id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1802.00326 | Mohd Shahalam | M. Shahalam, Weiqiang Yang, R. Myrzakulov, Anzhong Wang | Late-time acceleration with steep exponential potentials | 9 pages, 5 figures, 2 tables | Eur. Phys. J. C (2017) 77:894 | 10.1140/epjc/s10052-017-5468-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter, we study the cosmological dynamics of steeper potential than
exponential. Our analysis shows that a simple extension of an exponential
potential allows to capture late-time cosmic acceleration and retain the
tracker behavior. We also perform statefinder and $Om$ diagnostics to
distinguish dark energy models among themselves and with $\Lambda$CDM. In
addition, to put the observational constraints on the model parameters, we
modify the publicly available CosmoMC code and use an integrated data base of
baryon acoustic oscillation, latest Type Ia supernova from Joint Light Curves
sample and the local Hubble constant value measured by the Hubble Space
Telescope.
| [
{
"created": "Wed, 31 Jan 2018 07:27:41 GMT",
"version": "v1"
}
] | 2018-02-02 | [
[
"Shahalam",
"M.",
""
],
[
"Yang",
"Weiqiang",
""
],
[
"Myrzakulov",
"R.",
""
],
[
"Wang",
"Anzhong",
""
]
] | In this letter, we study the cosmological dynamics of steeper potential than exponential. Our analysis shows that a simple extension of an exponential potential allows to capture late-time cosmic acceleration and retain the tracker behavior. We also perform statefinder and $Om$ diagnostics to distinguish dark energy models among themselves and with $\Lambda$CDM. In addition, to put the observational constraints on the model parameters, we modify the publicly available CosmoMC code and use an integrated data base of baryon acoustic oscillation, latest Type Ia supernova from Joint Light Curves sample and the local Hubble constant value measured by the Hubble Space Telescope. |
gr-qc/0611053 | Hakan Andreasson | Hakan Andreasson, Gerhard Rein | On the steady states of the spherically symmetric Einstein-Vlasov system | 34 pages, 18 figures, LaTex | Class.Quant.Grav.24:1809-1832,2007 | 10.1088/0264-9381/24/7/008 | null | gr-qc | null | Using both numerical and analytical tools we study various features of
static, spherically symmetric solutions of the Einstein-Vlasov system. In
particular, we investigate the possible shapes of their mass-energy density and
find that they can be multi-peaked, we give numerical evidence and a partial
proof for the conjecture that the Buchdahl inequality $\sup_{r > 0} 2 m(r)/r <
8/9$, $m(r)$ the quasi-local mass, holds for all such steady states--both
isotropic {\em and} anisotropic--, and we give numerical evidence and a partial
proof for the conjecture that for any given microscopic equation of state--both
isotropic {\em and} anisotropic--the resulting one-parameter family of static
solutions generates a spiral in the radius-mass diagram.
| [
{
"created": "Wed, 8 Nov 2006 13:37:23 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Andreasson",
"Hakan",
""
],
[
"Rein",
"Gerhard",
""
]
] | Using both numerical and analytical tools we study various features of static, spherically symmetric solutions of the Einstein-Vlasov system. In particular, we investigate the possible shapes of their mass-energy density and find that they can be multi-peaked, we give numerical evidence and a partial proof for the conjecture that the Buchdahl inequality $\sup_{r > 0} 2 m(r)/r < 8/9$, $m(r)$ the quasi-local mass, holds for all such steady states--both isotropic {\em and} anisotropic--, and we give numerical evidence and a partial proof for the conjecture that for any given microscopic equation of state--both isotropic {\em and} anisotropic--the resulting one-parameter family of static solutions generates a spiral in the radius-mass diagram. |
1802.02661 | Jorge Pullin | Rodolfo Gambini and Jorge Pullin | Gravitation in terms of observables | 39 pages, 15 figures, RevTex, version published in CQG | Class. Quantum Grav. 35 215008 (2018) | 10.1088/1361-6382/aae449 | LSU-REL-020718 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the 1960's, Mandelstam proposed a new approach to gauge theories and
gravity based on loops. The program for gauge theories was completed for
Yang--Mills theories by Gambini and Trias in the 1980's. Gauge theories could
be understood as representations of certain group: the group of loops. The same
formalism could not be implemented at that time for the gravitational case.
Here we would like to propose an extension to the case of gravity. The
resulting theory is described in terms of loops and open paths and can provide
the underpinning for a new quantum representation for gravity distinct from the
one used in loop quantum gravity or string theory. In it, space-time points are
emergent entities that would only have quasi-classical status. The formulation
may be given entirely in terms of Dirac observables that form a complete set of
gauge invariant functions that completely define the Riemannian geometry of the
spacetime. At the quantum level this formulation will lead to a reduced phase
space quantization free of any constraints.
| [
{
"created": "Wed, 7 Feb 2018 22:36:42 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Mar 2018 15:31:12 GMT",
"version": "v2"
},
{
"created": "Wed, 17 Oct 2018 14:40:56 GMT",
"version": "v3"
}
] | 2018-10-18 | [
[
"Gambini",
"Rodolfo",
""
],
[
"Pullin",
"Jorge",
""
]
] | In the 1960's, Mandelstam proposed a new approach to gauge theories and gravity based on loops. The program for gauge theories was completed for Yang--Mills theories by Gambini and Trias in the 1980's. Gauge theories could be understood as representations of certain group: the group of loops. The same formalism could not be implemented at that time for the gravitational case. Here we would like to propose an extension to the case of gravity. The resulting theory is described in terms of loops and open paths and can provide the underpinning for a new quantum representation for gravity distinct from the one used in loop quantum gravity or string theory. In it, space-time points are emergent entities that would only have quasi-classical status. The formulation may be given entirely in terms of Dirac observables that form a complete set of gauge invariant functions that completely define the Riemannian geometry of the spacetime. At the quantum level this formulation will lead to a reduced phase space quantization free of any constraints. |
1408.4602 | Andrea Geralico | Donato Bini, Christian Cherubini, Simonetta Filippi, Andrea Geralico | The effective geometry of the $n=1$ uniformly rotating self-gravitating
polytrope | 16 pages, 8 figures; published version | Phys. Rev. D 82, 044005 (2010) | 10.1103/PhysRevD.82.044005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The \lq\lq effective geometry" formalism is used to study the perturbations
of a perfect barotropic Newtonian self-gravitating rotating and compressible
fluid coupled with gravitational backreaction. The case of a uniformly rotating
polytrope with index $n=1$ is investigated, due to its analytical tractability.
Special attention is devoted to the geometrical properties of the underlying
background acoustic metric, focusing in particular on null geodesics as well as
on the analog light cone structure.
| [
{
"created": "Wed, 20 Aug 2014 10:51:37 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Bini",
"Donato",
""
],
[
"Cherubini",
"Christian",
""
],
[
"Filippi",
"Simonetta",
""
],
[
"Geralico",
"Andrea",
""
]
] | The \lq\lq effective geometry" formalism is used to study the perturbations of a perfect barotropic Newtonian self-gravitating rotating and compressible fluid coupled with gravitational backreaction. The case of a uniformly rotating polytrope with index $n=1$ is investigated, due to its analytical tractability. Special attention is devoted to the geometrical properties of the underlying background acoustic metric, focusing in particular on null geodesics as well as on the analog light cone structure. |
1305.4603 | Semyon Dyatlov | Semyon Dyatlov and Maciej Zworski | Trapping of waves and null geodesics for rotating black holes | 8 pages, 7 figures; minor changes suggested by the referee | Phys. Rev. D 88, 084037 (2013) | 10.1103/PhysRevD.88.084037 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present dynamical properties of linear waves and null geodesics valid for
Kerr and Kerr-de Sitter black holes and their stationary perturbations. The two
are intimately linked by the geometric optics approximation. For the
nullgeodesic flow the key property is the r-normal hyperbolicity of the trapped
set and for linear waves it is the distribution of quasi-normal modes: the
exact quantization conditions do not hold for perturbations but the bounds on
decay rates and the statistics of frequencies are still valid.
| [
{
"created": "Mon, 20 May 2013 18:32:40 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Sep 2013 19:29:16 GMT",
"version": "v2"
},
{
"created": "Fri, 25 Oct 2013 15:22:58 GMT",
"version": "v3"
}
] | 2013-10-28 | [
[
"Dyatlov",
"Semyon",
""
],
[
"Zworski",
"Maciej",
""
]
] | We present dynamical properties of linear waves and null geodesics valid for Kerr and Kerr-de Sitter black holes and their stationary perturbations. The two are intimately linked by the geometric optics approximation. For the nullgeodesic flow the key property is the r-normal hyperbolicity of the trapped set and for linear waves it is the distribution of quasi-normal modes: the exact quantization conditions do not hold for perturbations but the bounds on decay rates and the statistics of frequencies are still valid. |
gr-qc/9502005 | Frank Gronwald | Frank Gronwald | ON NON-RIEMANNIAN PARALLEL TRANSPORT IN REGGE CALCULUS | 12 pages, Plain-TEX, two figures (available from the author) | Class.Quant.Grav.12:1181-1190,1995 | 10.1088/0264-9381/12/5/009 | CPP-94-38 | gr-qc | null | We discuss the possibility of incorporating non-Riemannian parallel transport
into Regge calculus. It is shown that every Regge lattice is locally equivalent
to a space of constant curvature. Therefore well known-concepts of differential
geometry imply the definition of an arbitrary linear affine connection on a
Regge lattice.
| [
{
"created": "Wed, 1 Feb 1995 11:21:31 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Gronwald",
"Frank",
""
]
] | We discuss the possibility of incorporating non-Riemannian parallel transport into Regge calculus. It is shown that every Regge lattice is locally equivalent to a space of constant curvature. Therefore well known-concepts of differential geometry imply the definition of an arbitrary linear affine connection on a Regge lattice. |
0803.4000 | Jurjen Koksma | Jurjen F. Koksma (UU) Tomislav Prokopec (UU) | Effect of the Trace Anomaly on the Cosmological Constant | 18 pages, 11 figures, published version | Phys.Rev.D78:023508,2008 | 10.1103/PhysRevD.78.023508 | ITP-UU-08/08, SPIN-08/08 | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been argued that the quantum (conformal) trace anomaly could
potentially provide us with a dynamical explanation of the cosmological
constant problem. In this paper, however, we show by means of a semiclassical
analysis that the trace anomaly does not affect the cosmological constant. We
construct the effective action of the conformal anomaly for flat FLRW
spacetimes consisting of local quadratic geometric curvature invariants.
Counterterms are thus expected to influence the numerical value of the
coefficients in the trace anomaly and we must therefore allow these parameters
to vary. We calculate the evolution of the Hubble parameter in quasi de Sitter
spacetime, where we restrict our Hubble parameter to vary slowly in time, and
in FLRW spacetimes. We show dynamically that a Universe consisting of matter
with a constant equation of state, a cosmological constant and the quantum
trace anomaly evolves either to the classical de Sitter attractor or to a
quantum trace anomaly driven one. When considering the trace anomaly truncated
to quasi de Sitter spacetime, we find a region in parameter space where the
quantum attractor destabilises. When considering the exact expression of the
trace anomaly, a stability analysis shows that whenever the trace anomaly
driven attractor is stable, the classical de Sitter attractor is unstable, and
vice versa. Semiclassically, the trace anomaly does not affect the classical
late time de Sitter attractor and hence it does not solve the cosmological
constant problem.
| [
{
"created": "Thu, 27 Mar 2008 19:52:33 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Aug 2008 13:20:59 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Koksma",
"Jurjen F.",
"",
"UU"
],
[
"Prokopec",
"Tomislav",
"",
"UU"
]
] | It has been argued that the quantum (conformal) trace anomaly could potentially provide us with a dynamical explanation of the cosmological constant problem. In this paper, however, we show by means of a semiclassical analysis that the trace anomaly does not affect the cosmological constant. We construct the effective action of the conformal anomaly for flat FLRW spacetimes consisting of local quadratic geometric curvature invariants. Counterterms are thus expected to influence the numerical value of the coefficients in the trace anomaly and we must therefore allow these parameters to vary. We calculate the evolution of the Hubble parameter in quasi de Sitter spacetime, where we restrict our Hubble parameter to vary slowly in time, and in FLRW spacetimes. We show dynamically that a Universe consisting of matter with a constant equation of state, a cosmological constant and the quantum trace anomaly evolves either to the classical de Sitter attractor or to a quantum trace anomaly driven one. When considering the trace anomaly truncated to quasi de Sitter spacetime, we find a region in parameter space where the quantum attractor destabilises. When considering the exact expression of the trace anomaly, a stability analysis shows that whenever the trace anomaly driven attractor is stable, the classical de Sitter attractor is unstable, and vice versa. Semiclassically, the trace anomaly does not affect the classical late time de Sitter attractor and hence it does not solve the cosmological constant problem. |
1205.6611 | Stephen Fairhurst | Stephen Fairhurst | Improved source localization with LIGO India | 7 pages, 3 figures, accepted for publication in proceedings of
ICGC2011 conference. Localization figures updated | null | 10.1088/1742-6596/484/1/012007 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A global network of advanced gravitational wave interferometric detectors is
under construction. These detectors will offer an order of magnitude
improvement in sensitivity over the initial detectors and will usher in the era
of gravitational wave astronomy. In this paper, we evaluate the benefits of
relocating one of the advanced LIGO detectors to India.
| [
{
"created": "Wed, 30 May 2012 10:02:38 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Sep 2012 09:03:23 GMT",
"version": "v2"
}
] | 2014-09-30 | [
[
"Fairhurst",
"Stephen",
""
]
] | A global network of advanced gravitational wave interferometric detectors is under construction. These detectors will offer an order of magnitude improvement in sensitivity over the initial detectors and will usher in the era of gravitational wave astronomy. In this paper, we evaluate the benefits of relocating one of the advanced LIGO detectors to India. |
1209.6098 | Kouji Nakamura | Kouji Nakamura | MG13 proceedings: Construction of gauge-invariant variables for
linear-order metric perturbations on an arbitrary background spacetime | 3 pages, no figure, Prepared for proceedings of the international
conference "Thirteenth Marcel Grossmann Meeting" | null | null | null | gr-qc astro-ph.CO hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An outline of a proof of the decomposition of the linear metric perturbation
into gauge-invariant and gauge-variant parts on an arbitrary background
spacetime is discussed through an exlicit construction of gauge-invariant and
gauge-variant parts. Although this outline is incomplete, yet, due to our
assumptions, we propose a conjecture which states that the linear metric
perturbation is always decomposed into its gauge-invariant and gageu-variant
parts. If this conjecture is true, we can develop the higher-order
gauge-invariant perturbation theory on an arbitrary background spacetime.
| [
{
"created": "Thu, 27 Sep 2012 00:20:30 GMT",
"version": "v1"
}
] | 2012-09-28 | [
[
"Nakamura",
"Kouji",
""
]
] | An outline of a proof of the decomposition of the linear metric perturbation into gauge-invariant and gauge-variant parts on an arbitrary background spacetime is discussed through an exlicit construction of gauge-invariant and gauge-variant parts. Although this outline is incomplete, yet, due to our assumptions, we propose a conjecture which states that the linear metric perturbation is always decomposed into its gauge-invariant and gageu-variant parts. If this conjecture is true, we can develop the higher-order gauge-invariant perturbation theory on an arbitrary background spacetime. |
gr-qc/9710123 | Vanzo Luciano | D. Klemm, V. Moretti and L. Vanzo | Rotating Topological Black Holes | 25 pages, LateX, five ps figures added, minor errors corrected,
addition of new references, improved discussion of the conserved charges | Phys.Rev.D57:6127-6137,1998; Erratum-ibid.D60:109902,1999 | 10.1103/PhysRevD.57.6127 10.1103/PhysRevD.60.109902 | preprint UTF 408 | gr-qc | null | A class of metrics solving Einstein's equations with negative cosmological
constant and representing rotating, topological black holes is presented. All
such solutions are in the Petrov type-$D$ class, and can be obtained from the
most general metric known in this class by acting with suitably chosen discrete
groups of isometries. First, by analytical continuation of the Kerr-de Sitter
metric, a solution describing uncharged, rotating black holes whose event
horizon is a Riemann surface of arbitrary genus $g > 1$, is obtained. Then a
solution representing a rotating, uncharged toroidal black hole is also
presented. The higher genus black holes appear to be quite exotic objects, they
lack global axial symmetry and have an intricate causal structure. The toroidal
blackholes appear to be simpler, they have rotational symmetry and the amount
of rotation they can have is bounded by some power of the mass.
| [
{
"created": "Tue, 28 Oct 1997 16:44:30 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Dec 1997 14:20:23 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Klemm",
"D.",
""
],
[
"Moretti",
"V.",
""
],
[
"Vanzo",
"L.",
""
]
] | A class of metrics solving Einstein's equations with negative cosmological constant and representing rotating, topological black holes is presented. All such solutions are in the Petrov type-$D$ class, and can be obtained from the most general metric known in this class by acting with suitably chosen discrete groups of isometries. First, by analytical continuation of the Kerr-de Sitter metric, a solution describing uncharged, rotating black holes whose event horizon is a Riemann surface of arbitrary genus $g > 1$, is obtained. Then a solution representing a rotating, uncharged toroidal black hole is also presented. The higher genus black holes appear to be quite exotic objects, they lack global axial symmetry and have an intricate causal structure. The toroidal blackholes appear to be simpler, they have rotational symmetry and the amount of rotation they can have is bounded by some power of the mass. |
2112.11432 | Sandeep Aashish | Sandeep Aashish, Abhijith Ajith, Sukanta Panda, Rahul Thakur | Inflation with antisymmetric tensor field: new candidates | 40 pages, 16 figures; erroneous calculations have been replaced in
section V, references added; published version | JCAP04(2022)043 | 10.1088/1475-7516/2022/04/043 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study classes of inflation models driven by antisymmetric tensor field,
with minimal and nonminimal couplings to gravity, that address known issues of
such models considered in the past. First we show that with a different choice
of the background structure of antisymmetric tensor field, inflation is
supported even for the minimal model with quadratic potential contrary to past
results. We also include the nonminimal coupling to gravity and analyse
perturbations to the antisymmetric tensor as well as the tensor modes of
perturbed metric. The two models differ in terms of the behaviour of tensor
modes, where the speed of gravitational wave can be tuned to $c$ in the latter
model. The power spectrum and spectral index receive slight scale dependence.
Finally, we consider a quartic potential motivated by the graceful exit to
reheating phase, which requires a nonminimal coupling to support inflation. The
two tensor modes of perturbed metric are found to evolve differently in this
model, and give rise to a highly scale-dependent power spectrum.
| [
{
"created": "Tue, 21 Dec 2021 18:49:37 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Dec 2021 14:19:54 GMT",
"version": "v2"
},
{
"created": "Fri, 22 Apr 2022 08:20:53 GMT",
"version": "v3"
}
] | 2022-04-25 | [
[
"Aashish",
"Sandeep",
""
],
[
"Ajith",
"Abhijith",
""
],
[
"Panda",
"Sukanta",
""
],
[
"Thakur",
"Rahul",
""
]
] | We study classes of inflation models driven by antisymmetric tensor field, with minimal and nonminimal couplings to gravity, that address known issues of such models considered in the past. First we show that with a different choice of the background structure of antisymmetric tensor field, inflation is supported even for the minimal model with quadratic potential contrary to past results. We also include the nonminimal coupling to gravity and analyse perturbations to the antisymmetric tensor as well as the tensor modes of perturbed metric. The two models differ in terms of the behaviour of tensor modes, where the speed of gravitational wave can be tuned to $c$ in the latter model. The power spectrum and spectral index receive slight scale dependence. Finally, we consider a quartic potential motivated by the graceful exit to reheating phase, which requires a nonminimal coupling to support inflation. The two tensor modes of perturbed metric are found to evolve differently in this model, and give rise to a highly scale-dependent power spectrum. |
2408.03998 | Kelly MacDevette | Kelly MacDevette and Jess Worsley and Peter Dunsby and Saikat
Chakraborty | A model independent approach to the study of structure growth in $f(R)$
gravity | 25 pages, 14 figures | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | Over the last decade, much attention has been given to the study of modified
gravity theories to find a more natural explanation for the late-time
acceleration of the Universe. Particular attention has focused on the so-called
$f(R)$ dark energy models. Instead of focusing on a particular f(R) model, we
present a completely model-independent approach to study the background
dynamics and the growth of matter density perturbations for those f(R) models
that mimic the $\Lambda$CDM evolution at the background level. We do this by
characterising the dynamics of the gravitational field using a set of
dimensionless variables and using cosmography to determine the expansion
history. We then illustrate the integrity of this method by fixing the
cosmography to be the same as an exact $\Lambda$CDM model, allowing us to test
the solution. We compare the exact evolution of the density contrast and growth
index with what one obtains from various levels of the quasi-static
approximation, without choosing the form of $f(R)$ dark energy.
| [
{
"created": "Wed, 7 Aug 2024 18:00:03 GMT",
"version": "v1"
}
] | 2024-08-09 | [
[
"MacDevette",
"Kelly",
""
],
[
"Worsley",
"Jess",
""
],
[
"Dunsby",
"Peter",
""
],
[
"Chakraborty",
"Saikat",
""
]
] | Over the last decade, much attention has been given to the study of modified gravity theories to find a more natural explanation for the late-time acceleration of the Universe. Particular attention has focused on the so-called $f(R)$ dark energy models. Instead of focusing on a particular f(R) model, we present a completely model-independent approach to study the background dynamics and the growth of matter density perturbations for those f(R) models that mimic the $\Lambda$CDM evolution at the background level. We do this by characterising the dynamics of the gravitational field using a set of dimensionless variables and using cosmography to determine the expansion history. We then illustrate the integrity of this method by fixing the cosmography to be the same as an exact $\Lambda$CDM model, allowing us to test the solution. We compare the exact evolution of the density contrast and growth index with what one obtains from various levels of the quasi-static approximation, without choosing the form of $f(R)$ dark energy. |
1210.0379 | Jose Geraldo Pereira | J. G. Pereira | Lorentz Connections and Gravitation | Lecture presented at the Sixth International School on Field Theory
and Gravity, Petropolis, Brazil, 2012 | AIP Conf. Proc. 1483 (2012) 239-259 | 10.1063/1.4756972 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The different roles played by Lorentz connections in general relativity and
in teleparallel gravity are reviewed. Some of the consequences of this
difference are discussed.
| [
{
"created": "Mon, 1 Oct 2012 12:56:53 GMT",
"version": "v1"
}
] | 2012-10-02 | [
[
"Pereira",
"J. G.",
""
]
] | The different roles played by Lorentz connections in general relativity and in teleparallel gravity are reviewed. Some of the consequences of this difference are discussed. |
1508.05196 | Mohammad Akbar | M. M. Akbar and M. A. H. MacCallum | Static Axisymmetric Einstein Equations in Vacuum: Symmetry, New
Solutions and Ricci Solitons | null | null | 10.1103/PhysRevD.92.063017 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An explicit one-parameter Lie point symmetry of the four-dimensional vacuum
Einstein equations with two commuting hypersurface-orthogonal Killing vector
fields is presented. The parameter takes values over all of the real line and
the action of the group can be effected algebraically on any solution of the
system. This enables one to construct particular one-parameter extended
families of axisymmetric static solutions and cylindrical gravitational wave
solutions from old ones, in a simpler way than most solution-generation
techniques, including the prescription given by Ernst for this system. As
examples, we obtain the families that generalize the Schwarzschild solution and
the $C$-metric. These in effect superpose a Levi-Civita cylindrical solution on
the seeds. Exploiting a correspondence between static solutions of Einstein's
equations and Ricci solitons (self-similar solutions of the Ricci flow), this
also enables us to construct new steady Ricci solitons.
| [
{
"created": "Fri, 21 Aug 2015 07:39:16 GMT",
"version": "v1"
}
] | 2015-10-07 | [
[
"Akbar",
"M. M.",
""
],
[
"MacCallum",
"M. A. H.",
""
]
] | An explicit one-parameter Lie point symmetry of the four-dimensional vacuum Einstein equations with two commuting hypersurface-orthogonal Killing vector fields is presented. The parameter takes values over all of the real line and the action of the group can be effected algebraically on any solution of the system. This enables one to construct particular one-parameter extended families of axisymmetric static solutions and cylindrical gravitational wave solutions from old ones, in a simpler way than most solution-generation techniques, including the prescription given by Ernst for this system. As examples, we obtain the families that generalize the Schwarzschild solution and the $C$-metric. These in effect superpose a Levi-Civita cylindrical solution on the seeds. Exploiting a correspondence between static solutions of Einstein's equations and Ricci solitons (self-similar solutions of the Ricci flow), this also enables us to construct new steady Ricci solitons. |
gr-qc/9611013 | Nami Fux Svaiter | R. De Paola and N.F. Svaiter | Radiative processes for Rindler and accelerating observers and the
stress-tensor detector | 36 pages, Latex | null | null | null | gr-qc | null | We consider a monopole detector interacting with a massive scalar field. The
radiative processes are discussed from the accelerated frame point of view.
