consider an exponential inflationary model in the
context of vacuum $F(R)$ gravity. By using well-known reconstruction
techniques, we shall investigate which $F(R)$ gravity can realize the
exponential inflation scenario at leading order in terms of the scalar
curvature, and we shall calculate the slow-roll indices and the corresponding
observational indices, in the context of slow-roll inflation. We also provide
some general formulas of the slow-roll and the corresponding observational
indices in terms of the $e$-foldings number. In addition, for the calculation
of the slow-roll and of the observational indices, we shall consider quite
general formulas for which the assumption that all the slow-roll indices are
much smaller than unity, is not necessary to hold true. Finally, we investigate
the phenomenological viability of the model by comparing it with the latest
Planck and BICEP2/Keck-Array observational data. As we demonstrate, the model
is compatible with the current observational data for a wide range of the free
parameters of the model.
|
[
{
"created": "Wed, 10 Jan 2018 15:46:03 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Feb 2018 01:57:25 GMT",
"version": "v2"
}
] |
2018-03-14
|
[
[
"Oikonomou",
"V. K.",
""
]
] |
In this paper we shall consider an exponential inflationary model in the context of vacuum $F(R)$ gravity. By using well-known reconstruction techniques, we shall investigate which $F(R)$ gravity can realize the exponential inflation scenario at leading order in terms of the scalar curvature, and we shall calculate the slow-roll indices and the corresponding observational indices, in the context of slow-roll inflation. We also provide some general formulas of the slow-roll and the corresponding observational indices in terms of the $e$-foldings number. In addition, for the calculation of the slow-roll and of the observational indices, we shall consider quite general formulas for which the assumption that all the slow-roll indices are much smaller than unity, is not necessary to hold true. Finally, we investigate the phenomenological viability of the model by comparing it with the latest Planck and BICEP2/Keck-Array observational data. As we demonstrate, the model is compatible with the current observational data for a wide range of the free parameters of the model.
|
1411.1943
|
Marcello Ortaggio
|
Marcello Ortaggio, Jiri Podolsky, Martin Zofka
|
Static and radiating p-form black holes in the higher dimensional
Robinson-Trautman class
|
34 pages. v2: improved discussion following eq. (84), references
updated, minor changes to match the published version
|
JHEP 1502 (2015) 045
|
10.1007/JHEP02(2015)045
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study Robinson-Trautman spacetimes in the presence of an aligned p-form
Maxwell field and an arbitrary cosmological constant in n>=4 dimensions. As it
turns out, the character of these exact solutions depends significantly on the
(relative) value of n and p. In odd dimensions the solutions reduce to static
black holes dressed by an electric and a magnetic field and whose horizon is an
Einstein space (further constrained by the Einstein-Maxwell equations) -- both
the Weyl and Maxwell type are D. Even dimensions, however, open up more
possibilities. In particular, when 2p=n there exist non-static solutions
describing black holes acquiring (or losing) mass by receiving (or emitting)
electromagnetic radiation. In this case the Weyl type is II (D) and the Maxwell
type can be II (D) or N. Conditions under which the Maxwell field is self-dual
(for odd p) are also discussed, and a few explicit examples presented. Finally,
the case p=1 is special in all dimensions and leads to static metrics with a
non-Einstein transverse space.
|
[
{
"created": "Fri, 7 Nov 2014 15:05:15 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Mar 2015 15:20:00 GMT",
"version": "v2"
}
] |
2015-03-03
|
[
[
"Ortaggio",
"Marcello",
""
],
[
"Podolsky",
"Jiri",
""
],
[
"Zofka",
"Martin",
""
]
] |
We study Robinson-Trautman spacetimes in the presence of an aligned p-form Maxwell field and an arbitrary cosmological constant in n>=4 dimensions. As it turns out, the character of these exact solutions depends significantly on the (relative) value of n and p. In odd dimensions the solutions reduce to static black holes dressed by an electric and a magnetic field and whose horizon is an Einstein space (further constrained by the Einstein-Maxwell equations) -- both the Weyl and Maxwell type are D. Even dimensions, however, open up more possibilities. In particular, when 2p=n there exist non-static solutions describing black holes acquiring (or losing) mass by receiving (or emitting) electromagnetic radiation. In this case the Weyl type is II (D) and the Maxwell type can be II (D) or N. Conditions under which the Maxwell field is self-dual (for odd p) are also discussed, and a few explicit examples presented. Finally, the case p=1 is special in all dimensions and leads to static metrics with a non-Einstein transverse space.
|
2407.19017
|
Arwa Elhashash
|
Arwa Elhashash, David A. Nichols
|
Waveform models for the gravitational-wave memory effect: Extreme
mass-ratio limit and final memory offset
|
23 pages, 13 figures
| null | null | null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The gravitational-wave (GW) memory effect is a strong-field relativistic
phenomenon that is associated with a persistent change in the GW strain after
the passage of a GW. The nonlinear effect arises from interactions of GWs
themselves in the wave zone and is an observable effect connected to the
infrared properties of general relativity. The detection of the GW memory
effect is possible with LIGO and Virgo in a population of binary-black-hole
(BBH) mergers or from individual events with next-generation ground- and
space-based GW detectors or pulsar timing arrays. Matched-filtering-based
searches for the GW memory require accurate, and preferably rapid-to-evaluate
waveform models of the memory effect's GW signal. One important element of such
a waveform model is a model for the final memory offset -- namely, the net
change in strain between early and late times. In this paper, we construct a
model for the final memory offset from the merger of nonspinning BBH systems in
quasicircular orbits. A novel ingredient of this model is that we first compute
the memory signal for extreme mass-ratio inspirals using a high
post-Newtonian-order analytic calculation, and we use this analytical result to
fix the coefficient in the fit which is linear in the mass-ratio. The resulting
memory-offset fit could be used for detecting the GW memory for binaries that
merge on a timescale that is short relative to the inverse of the low-frequency
cutoff of a GW detector. Additionally, this fit will be useful for analytic
waveform models of the GW memory signals in the time and frequency domains.
|
[
{
"created": "Fri, 26 Jul 2024 18:01:06 GMT",
"version": "v1"
}
] |
2024-07-30
|
[
[
"Elhashash",
"Arwa",
""
],
[
"Nichols",
"David A.",
""
]
] |
The gravitational-wave (GW) memory effect is a strong-field relativistic phenomenon that is associated with a persistent change in the GW strain after the passage of a GW. The nonlinear effect arises from interactions of GWs themselves in the wave zone and is an observable effect connected to the infrared properties of general relativity. The detection of the GW memory effect is possible with LIGO and Virgo in a population of binary-black-hole (BBH) mergers or from individual events with next-generation ground- and space-based GW detectors or pulsar timing arrays. Matched-filtering-based searches for the GW memory require accurate, and preferably rapid-to-evaluate waveform models of the memory effect's GW signal. One important element of such a waveform model is a model for the final memory offset -- namely, the net change in strain between early and late times. In this paper, we construct a model for the final memory offset from the merger of nonspinning BBH systems in quasicircular orbits. A novel ingredient of this model is that we first compute the memory signal for extreme mass-ratio inspirals using a high post-Newtonian-order analytic calculation, and we use this analytical result to fix the coefficient in the fit which is linear in the mass-ratio. The resulting memory-offset fit could be used for detecting the GW memory for binaries that merge on a timescale that is short relative to the inverse of the low-frequency cutoff of a GW detector. Additionally, this fit will be useful for analytic waveform models of the GW memory signals in the time and frequency domains.
|
1903.04845
|
Mohammad Ali Gorji
|
Mohammad Ali Gorji, Shinji Mukohyama, Hassan Firouzjahi
|
Cosmology in Mimetic SU(2) Gauge Theory
|
18 pages, 14 figures
|
JCAP 2019 (2020) no.05, 019
|
10.1088/1475-7516/2019/05/019
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
It is well known that the standard scalar field mimetic cosmology provides a
dark matter-like energy density component. Considering $SU(2)$ gauge symmetry,
we study the gauge field extension of the mimetic scenario in spatially flat
and curved FLRW spacetimes. Because of the mimetic constraint, the standard
Yang-Mills term plays the role of the cosmological constant while the mimetic
term provides two different contributions: one is the standard radiation
scaling like $ a^{-4}$ while the other contribution in energy density scales as
$\propto a^{-2}$. Consequently, in the Friedmann equation we have two different
energy densities which scale as $\propto a^{-2}$: one is the mimetic spatial
curvature-like and the other is the standard spatial curvature which can
compete with each other. The degeneracy between these two contributions are
disentangled in this scenario since the mimetic spatial curvature-like term
shows up only at the dynamical level while the standard spatial curvature term
shows up at both dynamical and kinematical levels.
|
[
{
"created": "Tue, 12 Mar 2019 11:18:06 GMT",
"version": "v1"
}
] |
2019-06-03
|
[
[
"Gorji",
"Mohammad Ali",
""
],
[
"Mukohyama",
"Shinji",
""
],
[
"Firouzjahi",
"Hassan",
""
]
] |
It is well known that the standard scalar field mimetic cosmology provides a dark matter-like energy density component. Considering $SU(2)$ gauge symmetry, we study the gauge field extension of the mimetic scenario in spatially flat and curved FLRW spacetimes. Because of the mimetic constraint, the standard Yang-Mills term plays the role of the cosmological constant while the mimetic term provides two different contributions: one is the standard radiation scaling like $ a^{-4}$ while the other contribution in energy density scales as $\propto a^{-2}$. Consequently, in the Friedmann equation we have two different energy densities which scale as $\propto a^{-2}$: one is the mimetic spatial curvature-like and the other is the standard spatial curvature which can compete with each other. The degeneracy between these two contributions are disentangled in this scenario since the mimetic spatial curvature-like term shows up only at the dynamical level while the standard spatial curvature term shows up at both dynamical and kinematical levels.
|
gr-qc/0401061
|
Muhammad Sharif
|
M. Sharif
|
Symmetries of the Energy-Momentum Tensor of Cylindrically Symmetric
Static Spacetimes
|
42 pages, no figure, LaTeX, Accepted for publication in J. Math. Phys
|
J.Math.Phys. 45 (2004) 1532-1560
|
10.1063/1.1668335
| null |
gr-qc
| null |
We investigate matter symmetries of cylindrically symmetric static
spacetimes. These are classified for both cases when the energy-momentum tensor
is non-degenerate and also when it is degenerate. It is found that the
non-degenerate energy-momentum tensor gives either three, four, five, six,
seven or ten independent matter collineations in which three are isometries and
the rest are proper. The worth mentioning cases are those where we obtain the
group of matter collineations finite-dimensional even the energy-momentum
tensor is degenerate. These are either three, four, five or ten. Some examples
are constructed satisfying the constraints on the energy-momentum tensor.
|
[
{
"created": "Wed, 14 Jan 2004 12:44:23 GMT",
"version": "v1"
}
] |
2015-06-25
|
[
[
"Sharif",
"M.",
""
]
] |
We investigate matter symmetries of cylindrically symmetric static spacetimes. These are classified for both cases when the energy-momentum tensor is non-degenerate and also when it is degenerate. It is found that the non-degenerate energy-momentum tensor gives either three, four, five, six, seven or ten independent matter collineations in which three are isometries and the rest are proper. The worth mentioning cases are those where we obtain the group of matter collineations finite-dimensional even the energy-momentum tensor is degenerate. These are either three, four, five or ten. Some examples are constructed satisfying the constraints on the energy-momentum tensor.
|
2005.02616
|
Konstantin Osetrin
|
Evgeny Osetrin, Konstantin Osetrin, Altair Filippov, Ilya Kirnos
|
Wave-like spatially homogeneous models of Stackel spacetimes (3.1) type
in the scalar-tensor theory of gravity
|
7 pages
|
International Journal of Geometric Methods in Modern Physics, 2020
|
10.1142/S0219887820501844
| null |
gr-qc math-ph math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
All classes of spatially homogeneous space-time models in the generalized
scalar-tensor theory of gravity are found that allow the integration of the
equations of motion of test particles and the eikonal equation by the method of
%complete separation of variables by type (3.1). Three classes of exact
solutions are obtained that relate to wave-like spacetime models. The resulting
spacetime models are of type IV, VI, and VII according to the Bianchi
classification and type N according to Petrov's classification.
|
[
{
"created": "Wed, 6 May 2020 06:54:55 GMT",
"version": "v1"
}
] |
2020-10-06
|
[
[
"Osetrin",
"Evgeny",
""
],
[
"Osetrin",
"Konstantin",
""
],
[
"Filippov",
"Altair",
""
],
[
"Kirnos",
"Ilya",
""
]
] |
All classes of spatially homogeneous space-time models in the generalized scalar-tensor theory of gravity are found that allow the integration of the equations of motion of test particles and the eikonal equation by the method of %complete separation of variables by type (3.1). Three classes of exact solutions are obtained that relate to wave-like spacetime models. The resulting spacetime models are of type IV, VI, and VII according to the Bianchi classification and type N according to Petrov's classification.
|
gr-qc/0409090
|
Thomas Roman
|
Thomas A. Roman
|
Some Thoughts on Energy Conditions and Wormholes
|
24 pages; to appear in the Proceedings of the Tenth Marcel Grossmann
Meeting on General Relativity and Gravitation
| null |
10.1142/9789812704030_0236
| null |
gr-qc hep-th quant-ph
| null |
This essay reviews some of the recent progress in the area of energy
conditions and wormholes. Most of the discussion centers on the subject of
``quantum inequality'' restrictions on negative energy. These are bounds on the
magnitude and duration of negative energy which put rather severe constraints
on its possible macroscopic effects. Such effects might include the
construction of wormholes and warp drives for faster-than-light travel, and
violations of the second law of thermodynamics. Open problems and future
directions are also discussed.
|
[
{
"created": "Thu, 23 Sep 2004 15:56:37 GMT",
"version": "v1"
}
] |
2016-11-09
|
[
[
"Roman",
"Thomas A.",
""
]
] |
This essay reviews some of the recent progress in the area of energy conditions and wormholes. Most of the discussion centers on the subject of ``quantum inequality'' restrictions on negative energy. These are bounds on the magnitude and duration of negative energy which put rather severe constraints on its possible macroscopic effects. Such effects might include the construction of wormholes and warp drives for faster-than-light travel, and violations of the second law of thermodynamics. Open problems and future directions are also discussed.
|
2405.08857
|
Michele Vallisneri
|
Michele Vallisneri, Marco Crisostomi, Aaron D. Johnson, Patrick M.
Meyers
|
Rapid parameter estimation for pulsar-timing-array datasets with
variational inference and normalizing flows
|
6 pages, 1 figure
| null | null | null |
gr-qc astro-ph.HE astro-ph.IM
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the gravitational-wave analysis of pulsar-timing-array datasets, parameter
estimation is usually performed using Markov Chain Monte Carlo methods to
explore posterior probability densities. We introduce an alternative procedure
that relies instead on stochastic gradient-descent Bayesian variational
inference, whereby we obtain the weights of a neural-network approximation of
the posterior by minimizing the Kullback-Leibler divergence of the
approximation from the exact posterior. This technique is distinct from
simulation-based inference with normalizing flows, since we train the network
for a single dataset, rather than the population of all possible datasets, and
we require the computation of the data likelihood and its gradient. Unlike
Markov Chain methods, our technique can transparently exploit highly parallel
computing platforms. This makes it extremely fast on modern graphical
processing units, where it can analyze the NANOGrav 15-yr dataset in few tens
of minutes, depending on the probabilistic model, as opposed to hours or days
with the analysis codes used until now. We expect that this speed will unlock
new kinds of astrophysical and cosmological studies of pulsar-timing-array
datasets. Furthermore, variational inference would be viable in other contexts
of gravitational-wave data analysis as long as differentiable and
parallelizable likelihoods are available.
|
[
{
"created": "Tue, 14 May 2024 18:00:00 GMT",
"version": "v1"
}
] |
2024-05-16
|
[
[
"Vallisneri",
"Michele",
""
],
[
"Crisostomi",
"Marco",
""
],
[
"Johnson",
"Aaron D.",
""
],
[
"Meyers",
"Patrick M.",
""
]
] |
In the gravitational-wave analysis of pulsar-timing-array datasets, parameter estimation is usually performed using Markov Chain Monte Carlo methods to explore posterior probability densities. We introduce an alternative procedure that relies instead on stochastic gradient-descent Bayesian variational inference, whereby we obtain the weights of a neural-network approximation of the posterior by minimizing the Kullback-Leibler divergence of the approximation from the exact posterior. This technique is distinct from simulation-based inference with normalizing flows, since we train the network for a single dataset, rather than the population of all possible datasets, and we require the computation of the data likelihood and its gradient. Unlike Markov Chain methods, our technique can transparently exploit highly parallel computing platforms. This makes it extremely fast on modern graphical processing units, where it can analyze the NANOGrav 15-yr dataset in few tens of minutes, depending on the probabilistic model, as opposed to hours or days with the analysis codes used until now. We expect that this speed will unlock new kinds of astrophysical and cosmological studies of pulsar-timing-array datasets. Furthermore, variational inference would be viable in other contexts of gravitational-wave data analysis as long as differentiable and parallelizable likelihoods are available.
|
1605.06635
|
Michael Good
|
Michael R.R. Good, Paul R. Anderson, and Charles R. Evans
|
Mirror Reflections of a Black Hole
|
25 pages, 7 figures
|
Phys. Rev. D 94, 065010 (2016)
|
10.1103/PhysRevD.94.065010
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
An exact correspondence between a black hole and an accelerating mirror is
demonstrated. It is shown that for a massless minimally coupled scalar field
the same Bogolubov coefficients connecting the "in" and "out" states occur for
a (1+1)D flat spacetime with a particular perfectly reflecting accelerating
boundary trajectory and a (1+1)D curved spacetime in which a null shell
collapses to form a black hole. Generalization of the latter to the (3+1)D case
is discussed. The spectral dynamics is computed in both (1+1)-dimensional
spacetimes along with the energy flux in the spacetime with a mirror. It is
shown that the approach to equilibrium is monotonic, asymmetric in terms of the
rate, and there is a specific time which characterizes the system when it is
the most out-of-equilibrium.
|
[
{
"created": "Sat, 21 May 2016 12:23:10 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Sep 2016 15:10:29 GMT",
"version": "v2"
}
] |
2016-09-26
|
[
[
"Good",
"Michael R. R.",
""
],
[
"Anderson",
"Paul R.",
""
],
[
"Evans",
"Charles R.",
""
]
] |
An exact correspondence between a black hole and an accelerating mirror is demonstrated. It is shown that for a massless minimally coupled scalar field the same Bogolubov coefficients connecting the "in" and "out" states occur for a (1+1)D flat spacetime with a particular perfectly reflecting accelerating boundary trajectory and a (1+1)D curved spacetime in which a null shell collapses to form a black hole. Generalization of the latter to the (3+1)D case is discussed. The spectral dynamics is computed in both (1+1)-dimensional spacetimes along with the energy flux in the spacetime with a mirror. It is shown that the approach to equilibrium is monotonic, asymmetric in terms of the rate, and there is a specific time which characterizes the system when it is the most out-of-equilibrium.
|
gr-qc/0006045
|
Marcus Ansorg
|
Marcus Ansorg
|
Differentially rotating disks of dust: Arbitrary rotation law
|
23 pages, 3 figures, submitted to 'General Relativity and
Gravitation'
|
Gen.Rel.Grav. 33 (2001) 309-338
|
10.1023/A:1002705402248
| null |
gr-qc
| null |
In this paper, solutions to the Ernst equation are investigated that depend
on two real analytic functions defined on the interval [0,1]. These solutions
are introduced by a suitable limiting process of Backlund transformations
applied to seed solutions of the Weyl class. It turns out that this class of
solutions contains the general relativistic gravitational field of an arbitrary
differentially rotating disk of dust, for which a continuous transition to some
Newtonian disk exists. It will be shown how for given boundary conditions (i.
e. proper surface mass density or angular velocity of the disk) the
gravitational field can be approximated in terms of the above solutions.
