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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1503.05943 | Seramika Ariwahjoedi | Seramika Ariwahjoedi, Jusak Sali Kosasih, Carlo Rovelli, Freddy P. Zen | Curvatures and discrete Gauss-Codazzi equation in (2+1)-dimensional loop
quantum gravity | 16 pages, 10 figures | IJGMMP 12: 1550112. (2015) | 10.1142/S0219887815501121 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive the Gauss-Codazzi equation in the holonomy and plane-angle
representations and we use the result to write a Gauss-Codazzi equation for a
discrete (2+1)-dimensional manifold, triangulated by isosceles tetrahedra. This
allows us to write operators acting on spin network states in (2+1)-dimensional
loop quantum gravity, representing the 3-dimensional intrinsic, 2-dimensional
intrinsic, and 2-dimensional extrinsic curvatures.
| [
{
"created": "Thu, 19 Mar 2015 20:56:48 GMT",
"version": "v1"
}
] | 2016-08-01 | [
[
"Ariwahjoedi",
"Seramika",
""
],
[
"Kosasih",
"Jusak Sali",
""
],
[
"Rovelli",
"Carlo",
""
],
[
"Zen",
"Freddy P.",
""
]
] | We derive the Gauss-Codazzi equation in the holonomy and plane-angle representations and we use the result to write a Gauss-Codazzi equation for a discrete (2+1)-dimensional manifold, triangulated by isosceles tetrahedra. This allows us to write operators acting on spin network states in (2+1)-dimensional loop quantum gravity, representing the 3-dimensional intrinsic, 2-dimensional intrinsic, and 2-dimensional extrinsic curvatures. |
1203.0748 | Leszek Soko{\l}owski | Leszek M. Sokolowski | On the twin paradox in static spacetimes: I. Schwarzschild metric | 18 pages, paper accepted for publication in Gen. Rel. Grav | Gen. Relativ. Gravit. (2012) 44:1267-1283 | 10.1007/s10714-012-1337-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by a conjecture put forward by Abramowicz and Bajtlik we reconsider
the twin paradox in static spacetimes. According to a well known theorem in
Lorentzian geometry the longest timelike worldline between two given points is
the unique geodesic line without points conjugate to the initial point on the
segment joining the two points. We calculate the proper times for static twins,
for twins moving on a circular orbit (if it is a geodesic) around a centre of
symmetry and for twins travelling on outgoing and ingoing radial timelike
geodesics. We show that the twins on the radial geodesic worldlines are always
the oldest ones and we explicitly find the conjugate points (if they exist)
outside the relevant segments. As it is of its own mathematical interest, we
find general Jacobi vector fields on the geodesic lines under consideration. In
the first part of the work we investigate Schwarzschild geometry.
| [
{
"created": "Sun, 4 Mar 2012 16:35:39 GMT",
"version": "v1"
}
] | 2012-04-11 | [
[
"Sokolowski",
"Leszek M.",
""
]
] | Motivated by a conjecture put forward by Abramowicz and Bajtlik we reconsider the twin paradox in static spacetimes. According to a well known theorem in Lorentzian geometry the longest timelike worldline between two given points is the unique geodesic line without points conjugate to the initial point on the segment joining the two points. We calculate the proper times for static twins, for twins moving on a circular orbit (if it is a geodesic) around a centre of symmetry and for twins travelling on outgoing and ingoing radial timelike geodesics. We show that the twins on the radial geodesic worldlines are always the oldest ones and we explicitly find the conjugate points (if they exist) outside the relevant segments. As it is of its own mathematical interest, we find general Jacobi vector fields on the geodesic lines under consideration. In the first part of the work we investigate Schwarzschild geometry. |
1504.07624 | Massimo Giovannini | Massimo Giovannini | Comment on "Accelerating cosmological expansion from shear and bulk
viscosity" | null | null | null | CERN-PH-TH-2015-101 | gr-qc astro-ph.GA hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a recent Letter [Phys. Rev. Lett. 114 091301 (2105)] the cause of the
acceleration of the present Universe has been identified with the shear
viscosity of an imperfect relativistic fluid even in the absence of any bulk
viscous contribution. The gist of this comment is that the shear viscosity, if
anything, can only lead to an accelerated expansion over sufficiently small
scales well inside the Hubble radius.
| [
{
"created": "Tue, 28 Apr 2015 16:22:09 GMT",
"version": "v1"
}
] | 2015-05-04 | [
[
"Giovannini",
"Massimo",
""
]
] | In a recent Letter [Phys. Rev. Lett. 114 091301 (2105)] the cause of the acceleration of the present Universe has been identified with the shear viscosity of an imperfect relativistic fluid even in the absence of any bulk viscous contribution. The gist of this comment is that the shear viscosity, if anything, can only lead to an accelerated expansion over sufficiently small scales well inside the Hubble radius. |
2102.01703 | Alexandre Pombo | Carlos A. R. Herdeiro, Alexandre M. Pombo, Eugen Radu, Pedro V. P.