After this, we obtain the Minkowski vacuum stress tensor measured by the
accelerated observer using a non-gravitational stress tensor detector as
discussed by Ford and Roman (PRD 48, 776 (1993)). Finally, we analyse radiative
processes of the monopole detector travelling in a world line that is inertial
in the infinite past and has a constant proper acceleration in the infinite
future.
| [
{
"created": "Tue, 5 Nov 1996 22:20:05 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"De Paola",
"R.",
""
],
[
"Svaiter",
"N. F.",
""
]
] | We consider a monopole detector interacting with a massive scalar field. The radiative processes are discussed from the accelerated frame point of view. After this, we obtain the Minkowski vacuum stress tensor measured by the accelerated observer using a non-gravitational stress tensor detector as discussed by Ford and Roman (PRD 48, 776 (1993)). Finally, we analyse radiative processes of the monopole detector travelling in a world line that is inertial in the infinite past and has a constant proper acceleration in the infinite future. |
2010.05040 | Peter Rau B | Peter B. Rau and Armen Sedrakian | Oscillations of hypermassive compact stars with gravitational radiation
and viscosity | 7 pages, 3 figures, 1 table. Accepted by ApJ Letters | ApJ Letters, 902 (2020) L41 | 10.3847/2041-8213/abc015 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Binary neutron star mergers, such as the multimessenger GW170817 event, may
produce hypermassive compact objects which are supported against collapse by
the internal circulation of the fluid within the star. We compute their
unstable modes of oscillations driven by gravitational wave radiation and shear
viscosity, modeling them as triaxial Riemann ellipsoids. We work in a
perturbative regime, where the gravitational radiation reaction force is taken
into account at 2.5-post-Newtonian order and find unstable modes with
dissipation timescales $\gtrsim 1$ ms which are relevant to the transient state
of a hypermassive remnant of a merger. We show that the secular instabilities
are dominated by gravitational wave radiation. If the shear viscosity is
included, it can increase the growth times or even stabilize the unstable
modes, but it must have values several orders of magnitude larger than
predicted for cold neutron stars.
| [
{
"created": "Sat, 10 Oct 2020 16:29:36 GMT",
"version": "v1"
}
] | 2020-11-03 | [
[
"Rau",
"Peter B.",
""
],
[
"Sedrakian",
"Armen",
""
]
] | Binary neutron star mergers, such as the multimessenger GW170817 event, may produce hypermassive compact objects which are supported against collapse by the internal circulation of the fluid within the star. We compute their unstable modes of oscillations driven by gravitational wave radiation and shear viscosity, modeling them as triaxial Riemann ellipsoids. We work in a perturbative regime, where the gravitational radiation reaction force is taken into account at 2.5-post-Newtonian order and find unstable modes with dissipation timescales $\gtrsim 1$ ms which are relevant to the transient state of a hypermassive remnant of a merger. We show that the secular instabilities are dominated by gravitational wave radiation. If the shear viscosity is included, it can increase the growth times or even stabilize the unstable modes, but it must have values several orders of magnitude larger than predicted for cold neutron stars. |
gr-qc/0405121 | Hongsheng Zhang | Hongsheng Zhang | Does the Cosmos have two times? Multi-time and cosmic acceleration | 5 pages, 3 figures, this version is heavily changed comparing to the
early one, main conclusion holds | null | null | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We put forward a multi-time theory, in frame of which the cosmic acceleration
is a natural phenomenon without cosmological constant or anything like that.
The main point of this theory is that each of the gravity interaction and
electromagnetic interaction has its own time, respectively. Also we give a
concrete model of this theory which can exactly simulate $\Lambda$CDM. Further
we discuss the possible observations which may improve this theory in the
future.
| [
{
"created": "Tue, 25 May 2004 02:30:17 GMT",
"version": "v1"
},
{
"created": "Wed, 26 May 2004 02:58:06 GMT",
"version": "v2"
},
{
"created": "Mon, 19 Jul 2004 06:16:14 GMT",
"version": "v3"
},
{
"created": "Thu, 15 Dec 2005 11:40:24 GMT",
"version": "v4"
},
{
"c... | 2010-04-16 | [
[
"Zhang",
"Hongsheng",
""
]
] | We put forward a multi-time theory, in frame of which the cosmic acceleration is a natural phenomenon without cosmological constant or anything like that. The main point of this theory is that each of the gravity interaction and electromagnetic interaction has its own time, respectively. Also we give a concrete model of this theory which can exactly simulate $\Lambda$CDM. Further we discuss the possible observations which may improve this theory in the future. |
gr-qc/0006065 | Hrvoje Nikolic | Neven Bilic, Hrvoje Nikolic (Rudjer Boskovic Institute, Zagreb,
Croatia) | Self-gravitating bosons at nonzero temperature | 21 pages, 11 figures included, revised, to appear in Nucl. Phys. B | Nucl.Phys.B590:575-595,2000 | 10.1016/S0550-3213(00)00455-7 | null | gr-qc astro-ph hep-ph | null | A system of charged bosons at finite temperature and chemical potential is
studied in a general-relativistic framework. We assume that the boson fields
interact only gravitationally. At sufficiently low temperature the system
exists in two phases: the gas and the condensate. By studying the condensation
process numerically we determine the critical temperature $T_c$ at which the
condensate emerges. As the temperature decreases, the system eventually settles
down in the ground state of a cold boson star.
| [
{
"created": "Mon, 19 Jun 2000 11:21:17 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Jul 2000 09:31:41 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Bilic",
"Neven",
"",
"Rudjer Boskovic Institute, Zagreb,\n Croatia"
],
[
"Nikolic",
"Hrvoje",
"",
"Rudjer Boskovic Institute, Zagreb,\n Croatia"
]
] | A system of charged bosons at finite temperature and chemical potential is studied in a general-relativistic framework. We assume that the boson fields interact only gravitationally. At sufficiently low temperature the system exists in two phases: the gas and the condensate. By studying the condensation process numerically we determine the critical temperature $T_c$ at which the condensate emerges. As the temperature decreases, the system eventually settles down in the ground state of a cold boson star. |
2108.02902 | Juilson Pereira | Juilson A. P. Paiva, Matheus J. Lazo, and Vilson T. Zanchin | Generalized nonconservative gravitational field equations from Herglotz
action principle | null | null | 10.1103/PhysRevD.105.124023 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an alternative nonconservative gravitational theory based on the
Herglotz variational principle in a fully covariant form. The present model may
be seen as an improvement of the theory proposed in Ref. [Lazo et al, Phys.
Rev. D 95, 101501 (2017)], whose resulting theory is meaningful just in
particular coordinate systems. In the present work, we report a new theory that
is free from such a restriction. It is also obtained using the Herglotz
variational principle and by taking advantage of the restricted equivalence
between Lagrangian functions in the scope of such action principle. The more
restricted class of equivalent Lagrangian functions, in comparison with the
Hamilton variational principle, is the key point to find a Lagrangian that
furnishes a new alternative gravitational theory that is fully covariant. Once
the equations that govern the dynamics of the gravitational field are obtained,
a few simple cosmological models are investigated. It is found that the
Herglotz gravitational field reduces to a single function that, under certain
conditions, plays the role of the cosmological constant in general relativity,
turning unnecessary the use of dark energy to explain the accelerated expansion
of the universe. The linearized version of the theory is also investigated and
it is verified that the theory shows a dissipative character in regard to
gravitational waves. From observational data, in both scenarios, the Herglotz
vector field is estimated.
| [
{
"created": "Fri, 6 Aug 2021 01:04:33 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Aug 2021 22:30:39 GMT",
"version": "v2"
}
] | 2022-06-22 | [
[
"Paiva",
"Juilson A. P.",
""
],
[
"Lazo",
"Matheus J.",
""
],
[
"Zanchin",
"Vilson T.",
""
]
] | We present an alternative nonconservative gravitational theory based on the Herglotz variational principle in a fully covariant form. The present model may be seen as an improvement of the theory proposed in Ref. [Lazo et al, Phys. Rev. D 95, 101501 (2017)], whose resulting theory is meaningful just in particular coordinate systems. In the present work, we report a new theory that is free from such a restriction. It is also obtained using the Herglotz variational principle and by taking advantage of the restricted equivalence between Lagrangian functions in the scope of such action principle. The more restricted class of equivalent Lagrangian functions, in comparison with the Hamilton variational principle, is the key point to find a Lagrangian that furnishes a new alternative gravitational theory that is fully covariant. Once the equations that govern the dynamics of the gravitational field are obtained, a few simple cosmological models are investigated. It is found that the Herglotz gravitational field reduces to a single function that, under certain conditions, plays the role of the cosmological constant in general relativity, turning unnecessary the use of dark energy to explain the accelerated expansion of the universe. The linearized version of the theory is also investigated and it is verified that the theory shows a dissipative character in regard to gravitational waves. From observational data, in both scenarios, the Herglotz vector field is estimated. |
gr-qc/9710102 | Beverly K. Berger | Beverly K. Berger, David Garfinkle | Phenomenology of the Gowdy Universe on $T^3 \times R$ | 19 pages, 21 figures, uses Revtex, psfig | Phys.Rev.D57:4767-4777,1998 | 10.1103/PhysRevD.57.4767 | null | gr-qc | null | Numerical studies of the plane symmetric, vacuum Gowdy universe on $T^3
\times R$ yield strong support for the conjectured asymptotically velocity term
dominated (AVTD) behavior of its evolution toward the singularity except,
perhaps, at isolated spatial points. A generic solution is characterized by
spiky features and apparent ``discontinuities'' in the wave amplitudes. It is
shown that the nonlinear terms in the wave equations drive the system
generically to the ``small velocity'' AVTD regime and that the spiky features
are caused by the absence of these terms at isolated spatial points.
| [
{
"created": "Tue, 21 Oct 1997 17:10:10 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Berger",
"Beverly K.",
""
],
[
"Garfinkle",
"David",
""
]
] | Numerical studies of the plane symmetric, vacuum Gowdy universe on $T^3 \times R$ yield strong support for the conjectured asymptotically velocity term dominated (AVTD) behavior of its evolution toward the singularity except, perhaps, at isolated spatial points. A generic solution is characterized by spiky features and apparent ``discontinuities'' in the wave amplitudes. It is shown that the nonlinear terms in the wave equations drive the system generically to the ``small velocity'' AVTD regime and that the spiky features are caused by the absence of these terms at isolated spatial points. |
2206.09954 | Saptaswa Ghosh | Saptaswa Ghosh, Arpan Bhattacharyya | Analytical study of gravitational lensing in Kerr-Newman black-bounce
spacetime | 45 pages, 7 figures, 5 Tables, minor typos corrected | JCAP 11 (2022) 006 | 10.1088/1475-7516/2022/11/006 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the equatorial deflection angle of light rays propagating in
Kerr-Newman black-bounce spacetime. Furthermore, we analyze the light ray
trajectories and derive a closed-form formula for deflection angle in terms of
elliptic integrals. The deflection angle increases with the decrease of charge
and regularisation parameter for a particular impact parameter. We also study
the strong field limit of the deflection angle. Using this strong deflection
angle formula and lens equation, we find the radius of the first Einstein ring
and study its dependence on the charge and the regularisation parameter. We
demonstrate that the charge has a robust effect on the size of the Einstein
rings, but the effect of the regularization parameter on the ring size is
negligible. We also investigate the non-equatorial lensing and the caustic
structures for small polar inclination, and the same observations appear to
hold. These results directly affect the observational appearance of the
Kerr-Newman black-bounce.
| [
{
"created": "Mon, 20 Jun 2022 18:31:07 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Oct 2022 11:28:29 GMT",
"version": "v2"
},
{
"created": "Fri, 11 Nov 2022 16:30:58 GMT",
"version": "v3"
},
{
"created": "Sun, 28 May 2023 16:06:46 GMT",
"version": "v4"
}
] | 2023-05-30 | [
[
"Ghosh",
"Saptaswa",
""
],
[
"Bhattacharyya",
"Arpan",
""
]
] | We investigate the equatorial deflection angle of light rays propagating in Kerr-Newman black-bounce spacetime. Furthermore, we analyze the light ray trajectories and derive a closed-form formula for deflection angle in terms of elliptic integrals. The deflection angle increases with the decrease of charge and regularisation parameter for a particular impact parameter. We also study the strong field limit of the deflection angle. Using this strong deflection angle formula and lens equation, we find the radius of the first Einstein ring and study its dependence on the charge and the regularisation parameter. We demonstrate that the charge has a robust effect on the size of the Einstein rings, but the effect of the regularization parameter on the ring size is negligible. We also investigate the non-equatorial lensing and the caustic structures for small polar inclination, and the same observations appear to hold. These results directly affect the observational appearance of the Kerr-Newman black-bounce. |
2007.01324 | Jasel Berra-Montiel | Jasel Berra-Montiel, Alberto Molgado | Quasi-probability distributions in Loop Quantum Cosmology | 12 pages, no figures | null | 10.1088/1361-6382/abb57a | null | gr-qc math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we introduce a complete family of parametrized
quasi-probability distributions in phase space and their corresponding Weyl
quantization maps with the aim to generalize the recently developed Wigner-Weyl
formalism within the Loop Quantum Cosmology program (LQC). In particular, we
intend to define those quasi-distributions for states valued on the Bohr
compactification of the real line in such a way that they are labeled by a
parameter that accounts for the ordering ambiguity corresponding to
non-commutative quantum operators. Hence, we notice that the projections of the
parametrized quasi-probability distributions result in marginal probability
densities which are invariant under any ordering prescription. We also note
that, in opposition to the standard Schr\"odinger representation, for an
arbitrary character the quasi-distributions determine a positive function
independently of the ordering. Further, by judiciously implementing a
parametric-ordered Weyl quantization map for LQG, we are able to recover in a
simple manner the relevant cases of the standard, anti-standard, and Weyl
symmetric orderings, respectively. We expect that our results may serve to
analyze several fundamental aspects within the LQC program, in special those
related to coherence, squeezed states, and the convergence of operators, as
extensively analyzed in the quantum optics and in the quantum information
frameworks.
| [
{
"created": "Thu, 2 Jul 2020 18:05:32 GMT",
"version": "v1"
}
] | 2020-10-28 | [
[
"Berra-Montiel",
"Jasel",
""
],
[
"Molgado",
"Alberto",
""
]
] | In this paper, we introduce a complete family of parametrized quasi-probability distributions in phase space and their corresponding Weyl quantization maps with the aim to generalize the recently developed Wigner-Weyl formalism within the Loop Quantum Cosmology program (LQC). In particular, we intend to define those quasi-distributions for states valued on the Bohr compactification of the real line in such a way that they are labeled by a parameter that accounts for the ordering ambiguity corresponding to non-commutative quantum operators. Hence, we notice that the projections of the parametrized quasi-probability distributions result in marginal probability densities which are invariant under any ordering prescription. We also note that, in opposition to the standard Schr\"odinger representation, for an arbitrary character the quasi-distributions determine a positive function independently of the ordering. Further, by judiciously implementing a parametric-ordered Weyl quantization map for LQG, we are able to recover in a simple manner the relevant cases of the standard, anti-standard, and Weyl symmetric orderings, respectively. We expect that our results may serve to analyze several fundamental aspects within the LQC program, in special those related to coherence, squeezed states, and the convergence of operators, as extensively analyzed in the quantum optics and in the quantum information frameworks. |
1411.2386 | Mustapha Azreg-A\~"iou | Mustapha Azreg-A\"inou | Black hole thermodynamics: No inconsistency via the inclusion of the
missing P-V terms | 15 pages, 2 figures. Minor changes | Phys. Rev. D 91, 064049 (2015) | 10.1103/PhysRevD.91.064049 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The early literature on black hole thermodynamics ignored the $P$-$V$ term
associated with the existence of a fundamental physical constant in the black
hole solution. The inclusion of this constant in the first law becomes
inconsistent with the Smarr relation. Once the missing $P$-$V$ term introduced
is, it becomes customary to introduce it only in problems where there is a
negative cosmological constant. This practice is inherited from cosmological
approaches which consider the quantity $-\Lambda/8\pi$ as the constant pressure
due to a cosmological fluid. However, the notions of pressure and thermodynamic
volume in black hole thermodynamics are very different from their counterparts
in classical thermodynamics. From this point of view, there is \textit{a
priori} no compelling reason to not extend this notion of pressure and
associate a partial pressure with each external" density $8\pi T_{t}{}^{t}$. In
this work, we associate a partial pressure with a variable mass parameter as
well as with each $tt$ component of the effective stress-energy tensor
$T_{\text{eff} \mu}{}^{\nu}$ but not with the linear component of the
electromagnetic field. Using the field equations $G_{\mu}{}^{\nu}=8\pi
T_{\text{eff} \mu}{}^{\nu}$, we derive universal expressions for the enthalpy,
internal energy, free energies, thermodynamic volume, equation of state, law of
corresponding states, criticality, and critical exponents of static
(nonrotating) charged black holes, with possibly a variable mass parameter,
whether they are solutions to the Einstein field equations or not. We extend
the derivation to the case where the black hole is immersed in the field of a
quintessence force and to the multiforce case. Many applications and extensions
are considered, including applications to regular black holes derived in
previous and present work. No inconsistency has been noticed in their
thermodynamics.
| [
{
"created": "Mon, 10 Nov 2014 11:28:59 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Mar 2015 14:29:59 GMT",
"version": "v2"
}
] | 2016-02-22 | [
[
"Azreg-Aïnou",
"Mustapha",
""
]
] | The early literature on black hole thermodynamics ignored the $P$-$V$ term associated with the existence of a fundamental physical constant in the black hole solution. The inclusion of this constant in the first law becomes inconsistent with the Smarr relation. Once the missing $P$-$V$ term introduced is, it becomes customary to introduce it only in problems where there is a negative cosmological constant. This practice is inherited from cosmological approaches which consider the quantity $-\Lambda/8\pi$ as the constant pressure due to a cosmological fluid. However, the notions of pressure and thermodynamic volume in black hole thermodynamics are very different from their counterparts in classical thermodynamics. From this point of view, there is \textit{a priori} no compelling reason to not extend this notion of pressure and associate a partial pressure with each external" density $8\pi T_{t}{}^{t}$. In this work, we associate a partial pressure with a variable mass parameter as well as with each $tt$ component of the effective stress-energy tensor $T_{\text{eff} \mu}{}^{\nu}$ but not with the linear component of the electromagnetic field. Using the field equations $G_{\mu}{}^{\nu}=8\pi T_{\text{eff} \mu}{}^{\nu}$, we derive universal expressions for the enthalpy, internal energy, free energies, thermodynamic volume, equation of state, law of corresponding states, criticality, and critical exponents of static (nonrotating) charged black holes, with possibly a variable mass parameter, whether they are solutions to the Einstein field equations or not. We extend the derivation to the case where the black hole is immersed in the field of a quintessence force and to the multiforce case. Many applications and extensions are considered, including applications to regular black holes derived in previous and present work. No inconsistency has been noticed in their thermodynamics. |
1910.12893 | Paolo Pani | Andrea Maselli, Paolo Pani, Leonardo Gualtieri, Emanuele Berti | Parametrized ringdown spin expansion coefficients: a data-analysis
framework for black-hole spectroscopy with multiple events | 15 pages, 8 figures. v2: matches published version | Phys. Rev. D 101, 024043 (2020) | 10.1103/PhysRevD.101.024043 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black-hole spectroscopy is arguably the most promising tool to test gravity
in extreme regimes and to probe the ultimate nature of black holes with
unparalleled precision. These tests are currently limited by the lack of a
ringdown parametrization that is both robust and accurate. We develop an
observable-based parametrization of the ringdown of spinning black holes beyond
general relativity, which we dub ParSpec (Parametrized Ringdown Spin Expansion
Coefficients). This approach is perturbative in the spin, but it can be made
arbitrarily precise (at least in principle) through a high-order expansion. It
requires O(10) ringdown detections, which should be routinely available with
the planned space mission LISA and with third-generation ground-based
detectors. We provide a preliminary analysis of the projected bounds on
parametrized ringdown parameters with LISA and with the Einstein Telescope, and
discuss extensions of our model that can be straightforwardly included in the
future.
| [
{
"created": "Mon, 28 Oct 2019 18:02:12 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Jan 2020 09:56:21 GMT",
"version": "v2"
}
] | 2020-01-24 | [
[
"Maselli",
"Andrea",
""
],
[
"Pani",
"Paolo",
""
],
[
"Gualtieri",
"Leonardo",
""
],
[
"Berti",
"Emanuele",
""
]
] | Black-hole spectroscopy is arguably the most promising tool to test gravity in extreme regimes and to probe the ultimate nature of black holes with unparalleled precision. These tests are currently limited by the lack of a ringdown parametrization that is both robust and accurate. We develop an observable-based parametrization of the ringdown of spinning black holes beyond general relativity, which we dub ParSpec (Parametrized Ringdown Spin Expansion Coefficients). This approach is perturbative in the spin, but it can be made arbitrarily precise (at least in principle) through a high-order expansion. It requires O(10) ringdown detections, which should be routinely available with the planned space mission LISA and with third-generation ground-based detectors. We provide a preliminary analysis of the projected bounds on parametrized ringdown parameters with LISA and with the Einstein Telescope, and discuss extensions of our model that can be straightforwardly included in the future. |
1206.5509 | Vladimir Khatsymovsky | V.M. Khatsymovsky | On area spectrum in the Faddeev gravity | 17 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider Faddeev formulation of gravity, in which the metric is bilinear
of $d = 10$ 4-vector fields. A unique feature of this formulation is that the
action remains finite for the discontinuous fields (although continuity is
recovered on the equations of motion). This means that the spacetime can be
decomposed into the 4-simplices virtually not coinciding on their common faces,
that is, independent. This allows, in particular, to consider a surface as
consisting of a set of virtually independent elementary pieces (2-simplices).