Furthermore, particular examples will be discussed, including disks with a
realistic profile for the angular velocity and more exotic disks possessing two
spatially separated ergoregions.
|
[
{
"created": "Tue, 13 Jun 2000 12:35:47 GMT",
"version": "v1"
}
] |
2015-06-25
|
[
[
"Ansorg",
"Marcus",
""
]
] |
In this paper, solutions to the Ernst equation are investigated that depend on two real analytic functions defined on the interval [0,1]. These solutions are introduced by a suitable limiting process of Backlund transformations applied to seed solutions of the Weyl class. It turns out that this class of solutions contains the general relativistic gravitational field of an arbitrary differentially rotating disk of dust, for which a continuous transition to some Newtonian disk exists. It will be shown how for given boundary conditions (i. e. proper surface mass density or angular velocity of the disk) the gravitational field can be approximated in terms of the above solutions. Furthermore, particular examples will be discussed, including disks with a realistic profile for the angular velocity and more exotic disks possessing two spatially separated ergoregions.
|
1906.04048
|
Pardyumn Kumar Sahoo
|
Parbati Sahoo, Annika Kirschner, P.K. Sahoo
|
Phantom fluid wormhole in $f(R,T)$ gravity
|
12 pages, 8 Figures. Revision submitted to MPLA
|
Modern Physics Letters A 34(37), (2019), 1950303
|
10.1142/S0217732319503036
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Wormholes (WHs) are considered as hypothetical shortcuts or tunnels in
spacetime. In general relativity (GR), the fundamental ingredient of WH
geometry is the presence of exotic matter at the throat, which is responsible
for the violation of null energy condition (NEC). However, the modified gravity
theories has shown to be able to provide WH solutions satisfying energy
conditions (ECs). In this paper, we study the static spherically symmetric WH
solutions in modified $f(R,T)$ gravity for a phantom fluid case. The exact
solutions of this model are obtained through the equation of state (EoS),
$p=\omega \rho$, associated with phantom dark energy (DE) $\omega<-1$. We find
the existence of spherically symmetric WH solution supported by phantom energy
distribution. The shape function of the WH is obtained in this model obeys all
the WH metric conditions. In modified gravity scenario the phantom fluid WH
violates the NEC in radial case, unlike in the tangential case. Furthermore,
using the "volume integral quantifier" (VIQ) method, the total amount of EC
violating matter in spacetime is discussed briefly.
|
[
{
"created": "Fri, 7 Jun 2019 16:01:13 GMT",
"version": "v1"
}
] |
2020-02-19
|
[
[
"Sahoo",
"Parbati",
""
],
[
"Kirschner",
"Annika",
""
],
[
"Sahoo",
"P. K.",
""
]
] |
Wormholes (WHs) are considered as hypothetical shortcuts or tunnels in spacetime. In general relativity (GR), the fundamental ingredient of WH geometry is the presence of exotic matter at the throat, which is responsible for the violation of null energy condition (NEC). However, the modified gravity theories has shown to be able to provide WH solutions satisfying energy conditions (ECs). In this paper, we study the static spherically symmetric WH solutions in modified $f(R,T)$ gravity for a phantom fluid case. The exact solutions of this model are obtained through the equation of state (EoS), $p=\omega \rho$, associated with phantom dark energy (DE) $\omega<-1$. We find the existence of spherically symmetric WH solution supported by phantom energy distribution. The shape function of the WH is obtained in this model obeys all the WH metric conditions. In modified gravity scenario the phantom fluid WH violates the NEC in radial case, unlike in the tangential case. Furthermore, using the "volume integral quantifier" (VIQ) method, the total amount of EC violating matter in spacetime is discussed briefly.
|
gr-qc/9806084
|
Dr. BG Sidharth
|
B.G. Sidharth
|
Space Time Quantization and the Big Bang
|
5 pages, TeX
| null | null | null |
gr-qc
| null |
A recent cosmological model is recapitulated which deduces the correct mass,
radius and age of the universe as also the Hubble constant and other well known
apparently coincidental relations. It also predicts an ever expanding
accelerating universe as is confirmed by latest supernovae observations.
Finally the Big Bang model is recovered as a suitable limiting case.
|
[
{
"created": "Sun, 21 Jun 1998 02:49:15 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Sidharth",
"B. G.",
""
]
] |
A recent cosmological model is recapitulated which deduces the correct mass, radius and age of the universe as also the Hubble constant and other well known apparently coincidental relations. It also predicts an ever expanding accelerating universe as is confirmed by latest supernovae observations. Finally the Big Bang model is recovered as a suitable limiting case.
|
gr-qc/9903077
|
N. K. Dadhich
|
Naresh Dadhich and L.K. Patel
|
A simple shear-free non-singular spherical model with heat flux
|
7 pages, LaTEX version
|
Grav.Cosmol. 6 (2000) 11-13
| null |
IUCAA-14/99
|
gr-qc
| null |
We obtain an exact simple solution of the Einstein equation describing a
spherically symmetric cosmological model without the big-bang or any other kind
of singularity. The matter content of the model is shear free isotropic fluid
with radial heat flux and it satisfies the weak and strong energy conditions.
It is pressure gradient combined with heat flux that prevents occurrence of
singularity. So far all known non-singular models have non-zero shear. This is
the first shear free non-singular model, which is also spherically symmetric.
|
[
{
"created": "Sat, 20 Mar 1999 07:14:28 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Dadhich",
"Naresh",
""
],
[
"Patel",
"L. K.",
""
]
] |
We obtain an exact simple solution of the Einstein equation describing a spherically symmetric cosmological model without the big-bang or any other kind of singularity. The matter content of the model is shear free isotropic fluid with radial heat flux and it satisfies the weak and strong energy conditions. It is pressure gradient combined with heat flux that prevents occurrence of singularity. So far all known non-singular models have non-zero shear. This is the first shear free non-singular model, which is also spherically symmetric.
|
0901.0603
|
Li Xiang
|
Li Xiang and X. Q. Wen
|
Black hole thermodynamics with generalized uncertainty principle
|
18 pages, great improvement on the first version; a Kerr-Newman black
hole is considered
|
JHEP 0910:046,2009
|
10.1088/1126-6708/2009/10/046
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the standard viewpoint, the temperature of a stationary black hole is
proportional to its surface gravity, $T_H=\hbar\kappa/2\pi$. This is a
semiclassical result and the quantum gravity effects are not taken into
consideration. This Letter explores a unified expression for the black hole
temperature in the sense of a generalized uncertainty principle(GUP). Our
discussion involves a heuristic analysis of a particle which is absorbed by the
black hole. Besides a class of static and spherically symmetric black holes, an
axially symmetric Kerr-Newman black hole is considered. Different from the
existing literature, we suggest that the black hole's irreducible mass
represent the characteristic size in the absorption process. The information
capacity of a remnant is also discussed by Bousso's D-bound in de Sitter
spacetime.
|
[
{
"created": "Tue, 6 Jan 2009 08:06:13 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Mar 2009 16:06:11 GMT",
"version": "v2"
}
] |
2009-11-19
|
[
[
"Xiang",
"Li",
""
],
[
"Wen",
"X. Q.",
""
]
] |
In the standard viewpoint, the temperature of a stationary black hole is proportional to its surface gravity, $T_H=\hbar\kappa/2\pi$. This is a semiclassical result and the quantum gravity effects are not taken into consideration. This Letter explores a unified expression for the black hole temperature in the sense of a generalized uncertainty principle(GUP). Our discussion involves a heuristic analysis of a particle which is absorbed by the black hole. Besides a class of static and spherically symmetric black holes, an axially symmetric Kerr-Newman black hole is considered. Different from the existing literature, we suggest that the black hole's irreducible mass represent the characteristic size in the absorption process. The information capacity of a remnant is also discussed by Bousso's D-bound in de Sitter spacetime.
|
2105.04283
|
Guillaume Boileau
|
Guillaume Boileau, Astrid Lamberts, Nelson Christensen, Neil J.
Cornish, Renate Meyer
|
Spectral separation of the stochastic gravitational-wave background for
LISA in the context of a modulated Galactic foreground
| null | null |
10.1093/mnras/stab2575
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Within its observational band the Laser Interferometer Space Antenna, LISA,
will simultaneously observe orbital modulated waveforms from Galactic white
dwarf binaries, a binary black hole produced gravitational-wave background, and
potentially a cosmologically created stochastic gravitational-wave background
(SGWB). The overwhelming majority of stars end their lives as white dwarfs,
making them very numerous in the Milky Way. We simulate Galactic white dwarf
binary gravitational-wave emission based on distributions from various mock
catalogs and determine a complex waveform from the Galactic foreground with
$3.5 \times 10^{7}$ binaries. We describe the effects from the Galactic binary
distribution population across mass, position within the Galaxy, core type, and
orbital frequency distribution. We generate the modulated Galactic white dwarf
signal detected by \textit{LISA} due to its orbital motion, and present a data
analysis strategy to address it. The Fisher Information and Markov Chain Monte
Carlo methods give an estimation of the \textit{LISA} noise and the parameters
for the different signal classes. We estimate the detectable limits for the
future LISA observation of the SGWB in the spectral domain with the 3
\textit{LISA} channels $A$, $E$, and $T$. We simultaneously estimate the
Galactic foreground, the astrophysical and cosmological backgrounds. Assuming
the expected astrophysical background and a Galactic foreground, a cosmological
background energy density of around $\Omega_{GW,Cosmo} \approx 8 \times
10^{-13}$ could be detected by LISA. LISA will either detect a cosmologically
produced SGWB, or set a limit that will have important consequences.
|
[
{
"created": "Mon, 10 May 2021 11:48:15 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Oct 2021 11:21:18 GMT",
"version": "v2"
}
] |
2021-10-08
|
[
[
"Boileau",
"Guillaume",
""
],
[
"Lamberts",
"Astrid",
""
],
[
"Christensen",
"Nelson",
""
],
[
"Cornish",
"Neil J.",
""
],
[
"Meyer",
"Renate",
""
]
] |
Within its observational band the Laser Interferometer Space Antenna, LISA, will simultaneously observe orbital modulated waveforms from Galactic white dwarf binaries, a binary black hole produced gravitational-wave background, and potentially a cosmologically created stochastic gravitational-wave background (SGWB). The overwhelming majority of stars end their lives as white dwarfs, making them very numerous in the Milky Way. We simulate Galactic white dwarf binary gravitational-wave emission based on distributions from various mock catalogs and determine a complex waveform from the Galactic foreground with $3.5 \times 10^{7}$ binaries. We describe the effects from the Galactic binary distribution population across mass, position within the Galaxy, core type, and orbital frequency distribution. We generate the modulated Galactic white dwarf signal detected by \textit{LISA} due to its orbital motion, and present a data analysis strategy to address it. The Fisher Information and Markov Chain Monte Carlo methods give an estimation of the \textit{LISA} noise and the parameters for the different signal classes. We estimate the detectable limits for the future LISA observation of the SGWB in the spectral domain with the 3 \textit{LISA} channels $A$, $E$, and $T$. We simultaneously estimate the Galactic foreground, the astrophysical and cosmological backgrounds. Assuming the expected astrophysical background and a Galactic foreground, a cosmological background energy density of around $\Omega_{GW,Cosmo} \approx 8 \times 10^{-13}$ could be detected by LISA. LISA will either detect a cosmologically produced SGWB, or set a limit that will have important consequences.
|
2309.14375
|
Vladimir Kassandrov
|
Vladimir V. Kassandrov and Ildus Sh. Khasanov
|
The algebrodynamics: super-conservative collective dynamics on a "Unique
Worldline'' and the Hubble's law
|
7 pages
|
Gravitation and Cosmology, 2023, Vol.29, No.1, pp.50-56
|
10.1134/S0202289323010048
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
We study the properties of roots of a polynomial system of equations which
define a set of identical point particles located on a Unique Worldline (UW),
in the spirit of the old Wheeler-Feynman's conception. As a consequence of the
Vieta's formulas, a great number of conservation laws is fulfilled for
collective algebraic dynamics on the UW. These, besides the canonical ones,
include the laws with higher derivatives and those containing multi-particle
correlation terms as well. On the other hand, such a ``super-conservative''
dynamics turns to be manifestly Lorentz invariant and quite nontrivial. At
great values of ``cosmic time'' $t$ roots-particles demonstrate universal
recession (resembling that in the Milne's cosmology and simulating
``expansion'' of the Universe) for which the Hubble's law does hold true, with
Hubble parameter being inversely proportional to $t$.
|
[
{
"created": "Sun, 24 Sep 2023 12:06:01 GMT",
"version": "v1"
}
] |
2023-09-27
|
[
[
"Kassandrov",
"Vladimir V.",
""
],
[
"Khasanov",
"Ildus Sh.",
""
]
] |
We study the properties of roots of a polynomial system of equations which define a set of identical point particles located on a Unique Worldline (UW), in the spirit of the old Wheeler-Feynman's conception. As a consequence of the Vieta's formulas, a great number of conservation laws is fulfilled for collective algebraic dynamics on the UW. These, besides the canonical ones, include the laws with higher derivatives and those containing multi-particle correlation terms as well. On the other hand, such a ``super-conservative'' dynamics turns to be manifestly Lorentz invariant and quite nontrivial. At great values of ``cosmic time'' $t$ roots-particles demonstrate universal recession (resembling that in the Milne's cosmology and simulating ``expansion'' of the Universe) for which the Hubble's law does hold true, with Hubble parameter being inversely proportional to $t$.
|
2310.07872
|
Patryk Mach
|
Patryk Mach, Adam Cie\'slik, Andrzej Odrzywolek
|
Monte Carlo methods for stationary solutions of general-relativistic
Vlasov systems: Collisionless accretion onto black holes
|
21 pages, 16 figures
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We develop a Monte Carlo simulation method for computing stationary solutions
of the general-relativistic Vlasov equation describing a gas of non-colliding
particles. As specific examples, we select planar or spherically symmetric
accretion models on the Schwarzschild background spacetime. In all cases the
gas extends to infinity, which poses an additional difficulty in the Monte
Carlo approach. We discuss models with monoenergetic particles as well as
solutions obeying the Maxwell-J\"{u}ttner distribution at infinity. For all
models, exact expressions for the particle current density are known or can be
computed analytically. We demonstrate perfect agreement between exact
expressions for the particle current density and the results of our Monte Carlo
simulations.
|
[
{
"created": "Wed, 11 Oct 2023 20:25:36 GMT",
"version": "v1"
}
] |
2023-10-13
|
[
[
"Mach",
"Patryk",
""
],
[
"Cieślik",
"Adam",
""
],
[
"Odrzywolek",
"Andrzej",
""
]
] |
We develop a Monte Carlo simulation method for computing stationary solutions of the general-relativistic Vlasov equation describing a gas of non-colliding particles. As specific examples, we select planar or spherically symmetric accretion models on the Schwarzschild background spacetime. In all cases the gas extends to infinity, which poses an additional difficulty in the Monte Carlo approach. We discuss models with monoenergetic particles as well as solutions obeying the Maxwell-J\"{u}ttner distribution at infinity. For all models, exact expressions for the particle current density are known or can be computed analytically. We demonstrate perfect agreement between exact expressions for the particle current density and the results of our Monte Carlo simulations.
|
1704.08311
|
Alvaro de la Cruz-Dombriz
|
Artyom V. Astashenok (1), Alvaro de la Cruz-Dombriz (2) and Sergei D.
Odintsov (3) ((1) I. Kant Baltic Federal University, (2) Cape Town U., Dept.
Math. & Cape Town U., Cosmology & Gravity group, (3) ICREA and IEEC-CSIC)
|
The realistic models of relativistic stars in f(R) = R + alpha R^2
gravity
|
Version published in Class. Quantum Grav. 34 (2017) 205008, 15 pages,
11 figures, 3 tables, conclusions unchanged
|
Class. Quantum Grav. 34 (2017) 205008
|
10.1088/1361-6382/aa8971
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the context of f(R)=R + alpha R^2 gravity, we study the existence of
neutron and quark stars with no intermediate approximations in the generalised
system of Tolman-Oppenheimer-Volkov equations. Analysis shows that for positive
alpha's the scalar curvature does not drop to zero at the star surface (as in
General Relativity) but exponentially decreases with distance. Also the stellar
mass bounded by star surface decreases when the value alpha increases.
Nonetheless distant observers would observe a gravitational mass due to
appearance of a so-called gravitational sphere around the star. The non-zero
curvature contribution to the gravitational mass eventually is shown to
compensate the stellar mass decrease for growing alpha's. We perform our
analysis for several equations of state including purely hadronic
configurations as well as hyperons and quark stars. In all cases, we assess
that the relation between the parameter $\alpha$ and the gravitational mass
weakly depend upon the chosen equation of state. Another interesting feature is
the increase of the star radius in comparison to General Relativity for stars
with masses close to maximal, whereas for intermediate masses around 1.4-1.6
solar masses, the radius of star depends upon alpha very weakly. Also the
decrease in the mass bounded by star surface may cause the surface redshift to
decrease in R^2-gravity when compared to Einsteinian predictions. This effect
is shown to hardly depend upon the observed gravitational mass. Finally, for
negative values of alpha our analysis shows that outside the star the scalar
curvature has damped oscillations but the contribution of the gravitational
sphere into the gravitational mass increases indefinitely with radial distance
putting into question the very existence of such relativistic stars.
|
[
{
"created": "Wed, 26 Apr 2017 19:22:16 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Sep 2017 07:52:44 GMT",
"version": "v2"
}
] |
2017-10-04
|
[
[
"Astashenok",
"Artyom V.",
""
],
[
"de la Cruz-Dombriz",
"Alvaro",
""
],
[
"Odintsov",
"Sergei D.",
""
]
] |
In the context of f(R)=R + alpha R^2 gravity, we study the existence of neutron and quark stars with no intermediate approximations in the generalised system of Tolman-Oppenheimer-Volkov equations. Analysis shows that for positive alpha's the scalar curvature does not drop to zero at the star surface (as in General Relativity) but exponentially decreases with distance. Also the stellar mass bounded by star surface decreases when the value alpha increases. Nonetheless distant observers would observe a gravitational mass due to appearance of a so-called gravitational sphere around the star. The non-zero curvature contribution to the gravitational mass eventually is shown to compensate the stellar mass decrease for growing alpha's. We perform our analysis for several equations of state including purely hadronic configurations as well as hyperons and quark stars. In all cases, we assess that the relation between the parameter $\alpha$ and the gravitational mass weakly depend upon the chosen equation of state. Another interesting feature is the increase of the star radius in comparison to General Relativity for stars with masses close to maximal, whereas for intermediate masses around 1.4-1.6 solar masses, the radius of star depends upon alpha very weakly. Also the decrease in the mass bounded by star surface may cause the surface redshift to decrease in R^2-gravity when compared to Einsteinian predictions. This effect is shown to hardly depend upon the observed gravitational mass. Finally, for negative values of alpha our analysis shows that outside the star the scalar curvature has damped oscillations but the contribution of the gravitational sphere into the gravitational mass increases indefinitely with radial distance putting into question the very existence of such relativistic stars.
|
0910.1323
|
Sonia Markes
|
Sonia Markes and Lucien Hardy
|
Entropy for theories with indefinite causal structure
|
11 pages, 2 figures
|
J.Phys.Conf.Ser.306:012043,2011
|
10.1088/1742-6596/306/1/012043
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Entropy is a concept that has traditionally been reliant on a definite notion
of causality. However, without a definite notion of causality, the concept of
entropy is not all lost. Indefinite causal structure results from combining
probabilistic predictions and dynamical space-time. Combining the probabilistic
nature of quantum theory and dynamical treatment space-time from general
relativity is an approach to the problem of quantum gravity. The causaloid
framework lays the mathematical groundwork to be able to treat indefinite
causal structure. In this paper, we build on the causaloid mathematics and
define a causally-unbiased entropy for an indefinite causal structure. In
defining a causally-unbiased entropy, there comes about an emergent idea of
causality in the form of a measure of causal connectedness, termed the Q
factor.
|
[
{
"created": "Wed, 7 Oct 2009 17:26:15 GMT",
"version": "v1"
}
] |
2011-07-13
|
[
[
"Markes",
"Sonia",
""
],
[
"Hardy",
"Lucien",
""
]
] |
Entropy is a concept that has traditionally been reliant on a definite notion of causality. However, without a definite notion of causality, the concept of entropy is not all lost. Indefinite causal structure results from combining probabilistic predictions and dynamical space-time. Combining the probabilistic nature of quantum theory and dynamical treatment space-time from general relativity is an approach to the problem of quantum gravity. The causaloid framework lays the mathematical groundwork to be able to treat indefinite causal structure. In this paper, we build on the causaloid mathematics and define a causally-unbiased entropy for an indefinite causal structure. In defining a causally-unbiased entropy, there comes about an emergent idea of causality in the form of a measure of causal connectedness, termed the Q factor.
|
gr-qc/0507011
|
Sanjit Mitra
|
S. Mitra, S. V. Dhurandhar and L. S. Finn
|
Improving the efficiency of the detection of gravitational wave signals
from inspiraling compact binaries: Chebyshev interpolation
|
23 pages, 5 figures, submitted to Phys. Rev. D
|
Phys.Rev. D72 (2005) 102001
|
10.1103/PhysRevD.72.102001
|
IUCAA - 19/05
|
gr-qc
| null |
Inspiraling compact binaries are promising sources of gravitational waves for
ground and space-based laser interferometric detectors. The time-dependent
signature of these sources in the detectors is a well-characterized function of
a relatively small number of parameters; thus, the favored analysis technique
makes use of matched filtering and maximum likelihood methods. Current analysis
methodology samples the matched filter output at parameter values chosen so
that the correlation between successive samples is 97% for which the filtered
output is closely correlated. Here we describe a straightforward and practical
way of using interpolation to take advantage of the correlation between the
matched filter output associated with nearby points in the parameter space to
significantly reduce the number of matched filter evaluations without
sacrificing the efficiency with which real signals are recognized. Because the
computational cost of the analysis is driven almost exclusively by the matched
filter evaluations, this translates directly into an increase in computational
efficiency, which in turn, translates into an increase in the size of the
parameter space that can be analyzed and, thus, the science that can be
accomplished with the data. As a demonstration we compare the present "dense
sampling" analysis methodology with our proposed "interpolation" methodology,
restricted to one dimension of the multi-dimensional analysis problem. We find
that the interpolated search reduces by 25% the number of filter evaluations
required by the dense search with 97% correlation to achieve the same
efficiency of detection for an expected false alarm probability. Generalized to
higher dimensional space of a generic binary including spins suggests an order
of magnitude increase in computational efficiency.
|
[
{
"created": "Mon, 4 Jul 2005 05:24:09 GMT",
"version": "v1"
}
] |
2015-06-25
|
[
[
"Mitra",
"S.",
""
],
[
"Dhurandhar",
"S. V.",
""
],
[
"Finn",
"L. S.",
""
]
] |
Inspiraling compact binaries are promising sources of gravitational waves for ground and space-based laser interferometric detectors. The time-dependent signature of these sources in the detectors is a well-characterized function of a relatively small number of parameters; thus, the favored analysis technique makes use of matched filtering and maximum likelihood methods. Current analysis methodology samples the matched filter output at parameter values chosen so that the correlation between successive samples is 97% for which the filtered output is closely correlated. Here we describe a straightforward and practical way of using interpolation to take advantage of the correlation between the matched filter output associated with nearby points in the parameter space to significantly reduce the number of matched filter evaluations without sacrificing the efficiency with which real signals are recognized. Because the computational cost of the analysis is driven almost exclusively by the matched filter evaluations, this translates directly into an increase in computational efficiency, which in turn, translates into an increase in the size of the parameter space that can be analyzed and, thus, the science that can be accomplished with the data. As a demonstration we compare the present "dense sampling" analysis methodology with our proposed "interpolation" methodology, restricted to one dimension of the multi-dimensional analysis problem. We find that the interpolated search reduces by 25% the number of filter evaluations required by the dense search with 97% correlation to achieve the same efficiency of detection for an expected false alarm probability. Generalized to higher dimensional space of a generic binary including spins suggests an order of magnitude increase in computational efficiency.
|
2108.07023
|
Quentin Ansel
|
Quentin Ansel
|
Loop quantum gravity with optimal control path integral, and application
to black hole tunneling
|
25 pages, 5 figures, source codes in supplementary materials
| null |
10.1007/s10714-022-02923-6
| null |
gr-qc quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This paper presents a novel path integral formalism for Einstein's theory of
gravitation from the viewpoint of optimal control theory. Despite its close
relation to the well-known variational principles of physicists, optimal
control turns out to be more general. Within this context, a Lagrangian
different from the Einstein-Hilbert Lagrangian is defined. Einstein field
equations are recovered exactly with variations of the new action functional.