Cunha and Nicolas Sanchis-Gual | The imitation game: Proca stars that can mimic the Schwarzschild shadow | Abstract abridged due to arXiv length limit; 22 pages, 9 figures | null | 10.1088/1475-7516/2021/04/051 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Can a dynamically robust bosonic star (BS) produce an (effective) shadow that
mimics that of a black hole (BH)? The BH shadow is linked to the existence of
light rings (LRs). For free bosonic fields, yielding mini-BSs, it is known that
these stars can become ultra-compact - i.e., possess LRs - but only for
perturbatively unstable solutions. We show this remains the case even when
different self-interactions are considered. However, an effective shadow can
arise in a different way: if BSs reproduce the existence of an innermost stable
circular orbit (ISCO) for timelike geodesics (located at $r_{\rm ISCO}=6M$ for
a Schwarzschild BH of mass M), the accretion flow morphology around BHs is
mimicked and an effective shadow arises in an astrophysical environment. Even
though spherical BSs may accommodate stable timelike circular orbits all the
way down to their centre, we show the angular velocity along such orbits may
have a maximum away from the origin, at $R_{\Omega}$; this scale was recently
observed to mimic the BH's ISCO in some scenarios of accretion flow. Then: (i)
for free scalar fields or with quartic self-interactions, $R_{\Omega}\neq 0$
only for perturbatively unstable BSs; (ii) for higher scalar self-interactions,
e.g. axionic, $R_{\Omega}\neq 0$ is possible for perturbatively stable BSs, but
no solution with $R_{\Omega}=6M$ was found in the parameter space explored;
(iii) but for free vector fields, yielding Proca stars (PSs), perturbatively
stable solutions with $R_{\Omega}\neq 0$ exist, and indeed $R_{\Omega}=6M$ for
a particular solution. Thus, dynamically robust spherical PSs can mimic the
shadow of a (near-)equilibrium Schwarzschild BH with the same M, in an
astrophysical environment, despite the absence of a LR, at least under some
observation conditions, as we confirm by comparing the lensing of such PSs and
Schwarzschild BHs.
| [
{
"created": "Tue, 2 Feb 2021 19:00:01 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Apr 2021 16:23:57 GMT",
"version": "v2"
}
] | 2021-04-20 | [
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Pombo",
"Alexandre M.",
""
],
[
"Radu",
"Eugen",
""
],
[
"Cunha",
"Pedro V. P.",
""
],
[
"Sanchis-Gual",
"Nicolas",
""
]
] | Can a dynamically robust bosonic star (BS) produce an (effective) shadow that mimics that of a black hole (BH)? The BH shadow is linked to the existence of light rings (LRs). For free bosonic fields, yielding mini-BSs, it is known that these stars can become ultra-compact - i.e., possess LRs - but only for perturbatively unstable solutions. We show this remains the case even when different self-interactions are considered. However, an effective shadow can arise in a different way: if BSs reproduce the existence of an innermost stable circular orbit (ISCO) for timelike geodesics (located at $r_{\rm ISCO}=6M$ for a Schwarzschild BH of mass M), the accretion flow morphology around BHs is mimicked and an effective shadow arises in an astrophysical environment. Even though spherical BSs may accommodate stable timelike circular orbits all the way down to their centre, we show the angular velocity along such orbits may have a maximum away from the origin, at $R_{\Omega}$; this scale was recently observed to mimic the BH's ISCO in some scenarios of accretion flow. Then: (i) for free scalar fields or with quartic self-interactions, $R_{\Omega}\neq 0$ only for perturbatively unstable BSs; (ii) for higher scalar self-interactions, e.g. axionic, $R_{\Omega}\neq 0$ is possible for perturbatively stable BSs, but no solution with $R_{\Omega}=6M$ was found in the parameter space explored; (iii) but for free vector fields, yielding Proca stars (PSs), perturbatively stable solutions with $R_{\Omega}\neq 0$ exist, and indeed $R_{\Omega}=6M$ for a particular solution. Thus, dynamically robust spherical PSs can mimic the shadow of a (near-)equilibrium Schwarzschild BH with the same M, in an astrophysical environment, despite the absence of a LR, at least under some observation conditions, as we confirm by comparing the lensing of such PSs and Schwarzschild BHs. |
gr-qc/9912101 | Konoplya | R.A. Konoplya | Small Perturbations in General Relativity: Tensor Harmonics of Arbitrary
Symmetry | 9 pages, LaTeX 2e with AMS fonts, minor changes, some misprints