Then the spectrum of surface area is the sum of the spectra of independent
elementary areas. We use connection representation of the Faddeev action for
the piecewise flat (simplicial) manifold earlier proposed in our work. The
spectrum of elementary areas is the spectrum of the field bilinears which are
canonically conjugate to the orthogonal connection matrices. We find that the
elementary area spectrum is proportional to the Barbero-Immirzi parameter
$\gamma$ in the Faddeev gravity and is similar to the spectrum of the angular
momentum in the space with the dimension $d - 2$. Knowing this spectrum allows
to estimate statistical black hole entropy. Requiring that this entropy
coincide with the Bekenstein-Hawking entropy gives the equation, known in the
literature. This equation allows to estimate $\gamma$ for arbitrary $d$, in
particular, $\gamma = 0.39...$ for genuine $d = 10$.
| [
{
"created": "Sun, 24 Jun 2012 15:40:03 GMT",
"version": "v1"
}
] | 2012-06-26 | [
[
"Khatsymovsky",
"V. M.",
""
]
] | We consider Faddeev formulation of gravity, in which the metric is bilinear of $d = 10$ 4-vector fields. A unique feature of this formulation is that the action remains finite for the discontinuous fields (although continuity is recovered on the equations of motion). This means that the spacetime can be decomposed into the 4-simplices virtually not coinciding on their common faces, that is, independent. This allows, in particular, to consider a surface as consisting of a set of virtually independent elementary pieces (2-simplices). Then the spectrum of surface area is the sum of the spectra of independent elementary areas. We use connection representation of the Faddeev action for the piecewise flat (simplicial) manifold earlier proposed in our work. The spectrum of elementary areas is the spectrum of the field bilinears which are canonically conjugate to the orthogonal connection matrices. We find that the elementary area spectrum is proportional to the Barbero-Immirzi parameter $\gamma$ in the Faddeev gravity and is similar to the spectrum of the angular momentum in the space with the dimension $d - 2$. Knowing this spectrum allows to estimate statistical black hole entropy. Requiring that this entropy coincide with the Bekenstein-Hawking entropy gives the equation, known in the literature. This equation allows to estimate $\gamma$ for arbitrary $d$, in particular, $\gamma = 0.39...$ for genuine $d = 10$. |
1508.03246 | Wenliang Li | Wenliang Li | Novel nonlinear kinetic terms for gravitons | 19 pages, two columns, v3.1; a reference is added | Phys. Rev. D 94, 064078 (2016) | 10.1103/PhysRevD.94.064078 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A set of novel derivative terms for spin-2 fields are proposed. They are the
wedge products of curvature two-forms and vielbeins. In this work, we
investigate the properties of novel two-derivative terms in the context of
bi-gravity. Based on a minisuperspace analysis, we identify a large class of
bi-gravity models where the Boulware-Deser ghost could be absent. We give a new
perspective that Weyl Gravity and New Massive Gravity belong to this class of
bi-gravity models involving novel derivative terms. In addition, we discuss the
UV cut-off scales, dynamical symmetric conditions and novel higher-derivative
terms.
| [
{
"created": "Thu, 13 Aug 2015 15:22:08 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Nov 2015 00:57:24 GMT",
"version": "v2"
},
{
"created": "Thu, 21 Jul 2016 17:38:21 GMT",
"version": "v3"
},
{
"created": "Thu, 19 Oct 2017 03:12:31 GMT",
"version": "v4"
}
] | 2017-10-20 | [
[
"Li",
"Wenliang",
""
]
] | A set of novel derivative terms for spin-2 fields are proposed. They are the wedge products of curvature two-forms and vielbeins. In this work, we investigate the properties of novel two-derivative terms in the context of bi-gravity. Based on a minisuperspace analysis, we identify a large class of bi-gravity models where the Boulware-Deser ghost could be absent. We give a new perspective that Weyl Gravity and New Massive Gravity belong to this class of bi-gravity models involving novel derivative terms. In addition, we discuss the UV cut-off scales, dynamical symmetric conditions and novel higher-derivative terms. |
2002.00221 | Roberto Casadio | R. Casadio, M. Lenzi, A. Ciarfella | Quantum black holes in bootstrapped Newtonian gravity | LaTeX, 27 pages, 6 figures, clarifications added, to appear in PRD | Phys. Rev. D 101, 124032 (2020) | 10.1103/PhysRevD.101.124032 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyse the classical configurations of a bootstrapped Newtonian potential
generated by homogeneous spherically symmetric sources in terms of a quantum
coherent state. We first compute how the mass and mean wavelength of these
solutions scale in terms of the number of quanta in the coherent state. We then
note that the classical relation between the ADM mass and the proper mass of
the source naturally gives rise to a Generalised Uncertainty Principle for the
size of the gravitational radius in the quantum theory. Consistency of the mass
and wavelength scalings with this GUP requires the compactness remains at most
of order one even for black holes, and the corpuscular predictions are thus
recovered, with the quantised horizon area expressed in terms of the number of
quanta in the coherent state. Our findings could be useful for analysing the
classicalization of gravity in the presence of matter and the avoidance of
singularities in the gravitational collapse of compact sources.
| [
{
"created": "Sat, 1 Feb 2020 14:36:39 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Jun 2020 21:10:48 GMT",
"version": "v2"
}
] | 2020-07-01 | [
[
"Casadio",
"R.",
""
],
[
"Lenzi",
"M.",
""
],
[
"Ciarfella",
"A.",
""
]
] | We analyse the classical configurations of a bootstrapped Newtonian potential generated by homogeneous spherically symmetric sources in terms of a quantum coherent state. We first compute how the mass and mean wavelength of these solutions scale in terms of the number of quanta in the coherent state. We then note that the classical relation between the ADM mass and the proper mass of the source naturally gives rise to a Generalised Uncertainty Principle for the size of the gravitational radius in the quantum theory. Consistency of the mass and wavelength scalings with this GUP requires the compactness remains at most of order one even for black holes, and the corpuscular predictions are thus recovered, with the quantised horizon area expressed in terms of the number of quanta in the coherent state. Our findings could be useful for analysing the classicalization of gravity in the presence of matter and the avoidance of singularities in the gravitational collapse of compact sources. |
0801.1686 | Arturo Avelino Huerta | Arturo Avelino, U. Nucamendi and F. S. Guzm\'an (Instituto de F\'isica
y Matem\'aticas, Universidad Michoacana de San Nicol\'as de Hidalgo, Morelia,
Michoac\'an, M\'exico) | Constraining a bulk viscous matter-dominated cosmological model using
SNe Ia, CMB and LSS | 4 pages, 1 figure. Work presented in the XI Mexican Workshop on
Particles and Fields, Tuxtla Gutierrez, Mexico, nov 7-12, 2007. Submitted to
AIP Conference Proceedings of this conference | AIP Conf.Proc.1026:300-302,2008 | 10.1063/1.2965067 | null | gr-qc astro-ph | null | We present and constrain a cosmological model which component is a
pressureless fluid with bulk viscosity as an explanation for the present
accelerated expansion of the universe. We study the particular model of a
constant bulk viscosity coefficient \zeta_m. The possible values of \zeta_m are
constrained using the cosmological tests of SNe Ia Gold 2006 sample, the CMB
shift parameter R from the three-year WMAP observations, the Baryon Acoustic
Oscillation (BAO) peak A from the Sloan Digital Sky Survey (SDSS) and the
Second Law of Thermodynamics (SLT). It was found that this model is in
agreement with the SLT using only the SNe Ia test. However when the model is
submitted to the three cosmological tests together (SNe+CMB+BAO) the results
are: 1.- the model violates the SLT, 2.- predicts a value of H_0 \approx 53 km
sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- we obtain a bad fit to data
with a \chi^2_{min} \approx 400 (\chi^2_{d.o.f.} \approx 2.2). These results
indicate that this model is ruled out by the observations.
| [
{
"created": "Thu, 10 Jan 2008 21:26:07 GMT",
"version": "v1"
}
] | 2009-03-24 | [
[
"Avelino",
"Arturo",
"",
"Instituto de Física\n y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Morelia,\n Michoacán, México"
],
[
"Nucamendi",
"U.",
"",
"Instituto de Física\n y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Morelia,\n Mich... | We present and constrain a cosmological model which component is a pressureless fluid with bulk viscosity as an explanation for the present accelerated expansion of the universe. We study the particular model of a constant bulk viscosity coefficient \zeta_m. The possible values of \zeta_m are constrained using the cosmological tests of SNe Ia Gold 2006 sample, the CMB shift parameter R from the three-year WMAP observations, the Baryon Acoustic Oscillation (BAO) peak A from the Sloan Digital Sky Survey (SDSS) and the Second Law of Thermodynamics (SLT). It was found that this model is in agreement with the SLT using only the SNe Ia test. However when the model is submitted to the three cosmological tests together (SNe+CMB+BAO) the results are: 1.- the model violates the SLT, 2.- predicts a value of H_0 \approx 53 km sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- we obtain a bad fit to data with a \chi^2_{min} \approx 400 (\chi^2_{d.o.f.} \approx 2.2). These results indicate that this model is ruled out by the observations. |
gr-qc/0501013 | Roberto Giambo' | Roberto Giamb\'o | Gravitational collapse of homogeneous scalar fields | LaTeX2e; revised version | Class.Quant.Grav.22:2295-2305,2005 | 10.1088/0264-9381/22/11/023 | null | gr-qc | null | Conditions under which gravity coupled to self interacting scalar field
determines singularity formation are found and discussed. It is shown that,
under a suitable matching with an external space, the boundary, if collapses
completely, may give rise to a naked singularity. Issues related to the
strength of the singularity are discussed.
| [
{
"created": "Wed, 5 Jan 2005 17:52:32 GMT",
"version": "v1"
},
{
"created": "Fri, 27 May 2005 14:54:05 GMT",
"version": "v2"
}
] | 2010-11-05 | [
[
"Giambó",
"Roberto",
""
]
] | Conditions under which gravity coupled to self interacting scalar field determines singularity formation are found and discussed. It is shown that, under a suitable matching with an external space, the boundary, if collapses completely, may give rise to a naked singularity. Issues related to the strength of the singularity are discussed. |
2005.02688 | Jonathan Gratus | Jonathan Gratus, Paolo Pinto, Spyridon Talaganis | The Distributional Stress-Energy Quadrupole | 42 pages, 2 figures. Accepted by Classical and Quantum Gravity.
url=http://iopscience.iop.org/article/10.1088/1361-6382/abccde | null | 10.1088/1361-6382/abccde | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate stress-energy tensors constructed from the delta function on a
worldline. We concentrate on quadrupoles as they make an excellent model for
the dominant source of gravitational waves and have significant novel features.
Unlike the dipole, we show that the quadrupole has 20 free components which are
not determined by the properties of the stress-energy tensor. These need to be
derived from an underlying model and we give an example motivated from a
divergent-free dust. We show that the components corresponding to the partial
derivatives representation of the quadrupole, have a gauge like freedom. We
give the change of coordinate formula which involves second derivatives and two
integrals. We also show how to define the quadrupole without reference to a
coordinate systems or a metric. For the representation using covariant
derivatives, we show how to split a quadrupole into a pure monopole, pure
dipole and pure quadrupole in a coordinate free way.
| [
{
"created": "Wed, 6 May 2020 09:51:59 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Nov 2020 09:36:19 GMT",
"version": "v2"
}
] | 2020-11-26 | [
[
"Gratus",
"Jonathan",
""
],
[
"Pinto",
"Paolo",
""
],
[
"Talaganis",
"Spyridon",
""
]
] | We investigate stress-energy tensors constructed from the delta function on a worldline. We concentrate on quadrupoles as they make an excellent model for the dominant source of gravitational waves and have significant novel features. Unlike the dipole, we show that the quadrupole has 20 free components which are not determined by the properties of the stress-energy tensor. These need to be derived from an underlying model and we give an example motivated from a divergent-free dust. We show that the components corresponding to the partial derivatives representation of the quadrupole, have a gauge like freedom. We give the change of coordinate formula which involves second derivatives and two integrals. We also show how to define the quadrupole without reference to a coordinate systems or a metric. For the representation using covariant derivatives, we show how to split a quadrupole into a pure monopole, pure dipole and pure quadrupole in a coordinate free way. |
0809.2678 | Ali Reza Amani | J. Sadeghi and A.R. Amani | The solution of tachyon inflation in curved universe | 8 pages, 21 figures | Int.J.Theor.Phys.48:14-21,2009 | 10.1007/s10773-008-9776-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we have considered the curved universe which is filled by
tachyonic field. We have found the exact solutions for the field, pressure,
density, and scale factor and some cosmological parameters. In such universe,
we have investigated the role of tachyonic field in different stages of k for
the evolution of the universe. Finally we draw the graphs for the scale factor,
Hubble's parameter, energy density, pressure, acceleration parameter, equation
of state and potential for the different values of k. Also we obtained the
exact form of field which shows that the tachyonic field has the kink form.
| [
{
"created": "Tue, 16 Sep 2008 10:59:53 GMT",
"version": "v1"
}
] | 2009-02-19 | [
[
"Sadeghi",
"J.",
""
],
[
"Amani",
"A. R.",
""
]
] | In this paper, we have considered the curved universe which is filled by tachyonic field. We have found the exact solutions for the field, pressure, density, and scale factor and some cosmological parameters. In such universe, we have investigated the role of tachyonic field in different stages of k for the evolution of the universe. Finally we draw the graphs for the scale factor, Hubble's parameter, energy density, pressure, acceleration parameter, equation of state and potential for the different values of k. Also we obtained the exact form of field which shows that the tachyonic field has the kink form. |
2304.08171 | Piotr Jaranowski | Andrzej Kr\'olak, Piotr Jaranowski, Micha{\l} Bejger, Pawe{\l}
Cieciel\k{a}g, Orest Dorosh, Andrzej Pisarski | Search for Postmerger Gravitational Waves from Binary Neutron Star
Mergers Using a Matched-filtering Statistic | LaTeX, 30 pages, 15 figures, identical to the published version | Class. Quantum Grav. 40, 215008 (2023) | 10.1088/1361-6382/acfa5d | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we present a new method to search for a short, a few tens of
milliseconds long, postmerger gravitational-wave signal following the merger of
two neutron stars. Such a signal could follow the event GW170817 observed by
LIGO and Virgo detectors. Our method is based on a matched filtering statistic
and an approximate template of the postmerger signal in the form of a damped
sinusoid. We test and validate our method using postmerger numerical
simulations from the CoRe database. We find no evidence of the short postmerger
signal in the LIGO data following the GW170817 event and we obtain upper
limits. For short postmerger signals investigated, our best upper limit on the
root sum square of the gravitational-wave strain emitted from 1.15 kHz to 4 kHz
is $h_{\text{rss}}^{50\%}=1.8\times 10^{-22}/\sqrt{\text{Hz}}$ at 50% detection
efficiency. The distance corresponding to this best upper limit is 4.64 Mpc.
| [
{
"created": "Mon, 17 Apr 2023 11:35:12 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Apr 2023 08:11:01 GMT",
"version": "v2"
},
{
"created": "Fri, 13 Oct 2023 09:22:48 GMT",
"version": "v3"
}
] | 2023-10-16 | [
[
"Królak",
"Andrzej",
""
],
[
"Jaranowski",
"Piotr",
""
],
[
"Bejger",
"Michał",
""
],
[
"Ciecieląg",
"Paweł",
""
],
[
"Dorosh",
"Orest",
""
],
[
"Pisarski",
"Andrzej",
""
]
] | In this paper, we present a new method to search for a short, a few tens of milliseconds long, postmerger gravitational-wave signal following the merger of two neutron stars. Such a signal could follow the event GW170817 observed by LIGO and Virgo detectors. Our method is based on a matched filtering statistic and an approximate template of the postmerger signal in the form of a damped sinusoid. We test and validate our method using postmerger numerical simulations from the CoRe database. We find no evidence of the short postmerger signal in the LIGO data following the GW170817 event and we obtain upper limits. For short postmerger signals investigated, our best upper limit on the root sum square of the gravitational-wave strain emitted from 1.15 kHz to 4 kHz is $h_{\text{rss}}^{50\%}=1.8\times 10^{-22}/\sqrt{\text{Hz}}$ at 50% detection efficiency. The distance corresponding to this best upper limit is 4.64 Mpc. |
gr-qc/0006038 | Ozay Gurtug | Ozay Gurtug and Mustafa Halilsoy | Horizon Instability in the Cross Polarized Bell-Szekeres Spacetime | Latex file, 26 pages, 1 ps figure | null | null | null | gr-qc | null | The quasiregular singularities (horizons) that form in the collision of cross
polarized electromagnetic waves are, as in the linear polarized case unstable.
The validity of the Helliwell-Konkowski stability conjecture is tested for a
number of exact back-reaction cases. In the test electromagnetic case the
conjecture fails to predict the correct nature of the singularity while in the
scalar field and in the null dust cases the aggrement is justified.
| [
{
"created": "Mon, 12 Jun 2000 11:44:44 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Gurtug",
"Ozay",
""
],
[
"Halilsoy",
"Mustafa",
""
]
] | The quasiregular singularities (horizons) that form in the collision of cross polarized electromagnetic waves are, as in the linear polarized case unstable. The validity of the Helliwell-Konkowski stability conjecture is tested for a number of exact back-reaction cases. In the test electromagnetic case the conjecture fails to predict the correct nature of the singularity while in the scalar field and in the null dust cases the aggrement is justified. |
gr-qc/0609117 | Clovis Jacinto de Matos | Clovis Jacinto de Matos | Generation of Closed Timelike Curves with Rotating Superconductors | 9 pages. Submitted to Classical and Quantum Gravity | Class.Quant.Grav.24:1693-1698,2007 | 10.1088/0264-9381/24/7/001 | null | gr-qc | null | The spacetime metric around a rotating SuperConductive Ring (SCR) is deduced
from the gravitomagnetic London moment in rotating superconductors. It is shown
that theoretically it is possible to generate Closed Timelike Curves (CTC) with
rotating SCRs. The possibility to use these CTC's to travel in time as
initially idealized by G\"{o}del is investigated. It is shown however, that
from a technology and experimental point of view these ideas are impossible to
implement in the present context.
| [
{
"created": "Tue, 26 Sep 2006 08:13:42 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Dec 2006 13:44:46 GMT",
"version": "v2"
},
{
"created": "Fri, 19 Jan 2007 16:50:40 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"de Matos",
"Clovis Jacinto",
""
]
] | The spacetime metric around a rotating SuperConductive Ring (SCR) is deduced from the gravitomagnetic London moment in rotating superconductors. It is shown that theoretically it is possible to generate Closed Timelike Curves (CTC) with rotating SCRs. The possibility to use these CTC's to travel in time as initially idealized by G\"{o}del is investigated. It is shown however, that from a technology and experimental point of view these ideas are impossible to implement in the present context. |
1808.04570 | Alexander Agathonov | Yurii Ignat'ev, Alexander Agathonov, Irina Kokh | The Peculiarities of the Cosmological Models Based on Non-Linear
Classical and Phantom Fields with Minimal Interaction. I. The Cosmological
Model Based on Scalar Singlet | 17 pages, 24 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | A detailed comparative qualitative analysis and numerical simulation of
evolution of the cosmological models based on classical and phantom scalar
fields with self-action was performed. The phase portraits of the dynamic
systems of classical and phantom fields and their projections to the Poincare
sphere were constructed. It was shown that the phase trajectories of the
corresponding dynamic systems can be split by bifurcation trajectories into 2,4
or 6 different dynamic streams corresponding to different pairwise symmetric
histories of the Universe depending on the parameters of the scalar field's
model. The phase space of such systems becomes multiply connected, the ranges
of negative total effective energy unavailable for motion, getting appear
there. In the case when attracting centers are situated inside these ranges,
the phase trajectories of the classical scalar field in the infinite future
tend to limit cycles, winding onto the boundaries of these ranges. The phase
trajectories of the scalar field, in turn, get away from the boundaries of
ranges with null effective energy and in the infinite future are wound onto one
of the symmetrical focuses (centers). Thus, the situations when the Universe,
in case of classical scalar field, begins its history with the inflation and
ends it up in the Euclidean future, or, in the case of phantom scalar field, in
opposite, has the Euclidian start and proceeds to inflation mode after
anomalous burst of the acceleration, both become possible. The potentials of
scalar fields on the surface of null curvature are distinct from zero and
thereby define a certain vacuum state.
| [
{
"created": "Tue, 14 Aug 2018 07:57:15 GMT",
"version": "v1"
}
] | 2018-08-15 | [
[
"Ignat'ev",
"Yurii",
""
],
[
"Agathonov",
"Alexander",
""
],
[
"Kokh",
"Irina",
""
]
] | A detailed comparative qualitative analysis and numerical simulation of evolution of the cosmological models based on classical and phantom scalar fields with self-action was performed. The phase portraits of the dynamic systems of classical and phantom fields and their projections to the Poincare sphere were constructed. It was shown that the phase trajectories of the corresponding dynamic systems can be split by bifurcation trajectories into 2,4 or 6 different dynamic streams corresponding to different pairwise symmetric histories of the Universe depending on the parameters of the scalar field's model. The phase space of such systems becomes multiply connected, the ranges of negative total effective energy unavailable for motion, getting appear there. In the case when attracting centers are situated inside these ranges, the phase trajectories of the classical scalar field in the infinite future tend to limit cycles, winding onto the boundaries of these ranges. The phase trajectories of the scalar field, in turn, get away from the boundaries of ranges with null effective energy and in the infinite future are wound onto one of the symmetrical focuses (centers). Thus, the situations when the Universe, in case of classical scalar field, begins its history with the inflation and ends it up in the Euclidean future, or, in the case of phantom scalar field, in opposite, has the Euclidian start and proceeds to inflation mode after anomalous burst of the acceleration, both become possible. The potentials of scalar fields on the surface of null curvature are distinct from zero and thereby define a certain vacuum state. |
0905.3655 | M. D. Maia | M. D. Maia, A. J. S.Capistrano and E. M. Monte | On the Nature of the Cosmological Constant Problem | LaTex, 5 pages no figutres. Correction on author list | Int.J.Mod.Phys.A24:1545-1548,2009 | 10.1142/S0217751X09044978 | null | gr-qc astro-ph.CO hep-ex | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | General relativity postulates the Minkowski space-time to be the standard
flat geometry against which we compare all curved space-times and the
gravitational ground state where particles, quantum fields and their vacuum
states are primarily conceived. On the other hand, experimental evidences show
that there exists a non-zero cosmological constant, which implies in a deSitter
space-time, not compatible with the assumed Minkowski structure. Such
inconsistency is shown to be a consequence of the lack of a application
independent curvature standard in Riemann's geometry, leading eventually to the
cosmological constant problem in general relativity.
We show how the curvature standard in Riemann's geometry can be fixed by
Nash's theorem on locally embedded Riemannian geometries, which imply in the
existence of extra dimensions. The resulting gravitational theory is more
general than general relativity, similar to brane-world gravity, but where the
propagation of the gravitational field along the extra dimensions is a
mathematical necessity, rather than being a a postulate. After a brief
introduction to Nash's theorem, we show that the vacuum energy density must
remain confined to four-dimensional space-times, but the cosmological constant
resulting from the contracted Bianchi identity is a gravitational contribution
which propagates in the extra dimensions. Therefore, the comparison between the
vacuum energy and the cosmological constant in general relativity ceases to be.
Instead, the geometrical fix provided by Nash's theorem suggests that the
vacuum energy density contributes to the perturbations of the gravitational
field.
| [
{
"created": "Fri, 22 May 2009 10:32:06 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Jun 2009 00:18:18 GMT",
"version": "v2"
}
] | 2015-05-13 | [
[
"Maia",
"M. D.",
""
],
[
"Capistrano",
"A. J. S.",
""
],
[
"Monte",
"E. M.",
""
]
] | General relativity postulates the Minkowski space-time to be the standard flat geometry against which we compare all curved space-times and the gravitational ground state where particles, quantum fields and their vacuum states are primarily conceived. On the other hand, experimental evidences show that there exists a non-zero cosmological constant, which implies in a deSitter space-time, not compatible with the assumed Minkowski structure. Such inconsistency is shown to be a consequence of the lack of a application independent curvature standard in Riemann's geometry, leading eventually to the cosmological constant problem in general relativity. We show how the curvature standard in Riemann's geometry can be fixed by Nash's theorem on locally embedded Riemannian geometries, which imply in the existence of extra dimensions. The resulting gravitational theory is more general than general relativity, similar to brane-world gravity, but where the propagation of the gravitational field along the extra dimensions is a mathematical necessity, rather than being a a postulate. After a brief introduction to Nash's theorem, we show that the vacuum energy density must remain confined to four-dimensional space-times, but the cosmological constant resulting from the contracted Bianchi identity is a gravitational contribution which propagates in the extra dimensions. Therefore, the comparison between the vacuum energy and the cosmological constant in general relativity ceases to be. Instead, the geometrical fix provided by Nash's theorem suggests that the vacuum energy density contributes to the perturbations of the gravitational field. |
2407.13793 | Faizuddin Ahmed | Jaydeep Goswami, Hafizur Rahman, Rimi Sikdar, Rina Parvin and
Faizuddin Ahmed | Morris-Thorne-type Wormhole with Global Monopole Charge and the Energy
Conditions | 31 pages, 27 figures, 2 tables. arXiv admin note: text overlap with
arXiv:1907.06726 by other authors | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper, we investigate topologically charged Morris-Thorne-type
wormholes using various shape function forms. We solve the Einstein field
equations incorporating an anisotropic energy-momentum tensor and obtain
different physical quantities associated with the matter content. A crucial
aspect of this study is the non-exotic matter distribution, examined through
the evaluation of energy conditions, and exploring how different shape
functions impact these conditions. Additionally, the anisotropy parameter is
calculated to quantify the extent of attractive or repulsive behavior. Our
study demonstrates that for different types of shape function forms, the energy
conditions are influenced by the global monopole parameter. Our findings
provide valuable insights for further theoretical explorations of these
fascinating hypothetical structures in the realm of general relativity and
beyond
| [
{
"created": "Tue, 16 Jul 2024 08:08:26 GMT",
"version": "v1"
}
] | 2024-07-22 | [
[
"Goswami",
"Jaydeep",
""
],
[
"Rahman",
"Hafizur",
""
],
[
"Sikdar",
"Rimi",
""
],
[
"Parvin",
"Rina",
""
],
[
"Ahmed",
"Faizuddin",
""
]
] | In this paper, we investigate topologically charged Morris-Thorne-type wormholes using various shape function forms. We solve the Einstein field equations incorporating an anisotropic energy-momentum tensor and obtain different physical quantities associated with the matter content. A crucial aspect of this study is the non-exotic matter distribution, examined through the evaluation of energy conditions, and exploring how different shape functions impact these conditions. Additionally, the anisotropy parameter is calculated to quantify the extent of attractive or repulsive behavior. Our study demonstrates that for different types of shape function forms, the energy conditions are influenced by the global monopole parameter. Our findings provide valuable insights for further theoretical explorations of these fascinating hypothetical structures in the realm of general relativity and beyond |
gr-qc/9910026 | Gaetano Lambiase | S. Capozziello, G. Lambiase | Neutrino Oscillations in Brans-Dicke Theory of Gravity | 9 pages, LATEX file, to appear in Mod. Phys. Lett. A | Mod.Phys.Lett.A14:2193,1999 | 10.1142/S0217732399002261 | null | gr-qc | null | Flavor oscillations of neutrinos are analyzed in the framework of Brans-Dicke
theory of gravity. We find a shift of quantum mechanical phase of neutrino
proportional to $G_N\Delta m^2$ and depending on the parameter $\omega$.