The quantum theory is obtained using Ashtekar variables and the loop scalar
product. By means of example, the tunneling process of a black hole into
another black hole or into a white hole is investigated with a toy model.
|
[
{
"created": "Mon, 16 Aug 2021 11:24:22 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Aug 2021 08:32:43 GMT",
"version": "v2"
}
] |
2022-05-11
|
[
[
"Ansel",
"Quentin",
""
]
] |
This paper presents a novel path integral formalism for Einstein's theory of gravitation from the viewpoint of optimal control theory. Despite its close relation to the well-known variational principles of physicists, optimal control turns out to be more general. Within this context, a Lagrangian different from the Einstein-Hilbert Lagrangian is defined. Einstein field equations are recovered exactly with variations of the new action functional. The quantum theory is obtained using Ashtekar variables and the loop scalar product. By means of example, the tunneling process of a black hole into another black hole or into a white hole is investigated with a toy model.
|
2205.03842
|
Shokoufe Faraji
|
Shokoufe Faraji, Audrey Trova, Hernando Quevedo
|
Relativistic equilibrium fluid configurations around rotating deformed
compact objects
| null | null |
10.1140/epjc/s10052-022-11075-5
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We investigate the physical properties of equilibrium sequences of
non-self-gravitating surfaces that characterize thick disks around a rotating
deformed compact object described by a stationary generalization of the static
q-metric. The spacetime corresponds to an exact solution of Einstein's field
equations so that we can perform the analysis for arbitrary values of the
quadrupole moment and rotation parameter. To study the properties of this
disk's model, we analyze bounded trajectories in this spacetime. Further, we
find that depending on the values of the parameters, we can have various disc
structures that can easily be distinguished from the static case and also from
the Schwarzschild background. We argue that this study may be used to evaluate
the rotation and quadrupole parameters of the central compact object.
|
[
{
"created": "Sun, 8 May 2022 11:55:17 GMT",
"version": "v1"
}
] |
2023-01-04
|
[
[
"Faraji",
"Shokoufe",
""
],
[
"Trova",
"Audrey",
""
],
[
"Quevedo",
"Hernando",
""
]
] |
We investigate the physical properties of equilibrium sequences of non-self-gravitating surfaces that characterize thick disks around a rotating deformed compact object described by a stationary generalization of the static q-metric. The spacetime corresponds to an exact solution of Einstein's field equations so that we can perform the analysis for arbitrary values of the quadrupole moment and rotation parameter. To study the properties of this disk's model, we analyze bounded trajectories in this spacetime. Further, we find that depending on the values of the parameters, we can have various disc structures that can easily be distinguished from the static case and also from the Schwarzschild background. We argue that this study may be used to evaluate the rotation and quadrupole parameters of the central compact object.
|
gr-qc/0307061
|
Yongge Ma
|
Xuejun Yang, Yongge Ma, Jianbing Shao, and Wei Zhou
|
Killing Reduction of 5-Dimensional Spacetimes
|
9 pages, references added
|
Phys.Rev. D68 (2003) 024006
|
10.1103/PhysRevD.68.024006
| null |
gr-qc hep-th
| null |
In a 5-dimensional spacetime ($M,g_{ab}$) with a Killing vector field $\xi
^a$ which is either everywhere timelike or everywhere spacelike, the collection
of all trajectories of $\xi ^a$ gives a 4-dimensional space $S$. The reduction
of ($M,g_{ab}$) is studied in the geometric language, which is a generalization
of Geroch's method for the reduction of 4-dimensional spacetime. A
4-dimensional gravity coupled to a vector field and a scalar field on $S$ is
obtained by the reduction of vacuum Einstein's equations on $M$, which gives
also an alternative description of the 5-dimensional Kaluza-Klein theory.
Besides the symmetry-reduced action from the Hilbert action on $M$, an
alternative action of the fields on $S$ is also obtained, the variations of
which lead to the same fields equations as those reduced from the vacuum
Einstein equation on $M$.
|
[
{
"created": "Sat, 12 Jul 2003 08:12:41 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Jul 2003 03:26:17 GMT",
"version": "v2"
}
] |
2009-11-10
|
[
[
"Yang",
"Xuejun",
""
],
[
"Ma",
"Yongge",
""
],
[
"Shao",
"Jianbing",
""
],
[
"Zhou",
"Wei",
""
]
] |
In a 5-dimensional spacetime ($M,g_{ab}$) with a Killing vector field $\xi ^a$ which is either everywhere timelike or everywhere spacelike, the collection of all trajectories of $\xi ^a$ gives a 4-dimensional space $S$. The reduction of ($M,g_{ab}$) is studied in the geometric language, which is a generalization of Geroch's method for the reduction of 4-dimensional spacetime. A 4-dimensional gravity coupled to a vector field and a scalar field on $S$ is obtained by the reduction of vacuum Einstein's equations on $M$, which gives also an alternative description of the 5-dimensional Kaluza-Klein theory. Besides the symmetry-reduced action from the Hilbert action on $M$, an alternative action of the fields on $S$ is also obtained, the variations of which lead to the same fields equations as those reduced from the vacuum Einstein equation on $M$.
|
1510.00085
|
Shao-Wen Wei
|
Shao-Wen Wei, Peng Cheng, Yu-Xiao Liu
|
Analytical and exact critical phenomena of $d$-dimensional singly
spinning Kerr-AdS black holes
|
16 pages, 9 figures, 3 tables
|
Phys. Rev. D 93, 084015 (2016)
|
10.1103/PhysRevD.93.084015
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the extended phase space, the $d$-dimensional singly spinning Kerr-AdS
black holes exhibit the van der Waals's phase transition and reentrant phase
transition. Since the black hole system is a single characteristic parameter
thermodynamic system, we show that the form of the critical point can be
uniquely determined by the dimensional analysis. When $d=4$, we get the
analytical critical point. The coexistence curve and phase diagrams are
obtained. The result shows that the fitting form of the coexistence curve in
the reduced parameter space is independent of the angular momentum. When
$d=5$---$9$, the exact critical points are numerically solved. It demonstrates
that when $d\geq6$, there are two critical points. However, the small one does
not participate in the phase transition. Moreover, the exact critical reentrant
phase transition points are also obtained. All the critical points are obtained
without any approximation.
|
[
{
"created": "Thu, 1 Oct 2015 01:36:26 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Apr 2016 02:45:43 GMT",
"version": "v2"
}
] |
2016-04-13
|
[
[
"Wei",
"Shao-Wen",
""
],
[
"Cheng",
"Peng",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] |
In the extended phase space, the $d$-dimensional singly spinning Kerr-AdS black holes exhibit the van der Waals's phase transition and reentrant phase transition. Since the black hole system is a single characteristic parameter thermodynamic system, we show that the form of the critical point can be uniquely determined by the dimensional analysis. When $d=4$, we get the analytical critical point. The coexistence curve and phase diagrams are obtained. The result shows that the fitting form of the coexistence curve in the reduced parameter space is independent of the angular momentum. When $d=5$---$9$, the exact critical points are numerically solved. It demonstrates that when $d\geq6$, there are two critical points. However, the small one does not participate in the phase transition. Moreover, the exact critical reentrant phase transition points are also obtained. All the critical points are obtained without any approximation.
|
1812.06970
|
Ido Ben-Dayan
|
Ido Ben-Dayan, Judy Kupferman
|
Sourced Scalar Fluctuations in Bouncing Cosmology
|
Corrected an error in writing the coupling to the gauge field in
terms of the scalar field and the corresponding equations. As a result, the
prediction is r=1/9. Matches the published erratum
|
JCAP 2019 (2019) no.07, 050, JCAP 12 (2020) E01 (erratum)
|
10.1088/1475-7516/2019/07/050
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We calculate the scalar power spectrum generated by sourced fluctuations due
to coupling between the scalar field, which holds most of the energy density of
the universe, and a gauge field for a general FLRW metric. For this purpose we
calculate the curvature perturbation to second order in the presence of gauge
fields, and show that the gauge fields behave like an additional potential
term. We then apply the analysis to the case of slow-contraction. Due to the
interaction between the scalar field and gauge fields additional 'sourced'
tensor and scalar spectra are generated. The resulting spectra are chiral,
slightly blue and arbitrarily close to scale invariance. The only difference
between the tensor and scalar spectra is the coupling constant with an
${\mathcal O}(1)$ numerical coefficient, and some momentum space polarization
vectors. As a result the tilt of the spectra are the same. For the nearly scale
invariant case, the momentum integration gives the same leading contribution.
Hence, $r\simeq 1/9$ where the deviation from this value is controlled by the
deviation from scale invariance, and is not in agreement with CMB observations.
Deviating considerably from near scale invariance, and considering a bluer tilt
with $n_T>0.12$, the model cannot account for CMB observations, but can be
detected by LIGO and/or LISA in the future.
|
[
{
"created": "Sun, 16 Dec 2018 21:01:05 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Aug 2019 20:35:08 GMT",
"version": "v2"
},
{
"created": "Thu, 18 Feb 2021 17:11:22 GMT",
"version": "v3"
}
] |
2021-02-19
|
[
[
"Ben-Dayan",
"Ido",
""
],
[
"Kupferman",
"Judy",
""
]
] |
We calculate the scalar power spectrum generated by sourced fluctuations due to coupling between the scalar field, which holds most of the energy density of the universe, and a gauge field for a general FLRW metric. For this purpose we calculate the curvature perturbation to second order in the presence of gauge fields, and show that the gauge fields behave like an additional potential term. We then apply the analysis to the case of slow-contraction. Due to the interaction between the scalar field and gauge fields additional 'sourced' tensor and scalar spectra are generated. The resulting spectra are chiral, slightly blue and arbitrarily close to scale invariance. The only difference between the tensor and scalar spectra is the coupling constant with an ${\mathcal O}(1)$ numerical coefficient, and some momentum space polarization vectors. As a result the tilt of the spectra are the same. For the nearly scale invariant case, the momentum integration gives the same leading contribution. Hence, $r\simeq 1/9$ where the deviation from this value is controlled by the deviation from scale invariance, and is not in agreement with CMB observations. Deviating considerably from near scale invariance, and considering a bluer tilt with $n_T>0.12$, the model cannot account for CMB observations, but can be detected by LIGO and/or LISA in the future.
|
1008.1127
|
Francisco Lobo
|
Francisco S. N. Lobo
|
Closed timelike curves and causality violation
|
19 pages, 6 figures. Invited chapter to appear in an edited
collection 'Classical and Quantum Gravity: Theory, Analysis and Applications'
|
Classical and Quantum Gravity: Theory, Analysis and Applications,
chap.6 , (2008), Nova Sci. Pub
| null | null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The conceptual definition and understanding of time, both quantitatively and
qualitatively is of the utmost difficulty and importance. As time is
incorporated into the proper structure of the fabric of spacetime, it is
interesting to note that General Relativity is contaminated with non-trivial
geometries which generate closed timelike curves. A closed timelike curve (CTC)
allows time travel, in the sense that an observer that travels on a trajectory
in spacetime along this curve, may return to an event before his departure.
This fact apparently violates causality, therefore time travel and it's
associated paradoxes have to be treated with great caution. The paradoxes fall
into two broad groups, namely the consistency paradoxes and the causal loops. A
great variety of solutions to the Einstein field equations containing CTCs
exist and it seems that two particularly notorious features stand out.
Solutions with a tipping over of the light cones due to a rotation about a
cylindrically symmetric axis and solutions that violate the energy conditions.
All these aspects are analyzed in this review paper.
|
[
{
"created": "Fri, 6 Aug 2010 07:24:39 GMT",
"version": "v1"
}
] |
2013-10-21
|
[
[
"Lobo",
"Francisco S. N.",
""
]
] |
The conceptual definition and understanding of time, both quantitatively and qualitatively is of the utmost difficulty and importance. As time is incorporated into the proper structure of the fabric of spacetime, it is interesting to note that General Relativity is contaminated with non-trivial geometries which generate closed timelike curves. A closed timelike curve (CTC) allows time travel, in the sense that an observer that travels on a trajectory in spacetime along this curve, may return to an event before his departure. This fact apparently violates causality, therefore time travel and it's associated paradoxes have to be treated with great caution. The paradoxes fall into two broad groups, namely the consistency paradoxes and the causal loops. A great variety of solutions to the Einstein field equations containing CTCs exist and it seems that two particularly notorious features stand out. Solutions with a tipping over of the light cones due to a rotation about a cylindrically symmetric axis and solutions that violate the energy conditions. All these aspects are analyzed in this review paper.
|
2008.04737
|
Gabriele Umberto Varieschi
|
Gabriele U. Varieschi
|
Newtonian Fractional-Dimension Gravity and Disk Galaxies
|
23 pages, including 6 figures: references added and other minor
changes after peer review. Final version to be published in The European
Physical Journal Plus, Springer
|
Eur. Phys. J. Plus 136, 183 (2021)
|
10.1140/epjp/s13360-021-01165-w
| null |
gr-qc astro-ph.GA
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This paper continues previous work on a novel alternative model of gravity,
based on the theory of fractional-dimension spaces applied to Newton's law of
gravitation. In particular, our Newtonian Fractional-Dimension Gravity is now
applied to axially-symmetric structures, such as thin/thick disk galaxies
described by exponential, Kuzmin, or other similar mass distributions.
As in the case of spherically-symmetric structures, which was studied in
previous work on the subject, we examine a possible connection between our
model and Modified Newtonian Dynamics, a leading alternative gravity model,
which accounts for the observed properties of galaxies and other astrophysical
structures without requiring the dark matter hypothesis.
By relating the MOND acceleration constant $a_{0} \simeq 1.2 \times 10^{
-10}\mbox{m}\thinspace \mbox{s}^{ -2}$ to a natural scale length $l_{0}$ of our
model, namely $a_{0} \approx GM/l_{0}^{2}$ for a galaxy of mass $M$, and by
using the empirical Radial Acceleration Relation, we are able to explain the
connection between the observed radial acceleration $g_{obs}$ and the baryonic
radial acceleration $g_{bar}$ in terms of a variable local dimension $D$. As an
example of this methodology, we provide a detailed rotation curve fitting for
the case of the field dwarf spiral galaxy NGC 6503.
|
[
{
"created": "Sat, 8 Aug 2020 05:09:38 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Sep 2020 23:36:59 GMT",
"version": "v2"
},
{
"created": "Fri, 5 Feb 2021 01:35:59 GMT",
"version": "v3"
}
] |
2021-02-15
|
[
[
"Varieschi",
"Gabriele U.",
""
]
] |
This paper continues previous work on a novel alternative model of gravity, based on the theory of fractional-dimension spaces applied to Newton's law of gravitation. In particular, our Newtonian Fractional-Dimension Gravity is now applied to axially-symmetric structures, such as thin/thick disk galaxies described by exponential, Kuzmin, or other similar mass distributions. As in the case of spherically-symmetric structures, which was studied in previous work on the subject, we examine a possible connection between our model and Modified Newtonian Dynamics, a leading alternative gravity model, which accounts for the observed properties of galaxies and other astrophysical structures without requiring the dark matter hypothesis. By relating the MOND acceleration constant $a_{0} \simeq 1.2 \times 10^{ -10}\mbox{m}\thinspace \mbox{s}^{ -2}$ to a natural scale length $l_{0}$ of our model, namely $a_{0} \approx GM/l_{0}^{2}$ for a galaxy of mass $M$, and by using the empirical Radial Acceleration Relation, we are able to explain the connection between the observed radial acceleration $g_{obs}$ and the baryonic radial acceleration $g_{bar}$ in terms of a variable local dimension $D$. As an example of this methodology, we provide a detailed rotation curve fitting for the case of the field dwarf spiral galaxy NGC 6503.
|
gr-qc/0701097
|
Eri Mena
|
E. Mena, O. Obregon and M. Sabido
|
WKB-type Approximation to Noncommutative Quantum Cosmology
|
Revtex4, 6 pages, no figures
|
Int.J.Mod.Phys.D18:95-106,2009
|
10.1142/S0218271809014376
| null |
gr-qc
| null |
In this work, we develop and apply the WKB approximation to several examples
of noncommutative quantum cosmology, obtaining the time evolution of the
noncommutative universe, this is done starting from a noncommutative quantum
formulation of cosmology where the noncommutativity is introduced by a
deformation on the minisuperspace variables. This procedure gives a
straightforward algorithm to incorporate noncommutativity to cosmology and
inflation.
|
[
{
"created": "Tue, 16 Jan 2007 23:12:49 GMT",
"version": "v1"
}
] |
2009-03-24
|
[
[
"Mena",
"E.",
""
],
[
"Obregon",
"O.",
""
],
[
"Sabido",
"M.",
""
]
] |
In this work, we develop and apply the WKB approximation to several examples of noncommutative quantum cosmology, obtaining the time evolution of the noncommutative universe, this is done starting from a noncommutative quantum formulation of cosmology where the noncommutativity is introduced by a deformation on the minisuperspace variables. This procedure gives a straightforward algorithm to incorporate noncommutativity to cosmology and inflation.
|
gr-qc/9503064
|
Troy Schilling
|
Troy A. Schilling
|
Non-covariance of the generalized holonomies: Examples
|
Silly LaTeX error fixed so that figure is properly included
|
J.Math.Phys.37:4041-4052,1996
|
10.1063/1.531615
|
GCPG-95/3-1
|
gr-qc
| null |
A key aspect of a recent proposal for a {\em generalized loop representation}
of quantum Yang-Mills theory and gravity is considered. Such a representation
of the quantum theory has been expected to arise via consideration of a
particular algebra of observables -- given by the traces of the holonomies of
{\em generalized loops}. We notice, however, a technical subtlety, which
prevents us from reaching the conclusion that the generalized holonomies are
covariant with respect to small gauge transformations. Further analysis is
given which shows that they are {\em not} covariant with respect to small gauge
transformations; their traces are {\em not} observables of the gauge theory.
This result indicates what may be a serious complication to the use of
generalized loops in physics.
|
[
{
"created": "Fri, 31 Mar 1995 21:50:30 GMT",
"version": "v1"
},
{
"created": "Fri, 7 Apr 1995 02:03:25 GMT",
"version": "v2"
}
] |
2010-11-01
|
[
[
"Schilling",
"Troy A.",
""
]
] |
A key aspect of a recent proposal for a {\em generalized loop representation} of quantum Yang-Mills theory and gravity is considered. Such a representation of the quantum theory has been expected to arise via consideration of a particular algebra of observables -- given by the traces of the holonomies of {\em generalized loops}. We notice, however, a technical subtlety, which prevents us from reaching the conclusion that the generalized holonomies are covariant with respect to small gauge transformations. Further analysis is given which shows that they are {\em not} covariant with respect to small gauge transformations; their traces are {\em not} observables of the gauge theory. This result indicates what may be a serious complication to the use of generalized loops in physics.
|
1911.09639
|
Marcin Kisielowski PhD
|
Marcin Kisielowski
|
Homogeneous-isotropic sector of loop quantum gravity: new approach
|
[v2] Published version. This is an open access article distributed
under the terms of the Creative Commons Attribution 4.0 License. Any further
distribution of this work must maintain attribution to the author and the
title of the work, journal citation and DOI
|
Class. Quantum Grav. 37 (2020) 185004
|
10.1088/1361-6382/ab9bb9
| null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
Recently, a new class of scalar constraint operators has been introduced in
loop quantum gravity. They are defined on a space of solutions to the Gauss
constraint and partial solutions to the vector constraint, called a vertex
Hilbert space. We propose a subspace of the vertex Hilbert space formed by
homogeneous-isotropic states, which is invariant under the action of the new
scalar constraint operators. As a result, the operators can be reduced to our
homogeneous-isotropic subspace. The (generalized) eigenstates of the reduced
operator are eigenstates of the full operator. We discuss the feasibility of
numerical diagonalization of the reduced scalar constraint operator.
|
[
{
"created": "Thu, 21 Nov 2019 17:52:41 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Apr 2021 10:55:08 GMT",
"version": "v2"
}
] |
2021-05-03
|
[
[
"Kisielowski",
"Marcin",
""
]
] |
Recently, a new class of scalar constraint operators has been introduced in loop quantum gravity. They are defined on a space of solutions to the Gauss constraint and partial solutions to the vector constraint, called a vertex Hilbert space. We propose a subspace of the vertex Hilbert space formed by homogeneous-isotropic states, which is invariant under the action of the new scalar constraint operators. As a result, the operators can be reduced to our homogeneous-isotropic subspace. The (generalized) eigenstates of the reduced operator are eigenstates of the full operator. We discuss the feasibility of numerical diagonalization of the reduced scalar constraint operator.
|
1507.07845
|
Yen Chin Ong
|
Yen Chin Ong
|
Hawking Evaporation Time Scale of Topological Black Holes in Anti-de
Sitter Spacetime
|
Published version
|
Nucl. Phys. B 903 (2016) 387
|
10.1016/j.nuclphysb.2016.01.005
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
It was recently pointed out that if an absorbing boundary condition is
imposed at infinity, an asymptotically anti-de Sitter Schwarzschild black hole
with a spherical horizon takes only a finite amount of time to evaporate away
even if its initial mass is arbitrarily large. We show that this is a rather
generic property in AdS spacetimes: regardless of their horizon topologies,
neutral AdS black holes in general relativity take about the same amount of
time to evaporate down to the same size of order L, the AdS length scale. Our
discussion focuses on the case in which the black hole has toral event horizon.