corrected | Phys.Lett. A268 (2000) 37-44 | 10.1016/S0375-9601(00)00160-2 | null | gr-qc | null | We develop a method for constructing of the basic functions with witch to
expand small perturbations of space-time in General Relativity. The method
allows to obtain the tensor harmonics for perturbations of the background
space-time admitting an arbitrary group of isometry, and to split the
linearized Einstein equations into the irreducible combinations. The essential
point of the work is the construction of the generalized Casimir operator for
the underlying group, which is defined not only on vector but also on tensor
fields. It is used to construct the basic functions for spaces of tensor
representations of the background metric's group of isometry. The method, being
general, is applied here to construction of the basic functions for the case of
the three-parameter group of isometry G_3 acting on the two-dimensional
non-isotropic surface of transitivity. As quick illustrations of the method we
consider the well-known particular cases: cylindrical harmonic for the flat
space-time, and Regge-Wheller spherical harmonics for the Schwarzschild metric.
| [
{
"created": "Thu, 23 Dec 1999 17:46:49 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jan 2000 16:24:33 GMT",
"version": "v2"
},
{
"created": "Sat, 25 Oct 2003 11:47:02 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Konoplya",
"R. A.",
""
]
] | We develop a method for constructing of the basic functions with witch to expand small perturbations of space-time in General Relativity. The method allows to obtain the tensor harmonics for perturbations of the background space-time admitting an arbitrary group of isometry, and to split the linearized Einstein equations into the irreducible combinations. The essential point of the work is the construction of the generalized Casimir operator for the underlying group, which is defined not only on vector but also on tensor fields. It is used to construct the basic functions for spaces of tensor representations of the background metric's group of isometry. The method, being general, is applied here to construction of the basic functions for the case of the three-parameter group of isometry G_3 acting on the two-dimensional non-isotropic surface of transitivity. As quick illustrations of the method we consider the well-known particular cases: cylindrical harmonic for the flat space-time, and Regge-Wheller spherical harmonics for the Schwarzschild metric. |
1008.4839 | Md. Rahman Atiqur | M. Atiqur Rahman | Quantum Nonthermal Radiation of Kerr-anti-de Sitter Black Holes | 13 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the properties of Quantum nonthermal radiation of a Kerr-anti-de
Sitter (KAdS) black holes. Assuming that a crossing of the positive and
negative Dirac energy levels occurs in a region near the event horizon of the
hole, and spontaneous quantum nonthermal radiation takes place in the overlap
region. We solve the biquadratic equation governing the location of the event
horizon of the KAdS black holes and present closed analytic expression for the
radii of the horizons.
| [
{
"created": "Sat, 28 Aug 2010 06:59:45 GMT",
"version": "v1"
}
] | 2010-08-31 | [
[
"Rahman",
"M. Atiqur",
""
]
] | We examine the properties of Quantum nonthermal radiation of a Kerr-anti-de Sitter (KAdS) black holes. Assuming that a crossing of the positive and negative Dirac energy levels occurs in a region near the event horizon of the hole, and spontaneous quantum nonthermal radiation takes place in the overlap region. We solve the biquadratic equation governing the location of the event horizon of the KAdS black holes and present closed analytic expression for the radii of the horizons. |
1810.03936 | Anuradha Samajdar | Anuradha Samajdar and Tim Dietrich | Waveform systematics for binary neutron star gravitational wave signals:
effects of the point-particle baseline and tidal descriptions | 12 pages, 6 figures, 3 tables | Phys. Rev. D 98, 124030 (2018) | 10.1103/PhysRevD.98.124030 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational wave (GW) astronomy has consolidated its role as a new
observational window to reveal the properties of compact binaries in the
Universe. In particular, the discovery of the first binary neutron star
coalescence, GW170817, led to a number of scientific breakthroughs as the
possibility to place constraints on the equation of state of cold matter at
supranuclear densities. These constraints and all scientific results based on
them require accurate models describing the GW signal to extract the source
properties from the measured signal.