Consequences on atmospheric, solar and astrophysical neutrinos are discussed.
| [
{
"created": "Thu, 7 Oct 1999 14:25:48 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Capozziello",
"S.",
""
],
[
"Lambiase",
"G.",
""
]
] | Flavor oscillations of neutrinos are analyzed in the framework of Brans-Dicke theory of gravity. We find a shift of quantum mechanical phase of neutrino proportional to $G_N\Delta m^2$ and depending on the parameter $\omega$. Consequences on atmospheric, solar and astrophysical neutrinos are discussed. |
1708.08176 | Shao-Wen Wei | Shao-Wen Wei, Yu-Xiao Liu | Charged AdS black hole heat engines | 14 pages, 17 figures, 1 table | Nucl. Phys. B 946, 114700 (2019) | 10.1016/j.nuclphysb.2019.114700 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the heat engine by a $d$-dimensional charged anti-de Sitter black
hole by making a comparison between the small-large black hole phase transition
and the liquid-vapour phase transition of water. With the help of the first law
and equal-area law, we obtain an exact formula for the efficiency of a black
hole engine modeled with a Rankine cycle with or without a back pressure
mechanism. When the low temperature is fixed, both the heat and work decreases
with the high temperature $T_{1}$. And the efficiency increases with $T_{1}$,
while decreases with the charge $q$. For a Rankine cycle with a back pressure
mechanism, we find that both the maximum work and efficiency can be approached
at the high temperature $T_{1}$. In the reduced parameter space, it also
confirms the similar result. Moreover, we observe that the work and efficiency
of the black hole heat engine rapidly increase with the number of spacetime
dimensions. Thus higher-dimensional charged anti-de Sitter black hole can act
as a more efficient power plant producing the mechanical work, and might be a
possible source of the power gamma rays and ultrahigh-energy cosmic rays.
| [
{
"created": "Mon, 28 Aug 2017 03:46:02 GMT",
"version": "v1"
},
{
"created": "Sat, 17 Aug 2019 08:40:22 GMT",
"version": "v2"
}
] | 2019-08-20 | [
[
"Wei",
"Shao-Wen",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] | We study the heat engine by a $d$-dimensional charged anti-de Sitter black hole by making a comparison between the small-large black hole phase transition and the liquid-vapour phase transition of water. With the help of the first law and equal-area law, we obtain an exact formula for the efficiency of a black hole engine modeled with a Rankine cycle with or without a back pressure mechanism. When the low temperature is fixed, both the heat and work decreases with the high temperature $T_{1}$. And the efficiency increases with $T_{1}$, while decreases with the charge $q$. For a Rankine cycle with a back pressure mechanism, we find that both the maximum work and efficiency can be approached at the high temperature $T_{1}$. In the reduced parameter space, it also confirms the similar result. Moreover, we observe that the work and efficiency of the black hole heat engine rapidly increase with the number of spacetime dimensions. Thus higher-dimensional charged anti-de Sitter black hole can act as a more efficient power plant producing the mechanical work, and might be a possible source of the power gamma rays and ultrahigh-energy cosmic rays. |
gr-qc/0407038 | Paul S. Wesson | Paul S. Wesson | Vacuum Instability | null | Found.Phys.Lett. 19 (2006) 285-291 | null | null | gr-qc | null | Following fresh attempts to resolve the problem of the energy density of the
vacuum, we reconsider the case where the cosmological constant is derived from
a higher-dimensional version of general relativity, and interpret the
gauge-dependence of $\Lambda $ as a dynamical effect. This leads to a relation
between the change in $\Lambda $ and the line element (action) which is
independent of gauge choices and fundamental constants: $d\Lambda ds^{2}=-3$.
This implies that the (classical) vacuum is unstable, with implications for
particle production.
| [
{
"created": "Fri, 9 Jul 2004 23:32:10 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Mar 2005 03:46:10 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Wesson",
"Paul S.",
""
]
] | Following fresh attempts to resolve the problem of the energy density of the vacuum, we reconsider the case where the cosmological constant is derived from a higher-dimensional version of general relativity, and interpret the gauge-dependence of $\Lambda $ as a dynamical effect. This leads to a relation between the change in $\Lambda $ and the line element (action) which is independent of gauge choices and fundamental constants: $d\Lambda ds^{2}=-3$. This implies that the (classical) vacuum is unstable, with implications for particle production. |
2005.02611 | Alexander Pavlov E | Alexander E. Pavlov | EoS of Casimir vacuum of massive fields in Friedmann Universe | 7 pages, 4 figures | null | 10.1142/S0217732320502715 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present paper we study equations of state of Casimir vacuum of massive
scalar field and massive bispinor field in compact Friedmann Universe. With use
of the Abel-Plana formula the renormalization of divergent series for
calculation of the quantum means of operators is implemented.
| [
{
"created": "Wed, 6 May 2020 06:37:57 GMT",
"version": "v1"
}
] | 2020-12-02 | [
[
"Pavlov",
"Alexander E.",
""
]
] | In the present paper we study equations of state of Casimir vacuum of massive scalar field and massive bispinor field in compact Friedmann Universe. With use of the Abel-Plana formula the renormalization of divergent series for calculation of the quantum means of operators is implemented. |
2404.14536 | Nils Siemonsen | Nils Siemonsen | Nonlinear treatment of a black hole mimicker ringdown | 5+9 pages, 4+7 figures, updated to match published version | Phys. Rev. Lett. 133, 031401 (2024) | 10.1103/PhysRevLett.133.031401 | null | gr-qc hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | We perform the first nonlinear and self-consistent study of the merger and
ringdown of a black hole mimicking object with stable light rings. To that end,
we numerically solve the full Einstein-Klein-Gordon equations governing the
head-on collisions of a series of binary boson stars in the large-mass-ratio
regime resulting in spinning horizonless remnants with stable light rings. We
broadly confirm the appearance of features in the extracted gravitational
waveforms expected based on perturbative methods: the signal from the prompt
response of the remnants approaches that of a Kerr black hole in the
large-compactness limit, and the subsequent emissions contain periodically
appearing bursts akin to so-called gravitational wave echoes. However, these
bursts occur at high frequencies and are sourced by perturbations of the
remnant's internal degrees of freedom. Furthermore, the emitted waveforms also
contain a large-amplitude and long-lived component comparable in frequency to
black hole quasi-normal modes. We further characterize the emissions, obtain
basic scaling relations of relevant timescales, and compute the energy emitted
in gravitational waves.
| [
{
"created": "Mon, 22 Apr 2024 19:07:54 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Jul 2024 07:25:38 GMT",
"version": "v2"
}
] | 2024-07-23 | [
[
"Siemonsen",
"Nils",
""
]
] | We perform the first nonlinear and self-consistent study of the merger and ringdown of a black hole mimicking object with stable light rings. To that end, we numerically solve the full Einstein-Klein-Gordon equations governing the head-on collisions of a series of binary boson stars in the large-mass-ratio regime resulting in spinning horizonless remnants with stable light rings. We broadly confirm the appearance of features in the extracted gravitational waveforms expected based on perturbative methods: the signal from the prompt response of the remnants approaches that of a Kerr black hole in the large-compactness limit, and the subsequent emissions contain periodically appearing bursts akin to so-called gravitational wave echoes. However, these bursts occur at high frequencies and are sourced by perturbations of the remnant's internal degrees of freedom. Furthermore, the emitted waveforms also contain a large-amplitude and long-lived component comparable in frequency to black hole quasi-normal modes. We further characterize the emissions, obtain basic scaling relations of relevant timescales, and compute the energy emitted in gravitational waves. |
1712.05068 | Yilin Chen | Yilin Chen, Jin Wang | A new inflationary Universe scenario with inhomogeneous quantum vacuum | 16 pages, 9 figures | null | 10.1155/2018/3916727 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the quantum vacuum and find the fluctuations can lead to the
inhomogeneous quantum vacuum. We find that the vacuum fluctuations can
significantly influence the cosmological inhomogeneity, which is different from
what previously expected. By introducing the modified Green's function, we
reach a new inflationary scenario which can explain why the Universe is still
expanding without slowing down. We also calculate the tunneling amplitude of
the Universe based on the inhomogeneous vacuum. We find that the inhomogeneity
can lead to the penetration of the universe over the potential barrier faster
than previously thought.
| [
{
"created": "Thu, 14 Dec 2017 01:47:46 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Feb 2018 10:53:22 GMT",
"version": "v2"
}
] | 2021-04-14 | [
[
"Chen",
"Yilin",
""
],
[
"Wang",
"Jin",
""
]
] | We investigate the quantum vacuum and find the fluctuations can lead to the inhomogeneous quantum vacuum. We find that the vacuum fluctuations can significantly influence the cosmological inhomogeneity, which is different from what previously expected. By introducing the modified Green's function, we reach a new inflationary scenario which can explain why the Universe is still expanding without slowing down. We also calculate the tunneling amplitude of the Universe based on the inhomogeneous vacuum. We find that the inhomogeneity can lead to the penetration of the universe over the potential barrier faster than previously thought. |
0711.0006 | Tanmay Vachaspati | Tanmay Vachaspati | Schrodinger Picture of Quantum Gravitational Collapse | 9 pages, 1 figure. Matches published version | Class.Quant.Grav.26:215007,2009 | 10.1088/0264-9381/26/21/215007 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The functional Schrodinger equation is used to study the quantum collapse of
a gravitating, spherical domain wall and a massless scalar field coupled to the
metric. The approach includes backreaction of pre-Hawking radiation on the
gravitational collapse. Truncating the degrees of freedom to a minisuperspace
leads to an integro-differential Schrodinger equation. We define a "black hole"
operator and find its eigenstates. The black hole operator does not commute
with the Hamiltonian, leading to an energy-black holeness uncertainty relation.
We discuss energy eigenstates and also obtain a partial differential equation
for the time-dependent gravitational collapse problem.
| [
{
"created": "Wed, 31 Oct 2007 20:08:05 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Oct 2009 02:14:32 GMT",
"version": "v2"
}
] | 2014-11-18 | [
[
"Vachaspati",
"Tanmay",
""
]
] | The functional Schrodinger equation is used to study the quantum collapse of a gravitating, spherical domain wall and a massless scalar field coupled to the metric. The approach includes backreaction of pre-Hawking radiation on the gravitational collapse. Truncating the degrees of freedom to a minisuperspace leads to an integro-differential Schrodinger equation. We define a "black hole" operator and find its eigenstates. The black hole operator does not commute with the Hamiltonian, leading to an energy-black holeness uncertainty relation. We discuss energy eigenstates and also obtain a partial differential equation for the time-dependent gravitational collapse problem. |
gr-qc/0111099 | Marcelo S. Berman | Marcelo S. Berman and Luis A. Trevisan | Static Generalized Brans-Dicke Universe and Gravitational Waves
Amplification | Submitted to Physics Letters A. Date of receipt 01 October 2001 | null | null | null | gr-qc | null | We find a static solution for the scale-factor in a Brans-Dicke generalized
theory where the scalar field and the coupling constant vary with time. We find
also that in the early Universe there may be amplification of gravitational
waves.
| [
{
"created": "Wed, 28 Nov 2001 16:47:43 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Berman",
"Marcelo S.",
""
],
[
"Trevisan",
"Luis A.",
""
]
] | We find a static solution for the scale-factor in a Brans-Dicke generalized theory where the scalar field and the coupling constant vary with time. We find also that in the early Universe there may be amplification of gravitational waves. |
gr-qc/9801098 | Ronggen Cai | Rong-Gen Cai | Propagation of vacuum polarized photons in topological black hole
spacetimes | 18 pages, Revtex, no figures | Nucl.Phys. B524 (1998) 639-657 | 10.1016/S0550-3213(98)00274-0 | SNUTP 97-165 | gr-qc | null | The one-loop effective action for QED in curved spacetime contains
equivalence principle violating interactions between the electromagnetic field
and the spacetime curvature. These interactions lead to the dependence of
photon velocity on the motion and polarization directions. In this paper we
investigate the gravitational analogue to the electromagnetic birefringence
phenomenon in the static and radiating topological black hole backgrounds,
respectively. For the static topological black hole spacetimes, the velocity
shift of photons is the same as the one in the Reissner-Nordstr\"om black
holes. This reflects that the propagation of vacuum polarized photons is not
sensitive to the asymptotic behavior and topological structure of spacetimes.
For the massless topological black hole and BTZ black hole, the light cone
condition keeps unchanged. In the radiating topological black hole backgrounds,
the light cone condition is changed even for the radially directed photons. The
velocity shifts depend on the topological structures. Due to the null fluid,
the velocity shift of photons does no longer vanish at the apparent horizons as
well as the event horizons. But the ``polarization sum rule'' is still valid.
| [
{
"created": "Thu, 29 Jan 1998 07:06:34 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Jul 1998 08:23:55 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Cai",
"Rong-Gen",
""
]
] | The one-loop effective action for QED in curved spacetime contains equivalence principle violating interactions between the electromagnetic field and the spacetime curvature. These interactions lead to the dependence of photon velocity on the motion and polarization directions. In this paper we investigate the gravitational analogue to the electromagnetic birefringence phenomenon in the static and radiating topological black hole backgrounds, respectively. For the static topological black hole spacetimes, the velocity shift of photons is the same as the one in the Reissner-Nordstr\"om black holes. This reflects that the propagation of vacuum polarized photons is not sensitive to the asymptotic behavior and topological structure of spacetimes. For the massless topological black hole and BTZ black hole, the light cone condition keeps unchanged. In the radiating topological black hole backgrounds, the light cone condition is changed even for the radially directed photons. The velocity shifts depend on the topological structures. Due to the null fluid, the velocity shift of photons does no longer vanish at the apparent horizons as well as the event horizons. But the ``polarization sum rule'' is still valid. |
1004.3191 | Nihan Katirci Ayse | Metin Ar{\i}k, Mehmet Cal{\i}k, and N. Katirci | A Cosmological Exact Solution of Complex Jordan-Brans-Dicke Theory and
its Phenomenological Implications | 4 pages, 1 figure | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | When Brans-Dicke Theory is formulated in terms of the Jordan scalar field
\phi, dark energy is related to the mass of this field. We show that if \phi is
taken to be a complex scalar field then an exact solution of the vacuum
equations shows that Friedmann equation possesses a term, proportional to the
inverse sixth power of the scale factor, as well as a constant term. Possible
interpretations and phenomenological implications of this result are discussed.
| [
{
"created": "Mon, 19 Apr 2010 13:35:43 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Aug 2010 11:52:00 GMT",
"version": "v2"
},
{
"created": "Mon, 4 Oct 2010 11:39:30 GMT",
"version": "v3"
},
{
"created": "Wed, 15 Dec 2010 11:54:16 GMT",
"version": "v4"
}
] | 2015-03-14 | [
[
"Arık",
"Metin",
""
],
[
"Calık",
"Mehmet",
""
],
[
"Katirci",
"N.",
""
]
] | When Brans-Dicke Theory is formulated in terms of the Jordan scalar field \phi, dark energy is related to the mass of this field. We show that if \phi is taken to be a complex scalar field then an exact solution of the vacuum equations shows that Friedmann equation possesses a term, proportional to the inverse sixth power of the scale factor, as well as a constant term. Possible interpretations and phenomenological implications of this result are discussed. |
2309.05599 | Matteo Luca Ruggiero | Matteo Luca Ruggiero | A note on the description of plane gravitational waves in Fermi
coordinates | 15 pages. arXiv admin note: text overlap with arXiv:2204.08914 | Eur. Phys. J. Plus (2023) 138:792 | 10.1140/epjp/s13360-023-04424-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use the formalism of Fermi coordinates to describe the interaction of a
plane gravitational wave in the proper detector frame. In doing so, we
emphasize that in this frame the action of the gravitational wave can be
explained in terms of a gravitoelectromagnetic analogy. In particular, up to
linear displacements from the reference world-line, the effects of the wave on
test masses can be described in terms of a Lorentz-like force equation. In this
framework we focus on the effects on time measurements provoked by the passage
of the wave, and evaluate their order of magnitude. Eventually, we calculate
the expression of the local spacetime metric in cylindrical coordinates adapted
to the symmetries of the gravitational field and show its relevance in
connection with the helicity-rotation coupling.
| [
{
"created": "Mon, 11 Sep 2023 16:26:20 GMT",
"version": "v1"
}
] | 2023-09-12 | [
[
"Ruggiero",
"Matteo Luca",
""
]
] | We use the formalism of Fermi coordinates to describe the interaction of a plane gravitational wave in the proper detector frame. In doing so, we emphasize that in this frame the action of the gravitational wave can be explained in terms of a gravitoelectromagnetic analogy. In particular, up to linear displacements from the reference world-line, the effects of the wave on test masses can be described in terms of a Lorentz-like force equation. In this framework we focus on the effects on time measurements provoked by the passage of the wave, and evaluate their order of magnitude. Eventually, we calculate the expression of the local spacetime metric in cylindrical coordinates adapted to the symmetries of the gravitational field and show its relevance in connection with the helicity-rotation coupling. |
0804.3824 | Hiroyuki Nakano | Carlos O. Lousto, Hiroyuki Nakano (RIT) | Regular second order perturbations of binary black holes: The extreme
mass ratio regime | 28 pages, no figure | Class.Quant.Grav.26:015007,2009 | 10.1088/0264-9381/26/1/015007 | null | gr-qc astro-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In order to derive the precise gravitational waveforms for extreme mass ratio
inspirals (EMRI), we develop a formulation for the second order metric
perturbations produced by a point particle moving in the Schwarzschild
spacetime. The second order waveforms satisfy a wave equation with an effective
source build up from products of the first order perturbations and its
derivatives. We have explicitly regularized this source at the horizon and at
spatial infinity. We show that the effective source does not contain squares of
the Dirac's delta and that perturbations are regular at the particle location.
We introduce an asymptotically flat gauge for the radiation fields and the
$\ell=0$ mode to compute explicitly the (leading) second order $\ell=2$
waveforms in the headon collision case. This case represents the first
completion of the radiation reaction program self-consistently.
| [
{
"created": "Thu, 24 Apr 2008 01:29:23 GMT",
"version": "v1"
}
] | 2008-12-25 | [
[
"Lousto",
"Carlos O.",
"",
"RIT"
],
[
"Nakano",
"Hiroyuki",
"",
"RIT"
]
] | In order to derive the precise gravitational waveforms for extreme mass ratio inspirals (EMRI), we develop a formulation for the second order metric perturbations produced by a point particle moving in the Schwarzschild spacetime. The second order waveforms satisfy a wave equation with an effective source build up from products of the first order perturbations and its derivatives. We have explicitly regularized this source at the horizon and at spatial infinity. We show that the effective source does not contain squares of the Dirac's delta and that perturbations are regular at the particle location. We introduce an asymptotically flat gauge for the radiation fields and the $\ell=0$ mode to compute explicitly the (leading) second order $\ell=2$ waveforms in the headon collision case. This case represents the first completion of the radiation reaction program self-consistently. |
gr-qc/9609020 | David Scialom | D. Scialom | Inflation with a Complex Scalar Field | latex file. Amstex package used. Contribution to the proceedings of
journees relativistes 96 | Helv.Phys.Acta 69:190-193,1996 | null | ZU-TH 25/96 | gr-qc hep-th | null | We discuss the coupled Einstein-Klein-Gordon equations for a complex scalar
field with and without a quartic self-interaction in a zero curvature
Friedman-Lema\^{\i}tre Universe. The complex scalar field, as well as the
metric, is decomposed in a homogeneous, isotropic part (the background) and in
first order gauge invariant scalar perturbation terms. The background equations
can be written as a set of four coupled first order non-linear differential
equations. These equations are analyzed using modern theory of dynamical
system. It is shown that, in all singular points where inflation occurs, the
phase of the complex scalar field is asymptotically constant. The analysis of
the first order equations is done for the inflationary phase. For the short
wavelength regime the first order perturbation term of the complex scalar field
is smeared out and the Bardeen potential oscillates around a nearly constant
mean value. Whereas for the long wavelength regime the first order perturbed
quantities increase.
| [
{
"created": "Mon, 9 Sep 1996 08:52:03 GMT",
"version": "v1"
}
] | 2011-04-15 | [
[
"Scialom",
"D.",
""
]
] | We discuss the coupled Einstein-Klein-Gordon equations for a complex scalar field with and without a quartic self-interaction in a zero curvature Friedman-Lema\^{\i}tre Universe. The complex scalar field, as well as the metric, is decomposed in a homogeneous, isotropic part (the background) and in first order gauge invariant scalar perturbation terms. The background equations can be written as a set of four coupled first order non-linear differential equations. These equations are analyzed using modern theory of dynamical system. It is shown that, in all singular points where inflation occurs, the phase of the complex scalar field is asymptotically constant. The analysis of the first order equations is done for the inflationary phase. For the short wavelength regime the first order perturbation term of the complex scalar field is smeared out and the Bardeen potential oscillates around a nearly constant mean value. Whereas for the long wavelength regime the first order perturbed quantities increase. |
gr-qc/9405027 | Guillermo Mena | Guillermo A Mena Marugan | Wormholes as Basis for the Hilbert Space in Lorentzian Gravity | 23 pages (Latex), Preprint IMAFF-RC-04-94, CGPG-94/5-2 | Phys.Rev.D50:3923-3931,1994 | 10.1103/PhysRevD.50.3923 | null | gr-qc | null | We carry out to completion the quantization of a Friedmann-Robertson-Walker
model provided with a conformal scalar field, and of a Kantowski-Sachs
spacetime minimally coupled to a massless scalar field. We prove that the
Hilbert space determined by the reality conditions that correspond to
Lorentzian gravity admits a basis of wormhole wave functions. This result
implies that the vector space spanned by the quantum wormholes can be equipped
with an unique inner product by demanding an adequate set of Lorentzian reality
conditions, and that the Hilbert space of wormholes obtained in this way can be
identified with the whole Hilbert space of physical states for Lorentzian
gravity. In particular, all the normalizable quantum states can then be
interpreted as superpositions of wormholes. For each of the models considered
here, we finally show that the physical Hilbert space is separable by
constructing a discrete orthonormal basis of wormhole solutions.
| [
{
"created": "Tue, 10 May 1994 21:33:59 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Marugan",
"Guillermo A Mena",
""
]
] | We carry out to completion the quantization of a Friedmann-Robertson-Walker model provided with a conformal scalar field, and of a Kantowski-Sachs spacetime minimally coupled to a massless scalar field. We prove that the Hilbert space determined by the reality conditions that correspond to Lorentzian gravity admits a basis of wormhole wave functions. This result implies that the vector space spanned by the quantum wormholes can be equipped with an unique inner product by demanding an adequate set of Lorentzian reality conditions, and that the Hilbert space of wormholes obtained in this way can be identified with the whole Hilbert space of physical states for Lorentzian gravity. In particular, all the normalizable quantum states can then be interpreted as superpositions of wormholes. For each of the models considered here, we finally show that the physical Hilbert space is separable by constructing a discrete orthonormal basis of wormhole solutions. |
2306.15484 | Aleksandar Mikovic | Aleksandar Mikovic | Finiteness of quantum gravity with matter on a PL spacetime | 30 pages | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We study the convergence of the path integral for General Relativity with
matter on a picewise linear (PL) spacetime that corresponds to a triangulation
of a smooth manifold by using a path-integral measure that renders the pure
gravity path integral finite. This measure depends on a parameter p, and in the
case when the matter content is just scalar fields, we show that the path
integral is absolutely convergent for p > 0,5 and not more than 2 scalar
fields. In the case of Yang-Mills fields, we show that the path integral is
absolutely convergent for the U(1) group and p > 0,5. In the case of Dirac
fermions, we show that the path integral is absolutely convergent for any
number of fermions and a sufficiently large p. When the matter content is given
by scalars, Yang-Mills fields and fermions, as in the case of the Standard
Model, we show that the path integral is absolutely convergent for p > 46,5.