A brief comment is made on the hyperbolic case, i.e. for black holes with
negatively curved horizons.
|
[
{
"created": "Tue, 28 Jul 2015 16:55:33 GMT",
"version": "v1"
},
{
"created": "Sat, 13 Feb 2016 21:26:05 GMT",
"version": "v2"
}
] |
2016-02-16
|
[
[
"Ong",
"Yen Chin",
""
]
] |
It was recently pointed out that if an absorbing boundary condition is imposed at infinity, an asymptotically anti-de Sitter Schwarzschild black hole with a spherical horizon takes only a finite amount of time to evaporate away even if its initial mass is arbitrarily large. We show that this is a rather generic property in AdS spacetimes: regardless of their horizon topologies, neutral AdS black holes in general relativity take about the same amount of time to evaporate down to the same size of order L, the AdS length scale. Our discussion focuses on the case in which the black hole has toral event horizon. A brief comment is made on the hyperbolic case, i.e. for black holes with negatively curved horizons.
|
2403.09388
|
Che-Yu Chen
|
Che-Yu Chen, Yuki Yokokura
|
Imaging a semi-classical horizonless compact object with strong redshift
|
15 pages, 10 figures. Matching published version
|
Phys. Rev. D 109 (2024) 104058
|
10.1103/PhysRevD.109.104058
|
RIKEN-iTHEMS-Report-24
|
gr-qc astro-ph.HE hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The recent advancements in black hole imaging have opened a new era of
probing horizon-scale physics with electromagnetic radiation. However, a
feature of the observed images, a bright ring encircling a relatively dark
region, has not sufficiently proved the existence of event horizons. It thus
requires extreme care when studying the possibility of using such image
features to examine quantum effects that may change the classical picture of
black holes slightly or drastically. In this work, we investigate the image of
a horizonless compact object, whose interior metric satisfies the 4D
semi-classical Einstein equation non-perturbatively for the Planck constant,
and whose entropy agrees with the Bekenstein-Hawking formula. Although the
absence of an event horizon allows light rays to pass through the dense
interior, the extremely strong redshift significantly darkens the image, making
it almost identical to the classical black-hole image. In particular, if there
is light emission a bit inside the surface of the object, the intensity around
the inner shadow is slightly enhanced, which could be a future observable
prediction to characterize the object. We also find through a phenomenological
parameter that the image is further darkened due to interactions inside. Thus,
the image is consistent with current observations, and the object could be a
candidate for black holes in quantum theory.
|
[
{
"created": "Thu, 14 Mar 2024 13:39:18 GMT",
"version": "v1"
},
{
"created": "Tue, 21 May 2024 08:47:48 GMT",
"version": "v2"
}
] |
2024-05-22
|
[
[
"Chen",
"Che-Yu",
""
],
[
"Yokokura",
"Yuki",
""
]
] |
The recent advancements in black hole imaging have opened a new era of probing horizon-scale physics with electromagnetic radiation. However, a feature of the observed images, a bright ring encircling a relatively dark region, has not sufficiently proved the existence of event horizons. It thus requires extreme care when studying the possibility of using such image features to examine quantum effects that may change the classical picture of black holes slightly or drastically. In this work, we investigate the image of a horizonless compact object, whose interior metric satisfies the 4D semi-classical Einstein equation non-perturbatively for the Planck constant, and whose entropy agrees with the Bekenstein-Hawking formula. Although the absence of an event horizon allows light rays to pass through the dense interior, the extremely strong redshift significantly darkens the image, making it almost identical to the classical black-hole image. In particular, if there is light emission a bit inside the surface of the object, the intensity around the inner shadow is slightly enhanced, which could be a future observable prediction to characterize the object. We also find through a phenomenological parameter that the image is further darkened due to interactions inside. Thus, the image is consistent with current observations, and the object could be a candidate for black holes in quantum theory.
|
1010.1124
|
Stefan Danilishin
|
Farid Khalili, Stefan Danilishin, Helge Mueller-Ebhardt, Haixing Miao,
Yanbei Chen and Chunnong Zhao
|
Negative optical inertia for enhancing the sensitivity of future
gravitational-wave detectors
|
7 pages, 3 figures
|
Phys.Rev.D83:062003,2011
|
10.1103/PhysRevD.83.062003
| null |
gr-qc physics.optics
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider enhancing the sensitivity of future gravitational-wave detectors
by using double optical spring. When the power, detuning and bandwidth of the
two carriers are chosen appropriately, the effect of the double optical spring
can be described as a "negative inertia", which cancels the positive inertia of
the test masses and thus increases their response to gravitational waves. This
allows us to surpass the free-mass Standard Quantum Limit (SQL) over a broad
frequency band, through signal amplification, rather than noise cancelation,
which has been the case for all broadband SQL-beating schemes so far considered
for gravitational-wave detectors. The merit of such signal amplification
schemes lies in the fact that they are less susceptible to optical losses than
noise cancelation schemes. We show that it is feasible to demonstrate such an
effect with the {\it Gingin High Optical Power Test Facility}, and it can
eventually be implemented in future advanced GW detectors.
|
[
{
"created": "Wed, 6 Oct 2010 11:21:52 GMT",
"version": "v1"
}
] |
2011-03-22
|
[
[
"Khalili",
"Farid",
""
],
[
"Danilishin",
"Stefan",
""
],
[
"Mueller-Ebhardt",
"Helge",
""
],
[
"Miao",
"Haixing",
""
],
[
"Chen",
"Yanbei",
""
],
[
"Zhao",
"Chunnong",
""
]
] |
We consider enhancing the sensitivity of future gravitational-wave detectors by using double optical spring. When the power, detuning and bandwidth of the two carriers are chosen appropriately, the effect of the double optical spring can be described as a "negative inertia", which cancels the positive inertia of the test masses and thus increases their response to gravitational waves. This allows us to surpass the free-mass Standard Quantum Limit (SQL) over a broad frequency band, through signal amplification, rather than noise cancelation, which has been the case for all broadband SQL-beating schemes so far considered for gravitational-wave detectors. The merit of such signal amplification schemes lies in the fact that they are less susceptible to optical losses than noise cancelation schemes. We show that it is feasible to demonstrate such an effect with the {\it Gingin High Optical Power Test Facility}, and it can eventually be implemented in future advanced GW detectors.
|
gr-qc/0607125
|
Farook Rahaman
|
F.Rahaman, M.Kalam, R.Mondal and B.Raychaudhuri
|
Global monopole, dark matter and scalar tensor theory
|
8 pages, Accepted in Mod. Phys. Lett. A
|
Mod.Phys.Lett.A22:971-978,2007
|
10.1142/S0217732307021317
| null |
gr-qc
| null |
In this article, we discuss the space-time of a global monopole field as a
candidate for galactic dark matter in the context of scalar tensor theory.
|
[
{
"created": "Thu, 27 Jul 2006 08:50:29 GMT",
"version": "v1"
}
] |
2008-11-26
|
[
[
"Rahaman",
"F.",
""
],
[
"Kalam",
"M.",
""
],
[
"Mondal",
"R.",
""
],
[
"Raychaudhuri",
"B.",
""
]
] |
In this article, we discuss the space-time of a global monopole field as a candidate for galactic dark matter in the context of scalar tensor theory.
|
2107.14522
|
Fabrizio Esposito
|
Fabrizio Esposito, Sante Carloni, Roberto Cianci, Stefano Vignolo
|
Reconstructing isotropic and anisotropic $f(\mathcal{Q})$ cosmologies
|
12 pages, 16 figures
|
Phys. Rev. D 105, 084061 (2022)
|
10.1103/PhysRevD.105.084061
| null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
We present a reconstruction algorithm for cosmological models based on
$f(\mathcal{Q})$ gravity. We specifically focus on obtaining exact Bianchi
Type-I and Friedmann-Lema\^{\i}tre-Robertson-Walker solutions, finding
solutions that might have application in a variety of scenarios such as
spontaneous isotropization of Bianchi Type-I models, dark energy, inflation as
well as pre-Big Bang cosmologies.
|
[
{
"created": "Fri, 30 Jul 2021 10:10:39 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Oct 2021 08:06:54 GMT",
"version": "v2"
},
{
"created": "Wed, 11 May 2022 09:47:36 GMT",
"version": "v3"
}
] |
2022-05-12
|
[
[
"Esposito",
"Fabrizio",
""
],
[
"Carloni",
"Sante",
""
],
[
"Cianci",
"Roberto",
""
],
[
"Vignolo",
"Stefano",
""
]
] |
We present a reconstruction algorithm for cosmological models based on $f(\mathcal{Q})$ gravity. We specifically focus on obtaining exact Bianchi Type-I and Friedmann-Lema\^{\i}tre-Robertson-Walker solutions, finding solutions that might have application in a variety of scenarios such as spontaneous isotropization of Bianchi Type-I models, dark energy, inflation as well as pre-Big Bang cosmologies.
|
2309.10282
|
Vinod Kumar Bhardwaj Dr.
|
Vinod Kumar Bhardwaj, Anil Kumar Yadav, Lalit Kumar Gupta, Rajendra
Prasad, Sudhir Kumar Srivastava
|
Constraining hybrid potential scalar field cosmological model in Lyra's
geometry with recent observational data
|
24 pages, 12 figures
| null | null | null |
gr-qc
|
http://creativecommons.org/licenses/by-nc-sa/4.0/
|
In the current study, we investigate a scalar field cosmological model with
Lyra's geometry to explain the present cosmic expansion in a homogeneous and
isotropic flat FRW universe. In Einstein's field equations, we presupposed a
variable displacement vector as an element of Lyra's geometry. In the context
of the conventional theory of gravity, we suggest a suitable parameterization
of the scalar field's dark energy density in the hybrid function of redshift
$z$, confirming the essential transition behavior of the universe from a
decelerating era to the present accelerated scenario. We present constraints on
model parameters using the most recent observational data sets from OHD,
BAO/CMB, and Pantheon, taking Markov Chain Monte Carlo (MCMC) analysis into
account. For the proposed model, the best estimated values of parameters for
the combined dataset (OHD, BAO/CMB, and Pantheon) are $ H_0 = 71.15\pm 0.26$
km/s/Mpc, $ \Omega_{m0}=0.2625\pm 0.0024$, $ \Omega_{\phi0} = 0.676\pm0.038$, $
\alpha=-0.22\pm0.13$, $n = 0.096\pm0.079$, and $k = 0.38\pm0.32$. The model
exhibits a flipping nature, and the redshift transition occurs at $z_t =
0.756^{+0.005}_{-0.015}$. The current value of the decelerated parameter for
the proposed model is calculated as $q_0 = -0.625^{+0.067}_{-0.085}$ for the
combined dataset. Some dynamical properties of the model like energy density
($\rho_{\phi}$), scalar field pressure ($p_{\phi}$), EoS parameter of scalar
field ($\omega_{\phi}$), and effective EoS parameter ($\omega_{eff}$) are
analyzed and presented. Further, we have also examined the statefinder
diagnosis and jerk parameters of the derived model. The total density parameter
for the derived model is found to be unity which is in nice agreement with
recent standard findings.
|
[
{
"created": "Tue, 19 Sep 2023 03:11:07 GMT",
"version": "v1"
},
{
"created": "Sun, 14 Jul 2024 06:37:36 GMT",
"version": "v2"
}
] |
2024-07-16
|
[
[
"Bhardwaj",
"Vinod Kumar",
""
],
[
"Yadav",
"Anil Kumar",
""
],
[
"Gupta",
"Lalit Kumar",
""
],
[
"Prasad",
"Rajendra",
""
],
[
"Srivastava",
"Sudhir Kumar",
""
]
] |
In the current study, we investigate a scalar field cosmological model with Lyra's geometry to explain the present cosmic expansion in a homogeneous and isotropic flat FRW universe. In Einstein's field equations, we presupposed a variable displacement vector as an element of Lyra's geometry. In the context of the conventional theory of gravity, we suggest a suitable parameterization of the scalar field's dark energy density in the hybrid function of redshift $z$, confirming the essential transition behavior of the universe from a decelerating era to the present accelerated scenario. We present constraints on model parameters using the most recent observational data sets from OHD, BAO/CMB, and Pantheon, taking Markov Chain Monte Carlo (MCMC) analysis into account. For the proposed model, the best estimated values of parameters for the combined dataset (OHD, BAO/CMB, and Pantheon) are $ H_0 = 71.15\pm 0.26$ km/s/Mpc, $ \Omega_{m0}=0.2625\pm 0.0024$, $ \Omega_{\phi0} = 0.676\pm0.038$, $ \alpha=-0.22\pm0.13$, $n = 0.096\pm0.079$, and $k = 0.38\pm0.32$. The model exhibits a flipping nature, and the redshift transition occurs at $z_t = 0.756^{+0.005}_{-0.015}$. The current value of the decelerated parameter for the proposed model is calculated as $q_0 = -0.625^{+0.067}_{-0.085}$ for the combined dataset. Some dynamical properties of the model like energy density ($\rho_{\phi}$), scalar field pressure ($p_{\phi}$), EoS parameter of scalar field ($\omega_{\phi}$), and effective EoS parameter ($\omega_{eff}$) are analyzed and presented. Further, we have also examined the statefinder diagnosis and jerk parameters of the derived model. The total density parameter for the derived model is found to be unity which is in nice agreement with recent standard findings.
|
gr-qc/9902082
|
Leor Barack
|
Leor Barack and Amos Ori
|
Late-time decay of scalar perturbations outside rotating black holes
|
Submitted to PRL in 16Nov98, resubmitted in 3Feb99; Reference added
|
Phys.Rev.Lett. 82 (1999) 4388
|
10.1103/PhysRevLett.82.4388
| null |
gr-qc
| null |
We present an analytic method for calculating the late-time tails of a linear
scalar field outside a Kerr black hole. We give the asymptotic behavior at
timelike infinity (for fixed $r$), at future null infinity, and along the event
horizon (EH). In all three asymptotic regions we find a power-law decay. We
show that the power indices describing the decay of the various modes at fixed
$r$ differ from the corresponding Schwarzschild values. Also, the scalar field
oscillates along the null generators of the EH (with advanced-time frequency
proportional to the mode's magnetic number $m$).
|
[
{
"created": "Thu, 25 Feb 1999 21:07:47 GMT",
"version": "v1"
},
{
"created": "Sun, 28 Feb 1999 20:13:15 GMT",
"version": "v2"
}
] |
2009-10-31
|
[
[
"Barack",
"Leor",
""
],
[
"Ori",
"Amos",
""
]
] |
We present an analytic method for calculating the late-time tails of a linear scalar field outside a Kerr black hole. We give the asymptotic behavior at timelike infinity (for fixed $r$), at future null infinity, and along the event horizon (EH). In all three asymptotic regions we find a power-law decay. We show that the power indices describing the decay of the various modes at fixed $r$ differ from the corresponding Schwarzschild values. Also, the scalar field oscillates along the null generators of the EH (with advanced-time frequency proportional to the mode's magnetic number $m$).
|
2207.10039
|
Bernardo Araneda
|
Steffen Aksteiner, Bernardo Araneda
|
Kaehler geometry of black holes and gravitational instantons
|
6 pages
| null |
10.1103/PhysRevLett.130.161502
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
We obtain a closed formula for the Kaehler potential of a broad class of
four-dimensional Lorentzian or Euclidean conformal "Kaehler" geometries,
including the Plebanski-Demianski class and various gravitational instantons
such as Fubini-Study and Chen-Teo. We show that the Kaehler potentials of
Schwarzschild and Kerr are related by a Newman-Janis shift. Our method also
shows that a class of supergravity black holes, including the Kerr-Sen
spacetime, is Hermitian (but not conformal Kaehler). We finally show that the
integrability conditions of complex structures lead naturally to the
(non-linear) Weyl double copy, and we give new vacuum and non-vacuum examples
of this relation.
|
[
{
"created": "Wed, 20 Jul 2022 17:08:18 GMT",
"version": "v1"
}
] |
2023-05-03
|
[
[
"Aksteiner",
"Steffen",
""
],
[
"Araneda",
"Bernardo",
""
]
] |
We obtain a closed formula for the Kaehler potential of a broad class of four-dimensional Lorentzian or Euclidean conformal "Kaehler" geometries, including the Plebanski-Demianski class and various gravitational instantons such as Fubini-Study and Chen-Teo. We show that the Kaehler potentials of Schwarzschild and Kerr are related by a Newman-Janis shift. Our method also shows that a class of supergravity black holes, including the Kerr-Sen spacetime, is Hermitian (but not conformal Kaehler). We finally show that the integrability conditions of complex structures lead naturally to the (non-linear) Weyl double copy, and we give new vacuum and non-vacuum examples of this relation.
|
2002.03186
|
Tiberiu Harko
|
Shahab Shahidi, Tiberiu Harko, Zolt\'an Kov\'acs
|
Distinguishing Brans-Dicke-Kerr type naked singularities and black holes
with their thin disk electromagnetic radiation properties
|
20 pages, 6 figures, accepted for publication in EPJC; references
added
|
The European Physical Journal C 80, 162 (2020)
|
10.1140/epjc/s10052-020-7736-x
| null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The possible existence of naked singularities, hypothetical astrophysical
objects, characterized by a gravitational singularity without an event horizon
is still an open problem in present day astrophysics. From an observational
point of view distinguishing between astrophysical black holes and naked
singularities also represents a major challenge. One possible way of
differentiating naked singularities from black holes is through the comparative
study of thin accretion disks properties around these different types of
compact objects. In the present paper we continue the comparative investigation
of accretion disk properties around axially-symmetric rotating geometries in
Brans-Dicke theory in the presence of a massless scalar field. The solution of
the field equations contains the Kerr metric as a particular case, and,
depending on the numerical values of the model parameter $\gamma$, has also
solutions corresponding to non-trivial black holes and naked singularities,
respectively. Due to the differences in the exterior geometries between black
holes and Brans-Dicke-Kerr naked singularities, the thermodynamic and
electromagnetic properties of the disks (energy flux, temperature distribution
and equilibrium radiation spectrum) are different for these two classes of
compact objects, consequently giving clear observational signatures that could
discriminate between black holes and naked singularities.
|
[
{
"created": "Sat, 8 Feb 2020 15:37:20 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Feb 2020 08:25:29 GMT",
"version": "v2"
}
] |
2020-05-19
|
[
[
"Shahidi",
"Shahab",
""
],
[
"Harko",
"Tiberiu",
""
],
[
"Kovács",
"Zoltán",
""
]
] |
The possible existence of naked singularities, hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon is still an open problem in present day astrophysics. From an observational point of view distinguishing between astrophysical black holes and naked singularities also represents a major challenge. One possible way of differentiating naked singularities from black holes is through the comparative study of thin accretion disks properties around these different types of compact objects. In the present paper we continue the comparative investigation of accretion disk properties around axially-symmetric rotating geometries in Brans-Dicke theory in the presence of a massless scalar field. The solution of the field equations contains the Kerr metric as a particular case, and, depending on the numerical values of the model parameter $\gamma$, has also solutions corresponding to non-trivial black holes and naked singularities, respectively. Due to the differences in the exterior geometries between black holes and Brans-Dicke-Kerr naked singularities, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures that could discriminate between black holes and naked singularities.
|
1105.1540
|
Yuri Pavlov
|
A. A. Grib, Yu. V. Pavlov, O. F. Piattella
|
High energy processes in the vicinity of the Kerr's black hole horizon
|
13 pages, 2 figures, added some formulas and one reference
|
Int. J. Mod. Phys. A 26, No. 22 (2011) 3856-3867
|
10.1142/S0217751X11054310
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Two particle collisions close to the horizon of the rotating nonextremal
black hole are analyzed. It is shown that high energy of the order of the Grand
Unification scale in the centre of mass of colliding particles can be obtained
when there is a multiple collision - the particle from the accretion disc gets
the critical momentum in first collision with the other particle close to the
horizon and then there is a second collision of the critical particle with the
ordinary one. High energy occurs due to a great relative velocity of two
particles and a large Lorentz factor. The dependence of the relative velocity
on the distance to horizon is analyzed, the time of movement from the point in
the accretion disc to the point of scattering with large energy as well as the
time of back movement to the Earth are calculated. It is shown that they have
reasonable order.
|
[
{
"created": "Sun, 8 May 2011 18:11:32 GMT",
"version": "v1"
},
{
"created": "Thu, 19 May 2011 15:29:18 GMT",
"version": "v2"
}
] |
2012-03-23
|
[
[
"Grib",
"A. A.",
""
],
[
"Pavlov",
"Yu. V.",
""
],
[
"Piattella",
"O. F.",
""
]
] |
Two particle collisions close to the horizon of the rotating nonextremal black hole are analyzed. It is shown that high energy of the order of the Grand Unification scale in the centre of mass of colliding particles can be obtained when there is a multiple collision - the particle from the accretion disc gets the critical momentum in first collision with the other particle close to the horizon and then there is a second collision of the critical particle with the ordinary one. High energy occurs due to a great relative velocity of two particles and a large Lorentz factor. The dependence of the relative velocity on the distance to horizon is analyzed, the time of movement from the point in the accretion disc to the point of scattering with large energy as well as the time of back movement to the Earth are calculated. It is shown that they have reasonable order.