In this article, we study potential systematic biases during the extraction
of source parameters using different descriptions for both, the point-particle
dynamics and tidal effects. We find that for the considered cases the mass and
spin recovery show almost no systematic bias with respect to the chosen
waveform model. However, the extracted tidal effects can be strongly biased,
where we find generally that Post-Newtonian approximants predict neutron stars
with larger deformability and radii than numerical relativity tuned models.
Noteworthy, an increase in the Post-Newtonian order in the tidal phasing does
not lead to a monotonic change in the estimated properties.
We find that for a signal with strength similar to GW170817, but observed
with design sensitivity, the estimated tidal parameters can differ by more than
a factor of two depending on the employed tidal description of the waveform
approximant. This shows the current need for the development of better waveform
models to extract reliably the source properties from upcoming GW detections.
| [
{
"created": "Tue, 9 Oct 2018 12:26:05 GMT",
"version": "v1"
}
] | 2018-12-26 | [
[
"Samajdar",
"Anuradha",
""
],
[
"Dietrich",
"Tim",
""
]
] | Gravitational wave (GW) astronomy has consolidated its role as a new observational window to reveal the properties of compact binaries in the Universe. In particular, the discovery of the first binary neutron star coalescence, GW170817, led to a number of scientific breakthroughs as the possibility to place constraints on the equation of state of cold matter at supranuclear densities. These constraints and all scientific results based on them require accurate models describing the GW signal to extract the source properties from the measured signal. In this article, we study potential systematic biases during the extraction of source parameters using different descriptions for both, the point-particle dynamics and tidal effects. We find that for the considered cases the mass and spin recovery show almost no systematic bias with respect to the chosen waveform model. However, the extracted tidal effects can be strongly biased, where we find generally that Post-Newtonian approximants predict neutron stars with larger deformability and radii than numerical relativity tuned models. Noteworthy, an increase in the Post-Newtonian order in the tidal phasing does not lead to a monotonic change in the estimated properties. We find that for a signal with strength similar to GW170817, but observed with design sensitivity, the estimated tidal parameters can differ by more than a factor of two depending on the employed tidal description of the waveform approximant. This shows the current need for the development of better waveform models to extract reliably the source properties from upcoming GW detections. |
gr-qc/0512104 | Orhan Donmez | Orhan Donmez | Solution of the 1D Special Relativistic Hydrodynamics(SRH) Equations
Using Different Numerical Method and Results from Different Test Problems | 8 figures | Appl.Math.Comput. 181 (2006) 256-270 | 10.1016/j.amc.2006.01.031 | null | gr-qc physics.comp-ph | null | In this paper, we have solved 1D special relativistic hydrodynamical
equations using different numerical method in computational gas dynamics. The
numerical solutions of these equations for smooth wave cases give better
solution when we use $Non-TVD$(Total Variable Diminishing) but solution of
discontinuity wave produces some oscillation behind the shock. On the other
hand, $TVD$ type schemes give good approximation at discontinuity cases.
Because $TVD$ schemes completely remove the oscillations, they reduce locally
the accuracy of the solution around the extrema.
| [
{
"created": "Mon, 19 Dec 2005 18:16:47 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Donmez",
"Orhan",
""
]
] | In this paper, we have solved 1D special relativistic hydrodynamical equations using different numerical method in computational gas dynamics. The numerical solutions of these equations for smooth wave cases give better solution when we use $Non-TVD$(Total Variable Diminishing) but solution of discontinuity wave produces some oscillation behind the shock. On the other hand, $TVD$ type schemes give good approximation at discontinuity cases. Because $TVD$ schemes completely remove the oscillations, they reduce locally the accuracy of the solution around the extrema. |
gr-qc/9907004 | Jorma Louko | Jorma Louko, Carlo Rovelli | Refined Algebraic Quantization in the oscillator representation of
SL(2,R) | 30 pages, REVTeX v3.1 with amsfonts. (v4: Published version.) | J.Math.Phys. 41 (2000) 132-155 | 10.1063/1.533126 | AEI 1999-010 | gr-qc hep-th math.QA | null | We investigate Refined Algebraic Quantization (RAQ) with group averaging in a
constrained Hamiltonian system with unreduced phase space T^*R^4 and gauge
group SL(2,R). The reduced phase space M is connected and contains four
mutually disconnected `regular' sectors with topology R x S^1, but these
sectors are connected to each other through an exceptional set where M is not a
manifold and where M has non-Hausdorff topology. The RAQ physical Hilbert space
H_{phys} decomposes as H_{phys} = (direct sum of) H_i, where the four subspaces
H_i naturally correspond to the four regular sectors of M. The RAQ observable
algebra A_{obs}, represented on H_{phys}, contains natural subalgebras
represented on each H_i. The group averaging takes place in the oscillator
representation of SL(2,R) on L^2(R^{2,2}), and ensuring convergence requires a
subtle choice for the test state space: the classical analogue of this choice
is to excise from M the exceptional set while nevertheless retaining
information about the connections between the regular sectors. A quantum theory
with the Hilbert space H_{phys} and a finitely-generated observable subalgebra
of A_{obs} is recovered through both Ashtekar's Algebraic Quantization and
Isham's group theoretic quantization.