Hence one can construct a finite quantum gravity theory on a PL spacetime such
that the classical limit is General Relativity coupled to the Standard Model.
| [
{
"created": "Tue, 27 Jun 2023 14:03:56 GMT",
"version": "v1"
}
] | 2023-06-28 | [
[
"Mikovic",
"Aleksandar",
""
]
] | We study the convergence of the path integral for General Relativity with matter on a picewise linear (PL) spacetime that corresponds to a triangulation of a smooth manifold by using a path-integral measure that renders the pure gravity path integral finite. This measure depends on a parameter p, and in the case when the matter content is just scalar fields, we show that the path integral is absolutely convergent for p > 0,5 and not more than 2 scalar fields. In the case of Yang-Mills fields, we show that the path integral is absolutely convergent for the U(1) group and p > 0,5. In the case of Dirac fermions, we show that the path integral is absolutely convergent for any number of fermions and a sufficiently large p. When the matter content is given by scalars, Yang-Mills fields and fermions, as in the case of the Standard Model, we show that the path integral is absolutely convergent for p > 46,5. Hence one can construct a finite quantum gravity theory on a PL spacetime such that the classical limit is General Relativity coupled to the Standard Model. |
0810.2575 | Gonzalo Garc\'ia-Reyes | Gonzalo Garc\'ia-Reyes and Guillermo A. Gonz\'alez | Charged perfect fluid disks as sources of Taub-NUT-type spacetimes | 6 pages, Revtex4 | Phys. Rev. D, 70, 104005 (2004) | 10.1103/PhysRevD.70.104005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The interpretation of a family of electrovacuum stationary Taub-NUT-type
fields in terms of finite charged perfect fluid disks is presented. The
interpretation is mades by means of an "inverse problem" approach used to
obtain disk sources of known solutions of the Einstein or Einstein-Maxwell
equations. The diagonalization of the energy-momentum tensor of the disks is
facilitated in this case by the fact that it can be written as an upper right
triangular matrix. We find that the inclusion of electromagnetic fields changes
significatively the different material properties of the disks and so we can
obtain, for some values of the parameters, finite charged perfect fluid disks
that are in agreement with all the energy conditions.
| [
{
"created": "Tue, 14 Oct 2008 22:57:14 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"García-Reyes",
"Gonzalo",
""
],
[
"González",
"Guillermo A.",
""
]
] | The interpretation of a family of electrovacuum stationary Taub-NUT-type fields in terms of finite charged perfect fluid disks is presented. The interpretation is mades by means of an "inverse problem" approach used to obtain disk sources of known solutions of the Einstein or Einstein-Maxwell equations. The diagonalization of the energy-momentum tensor of the disks is facilitated in this case by the fact that it can be written as an upper right triangular matrix. We find that the inclusion of electromagnetic fields changes significatively the different material properties of the disks and so we can obtain, for some values of the parameters, finite charged perfect fluid disks that are in agreement with all the energy conditions. |
gr-qc/0005065 | Alicia M. Sintes | A.M. Sintes, J. Carot | Perfect fluid space-times admitting a 3-dimensional conformal group
acting on null orbits | Latex 4 pages. Published in: "Some topics on General Relativity and
Gravitational Radiation". Edts. J.A. Mirales, J.A. Morales, and D. Saez;
Editions Frontiers. pp. 297-300 (1997) | null | null | null | gr-qc | null | Space-times admitting a 3-dimensional Lie group of conformal motions $C_3$
acting on null orbits are studied. Coordinate expressions for the metric and
the conformal Killing vectors (CKV) are then provided (irrespectively of the
matter content) and all possible perfect fluid solutions are found, although
none of them verifies the weak and dominant energy conditions over the whole
space-time manifold.
| [
{
"created": "Tue, 16 May 2000 14:46:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sintes",
"A. M.",
""
],
[
"Carot",
"J.",
""
]
] | Space-times admitting a 3-dimensional Lie group of conformal motions $C_3$ acting on null orbits are studied. Coordinate expressions for the metric and the conformal Killing vectors (CKV) are then provided (irrespectively of the matter content) and all possible perfect fluid solutions are found, although none of them verifies the weak and dominant energy conditions over the whole space-time manifold. |
1805.02318 | Gabriele Gionti S.J. | S.J. Gabriele Gionti | Hamiltonian Analysis of Asymptotically Safe Gravity | 15 pages, 1 figure, proceeding of the Corf\`u Summer Workshop
"Testing Fundamental Physics Principles", Corfu, Greece, September 22-28 2017 | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent results based on renormalization group approaches to Quantum Gravity
suggest that the Newton's and cosmological constants should be treated as
dynamical variables whose evolution depend on the characteristic energy scale
of the system. An open question is how to embed this modified Einstein's theory
in the Dirac constrained dynamics. In this work, the Hamiltonian formalism for
a renormalization-group scale dependent Einstein-Hilbert action is discussed
paying particular attention to Dirac's constraint analysis. It is shown that
the algebra of the Dirac's constraints, in some cases, is closed. Applications
to the physics of the Early Universe are explicitly discussed assuming the
framework of Asymptotic Safety. In particular, it is shown that in the
minisuperspace with FLRW metric, RG-improved Friedmann equations have bouncing
and emergent Universes solutions also for flat and negative curvature.
| [
{
"created": "Mon, 7 May 2018 02:19:27 GMT",
"version": "v1"
}
] | 2018-05-08 | [
[
"Gionti",
"S. J. Gabriele",
""
]
] | Recent results based on renormalization group approaches to Quantum Gravity suggest that the Newton's and cosmological constants should be treated as dynamical variables whose evolution depend on the characteristic energy scale of the system. An open question is how to embed this modified Einstein's theory in the Dirac constrained dynamics. In this work, the Hamiltonian formalism for a renormalization-group scale dependent Einstein-Hilbert action is discussed paying particular attention to Dirac's constraint analysis. It is shown that the algebra of the Dirac's constraints, in some cases, is closed. Applications to the physics of the Early Universe are explicitly discussed assuming the framework of Asymptotic Safety. In particular, it is shown that in the minisuperspace with FLRW metric, RG-improved Friedmann equations have bouncing and emergent Universes solutions also for flat and negative curvature. |
2103.12430 | Sumanta Chakraborty | Sumanta Chakraborty, Sayak Datta, and Subhadip Sau | Tidal heating of black holes and exotic compact objects on the brane | Published version, 46 pages, 7 figures | Physical Review D 104, 104001 (2021) | 10.1103/PhysRevD.104.104001 | LIGO-P2100094 | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | During the early phase of in-spiral of a binary system, the tidal heating of
a compact object due to its companion plays a significant role in the
determination of the orbital evolution of the binary. The phenomenon depends
crucially on the `hairs', as well as on the nature of the compact object. It
turns out that the presence of extra dimension affects both these properties,
by incorporating an extra tidal charge for braneworld black holes and also by
introducing quantum effects, leading to possible existence of exotic compact
objects. It turns out that the phasing information from tidal heating in the
gravitational wave waveform can constrain the tidal charge inherited from extra
dimension to a value $\sim 10^{-6}$, the most stringent constraint, to date.
Moreover, second order effects in tidal heating for exotic compact objects,
also reveals an oscillatory behaviour with respect to spin, which has unique
signatures.
| [
{
"created": "Tue, 23 Mar 2021 10:14:35 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Jul 2021 06:42:37 GMT",
"version": "v2"
},
{
"created": "Tue, 9 Nov 2021 02:09:19 GMT",
"version": "v3"
}
] | 2021-11-10 | [
[
"Chakraborty",
"Sumanta",
""
],
[
"Datta",
"Sayak",
""
],
[
"Sau",
"Subhadip",
""
]
] | During the early phase of in-spiral of a binary system, the tidal heating of a compact object due to its companion plays a significant role in the determination of the orbital evolution of the binary. The phenomenon depends crucially on the `hairs', as well as on the nature of the compact object. It turns out that the presence of extra dimension affects both these properties, by incorporating an extra tidal charge for braneworld black holes and also by introducing quantum effects, leading to possible existence of exotic compact objects. It turns out that the phasing information from tidal heating in the gravitational wave waveform can constrain the tidal charge inherited from extra dimension to a value $\sim 10^{-6}$, the most stringent constraint, to date. Moreover, second order effects in tidal heating for exotic compact objects, also reveals an oscillatory behaviour with respect to spin, which has unique signatures. |
1703.09696 | Marina Cort\^es | Marina Cort\^es and Lee Smolin | Reversing the irreversible: from limit cycles to emergent time symmetry | 22 pages, 8 figures | Phys. Rev. D 97, 026004 (2018) | 10.1103/PhysRevD.97.026004 | null | gr-qc astro-ph.CO nlin.AO physics.class-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In 1979 Penrose hypothesized that the arrows of time are explained by the
hypothesis that the fundamental laws are time irreversible. That is, our
reversible laws, such as the standard model and general relativity are
effective, and emerge from an underlying fundamental theory which is time
irreversible. In Cort\^{e}s and Smolin (2014a, 2014b, 2016) we put forward a
research program aiming at realizing just this. The aim is to find a
fundamental description of physics above the planck scale, based on
irreversible laws, from which will emerge the apparently reversible dynamics we
observe on intermediate scales. Here we continue that program and note that a
class of discrete dynamical systems are known to exhibit this very property:
they have an underlying discrete irreversible evolution, but in the long term
exhibit the properties of a time reversible system, in the form of limit
cycles. We connect this to our original model proposal in Cort\^{e}s and Smolin
(2014a), and show that the behaviours obtained there can be explained in terms
of the same phenomenon: the attraction of the system to a basin of limit
cycles, where the dynamics appears to be time reversible. Further than that, we
show that our original models exhibit the very same feature: the emergence of
quasi-particle excitations obtained in the earlier work in the space-time
description is an expression of the system's convergence to limit cycles when
seen in the causal set description.
| [
{
"created": "Mon, 27 Mar 2017 18:00:10 GMT",
"version": "v1"
}
] | 2018-01-17 | [
[
"Cortês",
"Marina",
""
],
[
"Smolin",
"Lee",
""
]
] | In 1979 Penrose hypothesized that the arrows of time are explained by the hypothesis that the fundamental laws are time irreversible. That is, our reversible laws, such as the standard model and general relativity are effective, and emerge from an underlying fundamental theory which is time irreversible. In Cort\^{e}s and Smolin (2014a, 2014b, 2016) we put forward a research program aiming at realizing just this. The aim is to find a fundamental description of physics above the planck scale, based on irreversible laws, from which will emerge the apparently reversible dynamics we observe on intermediate scales. Here we continue that program and note that a class of discrete dynamical systems are known to exhibit this very property: they have an underlying discrete irreversible evolution, but in the long term exhibit the properties of a time reversible system, in the form of limit cycles. We connect this to our original model proposal in Cort\^{e}s and Smolin (2014a), and show that the behaviours obtained there can be explained in terms of the same phenomenon: the attraction of the system to a basin of limit cycles, where the dynamics appears to be time reversible. Further than that, we show that our original models exhibit the very same feature: the emergence of quasi-particle excitations obtained in the earlier work in the space-time description is an expression of the system's convergence to limit cycles when seen in the causal set description. |
0805.3096 | Henning Rehbein | Henning Rehbein, Helge Mueller-Ebhardt, Kentaro Somiya, Stefan L.
Danilishin, Roman Schnabel, Karsten Danzmann and Yanbei Chen | Double optical spring enhancement for gravitational wave detectors | null | Phys.Rev.D78:062003,2008 | 10.1103/PhysRevD.78.062003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Currently planned second-generation gravitational-wave laser interferometers
such as Advanced LIGO exploit the extensively investigated signal-recycling
(SR) technique. Candidate Advanced LIGO configurations are usually designed to
have two resonances within the detection band, around which the sensitivity is
enhanced: a stable optical resonance and an unstable optomechanical resonance -
which is upshifted from the pendulum frequency due to the so-called
optical-spring effect. Alternative to a feedback control system, we propose an
all-optical stabilization scheme, in which a second optical spring is employed,
and the test mass is trapped by a stable ponderomotive potential well induced
by two carrier light fields whose detunings have opposite signs. The double
optical spring also brings additional flexibility in re-shaping the noise
spectral density and optimizing toward specific gravitational-wave sources. The
presented scheme can be extended easily to a multi-optical-spring system that
allows further optimization.
| [
{
"created": "Tue, 20 May 2008 15:03:26 GMT",
"version": "v1"
}
] | 2009-02-23 | [
[
"Rehbein",
"Henning",
""
],
[
"Mueller-Ebhardt",
"Helge",
""
],
[
"Somiya",
"Kentaro",
""
],
[
"Danilishin",
"Stefan L.",
""
],
[
"Schnabel",
"Roman",
""
],
[
"Danzmann",
"Karsten",
""
],
[
"Chen",
"Yanbei",
... | Currently planned second-generation gravitational-wave laser interferometers such as Advanced LIGO exploit the extensively investigated signal-recycling (SR) technique. Candidate Advanced LIGO configurations are usually designed to have two resonances within the detection band, around which the sensitivity is enhanced: a stable optical resonance and an unstable optomechanical resonance - which is upshifted from the pendulum frequency due to the so-called optical-spring effect. Alternative to a feedback control system, we propose an all-optical stabilization scheme, in which a second optical spring is employed, and the test mass is trapped by a stable ponderomotive potential well induced by two carrier light fields whose detunings have opposite signs. The double optical spring also brings additional flexibility in re-shaping the noise spectral density and optimizing toward specific gravitational-wave sources. The presented scheme can be extended easily to a multi-optical-spring system that allows further optimization. |
2307.13039 | M Herrero-Valea | M. Herrero-Valea | The Status of Horava Gravity | Invited review for the EPJP special issue on Higher Derivatives in
Quantum Gravity. 49 pages, 2 figures. Comments are welcome | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Horava gravity is a proposal for a UV completion of gravitation obtained by
endowing the space-time manifold with a preferred foliation in space-like
hypersurfaces. This allows for a power-counting renormalizable theory free of
ghosts, at the cost of breaking local Lorentz invariance and diffeomorphism
invariance down to foliation preserving transformations. In this updated
review, we report the main successes and challenges of the proposal, discussing
the main features of the projectable and non-projectable versions of Ho\v rava
gravity. We focus in three main aspects: (i) the UV regime, discussing the
renormalizability and renormalization group flow of the projectable theory, as
well as the obstacles towards similar results in the non-projectable case; (ii)
the low energy phenomenology of both models, including the PN regime, the most
updated constraints in the parameter space of the theory, the structure of
black holes at low energies, and the possibility of dark matter emerging from
gravitational dynamics in the projectable model; and (iii) the specific
phenomena induced by higher derivatives, such as the possibility of
regularizing singularities, the dynamical behavior of solutions to dispersive
equations, and the emission of Hawking radiation by universal horizons.
| [
{
"created": "Mon, 24 Jul 2023 18:00:05 GMT",
"version": "v1"
}
] | 2023-07-26 | [
[
"Herrero-Valea",
"M.",
""
]
] | Horava gravity is a proposal for a UV completion of gravitation obtained by endowing the space-time manifold with a preferred foliation in space-like hypersurfaces. This allows for a power-counting renormalizable theory free of ghosts, at the cost of breaking local Lorentz invariance and diffeomorphism invariance down to foliation preserving transformations. In this updated review, we report the main successes and challenges of the proposal, discussing the main features of the projectable and non-projectable versions of Ho\v rava gravity. We focus in three main aspects: (i) the UV regime, discussing the renormalizability and renormalization group flow of the projectable theory, as well as the obstacles towards similar results in the non-projectable case; (ii) the low energy phenomenology of both models, including the PN regime, the most updated constraints in the parameter space of the theory, the structure of black holes at low energies, and the possibility of dark matter emerging from gravitational dynamics in the projectable model; and (iii) the specific phenomena induced by higher derivatives, such as the possibility of regularizing singularities, the dynamical behavior of solutions to dispersive equations, and the emission of Hawking radiation by universal horizons. |
gr-qc/9902029 | Takeshi Shimomura | T. Shimomura, T. Okamura, T. Mishima and H. Ishihara | Does the generalized second law hold in the form of time derivative
expression? | 12 pages, 3 figures, revtex | Phys.Rev. D62 (2000) 044036; Addendum-ibid. D65 (2002) 107502 | 10.1103/PhysRevD.62.044036 | null | gr-qc | null | We investigate whether the generalized second law is valid, using two
dimensional black hole spacetime, irrespective of models. A time derivative
form of the generalized second law is formulated and it is shown that the law
might become invalid. The way to resolve this difficulty is also presented and
discussed.
| [
{
"created": "Thu, 11 Feb 1999 07:53:16 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Shimomura",
"T.",
""
],
[
"Okamura",
"T.",
""
],
[
"Mishima",
"T.",
""
],
[
"Ishihara",
"H.",
""
]
] | We investigate whether the generalized second law is valid, using two dimensional black hole spacetime, irrespective of models. A time derivative form of the generalized second law is formulated and it is shown that the law might become invalid. The way to resolve this difficulty is also presented and discussed. |
1111.5729 | Francisco Lobo | Remo Garattini, Francisco S.N. Lobo | Self-sustained wormholes in modified dispersion relations | 11 pages | Phys.Rev.D85:024043,2012 | 10.1103/PhysRevD.85.024043 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we consider the possibility that wormhole geometries are
sustained by their own quantum fluctuations, in the context of modified
dispersion relations. More specifically, the energy density of the graviton
one-loop contribution to a classical energy in a wormhole background is
considered as a self-consistent source for wormholes. In this semi-classical
context, we consider specific choices for the Rainbow's functions and find
solutions for wormhole geometries in the cis-planckian and trans-planckian
regimes. In the former regime, the wormhole spacetimes are not asymptotically
flat and need to be matched to an exterior vacuum solution. In the latter
trans-planckian regime, we find that the quantum corrections are exponentially
suppressed, which provide asymptotically flat wormhole geometries with a
constant shape function, i.e., b(r)=r_t, where r_t is the wormhole throat. In
addition to this analysis, we also fix the geometry by considering the
behaviour of a specific shape function through a variational approach which
imposes a local analysis to the problem at the wormhole throat. We further
explore the respective parameter range of the Rainbow's functions, and find a
good agreement with previous work.
| [
{
"created": "Thu, 24 Nov 2011 11:32:45 GMT",
"version": "v1"
}
] | 2012-01-27 | [
[
"Garattini",
"Remo",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] | In this work, we consider the possibility that wormhole geometries are sustained by their own quantum fluctuations, in the context of modified dispersion relations. More specifically, the energy density of the graviton one-loop contribution to a classical energy in a wormhole background is considered as a self-consistent source for wormholes. In this semi-classical context, we consider specific choices for the Rainbow's functions and find solutions for wormhole geometries in the cis-planckian and trans-planckian regimes. In the former regime, the wormhole spacetimes are not asymptotically flat and need to be matched to an exterior vacuum solution. In the latter trans-planckian regime, we find that the quantum corrections are exponentially suppressed, which provide asymptotically flat wormhole geometries with a constant shape function, i.e., b(r)=r_t, where r_t is the wormhole throat. In addition to this analysis, we also fix the geometry by considering the behaviour of a specific shape function through a variational approach which imposes a local analysis to the problem at the wormhole throat. We further explore the respective parameter range of the Rainbow's functions, and find a good agreement with previous work. |
gr-qc/0109036 | Alan Barnes | Alan Barnes | Some Restrictions on Symmetry Groups of Axially Symmetric Spacetimes | Plain TeX, 11 pages. No figures | Class.Quant.Grav. 18 (2001) 5511-5520 | 10.1088/0264-9381/18/24/313 | null | gr-qc | null | Lie transformation groups containing a one-dimensional subgroup acting
cyclically on a manifold are considered. The structure of the group is found to
be considerably restricted by the existence of a one-dimensional subgroup whose
orbits are circles. The results proved do not depend on the dimension of the
manifold nor on the existence of a metric, but merely on the fact that the Lie
group acts globally on the manifold. Firstly some results for the general case
of an $m+1$-dimensional Lie group are derived: those commutators of the
associated Lie algebra involving the generator of the cyclic subgroup, $X_0$
say, are severely restricted and, in a suitably chosen basis, take a simple
form. The Jacobi identities involving $X_0$ are then applied to show there are
further restrictions on the structure of the Lie algebra. All Lie algebras of
dimensions 2 and 3 compatible with cyclic symmetry are obtained. In the
two-dimensional case the group must be Abelian. For the three-dimensional case,
the Bianchi type of the Lie algebra must be I, II, III, VII$_0$, VIII or IX and
furthermore in all cases the vector $X_0$ forms part of a basis in which the
algebra takes its canonical form. Finally four-dimensional Lie algebras
compatible with cyclic symmetry are considered and the results are related to
the Petrov-Kruchkovich classification of all four-dimensional Lie algebras.
| [
{
"created": "Tue, 11 Sep 2001 13:43:22 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Barnes",
"Alan",
""
]
] | Lie transformation groups containing a one-dimensional subgroup acting cyclically on a manifold are considered. The structure of the group is found to be considerably restricted by the existence of a one-dimensional subgroup whose orbits are circles. The results proved do not depend on the dimension of the manifold nor on the existence of a metric, but merely on the fact that the Lie group acts globally on the manifold. Firstly some results for the general case of an $m+1$-dimensional Lie group are derived: those commutators of the associated Lie algebra involving the generator of the cyclic subgroup, $X_0$ say, are severely restricted and, in a suitably chosen basis, take a simple form. The Jacobi identities involving $X_0$ are then applied to show there are further restrictions on the structure of the Lie algebra. All Lie algebras of dimensions 2 and 3 compatible with cyclic symmetry are obtained. In the two-dimensional case the group must be Abelian. For the three-dimensional case, the Bianchi type of the Lie algebra must be I, II, III, VII$_0$, VIII or IX and furthermore in all cases the vector $X_0$ forms part of a basis in which the algebra takes its canonical form. Finally four-dimensional Lie algebras compatible with cyclic symmetry are considered and the results are related to the Petrov-Kruchkovich classification of all four-dimensional Lie algebras. |
1106.5056 | Clifford M. Will | Laleh Sadeghian and Clifford M. Will | Testing the black hole no-hair theorem at the galactic center:
Perturbing effects of stars in the surrounding cluster | 17 pages, 2 figures, submitted to Classical and Quantum Gravity | Class. Quantum Grav. 28, 225029 (2011) | 10.1088/0264-9381/28/22/225029 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Observations of the precessing orbits of stars very near the massive black
hole in the galactic center could provide measurements of the spin and
quadrupole moment of the hole and thereby test the no-hair theorem of general
relativity. Since the galactic center is likely to be populated by a
distribution of stars and small black holes, their gravitational interactions
will perturb the orbit of any given star. We estimate the effects of such
perturbations using analytic orbital perturbation theory, and show that for a
range of possible stellar distributions, and for an observed star sufficiently
close to the black hole, the relativistic spin and quadrupole effects will be
larger than the effects of stellar cluster perturbations. Our results are
consistent those from recent numerical N-body simulations by Merritt et al.
| [
{
"created": "Fri, 24 Jun 2011 20:16:18 GMT",
"version": "v1"
}
] | 2011-11-04 | [
[
"Sadeghian",
"Laleh",
""
],
[
"Will",
"Clifford M.",
""
]
] | Observations of the precessing orbits of stars very near the massive black hole in the galactic center could provide measurements of the spin and quadrupole moment of the hole and thereby test the no-hair theorem of general relativity. Since the galactic center is likely to be populated by a distribution of stars and small black holes, their gravitational interactions will perturb the orbit of any given star. We estimate the effects of such perturbations using analytic orbital perturbation theory, and show that for a range of possible stellar distributions, and for an observed star sufficiently close to the black hole, the relativistic spin and quadrupole effects will be larger than the effects of stellar cluster perturbations. Our results are consistent those from recent numerical N-body simulations by Merritt et al. |
2306.16318 | Chandrachur Chakraborty | Chandrachur Chakraborty (MCNS-MAHE), Banibrata Mukhopadhyay (IISc) | Geometric phase in Taub-NUT spacetime | 12 pages; Version published in EPJC | Eur. Phys. J. C 83, 937 (2023) | 10.1140/epjc/s10052-023-12070-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Constructing the Hamiltonian in the $\eta$-representation, we explore the
geometric phase in the Taub-NUT spacetime, which is spherically symmetric and
stationary. The geometric phase around a non-rotating Taub-NUT spacetime
reveals both the gravitational analog of Aharonov-Bohm effect and
Pancharatnam-Berry phase, similar to the rotating Kerr background. On the other
hand, only the latter emerges in the spherically symmetric Schwarzschild
geometry as well as in the axisymmetric magnetized Schwarzschild geometry. With
this result, we argue that the Aharonov-Bohm effect and Pancharatnam-Berry
phase both can emerge in the stationary spacetime, whereas only the latter
emerges in the static spacetime. We outline plausible measurements of these
effects/phases, mostly for primordial black holes.