|
gr-qc/0508035
|
David Delphenich
|
David Delphenich
|
Symmetries and pre-metric electromagnetism
|
53 pages. Annalen der Physik (Leipzig) (2005), to be published
|
AnnalenPhys.14:663-704,2005
|
10.1002/andp.200510159
| null |
gr-qc hep-th
| null |
The equations of pre-metric electromagnetism are formulated as an exterior
differential system on the bundle of exterior differential 2-forms over the
spacetime manifold. The general form for the symmetry equations of the system
is computed and then specialized to various possible forms for an
electromagnetic constitutive law, namely, uniform linear, non-uniform linear,
and uniform nonlinear. It is shown that in the uniform linear case, one has
four possible ways of prolonging the symmetry Lie algebra, including
prolongation to a Lie algebra of infinitesimal projective transformations of a
real four-dimensional projective space. In the most general non-uniform linear
case, th effect of non-uniformity on symmetry seems inconclusive in the absence
of further specifics, and in the uniform nonlinear case, the overall difference
from the uniform linear case amounts to a deformation of the electromagnetic
constitutive tensor by the electromagnetic fields strengths, which induces a
corresponding deformation of the symmetry Lie algebra that was obtained in the
uniform linear case.
|
[
{
"created": "Tue, 9 Aug 2005 20:15:35 GMT",
"version": "v1"
}
] |
2008-11-26
|
[
[
"Delphenich",
"David",
""
]
] |
The equations of pre-metric electromagnetism are formulated as an exterior differential system on the bundle of exterior differential 2-forms over the spacetime manifold. The general form for the symmetry equations of the system is computed and then specialized to various possible forms for an electromagnetic constitutive law, namely, uniform linear, non-uniform linear, and uniform nonlinear. It is shown that in the uniform linear case, one has four possible ways of prolonging the symmetry Lie algebra, including prolongation to a Lie algebra of infinitesimal projective transformations of a real four-dimensional projective space. In the most general non-uniform linear case, th effect of non-uniformity on symmetry seems inconclusive in the absence of further specifics, and in the uniform nonlinear case, the overall difference from the uniform linear case amounts to a deformation of the electromagnetic constitutive tensor by the electromagnetic fields strengths, which induces a corresponding deformation of the symmetry Lie algebra that was obtained in the uniform linear case.
|
gr-qc/9707056
|
Yoonbai Kim
|
Nakwoo Kim, Yoonbai Kim and Kyoungtae Kimm
|
Global Vortex and Black Cosmic String
|
35 pages, Latex
|
Phys.Rev. D56 (1997) 8029-8044
|
10.1103/PhysRevD.56.8029
|
SNUTP-97-088
|
gr-qc hep-th
| null |
We study global vortices coupled to (2+1) dimensional gravity with negative
cosmological constant. We found nonsingular vortex solutions in $\phi^4$-theory
with a broken U(1) symmetry, of which the spacetimes do not involve physical
curvature singularity. When the magnitude of negative cosmological constant is
larger than a critical value at a given symmetry breaking scale, the spacetime
structure is a regular hyperbola, however it becomes a charged black hole when
the magnitude of cosmological constant is less than the critical value. We
explain through duality transformation the reason why static global vortex
which is electrically neutral forms black hole with electric charge. Under the
present experimental bound of the cosmological constant, implications on
cosmology as a straight black cosmic string is also discussed in comparison
with global U(1) cosmic string in the spacetime of the zero cosmological
constant.
|
[
{
"created": "Sun, 27 Jul 1997 10:20:13 GMT",
"version": "v1"
}
] |
2009-10-30
|
[
[
"Kim",
"Nakwoo",
""
],
[
"Kim",
"Yoonbai",
""
],
[
"Kimm",
"Kyoungtae",
""
]
] |
We study global vortices coupled to (2+1) dimensional gravity with negative cosmological constant. We found nonsingular vortex solutions in $\phi^4$-theory with a broken U(1) symmetry, of which the spacetimes do not involve physical curvature singularity. When the magnitude of negative cosmological constant is larger than a critical value at a given symmetry breaking scale, the spacetime structure is a regular hyperbola, however it becomes a charged black hole when the magnitude of cosmological constant is less than the critical value. We explain through duality transformation the reason why static global vortex which is electrically neutral forms black hole with electric charge. Under the present experimental bound of the cosmological constant, implications on cosmology as a straight black cosmic string is also discussed in comparison with global U(1) cosmic string in the spacetime of the zero cosmological constant.
|
1806.03924
|
Jakub Mielczarek Ph.D.
|
Michal Artymowski, Jakub Mielczarek
|
Quantum Hubble horizon
|
15 pages, 3 figures
| null |
10.1140/epjc/s10052-019-7131-7
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The article addresses a possibility of obtaining cosmologically relevant
effects from the quantum nature of the Hubble horizon. Following the
observation made by E.~Bianchi and C.~Rovelli in Phys.\ Rev.\ D {\bf 84} (2011)
027502 we explore relationship between the Planck scale discreteness of the
Hubble horizon and deformations of the symmetry of rotations. We show that the
so-called $q$-deformations in a natural way lead to a mechanism of condensation
in the very early Universe. We argue that this provides a possible resolution
of the problem of initial homogeneity at the onset of inflation. Furthermore,
we perform entropic analysis of the quantum Hubble horizon and show that the
$\Lambda$CDM model may arise from linearly (in area of the horizon) corrected
Bekenstein-Hawking entropy. Based on this, we have shown that the current
accelerating expansion can be associated with the entropy decrease in the
Hubble volume. The presented results open new ways to explore relation between
the Planck scale effects and observationally relevant features of our Universe.
|
[
{
"created": "Mon, 11 Jun 2018 11:43:45 GMT",
"version": "v1"
}
] |
2019-09-04
|
[
[
"Artymowski",
"Michal",
""
],
[
"Mielczarek",
"Jakub",
""
]
] |
The article addresses a possibility of obtaining cosmologically relevant effects from the quantum nature of the Hubble horizon. Following the observation made by E.~Bianchi and C.~Rovelli in Phys.\ Rev.\ D {\bf 84} (2011) 027502 we explore relationship between the Planck scale discreteness of the Hubble horizon and deformations of the symmetry of rotations. We show that the so-called $q$-deformations in a natural way lead to a mechanism of condensation in the very early Universe. We argue that this provides a possible resolution of the problem of initial homogeneity at the onset of inflation. Furthermore, we perform entropic analysis of the quantum Hubble horizon and show that the $\Lambda$CDM model may arise from linearly (in area of the horizon) corrected Bekenstein-Hawking entropy. Based on this, we have shown that the current accelerating expansion can be associated with the entropy decrease in the Hubble volume. The presented results open new ways to explore relation between the Planck scale effects and observationally relevant features of our Universe.
|
gr-qc/0602020
|
Plyatsko Roman
|
Roman Plyatsko
|
Some partial solutions of Mathisson-Papapetrou equations in a
Schwarzschild field
|
27 pages, 8 figures
| null | null | null |
gr-qc
| null |
The analytical and numerical solutions of the Mathisson-Papapetrou equations
under the Mathisson-Pirani supplementary condition describing highly
relativistic (ultrarelativistic) motions of a spinning particle in a
Schwarzschild field are investigated. The known condition S/mr<<1, which is
necessary for a test particle, holds on all these solutions. The explicit
expressions for the non-equatorial circular orbits, in particular for the space
boundaries of the region of existence of these orbits, are obtained. The
dynamics of the deviation of a spinning particle from the equatorial
ultrarelativistic circular orbit with r=3M caused by the non-zero initial value
of the radial particle's velocity is studied. It is shown in the concrete cases
that spin can considerable influence the shape of an ultrarelativistic
trajectory, as compared to the corresponding geodesic trajectory, for the short
time, less than the time of one or two revolutions of a spinning particle
around a Schwarzschild mass.
|
[
{
"created": "Mon, 6 Feb 2006 14:21:40 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Feb 2006 09:28:24 GMT",
"version": "v2"
}
] |
2007-05-23
|
[
[
"Plyatsko",
"Roman",
""
]
] |
The analytical and numerical solutions of the Mathisson-Papapetrou equations under the Mathisson-Pirani supplementary condition describing highly relativistic (ultrarelativistic) motions of a spinning particle in a Schwarzschild field are investigated. The known condition S/mr<<1, which is necessary for a test particle, holds on all these solutions. The explicit expressions for the non-equatorial circular orbits, in particular for the space boundaries of the region of existence of these orbits, are obtained. The dynamics of the deviation of a spinning particle from the equatorial ultrarelativistic circular orbit with r=3M caused by the non-zero initial value of the radial particle's velocity is studied. It is shown in the concrete cases that spin can considerable influence the shape of an ultrarelativistic trajectory, as compared to the corresponding geodesic trajectory, for the short time, less than the time of one or two revolutions of a spinning particle around a Schwarzschild mass.
|
1511.03578
|
Maria Laura Pucheu
|
F. Briscese and M. L. Pucheu
|
Palatini formulation of non-local gravity
|
10 pages
| null |
10.1142/S0219887817500190
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We derive the dynamical equations for a non-local gravity model in the
Palatini formalism and we discuss some of the properties of this model. We have
shown that, in some specific cases, the vacuum solutions of general relativity
are also vacuum solutions of the non-local model, so we conclude that, at least
in this case, the singularities of Einstein's gravity are not removed.
|
[
{
"created": "Wed, 11 Nov 2015 17:11:43 GMT",
"version": "v1"
},
{
"created": "Mon, 11 Jan 2016 22:27:33 GMT",
"version": "v2"
},
{
"created": "Wed, 30 Nov 2016 12:42:11 GMT",
"version": "v3"
}
] |
2016-12-16
|
[
[
"Briscese",
"F.",
""
],
[
"Pucheu",
"M. L.",
""
]
] |
We derive the dynamical equations for a non-local gravity model in the Palatini formalism and we discuss some of the properties of this model. We have shown that, in some specific cases, the vacuum solutions of general relativity are also vacuum solutions of the non-local model, so we conclude that, at least in this case, the singularities of Einstein's gravity are not removed.
|
1912.04604
|
Mar\'ia Jos\'e Guzm\'an
|
Alexey Golovnev, Maria Jose Guzman
|
Disformal transformations in modified teleparallel gravity
|
12 pages, no figures; prepared for proceedings of the 10th
Mathematical Physics Meeting: School and Conference on Modern Mathematical
Physics, 9 - 14 September 2019, Belgrade, Serbia, in which one of us (AG)
participated; matches the published version
|
Symmetry 12 (2020) 152
|
10.3390/sym12010152
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by-nc-sa/4.0/
|
In this work, we explore disformal transformations in the context of the
teleparallel equivalent of general relativity and modified teleparallel
gravity. We present explicit formulas in components for disformal
transformations of the main geometric objects in these theories such as torsion
tensor, torsion vector and contortion. Most importantly, we consider the
boundary term which distinguishes the torsion scalar from the Ricci scalar.
With that we show for $f(T)$ gravity that disformal transformations from the
Jordan frame representation are unable to straightforwardly remove local
Lorentz breaking terms that characterize it. However, we have shown that
disformal transformations have interesting properties, which can be useful for
future applications in scalar-torsion gravity models, among others.
|
[
{
"created": "Tue, 10 Dec 2019 10:01:20 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Jan 2020 03:22:18 GMT",
"version": "v2"
}
] |
2020-01-15
|
[
[
"Golovnev",
"Alexey",
""
],
[
"Guzman",
"Maria Jose",
""
]
] |
In this work, we explore disformal transformations in the context of the teleparallel equivalent of general relativity and modified teleparallel gravity. We present explicit formulas in components for disformal transformations of the main geometric objects in these theories such as torsion tensor, torsion vector and contortion. Most importantly, we consider the boundary term which distinguishes the torsion scalar from the Ricci scalar. With that we show for $f(T)$ gravity that disformal transformations from the Jordan frame representation are unable to straightforwardly remove local Lorentz breaking terms that characterize it. However, we have shown that disformal transformations have interesting properties, which can be useful for future applications in scalar-torsion gravity models, among others.
|
gr-qc/0307001
|
Richard O'Shaughenssy
|
R. O'Shaughnessy
|
Geometrical optics analysis of the short-time stability properties of
the Einstein evolution equations
|
Submitted to Phys. Rev. D
|
Phys.Rev.D68:084024,2003
|
10.1103/PhysRevD.68.084024
| null |
gr-qc
| null |
Many alternative formulations of Einstein's evolution have lately been
examined, in an effort to discover one which yields slow growth of
constraint-violating errors. In this paper, rather than directly search for
well-behaved formulations, we instead develop analytic tools to discover which
formulations are particularly ill-behaved. Specifically, we examine the growth
of approximate (geometric-optics) solutions, studied only in the future domain
of dependence of the initial data slice (e.g. we study transients). By
evaluating the amplification of transients a given formulation will produce, we
may therefore eliminate from consideration the most pathological formulations
(e.g. those with numerically-unacceptable amplification). This technique has
the potential to provide surprisingly tight constraints on the set of
formulations one can safely apply. To illustrate the application of these
techniques to practical examples, we apply our technique to the 2-parameter
family of evolution equations proposed by Kidder, Scheel, and Teukolsky,
focusing in particular on flat space (in Rindler coordinates) and Schwarzchild
(in Painleve-Gullstrand coordinates).
|
[
{
"created": "Mon, 30 Jun 2003 20:08:07 GMT",
"version": "v1"
}
] |
2009-04-03
|
[
[
"O'Shaughnessy",
"R.",
""
]
] |
Many alternative formulations of Einstein's evolution have lately been examined, in an effort to discover one which yields slow growth of constraint-violating errors. In this paper, rather than directly search for well-behaved formulations, we instead develop analytic tools to discover which formulations are particularly ill-behaved. Specifically, we examine the growth of approximate (geometric-optics) solutions, studied only in the future domain of dependence of the initial data slice (e.g. we study transients). By evaluating the amplification of transients a given formulation will produce, we may therefore eliminate from consideration the most pathological formulations (e.g. those with numerically-unacceptable amplification). This technique has the potential to provide surprisingly tight constraints on the set of formulations one can safely apply. To illustrate the application of these techniques to practical examples, we apply our technique to the 2-parameter family of evolution equations proposed by Kidder, Scheel, and Teukolsky, focusing in particular on flat space (in Rindler coordinates) and Schwarzchild (in Painleve-Gullstrand coordinates).
|
0801.0212
|
Sergey Cherkas L
|
K. A. Viarenich, V. L. Kalashnikov, S. L. Cherkas
|
Quantum mechanics of the closed collapsing Universe
|
8 pages 1 figire
|
Vestnik Belarus State U., ser. Fiz. 2 (2007) 3-7
| null | null |
gr-qc
| null |
Two approaches to quantization of Freedman's closed Universe are compared. In
the first approach, the Shrodinger's norm of the wave function of Universe is
used, and in the second approach, the Klein-Gordon's norm is used. The second
one allows building the quasi-Heisenberg operators as functions of time and
finding their average values. It is shown that the average value of the
Universe scale factor oscillates with damping and approaches to some constant
value at the end of the Universe evolution.
|
[
{
"created": "Mon, 31 Dec 2007 14:52:18 GMT",
"version": "v1"
}
] |
2008-01-03
|
[
[
"Viarenich",
"K. A.",
""
],
[
"Kalashnikov",
"V. L.",
""
],
[
"Cherkas",
"S. L.",
""
]
] |
Two approaches to quantization of Freedman's closed Universe are compared. In the first approach, the Shrodinger's norm of the wave function of Universe is used, and in the second approach, the Klein-Gordon's norm is used. The second one allows building the quasi-Heisenberg operators as functions of time and finding their average values. It is shown that the average value of the Universe scale factor oscillates with damping and approaches to some constant value at the end of the Universe evolution.
|
0705.1565
|
Christopher Eling
|
Christopher Eling, Ted Jacobson, M. Coleman Miller
|
Neutron stars in Einstein-aether theory
|
25 pages, 4 figures; v2: simplified the discussion of aether-matter
couplings, removed one extraneous mass vs. pressure plot, added brief
discussion of ae-theory effects in Ozel's mass determination method; v3:
corrected the equation for aether stress tensor, results unchanged since
correct form was used in calculations
|
Phys.Rev.D76:042003,2007; Erratum-ibid.D80:129906,2009
|
10.1103/PhysRevD.76.042003 10.1103/PhysRevD.80.129906
| null |
gr-qc astro-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
As current and future experiments probe strong gravitational regimes around
neutron stars and black holes, it is desirable to have theoretically sound
alternatives to general relativity against which to test observations. Here we
study the consequences of one such generalization, Einstein-aether theory, for
the properties of non-rotating neutron stars. This theory has a parameter range
that satisfies all current weak-field tests. We find that within this range it
leads to lower maximum neutron star masses, as well as larger surface redshifts
at a particular mass, for a given nuclear equation of state. For non-rotating
black holes and neutron stars, the innermost stable circular orbit is only
slightly modified in this theory.
|
[
{
"created": "Thu, 10 May 2007 23:16:38 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Aug 2007 20:01:02 GMT",
"version": "v2"
},
{
"created": "Sun, 6 Dec 2009 14:19:48 GMT",
"version": "v3"
}
] |
2014-11-18
|
[
[
"Eling",
"Christopher",
""
],
[
"Jacobson",
"Ted",
""
],
[
"Miller",
"M. Coleman",
""
]
] |
As current and future experiments probe strong gravitational regimes around neutron stars and black holes, it is desirable to have theoretically sound alternatives to general relativity against which to test observations. Here we study the consequences of one such generalization, Einstein-aether theory, for the properties of non-rotating neutron stars. This theory has a parameter range that satisfies all current weak-field tests. We find that within this range it leads to lower maximum neutron star masses, as well as larger surface redshifts at a particular mass, for a given nuclear equation of state. For non-rotating black holes and neutron stars, the innermost stable circular orbit is only slightly modified in this theory.
|
2107.05656
|
Theodoros Nakas
|
Athanasios Bakopoulos and Theodoros Nakas
|
Analytic and asymptotically flat hairy (ultra-compact) black-hole
solutions and their axial perturbations
|
23 pages, 8 figures, title changed, analysis extended, references
updated, typos corrected, matches published version (to appear in JHEP)
| null |
10.1007/JHEP04(2022)096
| null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this work, we consider a very simple gravitational theory that contains a
scalar field with its kinetic and potential terms minimally coupled to gravity,
while the scalar field is assumed to have a coulombic form. In the context of
this theory, we study an analytic, asymptotically flat, and regular
(ultra-compact) black-hole solutions with non-trivial scalar hair of secondary
type. At first, we examine the properties of the static and spherically
symmetric black-hole solution -- firstly appeared in 1504.08209 [gr-qc] -- and
we find that in the causal region of the spacetime the stress-energy tensor,
needed to support our solution, satisfies the strong energy conditions. Then,
by using the slow-rotating approximation, we generalize the static solution
into a slowly rotating one, and we determine explicitly its angular velocity
$\omega(r)$. We also find that the angular velocity of our ultra-compact
solution is always larger compared to the angular velocity of the corresponding
equally massive slow-rotating Schwarzschild black hole. In addition, we
investigate the axial perturbations of the derived solutions by determining the
Schr\"{o}dinger-like equation and the effective potential. We show that there
is a region in the parameter space of the free parameters of our theory, which
allows for the existence of stable ultra-compact black hole solutions.
Specifically, we calculate that the most compact and stable black hole solution
is 0.551 times smaller than the Schwarzschild one, while it rotates 2.491 times
faster compared to the slow-rotating Schwarzschild black hole. Finally, we
present without going into details the generalization of the derived
asymptotically flat solutions to asymptotically (A)dS solutions.
|
[
{
"created": "Mon, 12 Jul 2021 18:00:13 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Apr 2022 17:00:33 GMT",
"version": "v2"
}
] |
2022-04-21
|
[
[
"Bakopoulos",
"Athanasios",
""
],
[
"Nakas",
"Theodoros",
""
]
] |
In this work, we consider a very simple gravitational theory that contains a scalar field with its kinetic and potential terms minimally coupled to gravity, while the scalar field is assumed to have a coulombic form. In the context of this theory, we study an analytic, asymptotically flat, and regular (ultra-compact) black-hole solutions with non-trivial scalar hair of secondary type. At first, we examine the properties of the static and spherically symmetric black-hole solution -- firstly appeared in 1504.08209 [gr-qc] -- and we find that in the causal region of the spacetime the stress-energy tensor, needed to support our solution, satisfies the strong energy conditions. Then, by using the slow-rotating approximation, we generalize the static solution into a slowly rotating one, and we determine explicitly its angular velocity $\omega(r)$. We also find that the angular velocity of our ultra-compact solution is always larger compared to the angular velocity of the corresponding equally massive slow-rotating Schwarzschild black hole. In addition, we investigate the axial perturbations of the derived solutions by determining the Schr\"{o}dinger-like equation and the effective potential. We show that there is a region in the parameter space of the free parameters of our theory, which allows for the existence of stable ultra-compact black hole solutions. Specifically, we calculate that the most compact and stable black hole solution is 0.551 times smaller than the Schwarzschild one, while it rotates 2.491 times faster compared to the slow-rotating Schwarzschild black hole. Finally, we present without going into details the generalization of the derived asymptotically flat solutions to asymptotically (A)dS solutions.
|
gr-qc/0406005
|
Grigory Volovik
|
G.E. Volovik
|
On thermodynamic and quantum fluctuations of cosmological constant
|
4 pages, version submitted to JETP Letters
|
JETP Lett. 80 (2004) 465-468
|
10.1134/1.1839291
| null |
gr-qc cond-mat.stat-mech hep-ph
| null |
We discuss from the condensed-matter point of view the recent idea that the
Poisson fluctuations of cosmological constant about zero could be a source of
the observed dark energy. We argue that the thermodynamic fluctuations of
Lambda are much bigger. Since the amplitude of fluctuations is proportional to
V^{-1/2}, where V is the volume of the Universe, the present constraint on the
cosmological constant provides the lower limit for V, which is much bigger than
the volume within the cosmological horizon.
|
[
{
"created": "Wed, 2 Jun 2004 13:36:02 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Jun 2004 12:26:58 GMT",
"version": "v2"
},
{
"created": "Mon, 12 Jul 2004 14:56:18 GMT",
"version": "v3"
},
{
"created": "Fri, 23 Jul 2004 13:55:49 GMT",
"version": "v4"
},
{
"created": "Mon, 6 Sep 2004 10:57:04 GMT",
"version": "v5"
}
] |
2009-11-10
|
[
[
"Volovik",
"G. E.",
""
]
] |
We discuss from the condensed-matter point of view the recent idea that the Poisson fluctuations of cosmological constant about zero could be a source of the observed dark energy. We argue that the thermodynamic fluctuations of Lambda are much bigger. Since the amplitude of fluctuations is proportional to V^{-1/2}, where V is the volume of the Universe, the present constraint on the cosmological constant provides the lower limit for V, which is much bigger than the volume within the cosmological horizon.
|
1812.09623
|
\.Izzet Sakall{\i}
|
\.Izzet Sakall{\i} and G\"ulnihal Tokg\"oz
|
Spectroscopy of Stringy Black Hole
|
Some typos have been fixed. 8 pages & 1 figure. The 10th
International Physics Conference of the Balkan Physical Union (BPU10), 26-30
August 2018. To be published in AIP Conference Proceedings in April 2019
|
AIP Conference Proceedings 2075, 040001 (2019)
|
10.1063/1.5091161
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The Maggiore's method, which evaluates the transition frequency that appears
in the adiabatic invariant from the highly damped modes, is used to investigate
the entropy/area spectra of the Garfinkle-Horowitz-Strominger black hole
(GHS-BH). We compute the resonance modes of the GHS-BH by using the confined
scalar waves having high azimuthal quantum number. Although the area and
entropy are characterized by the GHS-BH parameters, their quantizations are
shown to be independent of those parameters. However, both spectra are equally
spaced.
|
[
{
"created": "Sat, 22 Dec 2018 23:21:18 GMT",
"version": "v1"
},
{
"created": "Sat, 16 Feb 2019 20:44:39 GMT",
"version": "v2"
}
] |
2020-02-11
|
[
[
"Sakallı",
"İzzet",
""
],
[
"Tokgöz",
"Gülnihal",
""
]
] |
The Maggiore's method, which evaluates the transition frequency that appears in the adiabatic invariant from the highly damped modes, is used to investigate the entropy/area spectra of the Garfinkle-Horowitz-Strominger black hole (GHS-BH). We compute the resonance modes of the GHS-BH by using the confined scalar waves having high azimuthal quantum number. Although the area and entropy are characterized by the GHS-BH parameters, their quantizations are shown to be independent of those parameters. However, both spectra are equally spaced.
|
gr-qc/0512027
|
Peter Kuhfittig K.F.
|
Peter K.F. Kuhfittig
|
More on wormholes supported by small amounts of exotic matter
|
8 pages AMSTeX; 3 figures added
|
Phys.Rev. D73 (2006) 084014
|
10.1103/PhysRevD.73.084014
| null |
gr-qc
| null |
Recent papers by Fewster and Roman have emphasized that wormholes supported
by arbitrarily small amounts of exotic matter will have to be incredibly
fine-tuned if they are to be traversable. This paper discusses a wormhole model
that strikes a balance between two conflicting requirements, reducing the
amount of exotic matter and fine-tuning the metric coefficients, ultimately
resulting in an engineering challenge: one requirement can only be met at the
expense of the other. The wormhole model is macroscopic and satisfies various
traversability criteria.
|
[
{
"created": "Mon, 5 Dec 2005 15:34:59 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Apr 2006 20:24:13 GMT",
"version": "v2"
}
] |
2009-11-11
|
[
[
"Kuhfittig",
"Peter K. F.",
""
]
] |
Recent papers by Fewster and Roman have emphasized that wormholes supported by arbitrarily small amounts of exotic matter will have to be incredibly fine-tuned if they are to be traversable. This paper discusses a wormhole model that strikes a balance between two conflicting requirements, reducing the amount of exotic matter and fine-tuning the metric coefficients, ultimately resulting in an engineering challenge: one requirement can only be met at the expense of the other. The wormhole model is macroscopic and satisfies various traversability criteria.
|
2401.12454
|
Ming Chen
|
Ming Chen, Gabriele Tartaglino-Mazzucchelli, Yao-Zhong Zhang
|
Charged massless scalar fields in a charged $C$-metric black hole: Exact
solutions, Hawking radiation and scattering of scalar waves
|
33 pages
| null | null | null |
gr-qc hep-th math-ph math.MP
|
http://creativecommons.org/licenses/by/4.0/
|
We study Hawking radiation and wave scattering of charged scalar fields in a
charged $C$-metric black hole background. The conformally invariant wave
equation for charged scalar fields can be separated into radial and angular
parts, each with five singularities. We show that the radial and angular
equations can be respectively transformed into the general Heun equation. We
explore exact solutions of the radial Heun equation in terms of the local Heun
functions and connection coefficients. Exact behaviours of the asymptotic wave
functions are determined without approximations. We apply the exact results to
derive Hawking radiation, quasi-normal modes and superradiance. Since
quasinormal modes are significant for black holes through gravitional waves, we
present the numeric results for quasinormal modes, and show the dependence upon
the $C$-metric parameters and the charge of scalar fields. The analytic
expressions of the solutions allow us to make fast numerical calculations of
high precision without restrictions on the model parameters.
|
[
{
"created": "Tue, 23 Jan 2024 02:50:12 GMT",
"version": "v1"
},
{
"created": "Sun, 11 Feb 2024 01:00:10 GMT",
"version": "v2"
}
] |
2024-02-13
|
[
[
"Chen",
"Ming",
""
],
[
"Tartaglino-Mazzucchelli",
"Gabriele",
""
],
[
"Zhang",
"Yao-Zhong",
""
]
] |
We study Hawking radiation and wave scattering of charged scalar fields in a charged $C$-metric black hole background. The conformally invariant wave equation for charged scalar fields can be separated into radial and angular parts, each with five singularities. We show that the radial and angular equations can be respectively transformed into the general Heun equation. We explore exact solutions of the radial Heun equation in terms of the local Heun functions and connection coefficients. Exact behaviours of the asymptotic wave functions are determined without approximations. We apply the exact results to derive Hawking radiation, quasi-normal modes and superradiance. Since quasinormal modes are significant for black holes through gravitional waves, we present the numeric results for quasinormal modes, and show the dependence upon the $C$-metric parameters and the charge of scalar fields. The analytic expressions of the solutions allow us to make fast numerical calculations of high precision without restrictions on the model parameters.
|
0710.1430
|
Natalia Kiriushcheva
|
K. R. Green, N. Kiriushcheva, S. V. Kuzmin
|
Analysis of Hamiltonian formulations of linearized General Relativity
|
Section Discussion is modified and references are added; 19 pages
|
Eur. Phys. J. C71:1678,2011
|
10.1140/epjc/s10052-011-1678-2
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The different forms of the Hamiltonian formulations of linearized General
Relativity/spin-two theories are discussed in order to show their similarities
and differences. It is demonstrated that in the linear model, non-covariant
modifications to the initial covariant Lagrangian (similar to those
modifications used in full gravity) are in fact unnecessary. The Hamiltonians
and the constraints are different in these two formulations but the structure
of the constraint algebra and the gauge invariance derived from it are the
same. It is shown that these equivalent Hamiltonian formulations are related to
each other by a canonical transformation which is explicitly given. The
relevance of these results to the full theory of General Relativity is briefly
discussed.
|
[
{
"created": "Sun, 7 Oct 2007 16:28:33 GMT",
"version": "v1"
},
{
"created": "Tue, 5 Aug 2008 17:53:21 GMT",
"version": "v2"
},
{
"created": "Mon, 11 Jul 2011 00:20:04 GMT",
"version": "v3"
}
] |
2011-07-18
|
[
[
"Green",
"K. R.",
""
],
[
"Kiriushcheva",
"N.",
""
],
[
"Kuzmin",
"S. V.",
""
]
] |
The different forms of the Hamiltonian formulations of linearized General Relativity/spin-two theories are discussed in order to show their similarities and differences. It is demonstrated that in the linear model, non-covariant modifications to the initial covariant Lagrangian (similar to those modifications used in full gravity) are in fact unnecessary. The Hamiltonians and the constraints are different in these two formulations but the structure of the constraint algebra and the gauge invariance derived from it are the same. It is shown that these equivalent Hamiltonian formulations are related to each other by a canonical transformation which is explicitly given. The relevance of these results to the full theory of General Relativity is briefly discussed.
|
1701.06087
|
Anzhong Wang
|
Anzhong Wang
|
Ho\v{r}ava Gravity at a Lifshitz Point: A Progress Report
|
revtex4, three figures. Corrected various typos. Int. J. Mod. Phys.
D26 (2017) 1730014
|
Int. J. Mod. Phys. D26 (2017) 1730014
|
10.1142/S0218271817300142
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Ho\v{r}ava gravity at a Lifshitz point is a theory intended to quantize
gravity by using techniques of traditional quantum field theories. To avoid
Ostrogradsky's ghosts, a problem that has been plaguing quantization of general
relativity since the middle of 1970's, Ho\v{r}ava chose to break the Lorentz
invariance by a Lifshitz-type of anisotropic scaling between space and time at
the ultra-high energy, while recovering (approximately) the invariance at low
energies. With the stringent observational constraints and self-consistency, it
turns out that this is not an easy task, and various modifications have been
proposed, since the first incarnation of the theory in 2009. In this review, we
shall provide a progress report on the recent developments of Ho\v{r}ava
gravity. In particular, we first present four most-studied versions of
Ho\v{r}ava gravity, by focusing first on their self-consistency and then their
consistency with experiments, including the solar system tests and cosmological
observations. Then, we provide a general review on the recent developments of
the theory in three different but also related areas: (i) universal horizons,
black holes and their thermodynamics; (ii) non-relativistic gauge/gravity
duality; and (iii) quantization of the theory. The studies in these areas can
be generalized to other gravitational theories with broken Lorentz invariance.
|
[
{
"created": "Sat, 21 Jan 2017 21:12:15 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Feb 2017 00:27:23 GMT",
"version": "v2"
},
{
"created": "Tue, 4 Apr 2017 00:53:16 GMT",
"version": "v3"
}
] |
2017-04-05
|
[
[
"Wang",
"Anzhong",
""
]
] |
Ho\v{r}ava gravity at a Lifshitz point is a theory intended to quantize gravity by using techniques of traditional quantum field theories. To avoid Ostrogradsky's ghosts, a problem that has been plaguing quantization of general relativity since the middle of 1970's, Ho\v{r}ava chose to break the Lorentz invariance by a Lifshitz-type of anisotropic scaling between space and time at the ultra-high energy, while recovering (approximately) the invariance at low energies. With the stringent observational constraints and self-consistency, it turns out that this is not an easy task, and various modifications have been proposed, since the first incarnation of the theory in 2009. In this review, we shall provide a progress report on the recent developments of Ho\v{r}ava gravity. In particular, we first present four most-studied versions of Ho\v{r}ava gravity, by focusing first on their self-consistency and then their consistency with experiments, including the solar system tests and cosmological observations. Then, we provide a general review on the recent developments of the theory in three different but also related areas: (i) universal horizons, black holes and their thermodynamics; (ii) non-relativistic gauge/gravity duality; and (iii) quantization of the theory. The studies in these areas can be generalized to other gravitational theories with broken Lorentz invariance.
|
1410.2581
|
Ilya Lvovich Shapiro
|
Ilya L. Shapiro (UFJF), Ana M. Pelinson (UFSC), Filipe de O. Salles
(UFJF)
|
Gravitational Waves and Perspectives for Quantum Gravity
|
21 pages, 4 figures. LaTeX with WS style. Invited Brief Review
published in Modern Physics Letters A
|
Modern Physics Letters. A29 No. 30 (2014) 1430034-1
|
10.1142/S0217732314300341
| null |
gr-qc hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Understanding the role of higher derivatives is probably one of the most
relevant questions in quantum gravity theory. Already at the semiclassical
level, when gravity is a classical background for quantum matter fields, the
action of gravity should include fourth derivative terms to provide
renormalizability in the vacuum sector. The same situation holds in the quantum
theory of metric. At the same time, including the fourth derivative terms means
the presence of massive ghosts, which are gauge-independent massive states with
negative kinetic energy. At both classical and quantum level such ghosts
violate stability and hence the theory becomes inconsistent. Several approaches
to solve this contradiction were invented and we are proposing one more, which
looks simpler than those what were considered before. We explore the dynamics
of the gravitational waves on the background of classical solutions and give
certain arguments that massive ghosts produce instability only when they are
present as physical particles. At least on the cosmological background one can
observe that if the initial frequency of the metric perturbations is much
smaller than the mass of the ghost, no instabilities are present.
|
[
{
"created": "Thu, 9 Oct 2014 19:18:32 GMT",
"version": "v1"
}
] |
2014-10-10
|
[
[
"Shapiro",
"Ilya L.",
"",
"UFJF"
],
[
"Pelinson",
"Ana M.",
"",
"UFSC"
],
[
"Salles",
"Filipe de O.",
"",
"UFJF"
]
] |
Understanding the role of higher derivatives is probably one of the most relevant questions in quantum gravity theory. Already at the semiclassical level, when gravity is a classical background for quantum matter fields, the action of gravity should include fourth derivative terms to provide renormalizability in the vacuum sector. The same situation holds in the quantum theory of metric. At the same time, including the fourth derivative terms means the presence of massive ghosts, which are gauge-independent massive states with negative kinetic energy. At both classical and quantum level such ghosts violate stability and hence the theory becomes inconsistent. Several approaches to solve this contradiction were invented and we are proposing one more, which looks simpler than those what were considered before. We explore the dynamics of the gravitational waves on the background of classical solutions and give certain arguments that massive ghosts produce instability only when they are present as physical particles. At least on the cosmological background one can observe that if the initial frequency of the metric perturbations is much smaller than the mass of the ghost, no instabilities are present.
|
2201.00599
|
Yang Liu
|
Yang Liu
|
The effect of quantum correction on Hawking radiation for Schwarzschild
black holes
| null | null | null | null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
We investigate the effect of quantum correction on Hawking radiation for
Schwarzschild black holes. We consider Hawking temperature and entropy to order
G^2 and find that the area law of black holes should be modified. We think of
Hawking radiation as tunneling and find that at certain frequency {\omega} the
radiation spectrum of black holes can be pure blackbody spectrum. Therefore, it
is possible to break down information conservation. In order to ensure
information conservation at any energy scales, we suggest that black holes
cannot release all information they have. We briefly discuss the bound on
greybody factors for Schwarzschild black holes as well. Since the modification
of horizon is very tiny, the bound on greybody factors has a very small
difference between classical metric and quantum corrected metric.
|
[
{
"created": "Mon, 3 Jan 2022 12:02:32 GMT",
"version": "v1"
}
] |
2022-01-04
|
[
[
"Liu",
"Yang",
""
]
] |
We investigate the effect of quantum correction on Hawking radiation for Schwarzschild black holes. We consider Hawking temperature and entropy to order G^2 and find that the area law of black holes should be modified. We think of Hawking radiation as tunneling and find that at certain frequency {\omega} the radiation spectrum of black holes can be pure blackbody spectrum. Therefore, it is possible to break down information conservation. In order to ensure information conservation at any energy scales, we suggest that black holes cannot release all information they have. We briefly discuss the bound on greybody factors for Schwarzschild black holes as well. Since the modification of horizon is very tiny, the bound on greybody factors has a very small difference between classical metric and quantum corrected metric.
|
1105.2658
|
Jackson Levi Said
|
Jackson Levi Said, Kristian Zarb Adami
|
Rotating Charged Cylindrical Black Holes as Particle Accelerators
|
6 pages, 2 figures, Phys. Rev. D 83, 104047 (2011)
|
Phys.Rev.D83:104047,2011
|
10.1103/PhysRevD.83.104047
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
It has recently been pointed out that arbitrary center-of-mass energies may
be obtained for particle collisions near the horizon of an extremal Kerr black
hole. We investigate this mechanism in cylindrical topology. In particular we
consider the center-of-mass energies of a cylindrical black hole with an
extremal rotation and charge parameter. The geodesics are first derived with a
rotating charged cylindrical black hole producing the background gravitational
field. Finally the center-of-mass is determined for this background and its
extremal limit is taken.
|
[
{
"created": "Fri, 13 May 2011 08:40:54 GMT",
"version": "v1"
},
{
"created": "Sat, 28 May 2011 13:07:49 GMT",
"version": "v2"
},
{
"created": "Sun, 10 Jul 2011 21:27:01 GMT",
"version": "v3"
}
] |
2015-03-19
|
[
[
"Said",
"Jackson Levi",
""
],
[
"Adami",
"Kristian Zarb",
""
]
] |
It has recently been pointed out that arbitrary center-of-mass energies may be obtained for particle collisions near the horizon of an extremal Kerr black hole. We investigate this mechanism in cylindrical topology. In particular we consider the center-of-mass energies of a cylindrical black hole with an extremal rotation and charge parameter. The geodesics are first derived with a rotating charged cylindrical black hole producing the background gravitational field. Finally the center-of-mass is determined for this background and its extremal limit is taken.
|
2007.03211
|
Handhika Ramadhan
|
A S. Habibina and H.S. Ramadhan
|
Geodesic of nonlinear electrodynamics and stable photon orbits
|
30 pages, 19 figures
|
Phys.Rev. D101 (2020) no.12, 124036
|
10.1103/PhysRevD.101.124036
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the geodesics of charged black holes in polynomial Maxwell
Lagrangians, a subclass of models within the nonlinear electrodynamics (NLED).
Specifically, we consider black holes in Kruglov, power-law, and
Ayon-Beato-Garcia models. Our exploration on the corresponding null bound
states reveals that photon can orbit the extremal black holes in stable radii
outside the corresponding horizon. The reason behind this is the well-known
theorem that a photon in a NLED background propagates along its own {\it
effective} geometry. This nonlinearity is able to shift the local minimum of
the effective potential away from its corresponding outer horizon. For the null
scattering states we obtain corrections to the weak deflection angle off the
black holes. We rule out the power-law model to be physical since its
deflection angle does not reduce to the Schwarzschild in the limit of the
vanishing charge.
|
[
{
"created": "Tue, 7 Jul 2020 05:46:41 GMT",
"version": "v1"
}
] |
2020-07-08
|
[
[
"Habibina",
"A S.",
""
],
[
"Ramadhan",
"H. S.",
""
]
] |
We study the geodesics of charged black holes in polynomial Maxwell Lagrangians, a subclass of models within the nonlinear electrodynamics (NLED). Specifically, we consider black holes in Kruglov, power-law, and Ayon-Beato-Garcia models. Our exploration on the corresponding null bound states reveals that photon can orbit the extremal black holes in stable radii outside the corresponding horizon. The reason behind this is the well-known theorem that a photon in a NLED background propagates along its own {\it effective} geometry. This nonlinearity is able to shift the local minimum of the effective potential away from its corresponding outer horizon. For the null scattering states we obtain corrections to the weak deflection angle off the black holes. We rule out the power-law model to be physical since its deflection angle does not reduce to the Schwarzschild in the limit of the vanishing charge.
|
gr-qc/9606022
|
Jorge Pullin
|
Carsten Gundlach and Jorge Pullin
|
Ill-posedness of a double null free evolution scheme for black hole
spacetimes
|
5 pages, RevTeX, 1 figure, changes in introduction, title and
conclusions, figure added, to appear in Classical and Quantum Gravity
|
Class.Quant.Grav. 14 (1997) 991
|
10.1088/0264-9381/14/4/014
|
CGPG-96/6-3, LAEFF-96/11
|
gr-qc
| null |
We suggest that ``free evolution'' integration schemes for the Einstein
equations (that do not enforce constraints) may contain exponentially growing
modes that render them useless in numerical integrations of black hole
spacetimes, independently of how the equations are differenced. As an example
we consider the evolution of Schwarzschild and Reissner-Nordstr\"om spacetimes
in double null coordinates.
|
[
{
"created": "Tue, 11 Jun 1996 15:22:09 GMT",
"version": "v1"
},
{
"created": "Wed, 29 Jan 1997 15:23:17 GMT",
"version": "v2"
}
] |
2009-10-28
|
[
[
"Gundlach",
"Carsten",
""
],
[
"Pullin",
"Jorge",
""
]
] |
We suggest that ``free evolution'' integration schemes for the Einstein equations (that do not enforce constraints) may contain exponentially growing modes that render them useless in numerical integrations of black hole spacetimes, independently of how the equations are differenced. As an example we consider the evolution of Schwarzschild and Reissner-Nordstr\"om spacetimes in double null coordinates.
|
1705.01378
|
Peter Horvathy
|
P.-M. Zhang, C. Duval, G. W. Gibbons and P. A. Horvathy
|
Soft Gravitons & the Memory Effect for Plane Gravitational Waves
|
40 pages, many figures. Matches published version
|
Phys. Rev. D 96, 064013 (2017)
|
10.1103/PhysRevD.96.064013
| null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The "gravitational memory effect" due to an exact plane wave provides us with
an elementary description of the diffeomorphisms associated with soft
gravitons. It is explained how the presence of the latter may be detected by
observing the motion of freely falling particles or other forms of
gravitational wave detection. Numerical calculations confirm the relevance of
the first, second and third time integrals of the Riemann tensor pointed out
earlier. Solutions for various profiles are constructed. It is also shown how
to extend our treatment to Einstein-Maxwell plane waves and a midi-superspace
quantization is given.
|
[
{
"created": "Wed, 3 May 2017 12:13:07 GMT",
"version": "v1"
},
{
"created": "Wed, 10 May 2017 14:52:46 GMT",
"version": "v2"
},
{
"created": "Tue, 30 May 2017 06:06:09 GMT",
"version": "v3"
},
{
"created": "Fri, 29 Sep 2017 16:53:54 GMT",
"version": "v4"
}
] |
2017-10-02
|
[
[
"Zhang",
"P. -M.",
""
],
[
"Duval",
"C.",
""
],
[
"Gibbons",
"G. W.",
""
],
[
"Horvathy",
"P. A.",
""
]
] |
The "gravitational memory effect" due to an exact plane wave provides us with an elementary description of the diffeomorphisms associated with soft gravitons. It is explained how the presence of the latter may be detected by observing the motion of freely falling particles or other forms of gravitational wave detection. Numerical calculations confirm the relevance of the first, second and third time integrals of the Riemann tensor pointed out earlier. Solutions for various profiles are constructed. It is also shown how to extend our treatment to Einstein-Maxwell plane waves and a midi-superspace quantization is given.
|
0810.1120
|
Roberto A. Sussman
|
Roberto A. Sussman
|
Quasi-local variables and inhomogeneous cosmological sources with
spherical symmetry
|
8 pages, 2 pdf figures. Provides a concise summary of some of the
results of arXiv:0801.3324v4 [gr-qc]. Submitted to the AIP Conference
Proceedings of the III International Meeting on Gravitation and Cosmology,
Morelia, Mexico, May 26-30, 2008
|
AIP Conf.Proc.1083:228-235,2008
|
10.1063/1.3058574
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We examine a large class of inhomogeneous spherically symmetric spacetimes
that generalize the Lemaitre-Tolman-Bondi dust solutions to nonzero pressure
("LTB spacetimes"). Local covariant LTB objects can be expressed as
perturbations of covariant quasi-local (QL) scalars that satisfy evolution
equations of equivalent Friedman-Lemaitre-Robertson-Walker (FLRW) scalars.