| [
{
"created": "Wed, 28 Jun 2023 15:50:51 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Oct 2023 04:48:35 GMT",
"version": "v2"
}
] | 2023-10-19 | [
[
"Chakraborty",
"Chandrachur",
"",
"MCNS-MAHE"
],
[
"Mukhopadhyay",
"Banibrata",
"",
"IISc"
]
] | Constructing the Hamiltonian in the $\eta$-representation, we explore the geometric phase in the Taub-NUT spacetime, which is spherically symmetric and stationary. The geometric phase around a non-rotating Taub-NUT spacetime reveals both the gravitational analog of Aharonov-Bohm effect and Pancharatnam-Berry phase, similar to the rotating Kerr background. On the other hand, only the latter emerges in the spherically symmetric Schwarzschild geometry as well as in the axisymmetric magnetized Schwarzschild geometry. With this result, we argue that the Aharonov-Bohm effect and Pancharatnam-Berry phase both can emerge in the stationary spacetime, whereas only the latter emerges in the static spacetime. We outline plausible measurements of these effects/phases, mostly for primordial black holes. |
2407.08588 | Swapan K Majhi | Swapan Kumar Majhi | Thermodynamics of rotating black hole in the presence of cold dark
matter | 12 pages, 16 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We have computed the thermodynamic properties of a rotating black holes in
the presence of cold dark matter. The dependence of temperaure, Gibbs free
energy, specific heat on the horizon radius have been studied for various
values of critical density (\r{ho}c ) of the cold dark matter. The studies
shows that only small values of critical density of cold the dark matter, black
hole are stable.
| [
{
"created": "Thu, 11 Jul 2024 15:11:47 GMT",
"version": "v1"
}
] | 2024-07-12 | [
[
"Majhi",
"Swapan Kumar",
""
]
] | We have computed the thermodynamic properties of a rotating black holes in the presence of cold dark matter. The dependence of temperaure, Gibbs free energy, specific heat on the horizon radius have been studied for various values of critical density (\r{ho}c ) of the cold dark matter. The studies shows that only small values of critical density of cold the dark matter, black hole are stable. |
1503.04764 | David Garrison | David Garrison and Christopher Ramirez | Extracting Gravitational Waves Induced by Plasma Turbulence in the Early
Universe through an Averaging Process | 16 pages, 2 figures and 1 table | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work is a follow-up to the paper, "Numerical Relativity as a Tool for
Studying the Early Universe". In this article, we determine if cosmological
gravitational waves can be accurately extracted from a dynamical spacetime
using an averaging process as opposed to conventional methods of gravitational
wave extraction using a complex Weyl scalar. We calculate the normalized energy
density, strain and degree of polarization of gravitational waves produced by a
simulated turbulent plasma similar to what was believed to have existed shortly
after the electroweak scale. This calculation is completed using two numerical
codes, one which utilizes full General Relativity calculations based on
modified BSSN equations while the other utilizes a linearized approximation of
General Relativity. Our results show that the spectrum of gravitational waves
calculated from the nonlinear code using an averaging process are nearly
indistinguishable from those calculated from the linear code. This result
validates the use of the averaging process for gravitational wave extraction of
cosmological systems.
| [
{
"created": "Mon, 16 Mar 2015 18:49:29 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Jun 2015 14:20:32 GMT",
"version": "v2"
},
{
"created": "Wed, 17 Jun 2015 01:04:02 GMT",
"version": "v3"
},
{
"created": "Mon, 15 Feb 2016 16:03:36 GMT",
"version": "v4"
},
{
"c... | 2017-04-24 | [
[
"Garrison",
"David",
""
],
[
"Ramirez",
"Christopher",
""
]
] | This work is a follow-up to the paper, "Numerical Relativity as a Tool for Studying the Early Universe". In this article, we determine if cosmological gravitational waves can be accurately extracted from a dynamical spacetime using an averaging process as opposed to conventional methods of gravitational wave extraction using a complex Weyl scalar. We calculate the normalized energy density, strain and degree of polarization of gravitational waves produced by a simulated turbulent plasma similar to what was believed to have existed shortly after the electroweak scale. This calculation is completed using two numerical codes, one which utilizes full General Relativity calculations based on modified BSSN equations while the other utilizes a linearized approximation of General Relativity. Our results show that the spectrum of gravitational waves calculated from the nonlinear code using an averaging process are nearly indistinguishable from those calculated from the linear code. This result validates the use of the averaging process for gravitational wave extraction of cosmological systems. |
0910.5376 | Kazumi Kashiyama | Kazumi Kashiyama, Norihiro Tanahashi, Antonino Flachi and Takahiro
Tanaka | Quantum Back Reaction to asymptotically AdS Black Holes | 13 pages, 10 figures | JHEP 1001:099,2010 | 10.1007/JHEP01(2010)099 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the effects of the back reaction due to a conformal field theory
(CFT) on a black hole spacetime with negative cosmological constant. We study
the geometry numerically obtained by taking into account the energy momentum
tensor of CFT approximated by a radiation fluid. We find a sequence of
configurations without a horizon in thermal equilibrium (CFT stars), followed
by a sequence of configurations with a horizon. We discuss the thermodynamic
properties of the system and how back reaction effects alter the space-time
structure. We also provide an interpretation of the above sequence of solutions
in terms of the AdS/CFT correspondence. The dual five-dimensional description
is given by the Karch-Randall model, in which a sequence of five-dimensional
floating black holes followed by a sequence of brane localized black holes
correspond to the above solutions.
| [
{
"created": "Wed, 28 Oct 2009 14:35:31 GMT",
"version": "v1"
}
] | 2013-10-15 | [
[
"Kashiyama",
"Kazumi",
""
],
[
"Tanahashi",
"Norihiro",
""
],
[
"Flachi",
"Antonino",
""
],
[
"Tanaka",
"Takahiro",
""
]
] | We analyze the effects of the back reaction due to a conformal field theory (CFT) on a black hole spacetime with negative cosmological constant. We study the geometry numerically obtained by taking into account the energy momentum tensor of CFT approximated by a radiation fluid. We find a sequence of configurations without a horizon in thermal equilibrium (CFT stars), followed by a sequence of configurations with a horizon. We discuss the thermodynamic properties of the system and how back reaction effects alter the space-time structure. We also provide an interpretation of the above sequence of solutions in terms of the AdS/CFT correspondence. The dual five-dimensional description is given by the Karch-Randall model, in which a sequence of five-dimensional floating black holes followed by a sequence of brane localized black holes correspond to the above solutions. |
1805.11289 | Hassan Firouzjahi | Hassan Firouzjahi | The spectrum of perturbations inside the Schwarzschild black hole | 15 pages, 3 figures | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the spectrum of the bound state perturbations in the interior of the
Schwarzschild black hole for the scalar, electromagnetic and gravitational
perturbations. Demanding that the perturbations to be regular at the center of
the black hole determines the spectrum of the bound state solutions. We show
that our analytic expression for the spectrum is in very good agreement with
the imaginary parts of the high overtone quasi normal mode excitations obtained
for the exterior region. We also present a simple scheme to calculate the
spectrum numerically to good accuracies.
| [
{
"created": "Tue, 29 May 2018 08:04:15 GMT",
"version": "v1"
}
] | 2018-05-31 | [
[
"Firouzjahi",
"Hassan",
""
]
] | We study the spectrum of the bound state perturbations in the interior of the Schwarzschild black hole for the scalar, electromagnetic and gravitational perturbations. Demanding that the perturbations to be regular at the center of the black hole determines the spectrum of the bound state solutions. We show that our analytic expression for the spectrum is in very good agreement with the imaginary parts of the high overtone quasi normal mode excitations obtained for the exterior region. We also present a simple scheme to calculate the spectrum numerically to good accuracies. |
2305.18621 | Xiao Zhang | Yekun Yang, Xiao Zhang | Geodesics on metrics of Eguchi-Hanson type | 19 pages | null | 10.1140/epjc/s10052-023-11762-x | null | gr-qc math.DG | http://creativecommons.org/publicdomain/zero/1.0/ | Geodesic equations are solved when at least two of $\theta$, $\phi$ and
$\psi$ are constant, or $r$ is constant, on scalar flat metrics of
Eguchi-Hanson type. They can also be solved also on Eguchi-Hanson metrics which
are Ricci flat if only $\phi$ is constant. However, the explicit solution of
the geodesic equations is not available yet if only $\psi$ is constant.
| [
{
"created": "Fri, 26 May 2023 04:50:49 GMT",
"version": "v1"
}
] | 2023-07-26 | [
[
"Yang",
"Yekun",
""
],
[
"Zhang",
"Xiao",
""
]
] | Geodesic equations are solved when at least two of $\theta$, $\phi$ and $\psi$ are constant, or $r$ is constant, on scalar flat metrics of Eguchi-Hanson type. They can also be solved also on Eguchi-Hanson metrics which are Ricci flat if only $\phi$ is constant. However, the explicit solution of the geodesic equations is not available yet if only $\psi$ is constant. |
1206.2069 | Chen Songbai | Songbai Chen, Qiyuan Pan, Jiliang Jing | Holographic superconductors in quintessence AdS black hole | 19Page, 5 figures, Accepted by CQG | Class. Quantum Grav. 30 (2013) 145001 | 10.1088/0264-9381/30/14/145001 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a solution of Einstein equations describing a $d$-dimensional
planar quintessence AdS black hole which depends on the state parameter $w_q$
of quintessence. We investigate holographic superconductors in this background
and probe effects of the state parameter $w_q$ on the critical temperature
$T_c$, the condensation formation and conductivity. The larger absolute value
of $w_q$ leads to the lower critical temperature $T_c$ and the higher ratio
between the gap frequency in conductivity to the critical temperature for the
condensates. Moreover, we also find that the scalar condensate there exists an
additional constraint condition originating from the quintessence
$(d-1)w_q+\lambda_{\pm}>0$ for the operators $\mathcal{O}_{\pm}$, respectively.
Our results show that the scalar condensation is harder to form and the
occurrence of holographic dual superconductor needs the stronger coupling in
the quintessence AdS black hole spacetime.
| [
{
"created": "Sun, 10 Jun 2012 23:37:44 GMT",
"version": "v1"
},
{
"created": "Fri, 31 May 2013 02:46:54 GMT",
"version": "v2"
}
] | 2015-06-05 | [
[
"Chen",
"Songbai",
""
],
[
"Pan",
"Qiyuan",
""
],
[
"Jing",
"Jiliang",
""
]
] | We present a solution of Einstein equations describing a $d$-dimensional planar quintessence AdS black hole which depends on the state parameter $w_q$ of quintessence. We investigate holographic superconductors in this background and probe effects of the state parameter $w_q$ on the critical temperature $T_c$, the condensation formation and conductivity. The larger absolute value of $w_q$ leads to the lower critical temperature $T_c$ and the higher ratio between the gap frequency in conductivity to the critical temperature for the condensates. Moreover, we also find that the scalar condensate there exists an additional constraint condition originating from the quintessence $(d-1)w_q+\lambda_{\pm}>0$ for the operators $\mathcal{O}_{\pm}$, respectively. Our results show that the scalar condensation is harder to form and the occurrence of holographic dual superconductor needs the stronger coupling in the quintessence AdS black hole spacetime. |
1708.09505 | Gaurav Khanna | Caroline Mallary, Gaurav Khanna, Richard Price | Closed Timelike Curves and "Effective" Superluminal Travel with Naked
Line Singularities | 10 pages, 5 figures; animation available on YouTube at:
https://youtu.be/ub6PGaygVwA | null | 10.1088/1361-6382/aad306 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine closed timelike curves (CTCs) and "effective" superluminal travel
in a spacetime containing naked line singularities, which we call "wires". Each
wire may be straight-line singularity or a ring singularity. The Weak Energy
Condition (WEC) is preserved in all well-defined regions of the spacetime. (The
singularities themselves are not well-defined, so the WEC is undefined there,
but it is never explicitly violated.) Parallel to the wire, "effective"
superluminal travel is possible, in that the wire may be used as a shortcut
between distant regions of spacetime. Our purpose in presenting the
superluminal aspects of the wire is to dispel the commonly held view that
explicit WEC violation is necessary for effective superluminal travel, whereas
in truth the strictures against superluminal travel are more complicated. We
also demonstrate how the existence of such "wires" could create CTCs. We
present a model spacetime which contains two wires which are free to move
relative to each other. This spacetime is asymptotically flat: It becomes a
Minkowski spacetime a finite distance away from each of the wires. The CTCs
under investigation do not need to enter the wires' singularities, and can be
confined to regions that are weak-field: This means that if these wires were
physically possible, they would present causality problems even in nonsingular,
energetically realistic regions of the spacetime. We conclude that the Weak
Energy Condition alone is not sufficient to prevent superluminal travel in
asymptotically flat spacetimes.
| [
{
"created": "Wed, 30 Aug 2017 23:51:17 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Jul 2018 13:00:40 GMT",
"version": "v2"
}
] | 2018-08-29 | [
[
"Mallary",
"Caroline",
""
],
[
"Khanna",
"Gaurav",
""
],
[
"Price",
"Richard",
""
]
] | We examine closed timelike curves (CTCs) and "effective" superluminal travel in a spacetime containing naked line singularities, which we call "wires". Each wire may be straight-line singularity or a ring singularity. The Weak Energy Condition (WEC) is preserved in all well-defined regions of the spacetime. (The singularities themselves are not well-defined, so the WEC is undefined there, but it is never explicitly violated.) Parallel to the wire, "effective" superluminal travel is possible, in that the wire may be used as a shortcut between distant regions of spacetime. Our purpose in presenting the superluminal aspects of the wire is to dispel the commonly held view that explicit WEC violation is necessary for effective superluminal travel, whereas in truth the strictures against superluminal travel are more complicated. We also demonstrate how the existence of such "wires" could create CTCs. We present a model spacetime which contains two wires which are free to move relative to each other. This spacetime is asymptotically flat: It becomes a Minkowski spacetime a finite distance away from each of the wires. The CTCs under investigation do not need to enter the wires' singularities, and can be confined to regions that are weak-field: This means that if these wires were physically possible, they would present causality problems even in nonsingular, energetically realistic regions of the spacetime. We conclude that the Weak Energy Condition alone is not sufficient to prevent superluminal travel in asymptotically flat spacetimes. |
2203.14516 | Francesco Di Filippo | Francesco Di Filippo, Ra\'ul Carballo-Rubio, Stefano Liberati,
Costantino Pacilio, Matt Visser | On the inner horizon instability of non-singular black holes | Invited talk at the conference "The Quantum & The Gravity 2021" | null | null | YITP-22-22 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Regular black holes represent a conservative model in which the classical
singularity is replaced by a non-singular core without necessarily modifying
the spacetime outside the trapping horizon. Given the possible lack of
phenomenological signatures, it is crucial to study the consistency of the
model. In this short work, we review the physical mechanism leading to the
instability of the central core, arguing that non-perturbative backreaction is
non-negligible and must be taken into account to provide a meaningful
description of physical black holes.
| [
{
"created": "Mon, 28 Mar 2022 06:00:13 GMT",
"version": "v1"
}
] | 2022-03-29 | [
[
"Di Filippo",
"Francesco",
""
],
[
"Carballo-Rubio",
"Raúl",
""
],
[
"Liberati",
"Stefano",
""
],
[
"Pacilio",
"Costantino",
""
],
[
"Visser",
"Matt",
""
]
] | Regular black holes represent a conservative model in which the classical singularity is replaced by a non-singular core without necessarily modifying the spacetime outside the trapping horizon. Given the possible lack of phenomenological signatures, it is crucial to study the consistency of the model. In this short work, we review the physical mechanism leading to the instability of the central core, arguing that non-perturbative backreaction is non-negligible and must be taken into account to provide a meaningful description of physical black holes. |
0805.4585 | Carlo Rovelli | Carlo Rovelli, Francesca Vidotto | Stepping out of Homogeneity in Loop Quantum Cosmology | 16 pages | Class.Quant.Grav.25:225024,2008 | 10.1088/0264-9381/25/22/225024 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explore the extension of quantum cosmology outside the homogeneous
approximation, using the formalism of loop quantum gravity. We introduce a
model where some of the inhomogeneous degrees of freedom are present, providing
a tool for describing general fluctuations of quantum geometry near the initial
singularity. We show that the dynamical structure of the model reduces to that
of loop quantum cosmology in the Born-Oppenheimer approximation. This result
corroborates the assumptions that ground loop cosmology, sheds light on the
physical and mathematical relation between loop cosmology and full loop quantum
gravity, and on the nature of the cosmological approximation. Finally, we show
that the non-graph-changing Hamiltonian constraint considered in the context of
algebraic quantum gravity provides a viable effective dynamics within this
approximation.
| [
{
"created": "Thu, 29 May 2008 17:08:59 GMT",
"version": "v1"
}
] | 2008-12-18 | [
[
"Rovelli",
"Carlo",
""
],
[
"Vidotto",
"Francesca",
""
]
] | We explore the extension of quantum cosmology outside the homogeneous approximation, using the formalism of loop quantum gravity. We introduce a model where some of the inhomogeneous degrees of freedom are present, providing a tool for describing general fluctuations of quantum geometry near the initial singularity. We show that the dynamical structure of the model reduces to that of loop quantum cosmology in the Born-Oppenheimer approximation. This result corroborates the assumptions that ground loop cosmology, sheds light on the physical and mathematical relation between loop cosmology and full loop quantum gravity, and on the nature of the cosmological approximation. Finally, we show that the non-graph-changing Hamiltonian constraint considered in the context of algebraic quantum gravity provides a viable effective dynamics within this approximation. |
1912.12922 | Sebasti\'an Bahamonde Dr | Sebastian Bahamonde, Konstantinos Dialektopoulos, Ugur Camci | Exact spherically symmetric solutions in modified Gauss-Bonnet gravity
from Noether symmetry approach | 17 pages. Accepted for Publication in Symmetries in the special issue
"Noether's symmetry approach in gravity and cosmology" | Symmetry 2020, 12(1), 68 | 10.3390/sym12010068 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is broadly known that Lie point symmetries and their subcase, Noether
symmetries, can be used as a geometric criterion to select alternative theories
of gravity. Here, we use Noether symmetries as a selection criterion to
distinguish those models of $f(R,G)$ theory, with $R$ and $G$ being the Ricci
and the Gauss-Bonnet scalars respectively, that are invariant under point
transformations in a spherically symmetric background. In total, we find ten
different forms of $f$ that present symmetries and calculate their invariant
quantities, i.e Noether vector fields. Furthermore, we use these Noether
symmetries to find exact spherically symmetric solutions in some of the models
of $f(R,G)$ theory.
| [
{
"created": "Mon, 30 Dec 2019 13:37:23 GMT",
"version": "v1"
}
] | 2020-01-10 | [
[
"Bahamonde",
"Sebastian",
""
],
[
"Dialektopoulos",
"Konstantinos",
""
],
[
"Camci",
"Ugur",
""
]
] | It is broadly known that Lie point symmetries and their subcase, Noether symmetries, can be used as a geometric criterion to select alternative theories of gravity. Here, we use Noether symmetries as a selection criterion to distinguish those models of $f(R,G)$ theory, with $R$ and $G$ being the Ricci and the Gauss-Bonnet scalars respectively, that are invariant under point transformations in a spherically symmetric background. In total, we find ten different forms of $f$ that present symmetries and calculate their invariant quantities, i.e Noether vector fields. Furthermore, we use these Noether symmetries to find exact spherically symmetric solutions in some of the models of $f(R,G)$ theory. |
2211.14300 | Sergio Sevillano Mu\~noz | Sergio Sevillano Mu\~noz, Edmund J. Copeland, Peter Millington and
Michael Spannowsky | FeynMG: a FeynRules extension for scalar-tensor theories of gravity | 39 pages, 1 figure, GitLab link: https://gitlab.com/feynmg/FeynMG | Comput. Phys. Commun. 296 (2024), 109035 | 10.1016/j.cpc.2023.109035 | null | gr-qc astro-ph.CO hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | The ability to represent perturbative expansions of interacting quantum field
theories in terms of simple diagrammatic rules has revolutionized calculations
in particle physics (and elsewhere). Moreover, these rules are readily
automated, a process that has catalysed the rise of symbolic algebra packages.
However, in the case of extended theories of gravity, such as scalar-tensor
theories, it is necessary to precondition the Lagrangian to apply this
automation or, at the very least, to take advantage of existing software
pipelines. We present a Mathematica code FeynMG, which works in conjunction
with the well-known package FeynRules, to do just that: FeynMG takes as inputs
the FeynRules model file for a non-gravitational theory and a user-supplied
gravitational Lagrangian. FeynMG provides functionality that inserts the
minimal gravitational couplings of the degrees of freedom specified in the
model file, determines the couplings of the additional tensor and scalar
degrees of freedom (the metric and the scalar field from the gravitational
sector), and preconditions the resulting Lagrangian so that it can be passed to
FeynRules, either directly or by outputting an updated FeynRules model file.