Thus, the dynamics of these spacetimes can be rigorously described as
non-linear, gauge invariant and covariant perturbations on a formal FLRW
background given by the QL scalars. Since LTB spacetimes are compatible with a
wide variety of "equations of state" and theoretical assumptions, they provide
an ideal framework for numerical models of cosmological sources under idealized
but fully non-linear conditions. As an illustrative example, we briefly examine
the formation of a black hole in an expanding Chaplygin gas universe.
|
[
{
"created": "Tue, 7 Oct 2008 08:13:23 GMT",
"version": "v1"
}
] |
2010-05-12
|
[
[
"Sussman",
"Roberto A.",
""
]
] |
We examine a large class of inhomogeneous spherically symmetric spacetimes that generalize the Lemaitre-Tolman-Bondi dust solutions to nonzero pressure ("LTB spacetimes"). Local covariant LTB objects can be expressed as perturbations of covariant quasi-local (QL) scalars that satisfy evolution equations of equivalent Friedman-Lemaitre-Robertson-Walker (FLRW) scalars. Thus, the dynamics of these spacetimes can be rigorously described as non-linear, gauge invariant and covariant perturbations on a formal FLRW background given by the QL scalars. Since LTB spacetimes are compatible with a wide variety of "equations of state" and theoretical assumptions, they provide an ideal framework for numerical models of cosmological sources under idealized but fully non-linear conditions. As an illustrative example, we briefly examine the formation of a black hole in an expanding Chaplygin gas universe.
|
gr-qc/0109033
|
Nashed Gamal Gergess Lamee
|
Gamal G.L. Nashed
|
Vacuum Non Singular Black Hole Solutions in Tetrad Theory of Gravitation
|
11 pages, LaTex, no figures, Submitted to GRG
|
Gen.Rel.Grav. 34 (2002) 1047-1058
|
10.1023/A:1016509920499
| null |
gr-qc
| null |
Starting from a spherically symmetric tetrad with three unknown functions of
the radial coordinate, a general solution of M{\o}ller's field equations in
case of spherical symmetry nonsingular black hole is derived. The previously
obtained solutions are verified as special cases of the general solution. The
general solution is characterized by an arbitrary function and two constants of
integration. The general solution gives no more than the spherically symmetric
nonsingular black hole solution. The energy content of the general solution
depends on the asymptotic behavior of the arbitrary function, and is different
from the standard one.
|
[
{
"created": "Mon, 10 Sep 2001 21:08:04 GMT",
"version": "v1"
}
] |
2021-10-20
|
[
[
"Nashed",
"Gamal G. L.",
""
]
] |
Starting from a spherically symmetric tetrad with three unknown functions of the radial coordinate, a general solution of M{\o}ller's field equations in case of spherical symmetry nonsingular black hole is derived. The previously obtained solutions are verified as special cases of the general solution. The general solution is characterized by an arbitrary function and two constants of integration. The general solution gives no more than the spherically symmetric nonsingular black hole solution. The energy content of the general solution depends on the asymptotic behavior of the arbitrary function, and is different from the standard one.
|
2402.11343
|
Anele Ncube
|
Alan S. Cornell, Sheldon R. Herbst, Hajar Noshad, Anele M. Ncube
|
Solving the Regge-Wheeler and Teukolsky equations: supervised vs.
unsupervised physics-informed neural networks
|
22 pages, 3 figures
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Expanding on the research on physics-informed neural networks (PINNs) to
solve the eigenvalue problems in black hole (BH) perturbation theory, the
supervised learning approach was investigated to solve the Regge-Wheeler and
Teukolsky equations governing gravitational perturbations of Schwarzschild and
Kerr BHs. Previous works have applied unsupervised PINNs to compute quasinormal
mode frequencies, i.e. the discrete spectra of eigenvalues that satisfy the BH
perturbation equations; however, that was limited to only the zeroth and first
overtone (i.e. n = 0, 1). In this paper, supervised learning is used to compute
higher overtones with approximation errors accentuated primarily by the input
data rather than the PINNs themselves. Our results show the ability of PINNs to
approximate overtones up to the limits set by the input data, which concurs
with the universal approximation theory of neural networks.
|
[
{
"created": "Sat, 17 Feb 2024 17:35:06 GMT",
"version": "v1"
}
] |
2024-02-20
|
[
[
"Cornell",
"Alan S.",
""
],
[
"Herbst",
"Sheldon R.",
""
],
[
"Noshad",
"Hajar",
""
],
[
"Ncube",
"Anele M.",
""
]
] |
Expanding on the research on physics-informed neural networks (PINNs) to solve the eigenvalue problems in black hole (BH) perturbation theory, the supervised learning approach was investigated to solve the Regge-Wheeler and Teukolsky equations governing gravitational perturbations of Schwarzschild and Kerr BHs. Previous works have applied unsupervised PINNs to compute quasinormal mode frequencies, i.e. the discrete spectra of eigenvalues that satisfy the BH perturbation equations; however, that was limited to only the zeroth and first overtone (i.e. n = 0, 1). In this paper, supervised learning is used to compute higher overtones with approximation errors accentuated primarily by the input data rather than the PINNs themselves. Our results show the ability of PINNs to approximate overtones up to the limits set by the input data, which concurs with the universal approximation theory of neural networks.
|
1612.03259
|
Michael Maziashvili
|
Michael Maziashvili
|
Light incoherence due to background space fluctuations
|
6 pages, accepted for publication in Phys. Rev. D
|
Phys. Rev. D 94, 124044 (2016)
|
10.1103/PhysRevD.94.124044
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Working by analogy, we use the description of light fluctuations due to
random collisions of the radiating atoms to figure out why the reduction of the
coherence for light propagating a cosmological distance in the fluctuating
background space is negligibly small to be observed by the stellar
interferometry.
|
[
{
"created": "Sat, 10 Dec 2016 06:22:16 GMT",
"version": "v1"
}
] |
2016-12-30
|
[
[
"Maziashvili",
"Michael",
""
]
] |
Working by analogy, we use the description of light fluctuations due to random collisions of the radiating atoms to figure out why the reduction of the coherence for light propagating a cosmological distance in the fluctuating background space is negligibly small to be observed by the stellar interferometry.
|
1105.5830
|
J\"org Hennig
|
Gernot Neugebauer and J\"org Hennig
|
Stationary two-black-hole configurations: A non-existence proof
|
27 pages, 1 figure
|
J. Geom. Phys. 62, 613 (2012)
|
10.1016/j.geomphys.2011.05.008
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Based on the solution of a boundary problem for disconnected (Killing)
horizons and the resulting violation of characteristic black hole properties,
we present a non-existence proof for equilibrium configurations consisting of
two aligned rotating black holes. Our discussion is principally aimed at
developing the ideas of the proof and summarizing the results of two preceding
papers (Neugebauer and Hennig, 2009 [29], Hennig and Neugebauer, 2011 [12]).
From a mathematical point of view, this paper is a further example (Meinel et
al., 2008 [22]) for the application of the inverse ("scattering") method to a
non-linear elliptic differential equation.
|
[
{
"created": "Sun, 29 May 2011 21:31:43 GMT",
"version": "v1"
}
] |
2012-01-17
|
[
[
"Neugebauer",
"Gernot",
""
],
[
"Hennig",
"Jörg",
""
]
] |
Based on the solution of a boundary problem for disconnected (Killing) horizons and the resulting violation of characteristic black hole properties, we present a non-existence proof for equilibrium configurations consisting of two aligned rotating black holes. Our discussion is principally aimed at developing the ideas of the proof and summarizing the results of two preceding papers (Neugebauer and Hennig, 2009 [29], Hennig and Neugebauer, 2011 [12]). From a mathematical point of view, this paper is a further example (Meinel et al., 2008 [22]) for the application of the inverse ("scattering") method to a non-linear elliptic differential equation.
|
1608.07511
|
Klaus Kassner
|
Klaus Kassner
|
Why ghosts don't touch: a tale of two adventurers falling one after
another into a black hole
|
Submitted to European Journal of Physics, 1 figure with 2 panels
|
European Journal of Physics 38.1 (2016): 015605
|
10.1088/0143-0807/38/1/015605
| null |
gr-qc physics.ed-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The case for the utility of Kruskal-Szekeres coordinates in classroom made by
Augousti et al. in this journal (Eur. J. Phys. 33:1--11, 2012) is strengthened
by extending their discussion beyond the event horizon of the black hole.
Observations made by two adventurers following one another into a Schwarzschild
black hole are examined in terms of these nonsingular coordinates. Two
scenarios are considered, the first corresponding to one observer following the
other closely, the second to a significant distance between the two of them,
precluding the existence of a common inertial system. In particular, the
concepts of distance and temporal separation near the horizon and the redshift
of the first infaller's image as seen by the second are investigated. The
results show that the notion of "touching ghosts" does not correspond to the
local physics of two observers falling into a black hole. The story line is
interesting enough and the mathematical details are sufficiently simple to use
the example in a general relativity course, even at the undergraduate level.
|
[
{
"created": "Fri, 26 Aug 2016 16:34:21 GMT",
"version": "v1"
}
] |
2017-03-13
|
[
[
"Kassner",
"Klaus",
""
]
] |
The case for the utility of Kruskal-Szekeres coordinates in classroom made by Augousti et al. in this journal (Eur. J. Phys. 33:1--11, 2012) is strengthened by extending their discussion beyond the event horizon of the black hole. Observations made by two adventurers following one another into a Schwarzschild black hole are examined in terms of these nonsingular coordinates. Two scenarios are considered, the first corresponding to one observer following the other closely, the second to a significant distance between the two of them, precluding the existence of a common inertial system. In particular, the concepts of distance and temporal separation near the horizon and the redshift of the first infaller's image as seen by the second are investigated. The results show that the notion of "touching ghosts" does not correspond to the local physics of two observers falling into a black hole. The story line is interesting enough and the mathematical details are sufficiently simple to use the example in a general relativity course, even at the undergraduate level.
|
1303.1308
|
Tatyana P. Shestakova
|
T. P. Shestakova
|
Hamiltonian dynamics in extended phase space for gravity and its
consistency with Lagrangian formalism: a generalized spherically symmetric
model as an example
|
4 pages, talk presented at the XIII Marcel Grossmann Meeting,
Stockholm, Sweden, July 2012
|
Proceedings of the Thirteenth Marcel Grossmann Meeting on General
Relativity (Stockholm, Sweden, 2012), eds. by R. T Jantzen, K. Rosquist and
R. Ruffini, World Scientific, Singapore (2015), P. 1880 - 1882
|
10.1142/9789814623995_0305
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Among theoretical issues in General Relativity the problem of constructing
its Hamiltonian formulation is still of interest. The most of attempts to
quantize Gravity are based upon Dirac generalization of Hamiltonian dynamics
for system with constraints. At the same time there exists another way to
formulate Hamiltonian dynamics for constrained systems guided by the idea of
extended phase space. We have already considered some features of this approach
in the previous MG12 Meeting by the example of a simple isotropic model. Now we
apply the approach to a generalized spherically symmetric model which imitates
the structure of General Relativity much better. In particular, making use of a
global BRST symmetry and the Noether theorem, we construct the BRST charge that
generates correct gauge transformations for all gravitational degrees of
freedom.
|
[
{
"created": "Wed, 6 Mar 2013 12:09:29 GMT",
"version": "v1"
}
] |
2015-04-09
|
[
[
"Shestakova",
"T. P.",
""
]
] |
Among theoretical issues in General Relativity the problem of constructing its Hamiltonian formulation is still of interest. The most of attempts to quantize Gravity are based upon Dirac generalization of Hamiltonian dynamics for system with constraints. At the same time there exists another way to formulate Hamiltonian dynamics for constrained systems guided by the idea of extended phase space. We have already considered some features of this approach in the previous MG12 Meeting by the example of a simple isotropic model. Now we apply the approach to a generalized spherically symmetric model which imitates the structure of General Relativity much better. In particular, making use of a global BRST symmetry and the Noether theorem, we construct the BRST charge that generates correct gauge transformations for all gravitational degrees of freedom.
|
2110.02242
|
Parampreet Singh
|
Jorge Pullin, Parampreet Singh
|
Report on the session Loop Quantum Gravity: Cosmology and Black Holes of
the 16th Marcel Grossmann Meeting
|
5 pages
| null | null | null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We summarize the main results of 19 talks presented at the QG3 session (loop
quantum gravity: cosmology and black holes) of the 16th Marcel Grossmann
Meeting held online from July $5^{\mathrm{th}}$-10$^{\mathrm{th}}$, 2021.
|
[
{
"created": "Tue, 5 Oct 2021 18:00:14 GMT",
"version": "v1"
}
] |
2021-10-07
|
[
[
"Pullin",
"Jorge",
""
],
[
"Singh",
"Parampreet",
""
]
] |
We summarize the main results of 19 talks presented at the QG3 session (loop quantum gravity: cosmology and black holes) of the 16th Marcel Grossmann Meeting held online from July $5^{\mathrm{th}}$-10$^{\mathrm{th}}$, 2021.
|
1909.13272
|
Jing-Bo Wang
|
Jingbo Wang
|
Hawking Radiation from Boundary Scalar Field
|
7 pages;v2, add the discussion about the impact on the information
loss paradox,
|
Universe 2023, 9, 154
|
10.3390/universe9030154
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Hawking radiation is one essential property of quantum black hole. It results
in the information loss paradox, and give important clue to the unification of
quantum mechanics and general relativity. In the previous works, the boundary
scalar field on the horizon of black holes were used to give the microstates of
BTZ black holes and Kerr black holes. They are account for the
Bekenstein-Hawking entropy. In this paper, we show that the Hawking radiation
can also be derived from those scalar fields. Actually the Hawking radiation
are superposition of thermal radiation of right/left sector at different
temperatures. We also discuss the impact on the information loss paradox.
|
[
{
"created": "Sun, 29 Sep 2019 12:51:09 GMT",
"version": "v1"
},
{
"created": "Tue, 31 Dec 2019 08:30:45 GMT",
"version": "v2"
}
] |
2023-03-24
|
[
[
"Wang",
"Jingbo",
""
]
] |
Hawking radiation is one essential property of quantum black hole. It results in the information loss paradox, and give important clue to the unification of quantum mechanics and general relativity. In the previous works, the boundary scalar field on the horizon of black holes were used to give the microstates of BTZ black holes and Kerr black holes. They are account for the Bekenstein-Hawking entropy. In this paper, we show that the Hawking radiation can also be derived from those scalar fields. Actually the Hawking radiation are superposition of thermal radiation of right/left sector at different temperatures. We also discuss the impact on the information loss paradox.
|
0911.5560
|
Ryosuke Mizuno
|
Ryosuke Mizuno, Seiju Ohashi, Tetsuya Shiromizu
|
Static black hole uniqueness and Penrose inequality
|
6 pages
| null |
10.1103/PhysRevD.81.044030
| null |
gr-qc astro-ph.CO hep-th math-ph math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Under certain conditions, we give a new way to prove the uniqueness of static
black hole in higher dimensional asymptotically flat spacetimes. In the proof,
the Penrose inequality plays a key role in higher dimensions as well as four
dimensions.
|
[
{
"created": "Mon, 30 Nov 2009 07:34:37 GMT",
"version": "v1"
}
] |
2013-05-29
|
[
[
"Mizuno",
"Ryosuke",
""
],
[
"Ohashi",
"Seiju",
""
],
[
"Shiromizu",
"Tetsuya",
""
]
] |
Under certain conditions, we give a new way to prove the uniqueness of static black hole in higher dimensional asymptotically flat spacetimes. In the proof, the Penrose inequality plays a key role in higher dimensions as well as four dimensions.
|
2407.18790
|
Rubens R. S. Oliveira
|
R. R. S. Oliveira
|
Comment on "Exact massless spinor quasibound states of Schwarzschild
black hole"
|
3 pages. Comment on "Exact massless spinor quasibound states of
Schwarzschild black hole'' (DOI: 10.1016/j.physletb.2024.138714)
|
Phys. Lett. B 856 (2024) 138888
|
10.1016/j.physletb.2024.138888
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this comment, we point out a series of errors made by Senjaya in your
paper (2024) \cite{Senjaya}. In particular, these errors involved the Dirac
equation in the 3+1 dimensional Schwarzschild spacetime, tetrad field, curved
gamma matrices, and the time-independent Dirac equation written in terms of the
inner/scalar product between the gamma matrices and the orbital angular
momentum (i.e., $\vec{\gamma}\cdot\vec{L}$). Besides, the strange/peculiar
thing about all this is that even Senjaya \cite{Senjaya} citing Collas and
Klein \cite{Collas}, where the (mathematical) formalism is correct, everything
indicates that he ``ignored'' or ``forgot'' to use such formalism in your
paper. Therefore, using Ref. \cite{Collas}, we show here the correct form of
the errors made by Senjaya \cite{Senjaya}.
|
[
{
"created": "Fri, 26 Jul 2024 14:52:40 GMT",
"version": "v1"
}
] |
2024-07-29
|
[
[
"Oliveira",
"R. R. S.",
""
]
] |
In this comment, we point out a series of errors made by Senjaya in your paper (2024) \cite{Senjaya}. In particular, these errors involved the Dirac equation in the 3+1 dimensional Schwarzschild spacetime, tetrad field, curved gamma matrices, and the time-independent Dirac equation written in terms of the inner/scalar product between the gamma matrices and the orbital angular momentum (i.e., $\vec{\gamma}\cdot\vec{L}$). Besides, the strange/peculiar thing about all this is that even Senjaya \cite{Senjaya} citing Collas and Klein \cite{Collas}, where the (mathematical) formalism is correct, everything indicates that he ``ignored'' or ``forgot'' to use such formalism in your paper. Therefore, using Ref. \cite{Collas}, we show here the correct form of the errors made by Senjaya \cite{Senjaya}.
|
gr-qc/9412021
|
Harald Mueller
|
Harald F. Muller and Christoph Schmid
|
Energy Density Fluctuations in Inflationary Cosmology
|
20 pages, uses AMSTex, 7 figures (not included)
| null | null |
ETH-TH/94-25
|
gr-qc astro-ph
| null |
We analyze the energy density fluctuations contributed by scalar fields
$\Phi$ with vanishing expectation values, $\langle\Phi\rangle=0$, which are
present in addition to the inflaton field. For simplicity we take $\Phi$ to be
non--interacting and minimally coupled to gravity. We use normal ordering to
define the renormalized energy density operator $\rho$, and we show that any
normal ordering gives the same result for correlation functions of $\rho$. We
first consider massless fields and derive the energy fluctuations in a single
mode $\vk$, the two--point correlation function of the energy density, the
power spectrum, and the variance of the smeared energy density, $\ddR$. Mass
effects are investigated for energy fluctuations in single modes. All
quantities considered are scale invariant at the second horizon crossing
(Harrison--Zel'dovich type) for massless and for unstable massive fields. The
magnitude of the relative fluctuations $\de\rho/\rt$ is of order $(\Hi/\Mp)^2$
in the massless case, where $\Hi$ is the Hubble constant during inflation. For
an unstable field of mass $m_\Phi\ll\Hi$ with a decay rate $\Gamma_\Phi$ the
magnitude is enhanced by a factor $\sqrt{m_\Phi/\Gamma_\Phi}$. Finally, the
prediction for the cosmic variance of the average energy density in a sample is
given in the massless case.
|
[
{
"created": "Wed, 7 Dec 1994 15:27:22 GMT",
"version": "v1"
}
] |
2009-09-25
|
[
[
"Muller",
"Harald F.",
""
],
[
"Schmid",
"Christoph",
""
]
] |
We analyze the energy density fluctuations contributed by scalar fields $\Phi$ with vanishing expectation values, $\langle\Phi\rangle=0$, which are present in addition to the inflaton field. For simplicity we take $\Phi$ to be non--interacting and minimally coupled to gravity. We use normal ordering to define the renormalized energy density operator $\rho$, and we show that any normal ordering gives the same result for correlation functions of $\rho$. We first consider massless fields and derive the energy fluctuations in a single mode $\vk$, the two--point correlation function of the energy density, the power spectrum, and the variance of the smeared energy density, $\ddR$. Mass effects are investigated for energy fluctuations in single modes. All quantities considered are scale invariant at the second horizon crossing (Harrison--Zel'dovich type) for massless and for unstable massive fields. The magnitude of the relative fluctuations $\de\rho/\rt$ is of order $(\Hi/\Mp)^2$ in the massless case, where $\Hi$ is the Hubble constant during inflation. For an unstable field of mass $m_\Phi\ll\Hi$ with a decay rate $\Gamma_\Phi$ the magnitude is enhanced by a factor $\sqrt{m_\Phi/\Gamma_\Phi}$. Finally, the prediction for the cosmic variance of the average energy density in a sample is given in the massless case.
|
1407.1188
|
Yusuf Kucukakca
|
Yusuf Kucukakca
|
Teleparallel dark energy model with a fermionic field via Noether
symmetry
|
7 pages, no figure, the version accepted for publication in The
European Physical Journal C
| null |
10.1140/epjc/s10052-014-3086-x
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the present work, we consider a model with a fermionic field that is
non-minimally coupled to gravity in the framework of teleparallel gravity. In
order to determine forms of the coupling and potential function of fermionic
field for the considered model, we use Noether symmetry approach. By applying
this approach, for the Friedman-Robertson-Walker metric, we obtain respective
potential and coupling function as a linear and power-law form of the bilinear
$\Psi$. Further we search the exact cosmological solution of the model. It is
shown that the fermionic field plays role of the dark energy.
|
[
{
"created": "Fri, 4 Jul 2014 10:54:37 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Sep 2014 07:23:35 GMT",
"version": "v2"
}
] |
2015-06-22
|
[
[
"Kucukakca",
"Yusuf",
""
]
] |
In the present work, we consider a model with a fermionic field that is non-minimally coupled to gravity in the framework of teleparallel gravity. In order to determine forms of the coupling and potential function of fermionic field for the considered model, we use Noether symmetry approach. By applying this approach, for the Friedman-Robertson-Walker metric, we obtain respective potential and coupling function as a linear and power-law form of the bilinear $\Psi$. Further we search the exact cosmological solution of the model. It is shown that the fermionic field plays role of the dark energy.
|
2402.14265
|
Wen-Di Guo
|
Wen-Di Guo and Qin Tan
|
Quasinormal modes of a charged black hole with scalar hair
|
10 pages, 4 figures, and 3 tables
|
Universe 9, 97, 320 (2023)
|
10.3390/universe9070320
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
From a five-dimensional Einstein-Maxwell theory, Bah et al. constructed a
singularity free topology star/black hole [Phys. Rev. Lett. 126, 151101
(2021)]. After the Klein-Kluza reduction, i.e., integrating the extra space
dimension, it can obtain an effective four-dimensional static spherical charged
black hole with scalar hair. In this paper, we study the quasinormal modes
(QNMs) of the scalar field, electromagnetic field, and gravitational field on
the background of this effective four-dimensional charged black hole. The
radial parts of the perturbed fields all satisfy a Schr\"{o}dinger-like
equation. Using the asymptotic iteration method, we obtain the QNM frequencies
semianalytically. For low overtone QNMs, the results obtained from the
asymptotic iteration method and the Wentzel-Kramers-Brillouin approximation
method agree well. In the null coordinates, the evolution of a Gaussian package
is also studied. The QNM frequencies obtained by fitting the evolution data
also agree well with the results obtained by the asymptotic iteration method.
|
[
{
"created": "Thu, 22 Feb 2024 04:03:38 GMT",
"version": "v1"
}
] |
2024-02-23
|
[
[
"Guo",
"Wen-Di",
""
],
[
"Tan",
"Qin",
""
]
] |
From a five-dimensional Einstein-Maxwell theory, Bah et al. constructed a singularity free topology star/black hole [Phys. Rev. Lett. 126, 151101 (2021)]. After the Klein-Kluza reduction, i.e., integrating the extra space dimension, it can obtain an effective four-dimensional static spherical charged black hole with scalar hair. In this paper, we study the quasinormal modes (QNMs) of the scalar field, electromagnetic field, and gravitational field on the background of this effective four-dimensional charged black hole. The radial parts of the perturbed fields all satisfy a Schr\"{o}dinger-like equation. Using the asymptotic iteration method, we obtain the QNM frequencies semianalytically. For low overtone QNMs, the results obtained from the asymptotic iteration method and the Wentzel-Kramers-Brillouin approximation method agree well. In the null coordinates, the evolution of a Gaussian package is also studied. The QNM frequencies obtained by fitting the evolution data also agree well with the results obtained by the asymptotic iteration method.
|
gr-qc/9512036
|
Bernd Bruegmann
|
Bernd Bruegmann
|
On the constraint algebra of quantum gravity in the loop representation
|
17 pages, LaTeX, 2 figures included with epsf
|
Nucl.Phys.B474:249-268,1996
|
10.1016/0550-3213(96)00241-6
| null |
gr-qc
| null |
Although an important issue in canonical quantization, the problem of
representing the constraint algebra in the loop representation of quantum
gravity has received little attention. The only explicit computation was
performed by Gambini, Garat and Pullin for a formal point-splitting
regularization of the diffeomorphism and Hamiltonian constraints. It is shown
that the calculation of the algebra simplifies considerably when the
constraints are expressed not in terms of generic area derivatives but rather
as the specific shift operators that reflect the geometric meaning of the
constraints.
|
[
{
"created": "Wed, 20 Dec 1995 16:15:50 GMT",
"version": "v1"
}
] |
2008-11-26
|
[
[
"Bruegmann",
"Bernd",
""
]
] |
Although an important issue in canonical quantization, the problem of representing the constraint algebra in the loop representation of quantum gravity has received little attention. The only explicit computation was performed by Gambini, Garat and Pullin for a formal point-splitting regularization of the diffeomorphism and Hamiltonian constraints. It is shown that the calculation of the algebra simplifies considerably when the constraints are expressed not in terms of generic area derivatives but rather as the specific shift operators that reflect the geometric meaning of the constraints.
|
0707.1202
|
Emanuele Berti
|
Emanuele Berti, Jaime Cardoso, Vitor Cardoso, Marco Cavaglia
|
Matched-filtering and parameter estimation of ringdown waveforms
|
19 pages, 9 figures, matches version in press in PRD
|
Phys.Rev.D76:104044,2007
|
10.1103/PhysRevD.76.104044
| null |
gr-qc astro-ph
| null |
Using recent results from numerical relativity simulations of non-spinning
binary black hole mergers we revisit the problem of detecting ringdown
waveforms and of estimating the source parameters, considering both LISA and
Earth-based interferometers. We find that Advanced LIGO and EGO could detect
intermediate-mass black holes of mass up to about 1000 solar masses out to a
luminosity distance of a few Gpc. For typical multipolar energy distributions,
we show that the single-mode ringdown templates presently used for ringdown
searches in the LIGO data stream can produce a significant event loss (> 10%
for all detectors in a large interval of black hole masses) and very large
parameter estimation errors on the black hole's mass and spin. We estimate that
more than 10^6 templates would be needed for a single-stage multi-mode search.
Therefore, we recommend a "two stage" search to save on computational costs:
single-mode templates can be used for detection, but multi-mode templates or
Prony methods should be used to estimate parameters once a detection has been
made. We update estimates of the critical signal-to-noise ratio required to
test the hypothesis that two or more modes are present in the signal and to
resolve their frequencies, showing that second-generation Earth-based detectors
and LISA have the potential to perform no-hair tests.
|
[
{
"created": "Mon, 9 Jul 2007 09:10:13 GMT",
"version": "v1"
},
{
"created": "Sun, 18 Nov 2007 03:25:22 GMT",
"version": "v2"
}
] |
2008-11-26
|
[
[
"Berti",
"Emanuele",
""
],
[
"Cardoso",
"Jaime",
""
],
[
"Cardoso",
"Vitor",
""
],
[
"Cavaglia",
"Marco",
""
]
] |
Using recent results from numerical relativity simulations of non-spinning binary black hole mergers we revisit the problem of detecting ringdown waveforms and of estimating the source parameters, considering both LISA and Earth-based interferometers. We find that Advanced LIGO and EGO could detect intermediate-mass black holes of mass up to about 1000 solar masses out to a luminosity distance of a few Gpc. For typical multipolar energy distributions, we show that the single-mode ringdown templates presently used for ringdown searches in the LIGO data stream can produce a significant event loss (> 10% for all detectors in a large interval of black hole masses) and very large parameter estimation errors on the black hole's mass and spin. We estimate that more than 10^6 templates would be needed for a single-stage multi-mode search. Therefore, we recommend a "two stage" search to save on computational costs: single-mode templates can be used for detection, but multi-mode templates or Prony methods should be used to estimate parameters once a detection has been made. We update estimates of the critical signal-to-noise ratio required to test the hypothesis that two or more modes are present in the signal and to resolve their frequencies, showing that second-generation Earth-based detectors and LISA have the potential to perform no-hair tests.
|
2108.04146
|
Mengjie Wang
|
Yunhe Lei, Mengjie Wang, Jiliang Jing
|
Maxwell perturbations in a cavity with Robin boundary conditions: two
branches of modes with spectrum bifurcation on Schwarzschild black holes
|
11 pages, 5 figures, published in EPJC
| null |
10.1140/epjc/s10052-021-09942-8
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We perform a systematic study of the Maxwell quasinormal spectrum in a
mirror-like cavity following the generic Robin type vanishing energy flux
principle, by starting with the Schwarzschild black holes in this paper. It is
shown that, for black holes in a cavity, the vanishing energy flux principle
leads to \textit{two} different sets of boundary conditions. By solving the
Maxwell equations with these two boundary conditions both analytically and
numerically, we observe \textit{two} distinct sets of modes. This indicates
that the vanishing energy flux principle may be applied not only to
asymptotically anti-de Sitter (AdS) black holes but also to black holes in a
cavity. In the analytic calculations, the imaginary part of the Maxwell
quasinormal modes are derived analytically for both boundary conditions, which
match well with the numeric results. While in the numeric calculations, we
complete a thorough study on the two sets of the Maxwell spectrum by varying
the mirror radius $r_m$, the angular momentum quantum number $\ell$, and the
overtone number $N$. In particular, we proclaim that the Maxwell spectrum may
\textit{bifurcate} for both modes when the mirror is placed around the black
hole event horizon, which is analogous to the spectrum bifurcation effects
found for the Maxwell fields on asymptotically AdS black holes. This
observation provides another example to exhibit the similarity between black
holes in a cavity and the AdS black holes.
|
[
{
"created": "Mon, 9 Aug 2021 16:15:09 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Dec 2021 09:50:29 GMT",
"version": "v2"
}
] |
2021-12-28
|
[
[
"Lei",
"Yunhe",
""
],
[
"Wang",
"Mengjie",
""
],
[
"Jing",
"Jiliang",
""
]
] |
We perform a systematic study of the Maxwell quasinormal spectrum in a mirror-like cavity following the generic Robin type vanishing energy flux principle, by starting with the Schwarzschild black holes in this paper. It is shown that, for black holes in a cavity, the vanishing energy flux principle leads to \textit{two} different sets of boundary conditions. By solving the Maxwell equations with these two boundary conditions both analytically and numerically, we observe \textit{two} distinct sets of modes. This indicates that the vanishing energy flux principle may be applied not only to asymptotically anti-de Sitter (AdS) black holes but also to black holes in a cavity. In the analytic calculations, the imaginary part of the Maxwell quasinormal modes are derived analytically for both boundary conditions, which match well with the numeric results. While in the numeric calculations, we complete a thorough study on the two sets of the Maxwell spectrum by varying the mirror radius $r_m$, the angular momentum quantum number $\ell$, and the overtone number $N$. In particular, we proclaim that the Maxwell spectrum may \textit{bifurcate} for both modes when the mirror is placed around the black hole event horizon, which is analogous to the spectrum bifurcation effects found for the Maxwell fields on asymptotically AdS black holes. This observation provides another example to exhibit the similarity between black holes in a cavity and the AdS black holes.
|
2307.13041
|
Marcelo E. Rubio
|
Marcelo E. Rubio, \'Aron D. Kov\'acs, M. Herrero-Valea, Miguel
Bezares, Enrico Barausse
|
Well-posed evolution of field theories with anisotropic scaling: the
Lifshitz scalar field in a black hole space-time
|
28 pages, 11 figures, 1 table. Accepted for publication in JCAP
|
JCAP11(2023)001
|
10.1088/1475-7516/2023/11/001
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
Partial differential equations exhibiting an anisotropic scaling between
space and time -- such as those of Horava-Lifshitz gravity -- have a dispersive
nature. They contain higher-order spatial derivatives, but remain second order
in time. This is inconvenient for performing long-time numerical evolutions, as
standard explicit schemes fail to maintain convergence unless the time step is
chosen to be very small. In this work, we develop an implicit evolution scheme
that does not suffer from this drawback, and which is stable and second-order
accurate. As a proof of concept, we study the numerical evolution of a Lifshitz
scalar field on top of a spherically symmetric black hole space-time. We
explore the evolution of a static pulse and an (approximately) ingoing
wave-packet for different strengths of the Lorentz-breaking terms, accounting
also for the effect of the angular momentum eigenvalue and the resulting
effective centrifugal barrier. Our results indicate that the dispersive terms
produce a cascade of modes that accumulate in the region in between the Killing
and universal horizons, indicating a possible instability of the latter.
|
[
{
"created": "Mon, 24 Jul 2023 18:00:08 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Sep 2023 09:26:50 GMT",
"version": "v2"
}
] |
2023-11-23
|
[
[
"Rubio",
"Marcelo E.",
""
],
[
"Kovács",
"Áron D.",
""
],
[
"Herrero-Valea",
"M.",
""
],
[
"Bezares",
"Miguel",
""
],
[
"Barausse",
"Enrico",
""
]
] |
Partial differential equations exhibiting an anisotropic scaling between space and time -- such as those of Horava-Lifshitz gravity -- have a dispersive nature. They contain higher-order spatial derivatives, but remain second order in time. This is inconvenient for performing long-time numerical evolutions, as standard explicit schemes fail to maintain convergence unless the time step is chosen to be very small. In this work, we develop an implicit evolution scheme that does not suffer from this drawback, and which is stable and second-order accurate. As a proof of concept, we study the numerical evolution of a Lifshitz scalar field on top of a spherically symmetric black hole space-time. We explore the evolution of a static pulse and an (approximately) ingoing wave-packet for different strengths of the Lorentz-breaking terms, accounting also for the effect of the angular momentum eigenvalue and the resulting effective centrifugal barrier. Our results indicate that the dispersive terms produce a cascade of modes that accumulate in the region in between the Killing and universal horizons, indicating a possible instability of the latter.
|
0911.0593
|
Sandipan Sengupta
|
Sandipan Sengupta
|
Quantum realizations of Hilbert-Palatini second-class constraints
|
Published version
|
Class.Quant.Grav.27:145008,2010
|
10.1088/0264-9381/27/14/145008
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In a classical theory of gravity, the Barbero-Immirzi parameter ($\eta$)
appears as a topological coupling constant through the Lagrangian density
containing the Hilbert-Palatini term and the Nieh-Yan invariant. In a quantum
framework, the topological interpretation of $\eta$ can be captured through a
rescaling of the wavefunctional representing the Hilbert-Palatini theory, as in
the case of the QCD vacuum angle. However, such a rescaling cannot be realized
for pure gravity within the standard (Dirac) quantization procedure where the
second-class constraints of Hilbert-Palatini theory are eliminated beforehand.
Here we present a different treatment of the Hilbert-Palatini second-class
constraints in order to set up a general rescaling procedure (a) for gravity
with or without matter and (b) for any choice of gauge (e.g. time gauge). The
analysis is developed using the Gupta-Bleuler and the coherent state
quantization methods.
|
[
{
"created": "Tue, 3 Nov 2009 15:35:26 GMT",
"version": "v1"
},
{
"created": "Sat, 29 May 2010 03:27:24 GMT",
"version": "v2"
}
] |
2014-11-20
|
[
[
"Sengupta",
"Sandipan",
""
]
] |
In a classical theory of gravity, the Barbero-Immirzi parameter ($\eta$) appears as a topological coupling constant through the Lagrangian density containing the Hilbert-Palatini term and the Nieh-Yan invariant. In a quantum framework, the topological interpretation of $\eta$ can be captured through a rescaling of the wavefunctional representing the Hilbert-Palatini theory, as in the case of the QCD vacuum angle. However, such a rescaling cannot be realized for pure gravity within the standard (Dirac) quantization procedure where the second-class constraints of Hilbert-Palatini theory are eliminated beforehand. Here we present a different treatment of the Hilbert-Palatini second-class constraints in order to set up a general rescaling procedure (a) for gravity with or without matter and (b) for any choice of gauge (e.g. time gauge). The analysis is developed using the Gupta-Bleuler and the coherent state quantization methods.
|
2009.02928
|
Naoki Seto
|
Naoki Seto
|
Measuring Parity Asymmetry of Gravitational Wave Backgrounds with a
Heliocentric Detector Network in the mHz Band
|
6 pages, 4 figures, to appear in PRL
|
Phys. Rev. Lett. 125, 251101 (2020)
|
10.1103/PhysRevLett.125.251101
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We discuss exploration for isotropic gravitational wave backgrounds around 1
mHz by correlation analysis, targeting both parity odd and even polarization
modes. Even though the space interferometer LISA alone cannot probe the two
modes due to cancellations, the outlook is being changed drastically by the
strong development of other space detectors such as Taiji. In fact, a
heliocentric interferometer network holds a preferable geometrical symmetry
{illuminated by a virtual sphere off-center from the Sun}. By utilizing an
internal symmetry of data streams, we can optimally decompose the odd and even
parity modes at correlation analysis. By simultaneously using LISA and Taiji
for 10 years, our sensitivity to the two modes could reach $\sim 10^{-12}$ in
terms of the normalized energy density.
|
[
{
"created": "Mon, 7 Sep 2020 08:00:14 GMT",
"version": "v1"
},
{
"created": "Fri, 20 Nov 2020 03:35:46 GMT",
"version": "v2"
}
] |
2021-01-04
|
[
[
"Seto",
"Naoki",
""
]
] |
We discuss exploration for isotropic gravitational wave backgrounds around 1 mHz by correlation analysis, targeting both parity odd and even polarization modes. Even though the space interferometer LISA alone cannot probe the two modes due to cancellations, the outlook is being changed drastically by the strong development of other space detectors such as Taiji. In fact, a heliocentric interferometer network holds a preferable geometrical symmetry {illuminated by a virtual sphere off-center from the Sun}. By utilizing an internal symmetry of data streams, we can optimally decompose the odd and even parity modes at correlation analysis. By simultaneously using LISA and Taiji for 10 years, our sensitivity to the two modes could reach $\sim 10^{-12}$ in terms of the normalized energy density.
|
1803.10947
|
Song Ming Du
|
Song Ming Du and Yanbei Chen
|
Searching for near-horizon quantum structures in the binary black-hole
stochastic gravitational-wave background
|
5 pages, 5 figures
|
Phys. Rev. Lett. 121, 051105 (2018)
|
10.1103/PhysRevLett.121.051105
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
It has been speculated that quantum gravity corrections may lead to
modifications to space-time geometry near black hole horizons. Such structures
may cause reflections to gravitational waves, causing {\it echoes} that follow
the main gravitational waves from binary black hole coalescence. We show that
such echoes, if exist, will give rise to a stochastic gravitational-wave
background, which is very substantial if the near-horizon structure has a near
unity reflectivity for gravitational waves, readily detectable by Advanced
LIGO. In case reflectivity is much less than unity, the background will mainly
be arising from the first echo, with a level proportional to the power
reflectivity of the near-horizon structure, but robust against uncertainties in
the location of the structure --- as long as it is very close to the horizon.
Sensitivity of third-generation detectors allows the detection of a background
that corresponds to power reflectivity $\sim 10^{-3}$, if the uncertainties in
the binary black-hole merger rate can be removed. We note that the echoes do
alter the $f^{2/3}$ power law of the background spectra at low frequencies,
which is rather robust against the uncertainties.
|
[
{
"created": "Thu, 29 Mar 2018 07:49:25 GMT",
"version": "v1"
},
{
"created": "Sat, 4 Aug 2018 21:18:14 GMT",
"version": "v2"
}
] |
2018-08-07
|
[
[
"Du",
"Song Ming",
""
],
[
"Chen",
"Yanbei",
""
]
] |
It has been speculated that quantum gravity corrections may lead to modifications to space-time geometry near black hole horizons. Such structures may cause reflections to gravitational waves, causing {\it echoes} that follow the main gravitational waves from binary black hole coalescence. We show that such echoes, if exist, will give rise to a stochastic gravitational-wave background, which is very substantial if the near-horizon structure has a near unity reflectivity for gravitational waves, readily detectable by Advanced LIGO. In case reflectivity is much less than unity, the background will mainly be arising from the first echo, with a level proportional to the power reflectivity of the near-horizon structure, but robust against uncertainties in the location of the structure --- as long as it is very close to the horizon. Sensitivity of third-generation detectors allows the detection of a background that corresponds to power reflectivity $\sim 10^{-3}$, if the uncertainties in the binary black-hole merger rate can be removed. We note that the echoes do alter the $f^{2/3}$ power law of the background spectra at low frequencies, which is rather robust against the uncertainties.
|
1901.09808
|
B. S. Ratanpal
|
B. S. Ratanpal
|
Cracking and Stability of Non-Rotating Relativistic Spheres with
Anisotropic Internal Stresses
| null | null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The stability of static uncharged spheres with anisotropic internal stresses
is studied in general relativity. It has been noticed that pressure anisotropy
plays an important role for stability of stellar structure. It is shown that
radial profile of the stress anisotropy can be considered to decide potentially
stable/unstable regions. Finally, pontentially stable/unstable regions of two
known models of relativistic star have been examined.
|
[
{
"created": "Wed, 23 Jan 2019 05:50:10 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Jun 2020 08:42:47 GMT",
"version": "v2"
}
] |
2020-06-29
|
[
[
"Ratanpal",
"B. S.",
""
]
] |
The stability of static uncharged spheres with anisotropic internal stresses is studied in general relativity. It has been noticed that pressure anisotropy plays an important role for stability of stellar structure. It is shown that radial profile of the stress anisotropy can be considered to decide potentially stable/unstable regions. Finally, pontentially stable/unstable regions of two known models of relativistic star have been examined.
|
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