The Feynman rules can then be determined and output through FeynRules, using
existing universal output formats and interfaces to other analysis packages.
| [
{
"created": "Fri, 25 Nov 2022 18:58:15 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Dec 2023 11:03:19 GMT",
"version": "v2"
}
] | 2024-07-30 | [
[
"Muñoz",
"Sergio Sevillano",
""
],
[
"Copeland",
"Edmund J.",
""
],
[
"Millington",
"Peter",
""
],
[
"Spannowsky",
"Michael",
""
]
] | The ability to represent perturbative expansions of interacting quantum field theories in terms of simple diagrammatic rules has revolutionized calculations in particle physics (and elsewhere). Moreover, these rules are readily automated, a process that has catalysed the rise of symbolic algebra packages. However, in the case of extended theories of gravity, such as scalar-tensor theories, it is necessary to precondition the Lagrangian to apply this automation or, at the very least, to take advantage of existing software pipelines. We present a Mathematica code FeynMG, which works in conjunction with the well-known package FeynRules, to do just that: FeynMG takes as inputs the FeynRules model file for a non-gravitational theory and a user-supplied gravitational Lagrangian. FeynMG provides functionality that inserts the minimal gravitational couplings of the degrees of freedom specified in the model file, determines the couplings of the additional tensor and scalar degrees of freedom (the metric and the scalar field from the gravitational sector), and preconditions the resulting Lagrangian so that it can be passed to FeynRules, either directly or by outputting an updated FeynRules model file. The Feynman rules can then be determined and output through FeynRules, using existing universal output formats and interfaces to other analysis packages. |
2206.09227 | Kirill Bronnikov | K. A. Bronnikov | On black bounces, wormholes and partly phantom scalar fields | 12 pages, 6 figures. Significant corrections in some expressions for
particular examples. One reference added | Phys. Rev. D 106, 064029 (2022) | 10.1103/PhysRevD.106.064029 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Simpson and Visser recently proposed a phenomenological way to avoid some
kinds of space-time singularities by replacing a parameter whose zero value
corresponds to a singularity (say, $r$) with the manifestly nonzero expression
$r(u) = \sqrt{u^2 + b^2}$, where $u$ is a new coordinate, and $b =$ \const
$>0$. This trick, generically leading to a regular minimum of $r$ beyond a
black hole horizon (called a "black bounce"), may hopefully mimic some expected
results of quantum gravity, and was previously applied to regularize the
Schwarzschild, Reissner-Nordstr\"om, Kerr and some other metrics. In this paper
it is applied to regularize the Fisher solution with a massless canonical
scalar field in general relativity (resulting in a traversable wormhole) and a
family of static, spherically symmetric dilatonic black holes (resulting in
regular black holes and wormholes). These new regular metrics represent exact
solutions of general relativity with a sum of stress-energy tensors of a scalar
field with a nonzero self-interaction potential and a magnetic field in the
framework of nonlinear electrodynamics with a Lagrangian function $L(F)$, $F =
F_{\mu\nu} F^{\mu\nu}$. A novel feature in the present study is that the scalar
fields involved have "trapped ghost" properties, that is, are phantom in a
strong-field region and canonical outside it, with a smooth transition between
the regions. It is also shown that any static, spherically symmetric metric can
be obtained as an exact solution to the Einstein equations with the
stress-energy tensor of the above field combination.
| [
{
"created": "Sat, 18 Jun 2022 15:48:28 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Jun 2022 15:09:11 GMT",
"version": "v2"
},
{
"created": "Thu, 15 Sep 2022 14:09:14 GMT",
"version": "v3"
},
{
"created": "Thu, 9 Feb 2023 17:18:04 GMT",
"version": "v4"
}
] | 2023-02-10 | [
[
"Bronnikov",
"K. A.",
""
]
] | Simpson and Visser recently proposed a phenomenological way to avoid some kinds of space-time singularities by replacing a parameter whose zero value corresponds to a singularity (say, $r$) with the manifestly nonzero expression $r(u) = \sqrt{u^2 + b^2}$, where $u$ is a new coordinate, and $b =$ \const $>0$. This trick, generically leading to a regular minimum of $r$ beyond a black hole horizon (called a "black bounce"), may hopefully mimic some expected results of quantum gravity, and was previously applied to regularize the Schwarzschild, Reissner-Nordstr\"om, Kerr and some other metrics. In this paper it is applied to regularize the Fisher solution with a massless canonical scalar field in general relativity (resulting in a traversable wormhole) and a family of static, spherically symmetric dilatonic black holes (resulting in regular black holes and wormholes). These new regular metrics represent exact solutions of general relativity with a sum of stress-energy tensors of a scalar field with a nonzero self-interaction potential and a magnetic field in the framework of nonlinear electrodynamics with a Lagrangian function $L(F)$, $F = F_{\mu\nu} F^{\mu\nu}$. A novel feature in the present study is that the scalar fields involved have "trapped ghost" properties, that is, are phantom in a strong-field region and canonical outside it, with a smooth transition between the regions. It is also shown that any static, spherically symmetric metric can be obtained as an exact solution to the Einstein equations with the stress-energy tensor of the above field combination. |
gr-qc/0012047 | Tevian Dray | Tevian Dray, George Ellis, and Charles Hellaby | Note on Signature Change and Colombeau Theory | REVTex, 3 pages; to appear in GRG | Gen.Rel.Grav. 33 (2001) 1041-1046 | 10.1023/A:1010228315205 | null | gr-qc | null | Recent work alludes to various `controversies' associated with signature
change in general relativity. As we have argued previously, these are in fact
disagreements about the (often unstated) assumptions underlying various
possible approaches. The choice between approaches remains open.
| [
{
"created": "Wed, 13 Dec 2000 21:53:33 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Dray",
"Tevian",
""
],
[
"Ellis",
"George",
""
],
[
"Hellaby",
"Charles",
""
]
] | Recent work alludes to various `controversies' associated with signature change in general relativity. As we have argued previously, these are in fact disagreements about the (often unstated) assumptions underlying various possible approaches. The choice between approaches remains open. |
1508.04951 | Parthapratim Pradhan | Parthapratim Pradhan | Thermodynamic Product Formula for Taub-NUT Black Hole | 10 Pages, Accepted in Journal of Experimental and Theoretical
Physics(JETP), 05/08/2015 | JETP Vol. 149 (1) (2016) | 10.1134/S1063776116010088 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive various important thermodynamic relations of the inner and outer
horizon in the background of Taub-NUT(Newman-Unti-Tamburino) black hole in four
dimensional \emph{Lorentzian geometry}. We compare these properties with the
properties of Reissner Nordstr{\o}m black hole. We compute \emph{area product,
area sum, area minus and area division} of black hole horizons. We show that
they all are not universal quantities. Based on these relations, we compute the
area bound of all horizons. From area bound, we derive entropy bound and
irreducible mass bound for both the horizons. We further study the stability of
such black hole by computing the specific heat for both the horizons. It is
shown that due to negative specific heat the black hole is thermodynamically
unstable. All these calculations might be helpful to understanding the nature
of black hole entropy both \emph{interior} and exterior at the microscopic
level.
| [
{
"created": "Thu, 20 Aug 2015 10:51:41 GMT",
"version": "v1"
}
] | 2016-05-04 | [
[
"Pradhan",
"Parthapratim",
""
]
] | We derive various important thermodynamic relations of the inner and outer horizon in the background of Taub-NUT(Newman-Unti-Tamburino) black hole in four dimensional \emph{Lorentzian geometry}. We compare these properties with the properties of Reissner Nordstr{\o}m black hole. We compute \emph{area product, area sum, area minus and area division} of black hole horizons. We show that they all are not universal quantities. Based on these relations, we compute the area bound of all horizons. From area bound, we derive entropy bound and irreducible mass bound for both the horizons. We further study the stability of such black hole by computing the specific heat for both the horizons. It is shown that due to negative specific heat the black hole is thermodynamically unstable. All these calculations might be helpful to understanding the nature of black hole entropy both \emph{interior} and exterior at the microscopic level. |
gr-qc/0204030 | Roberto Giambo' | Roberto Giambo', Fabio Giannoni, Giulio Magli, Paolo Piccione | New solutions of Einstein equations in spherical symmetry: the Cosmic
Censor to the court | LaTeX2e, 18 pages, to appear in Comm. Math. Phys | Commun.Math.Phys. 235 (2003) 545-563 | 10.1007/s00220-003-0793-9 | null | gr-qc | null | A new class of solutions of the Einstein field equations in spherical
symmetry is found. The new solutions are mathematically described as the
metrics admitting separation of variables in area-radius coordinates.
Physically, they describe the gravitational collapse of a class of anisotropic
elastic materials. Standard requirements of physical acceptability are
satisfied, in particular, existence of an equation of state in closed form,
weak energy condition, and existence of a regular Cauchy surface at which the
collapse begins. The matter properties are generic in the sense that both the
radial and the tangential stresses are non vanishing, and the kinematical
properties are generic as well, since shear, expansion, and acceleration are
also non-vanishing. As a test-bed for cosmic censorship, the nature of the
future singularity forming at the center is analyzed as an existence problem
for o.d.e. at a singular point using techniques based on comparison theorems,
and the spectrum of endstates - blackholes or naked singularities - is found in
full generality. Consequences of these results on the Cosmic Censorship
conjecture are discussed.
| [
{
"created": "Sat, 6 Apr 2002 17:11:19 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Dec 2002 17:24:16 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Giambo'",
"Roberto",
""
],
[
"Giannoni",
"Fabio",
""
],
[
"Magli",
"Giulio",
""
],
[
"Piccione",
"Paolo",
""
]
] | A new class of solutions of the Einstein field equations in spherical symmetry is found. The new solutions are mathematically described as the metrics admitting separation of variables in area-radius coordinates. Physically, they describe the gravitational collapse of a class of anisotropic elastic materials. Standard requirements of physical acceptability are satisfied, in particular, existence of an equation of state in closed form, weak energy condition, and existence of a regular Cauchy surface at which the collapse begins. The matter properties are generic in the sense that both the radial and the tangential stresses are non vanishing, and the kinematical properties are generic as well, since shear, expansion, and acceleration are also non-vanishing. As a test-bed for cosmic censorship, the nature of the future singularity forming at the center is analyzed as an existence problem for o.d.e. at a singular point using techniques based on comparison theorems, and the spectrum of endstates - blackholes or naked singularities - is found in full generality. Consequences of these results on the Cosmic Censorship conjecture are discussed. |
1901.04302 | Muhammad Sharif | M. Sharif and Aisha Siddiqa | Models of Collapsing and Expanding Cylindrical Source in f(R,T) Theory | 29 pages, 22 figures, to appear in AHEP | Ad. High Energy Phys. 2019(2019)8702795 | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the collapsing and expanding solutions of anisotropic charged
cylinder in the context of $f(R,T)$ theory ($R$ represents the Ricci scalar and
$T$ denotes the trace of energy-momentum tensor). For this purpose, we take an
auxiliary solution of Einstein-Maxwell field equations and evaluate expansion
scalar whose negative values lead to collapse and positive values give
expansion. For both cases, the behavior of density, pressure, anisotropic
parameter as well as mass is explored and the effects of charge as well as
model parameter on these quantities are examined. The energy conditions are
found to be satisfied for both solutions.
| [
{
"created": "Thu, 10 Jan 2019 06:50:13 GMT",
"version": "v1"
}
] | 2019-02-19 | [
[
"Sharif",
"M.",
""
],
[
"Siddiqa",
"Aisha",
""
]
] | We discuss the collapsing and expanding solutions of anisotropic charged cylinder in the context of $f(R,T)$ theory ($R$ represents the Ricci scalar and $T$ denotes the trace of energy-momentum tensor). For this purpose, we take an auxiliary solution of Einstein-Maxwell field equations and evaluate expansion scalar whose negative values lead to collapse and positive values give expansion. For both cases, the behavior of density, pressure, anisotropic parameter as well as mass is explored and the effects of charge as well as model parameter on these quantities are examined. The energy conditions are found to be satisfied for both solutions. |
gr-qc/9912082 | Daniele Oriti | Daniele Oriti (1) ((1) I.C.R.A. - International Center for
Relativistic Astrophysics) | The spinor field in Rindler spacetime: an analysis of the Unruh effect | 20 pages, 1 figure, to be published in the Proceedings of The 3rd
Icra Network Workshop and 6th Italo-Korean Meeting on Relativistic
Astrophysics | Nuovo Cim.B115:1005-1024,2000 | null | null | gr-qc | null | We analyse the quantization procedure of the spinor field in the Rindler
spacetime, showing the boundary conditions that should be imposed to the field,
in order to have a well posed theory. We then investigate the relationship
between this construction and the usual one in Minkowski spacetime. This leads
to the concept of "Unruh effect", that is the thermal nature of the Minkowski
vacuum state from the point of view of an accelerated observer. It is
demostrated that the two constructions are qualitatively different and can not
be compared and consequently the conventional interpretation of the Unruh
effect is questionable.
| [
{
"created": "Mon, 20 Dec 1999 16:16:17 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Oriti",
"Daniele",
""
]
] | We analyse the quantization procedure of the spinor field in the Rindler spacetime, showing the boundary conditions that should be imposed to the field, in order to have a well posed theory. We then investigate the relationship between this construction and the usual one in Minkowski spacetime. This leads to the concept of "Unruh effect", that is the thermal nature of the Minkowski vacuum state from the point of view of an accelerated observer. It is demostrated that the two constructions are qualitatively different and can not be compared and consequently the conventional interpretation of the Unruh effect is questionable. |
gr-qc/0205102 | Eric Gourgoulhon | Dorota Gondek-Rosinska and Eric Gourgoulhon (LUTH, CNRS / Observatoire
de Paris) | Jacobi-like bar mode instability of relativistic rotating bodies | 15 pages, 8 figures, submitted to Phys. Rev. D | Phys.Rev. D66 (2002) 044021 | 10.1103/PhysRevD.66.044021 | null | gr-qc astro-ph | null | We perform some numerical study of the secular triaxial instability of
rigidly rotating homogeneous fluid bodies in general relativity. In the
Newtonian limit, this instability arises at the bifurcation point between the
Maclaurin and Jacobi sequences. It can be driven in astrophysical systems by
viscous dissipation. We locate the onset of instability along several constant
baryon mass sequences of uniformly rotating axisymmetric bodies for compaction
parameter $M/R = 0-0.275$. We find that general relativity weakens the Jacobi
like bar mode instability, but the stabilizing effect is not very strong.
According to our analysis the critical value of the ratio of the kinetic energy
to the absolute value of the gravitational potential energy $(T/|W|)_{\rm
crit}$ for compaction parameter as high as 0.275 is only 30% higher than the
Newtonian value. The critical value of the eccentricity depends very weakly on
the degree of relativity and for $M/R=0.275$ is only 2% larger than the
Newtonian value at the onset for the secular bar mode instability. We compare
our numerical results with recent analytical investigations based on the
post-Newtonian expansion.
| [
{
"created": "Thu, 23 May 2002 13:43:59 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Gondek-Rosinska",
"Dorota",
"",
"LUTH, CNRS / Observatoire\n de Paris"
],
[
"Gourgoulhon",
"Eric",
"",
"LUTH, CNRS / Observatoire\n de Paris"
]
] | We perform some numerical study of the secular triaxial instability of rigidly rotating homogeneous fluid bodies in general relativity. In the Newtonian limit, this instability arises at the bifurcation point between the Maclaurin and Jacobi sequences. It can be driven in astrophysical systems by viscous dissipation. We locate the onset of instability along several constant baryon mass sequences of uniformly rotating axisymmetric bodies for compaction parameter $M/R = 0-0.275$. We find that general relativity weakens the Jacobi like bar mode instability, but the stabilizing effect is not very strong. According to our analysis the critical value of the ratio of the kinetic energy to the absolute value of the gravitational potential energy $(T/|W|)_{\rm crit}$ for compaction parameter as high as 0.275 is only 30% higher than the Newtonian value. The critical value of the eccentricity depends very weakly on the degree of relativity and for $M/R=0.275$ is only 2% larger than the Newtonian value at the onset for the secular bar mode instability. We compare our numerical results with recent analytical investigations based on the post-Newtonian expansion. |
0911.3062 | Betti Hartmann | Betti Hartmann and Jon Urrestilla | Gravitating Semilocal strings | Contribution to the Proceedings of the Spanish Relativity Meeting
(ERE) 2009, Bilbao, Spain | J.Phys.Conf.Ser.229:012008,2010 | 10.1088/1742-6596/229/1/012008 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the properties of semilocal strings minimally coupled to gravity.
Semilocal strings are solutions of the bosonic sector of the Standard Model in
the limit $\sin^2\theta_W=1$ (where $\theta_W$ is the Weinberg angle) and
correspond to embedded Abelian-Higgs strings for a particular choice of the
scalar doublet. We focus on the limit where the gauge boson mass is equal to
the Higgs boson mass such that the solutions fulfill the
Bogomolnyi-Prasad-Sommerfield (BPS) bound.
| [
{
"created": "Mon, 16 Nov 2009 16:00:58 GMT",
"version": "v1"
}
] | 2014-11-20 | [
[
"Hartmann",
"Betti",
""
],
[
"Urrestilla",
"Jon",
""
]
] | We discuss the properties of semilocal strings minimally coupled to gravity. Semilocal strings are solutions of the bosonic sector of the Standard Model in the limit $\sin^2\theta_W=1$ (where $\theta_W$ is the Weinberg angle) and correspond to embedded Abelian-Higgs strings for a particular choice of the scalar doublet. We focus on the limit where the gauge boson mass is equal to the Higgs boson mass such that the solutions fulfill the Bogomolnyi-Prasad-Sommerfield (BPS) bound. |
2308.02115 | Junpei Harada | Junpei Harada | Gravity at cosmological distances: Explaining the accelerating expansion
without dark energy | 7 pages, 1 figure; accepted for publication in Phys.Rev.D, v2:
published version | Phys. Rev. D 108, 044031 (2023) | 10.1103/PhysRevD.108.044031 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Three theoretical criteria for gravitational theories beyond general
relativity are considered: obtaining the cosmological constant as an
integration constant, deriving the energy conservation law as a consequence of
the field equations, rather than assuming it, and not necessarily considering
conformally flat metrics as vacuum solutions. Existing theories, including
general relativity, do not simultaneously fulfill all three criteria. To
address this, a new gravitational field equation is proposed that satisfies
these criteria. From this equation, a spherically symmetric exact solution is
derived, which is a generalization of the Schwarzschild solution. It
incorporates three terms: the Schwarzschild term, the de Sitter term, and a
newly discovered term, which is proportional to $r^4$ in a radial coordinate,
that becomes significant only at large distances. The equation is further
applied to cosmology, deriving an equation for the scale factor. It then
presents a solution that describes the transition from decelerating to
accelerating expansion in a matter-dominated universe. This is achieved without
the need for negative pressure as dark energy or the positive cosmological
constant. This provides a novel explanation for the current accelerating
expansion of the universe.
| [
{
"created": "Fri, 4 Aug 2023 02:44:23 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Aug 2023 04:28:35 GMT",
"version": "v2"
}
] | 2023-08-17 | [
[
"Harada",
"Junpei",
""
]
] | Three theoretical criteria for gravitational theories beyond general relativity are considered: obtaining the cosmological constant as an integration constant, deriving the energy conservation law as a consequence of the field equations, rather than assuming it, and not necessarily considering conformally flat metrics as vacuum solutions. Existing theories, including general relativity, do not simultaneously fulfill all three criteria. To address this, a new gravitational field equation is proposed that satisfies these criteria. From this equation, a spherically symmetric exact solution is derived, which is a generalization of the Schwarzschild solution. It incorporates three terms: the Schwarzschild term, the de Sitter term, and a newly discovered term, which is proportional to $r^4$ in a radial coordinate, that becomes significant only at large distances. The equation is further applied to cosmology, deriving an equation for the scale factor. It then presents a solution that describes the transition from decelerating to accelerating expansion in a matter-dominated universe. This is achieved without the need for negative pressure as dark energy or the positive cosmological constant. This provides a novel explanation for the current accelerating expansion of the universe. |
1402.0600 | Viktor Toth | Viktor T. Toth | Self-gravitating Bose-Einstein condensates and the Thomas-Fermi
approximation | 8 pages, 2 figures. Updated manuscript to match published version | Galaxies 2016, 4(3), 9 | 10.3390/galaxies4030009 | null | gr-qc astro-ph.GA cond-mat.quant-gas | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Self-gravitating Bose-Einstein condensates (BEC) have been proposed in
various astrophysical contexts, including Bose-stars and BEC dark matter halos.
These systems are described by a combination of the Gross-Pitaevskii and
Poisson equations (the GPP system). In the analysis of these hypothetical
objects, the Thomas-Fermi (TF) approximation is widely used. This approximation
is based on the assumption that in the presence of a large number of particles,
the kinetic term in the Gross-Pitaevskii energy functional can be neglected,
yet it is well known that this assumption is violated near the condensate
surface. We also show that the total energy of the self-gravitating condensate
in the TF-approximation is positive. The stability of a self-gravitating system
is dependent on the total energy being negative. Therefore, the
TF-approximation is ill suited to formulate initial conditions in numerical
simulations. As an alternative, we offer an approximate solution of the full
GPP system.
| [
{
"created": "Tue, 4 Feb 2014 03:12:44 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Mar 2014 19:34:21 GMT",
"version": "v2"
},
{
"created": "Mon, 15 Aug 2016 13:03:33 GMT",
"version": "v3"
}
] | 2016-08-16 | [
[
"Toth",
"Viktor T.",
""
]
] | Self-gravitating Bose-Einstein condensates (BEC) have been proposed in various astrophysical contexts, including Bose-stars and BEC dark matter halos. These systems are described by a combination of the Gross-Pitaevskii and Poisson equations (the GPP system). In the analysis of these hypothetical objects, the Thomas-Fermi (TF) approximation is widely used. This approximation is based on the assumption that in the presence of a large number of particles, the kinetic term in the Gross-Pitaevskii energy functional can be neglected, yet it is well known that this assumption is violated near the condensate surface. We also show that the total energy of the self-gravitating condensate in the TF-approximation is positive. The stability of a self-gravitating system is dependent on the total energy being negative. Therefore, the TF-approximation is ill suited to formulate initial conditions in numerical simulations. As an alternative, we offer an approximate solution of the full GPP system. |
1612.06689 | Iver Brevik | I. Brevik and A. V. Timoshkin | Dissipative Universe-Inflation with Soft Singularity | 7 pages, no figures. To appear in Int. J. of Geometric Methods in
Modern Physics (IJGMMP) | Int. J. Geometric Meth. Mod. Phys. Vol. 14, No. 4 (2017) 1750061 | 10.1142/S021988781750061X | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the early-time accelerated universe after the Big Bang. We pay
attention to the dissipative properties of the inflationary universe in the
presence of a soft type singularity, making use of the parameters of the
generalized equation of state of the fluid. Flat Friedmann-Robertson-Walker
metric is being used. We consider cosmological models leading to the so-called
type IV singular inflation. Our obtained theoretical results are compared with
observational data from the Planck satellite. The theoretical predictions for
the spectral index turn out to be in agreement with the data, while for the
scalar-to tensor ratio there are minor deviations.
| [
{
"created": "Tue, 20 Dec 2016 14:48:37 GMT",
"version": "v1"
}
] | 2017-03-23 | [
[
"Brevik",
"I.",
""
],
[
"Timoshkin",
"A. V.",
""
]
] | We investigate the early-time accelerated universe after the Big Bang. We pay attention to the dissipative properties of the inflationary universe in the presence of a soft type singularity, making use of the parameters of the generalized equation of state of the fluid. Flat Friedmann-Robertson-Walker metric is being used. We consider cosmological models leading to the so-called type IV singular inflation. Our obtained theoretical results are compared with observational data from the Planck satellite. The theoretical predictions for the spectral index turn out to be in agreement with the data, while for the scalar-to tensor ratio there are minor deviations. |
1006.1027 | Kourosh Nozari | Kourosh Nozari and S. Shafizadeh | Non-Minimal Inflation Revisited | 17 pages, 5 figures | Phys.Scripta 82:015901,2010 | 10.1088/0031-8949/82/01/015901 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We reconsider an inflationary model that inflaton field is non-minimally
coupled to gravity. We study parameter space of the model up to the second (
and in some cases third ) order of the slow-roll parameters. We calculate
inflation parameters in both Jordan and Einstein frames and the results are
compared in these two frames and also with observations. Using the recent
observational data from combined WMAP5+SDSS+SNIa datasets, we study constraint
imposed on our model parameters especially the nonminimal coupling $\xi$.
| [
{
"created": "Sat, 5 Jun 2010 07:24:18 GMT",
"version": "v1"
}
] | 2014-11-21 | [
[
"Nozari",
"Kourosh",
""
],
[
"Shafizadeh",
"S.",
""
]
] | We reconsider an inflationary model that inflaton field is non-minimally coupled to gravity. We study parameter space of the model up to the second ( and in some cases third ) order of the slow-roll parameters. We calculate inflation parameters in both Jordan and Einstein frames and the results are compared in these two frames and also with observations. Using the recent observational data from combined WMAP5+SDSS+SNIa datasets, we study constraint imposed on our model parameters especially the nonminimal coupling $\xi$. |
gr-qc/0512061 | Jos\'e Gaite | Jose Gaite | Stability of Self-Similar Spherical Accretion | Contribution to Spanish Relativity Meeting (ERE) 2005, held in
Oviedo, AIP Conference Proceedings, based on astro-ph/0511624, 4 pages | AIPConf.Proc.841:433-436,2006 | 10.1063/1.2218207 | null | gr-qc astro-ph | null | Spherical accretion flows are simple enough for analytical study, by solution
of the corresponding fluid dynamic equations. The solutions of stationary
spherical flow are due to Bondi. The questions of the choice of a physical
solution and of stability have been widely discussed. The answer to these
questions is very dependent on the problem of boundary conditions, which vary
according to whether the accretor is a compact object or a black hole. We
introduce a particular, simple form of stationary spherical flow, namely,
self-similar Bondi flow, as a case with physical interest in which analytic
solutions for perturbations can be found. With suitable no
matter-flux-perturbation boundary conditions, we will show that acoustic modes
are stable in time and have no spatial instability at r=0. Furthermore, their
evolution eventually becomes ergodic-like and shows no trace of instability or
of acquiring any remarkable pattern.
| [
{
"created": "Mon, 12 Dec 2005 11:09:24 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Gaite",
"Jose",
""
]
] | Spherical accretion flows are simple enough for analytical study, by solution of the corresponding fluid dynamic equations. The solutions of stationary spherical flow are due to Bondi. The questions of the choice of a physical solution and of stability have been widely discussed. The answer to these questions is very dependent on the problem of boundary conditions, which vary according to whether the accretor is a compact object or a black hole. We introduce a particular, simple form of stationary spherical flow, namely, self-similar Bondi flow, as a case with physical interest in which analytic solutions for perturbations can be found. With suitable no matter-flux-perturbation boundary conditions, we will show that acoustic modes are stable in time and have no spatial instability at r=0. Furthermore, their evolution eventually becomes ergodic-like and shows no trace of instability or of acquiring any remarkable pattern. |
2407.03031 | Beatriz Elizaga Navascu\'es | Ivan Agullo, Paula Calizaya Cabrera and Beatriz Elizaga Navascu\'es | Entangled pairs in evaporating black holes without event horizons | 31 pages, 5 figures, 3 appendices | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Investigations into Hawking radiation often assume a black hole model
featuring an event horizon, despite the growing consensus that such causal
structures may not exist in nature. While this assumption is not crucial for
deriving the local properties of radiation at future null infinity, it plays a
significant role in discussions about Hawking partners -- the field modes that
purify Hawking radiation. This article aims to explore the definition and fate
of Hawking partners in black hole scenarios where semiclassical mass loss due
to Hawking radiation is considered. Our analysis avoids the assumption of event
horizons and instead focuses on collapse processes that feature a trapped
region bounded by a dynamical horizon. We derive the form of the partners,
accounting for the effects of back-scattering. Furthermore, using these results
and mild assumptions, we find that Hawking partners cannot "leak" out of the
dynamical horizon to partially purify the Hawking radiation in the regime where
general relativity coexists semiclassically with quantum field theory. This
finding emphasizes the necessity for new physics, such as quantum gravity, to
resolve the final fate of information.
| [
{
"created": "Wed, 3 Jul 2024 11:51:02 GMT",
"version": "v1"
}
] | 2024-07-04 | [
[
"Agullo",
"Ivan",
""
],
[
"Cabrera",
"Paula Calizaya",
""
],
[
"Navascués",
"Beatriz Elizaga",
""
]
] | Investigations into Hawking radiation often assume a black hole model featuring an event horizon, despite the growing consensus that such causal structures may not exist in nature. While this assumption is not crucial for deriving the local properties of radiation at future null infinity, it plays a significant role in discussions about Hawking partners -- the field modes that purify Hawking radiation. This article aims to explore the definition and fate of Hawking partners in black hole scenarios where semiclassical mass loss due to Hawking radiation is considered. Our analysis avoids the assumption of event horizons and instead focuses on collapse processes that feature a trapped region bounded by a dynamical horizon. We derive the form of the partners, accounting for the effects of back-scattering. Furthermore, using these results and mild assumptions, we find that Hawking partners cannot "leak" out of the dynamical horizon to partially purify the Hawking radiation in the regime where general relativity coexists semiclassically with quantum field theory. This finding emphasizes the necessity for new physics, such as quantum gravity, to resolve the final fate of information. |
gr-qc/0608067 | Tetsuya Hara | Tetsuya Hara, Keita Sakai and Daigo Kajiura | Adopting the Uncertainty Principle for the Entropy Estimation of Black
Holes, de Sitter Space and Rindler Space | 11pages | null | null | null | gr-qc | null | By a simple physical consideration and uncertain principle, we derive that
temperature is proportional to the surface gravity and entropy is proportional
to the surface area of the black hole. We apply the same consideration to de
Sitter space and estimate the temperature and entropy of the space, then we
deduce that the entropy is proportional to the boundary surface area. By the
same consideration, we estimate the temperature and entropy in the uniformly
accelerated system (Rindler coordinate). The cases in higher dimensions are
considered.
| [
{
"created": "Mon, 14 Aug 2006 03:28:34 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Hara",
"Tetsuya",
""
],
[
"Sakai",
"Keita",
""
],
[
"Kajiura",
"Daigo",
""
]
] | By a simple physical consideration and uncertain principle, we derive that temperature is proportional to the surface gravity and entropy is proportional to the surface area of the black hole. We apply the same consideration to de Sitter space and estimate the temperature and entropy of the space, then we deduce that the entropy is proportional to the boundary surface area. By the same consideration, we estimate the temperature and entropy in the uniformly accelerated system (Rindler coordinate). The cases in higher dimensions are considered. |
gr-qc/9504040 | Franz Embacher | Franz Embacher | Dimensionality, topology, energy, the cosmological constant, and
signature change | 34 pages, LaTeX, no figures | Class.Quant.Grav. 13 (1996) 921-942 | 10.1088/0264-9381/13/5/012 | UWThPh-1995-11 | gr-qc | null | Using the concept of real tunneling configurations (classical signature
change) and nucleation energy, we explore the consequences of an alternative
minimization procedure for the Euclidean action in multiple-dimensional quantum
cosmology. In both standard Hartle-Hawking type as well as Coleman type
wormhole-based approaches, it is suggested that the action should be minimized
among configurations of equal energy. In a simplified model, allowing for
arbitrary products of spheres as Euclidean solutions, the favoured space-time
dimension is 4, the global topology of spacelike slices being ${\bf S}^1 \times
{\bf S}^2$ (hence predicting a universe of Kantowski-Sachs type). There is,
however, some freedom for a Kaluza-Klein scenario, in which case the observed
spacelike slices are ${\bf S}^3$. In this case, the internal space is a product
of two-spheres, and the total space-time dimension is 6, 8, 10 or 12.
| [
{
"created": "Tue, 25 Apr 1995 13:37:00 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Embacher",
"Franz",
""
]
] | Using the concept of real tunneling configurations (classical signature change) and nucleation energy, we explore the consequences of an alternative minimization procedure for the Euclidean action in multiple-dimensional quantum cosmology. In both standard Hartle-Hawking type as well as Coleman type wormhole-based approaches, it is suggested that the action should be minimized among configurations of equal energy. In a simplified model, allowing for arbitrary products of spheres as Euclidean solutions, the favoured space-time dimension is 4, the global topology of spacelike slices being ${\bf S}^1 \times {\bf S}^2$ (hence predicting a universe of Kantowski-Sachs type). There is, however, some freedom for a Kaluza-Klein scenario, in which case the observed spacelike slices are ${\bf S}^3$. In this case, the internal space is a product of two-spheres, and the total space-time dimension is 6, 8, 10 or 12. |
1201.1371 | Zhi-Guo Liu | Zhi-Guo Liu, Yun-Song Piao | Scalar Perturbations Through Cycles | 7 pages, 10 figures | null | 10.1103/PhysRevD.86.083510 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analytically and numerically investigate the evolutions of the scalar
perturbations through the cycles with nonsingular bounce. It is found that the
amplitude of the curvature perturbation on large scale will be amplified cycle
by cycle, and the isocurvature perturbations also obtain an amplification, but
the rate of its amplification is slower than that of curvature perturbation,
unless its coupling to the metric perturbation is not negligible.
| [
{
"created": "Fri, 6 Jan 2012 08:53:02 GMT",
"version": "v1"
}
] | 2015-06-03 | [
[
"Liu",
"Zhi-Guo",
""
],
[
"Piao",
"Yun-Song",
""
]
] | We analytically and numerically investigate the evolutions of the scalar perturbations through the cycles with nonsingular bounce. It is found that the amplitude of the curvature perturbation on large scale will be amplified cycle by cycle, and the isocurvature perturbations also obtain an amplification, but the rate of its amplification is slower than that of curvature perturbation, unless its coupling to the metric perturbation is not negligible. |
0909.5435 | Andrew Randono | Andrew Randono | de Sitter Spaces | V2: Significant changes to argument for why solutions are physically
distinct. Two diagrams, many references added | Class.Quant.Grav.27:105008,2010 | 10.1088/0264-9381/27/10/105008 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We exploit an interpretation of gravity as the symmetry broken phase of a de
Sitter gauge theory to construct new solutions to the first order field
equations. The new solutions are constructed by performing large $Spin(4,1)$
gauge transformations on the ordinary de Sitter solution and extracting first
the tetrad, then the induced metric. The class of metrics so obtained is an
infinite class labelled by an integer, $q$. Each solution satisfies the local
field equations defining constant positive curvature, and is therefore locally
isometric to de Sitter space wherever the metric is non-degenerate. The
degeneracy structure of the tetrad and metric reflects the topological
differences among the solutions with different $q$. By topological arguments we
show that the solutions are physically distinct with respect to the symmetries
of Einstein-Cartan theory. Ultimately, the existence of solutions of this type
may be a distinguishing characteristic of gravity as a metric theory versus
gravity as a gauge theory.
| [
{
"created": "Tue, 29 Sep 2009 20:29:43 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Feb 2010 02:48:48 GMT",
"version": "v2"
}
] | 2010-11-01 | [
[
"Randono",
"Andrew",
""
]
] | We exploit an interpretation of gravity as the symmetry broken phase of a de Sitter gauge theory to construct new solutions to the first order field equations. The new solutions are constructed by performing large $Spin(4,1)$ gauge transformations on the ordinary de Sitter solution and extracting first the tetrad, then the induced metric. The class of metrics so obtained is an infinite class labelled by an integer, $q$. Each solution satisfies the local field equations defining constant positive curvature, and is therefore locally isometric to de Sitter space wherever the metric is non-degenerate. The degeneracy structure of the tetrad and metric reflects the topological differences among the solutions with different $q$. By topological arguments we show that the solutions are physically distinct with respect to the symmetries of Einstein-Cartan theory. Ultimately, the existence of solutions of this type may be a distinguishing characteristic of gravity as a metric theory versus gravity as a gauge theory. |
2107.00046 | Pedro Fernandes | Pedro G. S. Fernandes, Pedro Carrilho, Timothy Clifton, David J.
Mulryne | Black Holes in the Scalar-Tensor Formulation of 4D Einstein-Gauss-Bonnet
Gravity: Uniqueness of Solutions, and a New Candidate for Dark Matter | 15 pages, 4 figures | Phys. Rev. D 104, 044029 (2021) | 10.1103/PhysRevD.104.044029 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we study static black holes in the regularized 4D
Einstein-Gauss-Bonnet theory of gravity; a shift-symmetric scalar-tensor theory
that belongs to the Horndeski class. This theory features a simple black hole
solution that can be written in closed form, and which we show is the unique
static, spherically-symmetric and asymptotically-flat black hole vacuum
solution of the theory. We further show that no asymptotically-flat,
time-dependent, spherically-symmetric perturbations to this geometry are
allowed, which suggests that it may be the only spherically-symmetric vacuum
solution that this theory admits (a result analogous to Birkhoff's theorem).
Finally, we consider the thermodynamic properties of these black holes, and
find that their final state after evaporation is a remnant with a size
determined by the coupling constant of the theory. We speculate that remnants
of this kind from primordial black holes could act as dark matter, and we
constrain the parameter space for their formation mass, as well as the coupling
constant of the theory.
| [
{
"created": "Wed, 30 Jun 2021 18:08:35 GMT",
"version": "v1"
}
] | 2021-08-18 | [
[
"Fernandes",
"Pedro G. S.",
""
],
[
"Carrilho",
"Pedro",
""
],
[
"Clifton",
"Timothy",
""
],
[
"Mulryne",
"David J.",
""
]
] | In this work we study static black holes in the regularized 4D Einstein-Gauss-Bonnet theory of gravity; a shift-symmetric scalar-tensor theory that belongs to the Horndeski class. This theory features a simple black hole solution that can be written in closed form, and which we show is the unique static, spherically-symmetric and asymptotically-flat black hole vacuum solution of the theory. We further show that no asymptotically-flat, time-dependent, spherically-symmetric perturbations to this geometry are allowed, which suggests that it may be the only spherically-symmetric vacuum solution that this theory admits (a result analogous to Birkhoff's theorem). Finally, we consider the thermodynamic properties of these black holes, and find that their final state after evaporation is a remnant with a size determined by the coupling constant of the theory. We speculate that remnants of this kind from primordial black holes could act as dark matter, and we constrain the parameter space for their formation mass, as well as the coupling constant of the theory. |
gr-qc/9212011 | Sukanya Sinha | Marcos Rosenbaum, Michael P. Ryan and Sukanya Sinha | A Nonlinear Model of a Quantum Minisuperspace System with Back Reaction | 31 pages, 7 figures(available on request) | Phys.Rev.D47:4443-4457,1993 | 10.1103/PhysRevD.47.4443 | null | gr-qc | null | We consider the quantum evolution of the space-independent mode of a $\lambda
{\phi}^4$ theory as a minisuperspace in the space of all $\phi$. The motion of
the wave packet in the minisuperspace is then compared to the motion of a wave
packet in a larger minisuperspace consisting of the original minisuperspace
plus one space-dependent mode. By comparing the motion of the two packets we
develop criteria that tell us when the quantum evolution in the
space-independent minisuperspace gives us useful information about the true
evolution in the larger minisuperspace. These criteria serve as a toy model for
similar(but much more complex) criteria that will tell us whether or when
quantized gravitational minisuperspaces can possibly give any useful
information about quantum gravity.
| [
{
"created": "Wed, 16 Dec 1992 21:20:00 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Rosenbaum",
"Marcos",
""
],
[
"Ryan",
"Michael P.",
""
],
[
"Sinha",
"Sukanya",
""
]
] | We consider the quantum evolution of the space-independent mode of a $\lambda {\phi}^4$ theory as a minisuperspace in the space of all $\phi$. The motion of the wave packet in the minisuperspace is then compared to the motion of a wave packet in a larger minisuperspace consisting of the original minisuperspace plus one space-dependent mode. By comparing the motion of the two packets we develop criteria that tell us when the quantum evolution in the space-independent minisuperspace gives us useful information about the true evolution in the larger minisuperspace. These criteria serve as a toy model for similar(but much more complex) criteria that will tell us whether or when quantized gravitational minisuperspaces can possibly give any useful information about quantum gravity. |
2201.03640 | Gustavo Dotti | Gustavo Dotti | Linear Stability of Black Holes and Naked Singularities | Lecture notes delivered at the V Jos\'e Pl\'{\i}nio Baptista School
of Cosmology (Guarapari (Esp\'{\i}rito Santo) Brazil, September 30th to
October 5th, 2021) | Universe 2022, 8, 38 | 10.3390/universe8010038 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | These notes follow from a course delivered at the V Jos\'e Pl\'{\i}nio
Baptista School of Cosmology, held at Guarapari (Esp\'{\i}rito Santo) Brazil,
from 30 September to 5 October 2021. A review of the current status of the
linear stability of black holes and naked singularities is given. The standard
modal approach, that takes advantage of the background symmetries and analyze
separately the harmonic components of linear perturbations, is briefly
introduced and used to prove that the naked singularities in the Kerr--Newman
family, as well as the inner black hole regions beyond Cauchy horizons, are
unstable and therefore unphysical. The proofs require a treatment of the
boundary condition at the timelike boundary, which is given in detail. The
nonmodal linear stability concept is then introduced, and used to prove that
the domain of outer communications of a Schwarzschild black hole with a
non-negative cosmological constant satisfies this stronger stability condition,
which rules out transient growths of perturbations, and also to show that the
perturbed black hole settles into a slowly rotating Kerr black hole. The
encoding of the perturbation fields in gauge invariant curvature scalars and
the effects of the perturbation on the geometry of the spacetime is discussed.
| [
{
"created": "Mon, 10 Jan 2022 20:44:56 GMT",
"version": "v1"
}
] | 2022-01-12 | [
[
"Dotti",
"Gustavo",
""
]
] | These notes follow from a course delivered at the V Jos\'e Pl\'{\i}nio Baptista School of Cosmology, held at Guarapari (Esp\'{\i}rito Santo) Brazil, from 30 September to 5 October 2021. A review of the current status of the linear stability of black holes and naked singularities is given. The standard modal approach, that takes advantage of the background symmetries and analyze separately the harmonic components of linear perturbations, is briefly introduced and used to prove that the naked singularities in the Kerr--Newman family, as well as the inner black hole regions beyond Cauchy horizons, are unstable and therefore unphysical. The proofs require a treatment of the boundary condition at the timelike boundary, which is given in detail. The nonmodal linear stability concept is then introduced, and used to prove that the domain of outer communications of a Schwarzschild black hole with a non-negative cosmological constant satisfies this stronger stability condition, which rules out transient growths of perturbations, and also to show that the perturbed black hole settles into a slowly rotating Kerr black hole. The encoding of the perturbation fields in gauge invariant curvature scalars and the effects of the perturbation on the geometry of the spacetime is discussed. |
1506.07588 | Samuel Wilkinson Mr | Samuel A. Wilkinson and Andrew D. Greentree | Geometrogenesis under Quantum Graphity: problems with the ripening
Universe | 8 pages,4 figures | Phys. Rev. D 92, 084007 (2015) | 10.1103/PhysRevD.92.084007 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quantum Graphity (QG) is a model of emergent geometry in which space is
represented by a dynamical graph. The graph evolves under the action of a
Hamiltonian from a high-energy pre-geometric state to a low-energy state in
which geometry emerges as a coarse-grained effective property of space. Here we
show the results of numerical modelling of the evolution of the QG Hamiltonian,
a process we term "ripening" by analogy with crystallographic growth. We find
that the model as originally presented favours a graph composed of small
disjoint subgraphs. Such a disconnected space is a poor representation of our
universe. A new term is introduced to the original QG Hamiltonian, which we
call the hypervalence term. It is shown that the inclusion of a hypervalence
term causes a connected lattice-like graph to be favoured over small isolated
subgraphs.
| [
{
"created": "Thu, 25 Jun 2015 00:45:50 GMT",
"version": "v1"
}
] | 2015-10-07 | [
[
"Wilkinson",
"Samuel A.",
""
],
[
"Greentree",
"Andrew D.",
""
]
] | Quantum Graphity (QG) is a model of emergent geometry in which space is represented by a dynamical graph. The graph evolves under the action of a Hamiltonian from a high-energy pre-geometric state to a low-energy state in which geometry emerges as a coarse-grained effective property of space. Here we show the results of numerical modelling of the evolution of the QG Hamiltonian, a process we term "ripening" by analogy with crystallographic growth. We find that the model as originally presented favours a graph composed of small disjoint subgraphs. Such a disconnected space is a poor representation of our universe. A new term is introduced to the original QG Hamiltonian, which we call the hypervalence term. It is shown that the inclusion of a hypervalence term causes a connected lattice-like graph to be favoured over small isolated subgraphs. |
1703.05360 | F\'elix-Louis Juli\'e | F\'elix-Louis Juli\'e, Nathalie Deruelle | Two-body problem in Scalar-Tensor theories as a deformation of General
Relativity : an Effective-One-Body approach | null | Phys. Rev. D 95, 124054 (2017) | 10.1103/PhysRevD.95.124054 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we address the two-body problem in massless Scalar-Tensor (ST)
theories within an Effective-One-Body (EOB) framework. We focus on the first
building block of the EOB approach, that is, mapping the conservative part of
the two-body dynamics onto the geodesic motion of a test particle in an
effective external metric. To this end, we first deduce the second
post-Keplerian (2PK) Hamiltonian of the two-body problem from the known 2PK
Lagrangian. We then build, by means of a canonical transformation a
ST-deformation of the general relativistic EOB Hamiltonian which allows to
incorporate the Scalar-Tensor (2PK) corrections to the currently best available
General Relativity EOB results. This EOB-ST Hamiltonian defines a resummation
of the dynamics that may provide information on the strong-field regime, in
particular, the ISCO location and associated orbital frequency and can be
compared to other, e.g. tidal, corrections.
| [
{
"created": "Wed, 15 Mar 2017 19:17:36 GMT",
"version": "v1"
}
] | 2017-07-05 | [
[
"Julié",
"Félix-Louis",
""
],
[
"Deruelle",
"Nathalie",
""
]
] | In this paper we address the two-body problem in massless Scalar-Tensor (ST) theories within an Effective-One-Body (EOB) framework. We focus on the first building block of the EOB approach, that is, mapping the conservative part of the two-body dynamics onto the geodesic motion of a test particle in an effective external metric. To this end, we first deduce the second post-Keplerian (2PK) Hamiltonian of the two-body problem from the known 2PK Lagrangian. We then build, by means of a canonical transformation a ST-deformation of the general relativistic EOB Hamiltonian which allows to incorporate the Scalar-Tensor (2PK) corrections to the currently best available General Relativity EOB results. This EOB-ST Hamiltonian defines a resummation of the dynamics that may provide information on the strong-field regime, in particular, the ISCO location and associated orbital frequency and can be compared to other, e.g. tidal, corrections. |
1409.4693 | Pierre-Henry Lambert | Pierre-Henry Lambert | Conformal symmetries of gravity from asymptotic methods: further
developments | PhD thesis, 144 pages; v2: reference 35 has been updated | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this thesis, the symmetry structure of gravitational theories at null
infinity is studied further, in the case of pure gravity in four dimensions and
also in the case of Einstein-Yang-Mills theory in $d$ dimensions with and
without a cosmological constant. The first part of this thesis is devoted to
the presentation of asymptotic methods (symmetries, solution space and surface
charges) applied to gravity in the case of the BMS gauge in three and four
spacetime dimensions. The second part of this thesis contains the original
contributions. Firstly, it is shown that the enhancement from Lorentz to
Virasoro algebra also occurs for asymptotically flat spacetimes defined in the
sense of Newman-Unti. As a first application, the transformation laws of the
Newman-Penrose coefficients characterizing solution space of the Newman-Unti
approach are worked out, focusing on the inhomogeneous terms that contain the
information about central extensions of the theory. These transformations laws
make the conformal structure particularly transparent, and constitute the main
original result of the thesis. Secondly, asymptotic symmetries of the
Einstein-Yang-Mills system with or without cosmological constant are explicitly
worked out in a unified manner in $d$ dimensions. In agreement with a recent
conjecture, a Virasoro-Kac-Moody type algebra is found not only in three
dimensions but also in the four dimensional asymptotically flat case. These two
parts of the thesis are supplemented by appendices.
| [
{
"created": "Tue, 16 Sep 2014 16:42:00 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Aug 2015 17:58:46 GMT",
"version": "v2"
}
] | 2015-08-11 | [
[
"Lambert",
"Pierre-Henry",
""
]
] | In this thesis, the symmetry structure of gravitational theories at null infinity is studied further, in the case of pure gravity in four dimensions and also in the case of Einstein-Yang-Mills theory in $d$ dimensions with and without a cosmological constant. The first part of this thesis is devoted to the presentation of asymptotic methods (symmetries, solution space and surface charges) applied to gravity in the case of the BMS gauge in three and four spacetime dimensions. The second part of this thesis contains the original contributions. Firstly, it is shown that the enhancement from Lorentz to Virasoro algebra also occurs for asymptotically flat spacetimes defined in the sense of Newman-Unti. As a first application, the transformation laws of the Newman-Penrose coefficients characterizing solution space of the Newman-Unti approach are worked out, focusing on the inhomogeneous terms that contain the information about central extensions of the theory. These transformations laws make the conformal structure particularly transparent, and constitute the main original result of the thesis. Secondly, asymptotic symmetries of the Einstein-Yang-Mills system with or without cosmological constant are explicitly worked out in a unified manner in $d$ dimensions. In agreement with a recent conjecture, a Virasoro-Kac-Moody type algebra is found not only in three dimensions but also in the four dimensional asymptotically flat case. These two parts of the thesis are supplemented by appendices. |
1602.03847 | lVC Publications | The LIGO Scientific Collaboration, the Virgo Collaboration | GW150914: Implications for the stochastic gravitational wave background
from binary black holes | 12 pages, 3 figures | Phys. Rev. Lett. 116, 131102 (2016) | 10.1103/PhysRevLett.116.131102 | LIGO-P1500222 | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The LIGO detection of the gravitational wave transient GW150914, from the
inspiral and merger of two black holes with masses $\gtrsim 30\,
\text{M}_\odot$, suggests a population of binary black holes with relatively
high mass. This observation implies that the stochastic gravitational-wave
background from binary black holes, created from the incoherent superposition
of all the merging binaries in the Universe, could be higher than previously
expected. Using the properties of GW150914, we estimate the energy density of
such a background from binary black holes. In the most sensitive part of the
Advanced LIGO/Virgo band for stochastic backgrounds (near 25 Hz), we predict
$\Omega_\text{GW}(f=25 Hz) = 1.1_{-0.9}^{+2.7} \times 10^{-9}$ with 90\%
confidence. This prediction is robustly demonstrated for a variety of formation
scenarios with different parameters. The differences between models are small
compared to the statistical uncertainty arising from the currently poorly
constrained local coalescence rate. We conclude that this background is
potentially measurable by the Advanced LIGO/Virgo detectors operating at their
projected final sensitivity.
| [
{
"created": "Thu, 11 Feb 2016 19:26:54 GMT",
"version": "v1"
},
{
"created": "Sun, 20 Mar 2016 19:13:21 GMT",
"version": "v2"
}
] | 2016-04-06 | [
[
"The LIGO Scientific Collaboration",
"",
""
],
[
"the Virgo Collaboration",
"",
""
]
] | The LIGO detection of the gravitational wave transient GW150914, from the inspiral and merger of two black holes with masses $\gtrsim 30\, \text{M}_\odot$, suggests a population of binary black holes with relatively high mass. This observation implies that the stochastic gravitational-wave background from binary black holes, created from the incoherent superposition of all the merging binaries in the Universe, could be higher than previously expected. Using the properties of GW150914, we estimate the energy density of such a background from binary black holes. In the most sensitive part of the Advanced LIGO/Virgo band for stochastic backgrounds (near 25 Hz), we predict $\Omega_\text{GW}(f=25 Hz) = 1.1_{-0.9}^{+2.7} \times 10^{-9}$ with 90\% confidence. This prediction is robustly demonstrated for a variety of formation scenarios with different parameters. The differences between models are small compared to the statistical uncertainty arising from the currently poorly constrained local coalescence rate. We conclude that this background is potentially measurable by the Advanced LIGO/Virgo detectors operating at their projected final sensitivity. |
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