| [
{
"created": "Fri, 2 Jul 1999 10:04:45 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Jul 1999 19:39:30 GMT",
"version": "v2"
},
{
"created": "Mon, 13 Sep 1999 10:38:27 GMT",
"version": "v3"
},
{
"created": "Sun, 16 Jan 2000 15:14:16 GMT",
"version": "v4"
}
] | 2009-10-31 | [
[
"Louko",
"Jorma",
""
],
[
"Rovelli",
"Carlo",
""
]
] | We investigate Refined Algebraic Quantization (RAQ) with group averaging in a constrained Hamiltonian system with unreduced phase space T^*R^4 and gauge group SL(2,R). The reduced phase space M is connected and contains four mutually disconnected `regular' sectors with topology R x S^1, but these sectors are connected to each other through an exceptional set where M is not a manifold and where M has non-Hausdorff topology. The RAQ physical Hilbert space H_{phys} decomposes as H_{phys} = (direct sum of) H_i, where the four subspaces H_i naturally correspond to the four regular sectors of M. The RAQ observable algebra A_{obs}, represented on H_{phys}, contains natural subalgebras represented on each H_i. The group averaging takes place in the oscillator representation of SL(2,R) on L^2(R^{2,2}), and ensuring convergence requires a subtle choice for the test state space: the classical analogue of this choice is to excise from M the exceptional set while nevertheless retaining information about the connections between the regular sectors. A quantum theory with the Hilbert space H_{phys} and a finitely-generated observable subalgebra of A_{obs} is recovered through both Ashtekar's Algebraic Quantization and Isham's group theoretic quantization. |
2311.01300 | Niels Warburton | LISA Consortium Waveform Working Group: Niayesh Afshordi, Sarp
Ak\c{c}ay, Pau Amaro Seoane, Andrea Antonelli, Josu C. Aurrekoetxea, Leor
Barack, Enrico Barausse, Robert Benkel, Laura Bernard, Sebastiano Bernuzzi,
Emanuele Berti, Matteo Bonetti, B\'eatrice Bonga, Gabriele Bozzola, Richard
Brito, Alessandra Buonanno, Alejandro C\'ardenas-Avenda\~no, Marc Casals,
David F. Chernoff, Alvin J. K. Chua, Katy Clough, Marta Colleoni, Mekhi
Dhesi, Adrien Druart, Leanne Durkan, Guillaume Faye, Deborah Ferguson, Scott
E. Field, William E. Gabella, Juan Garc\'ia-Bellido, Miguel Gracia-Linares,
Davide Gerosa, Stephen R. Green, Maria Haney, Mark Hannam, Anna Heffernan,
Tanja Hinderer, Thomas Helfer, Scott A. Hughes, Sascha Husa, Soichiro
Isoyama, Michael L. Katz, Chris Kavanagh, Gaurav Khanna, Larry E. Kidder,
Valeriya Korol, Lorenzo K\"uchler, Pablo Laguna, Fran\c{c}ois Larrouturou,
Alexandre Le Tiec, Benjamin Leather, Eugene A. Lim, Hyun Lim, Tyson B.
Littenberg, Oliver Long, Carlos O. Lousto, Geoffrey Lovelace, Georgios
Lukes-Gerakopoulos, Philip Lynch, Rodrigo P. Macedo, Charalampos Markakis,
Elisa Maggio, Ilya Mandel, Andrea Maselli, Josh Mathews, Pierre Mourier,
David Neilsen, Alessandro Nagar, David A. Nichols, Jan Nov\'ak, Maria
Okounkova, Richard O'Shaughnessy, Naritaka Oshita, Conor O'Toole, Zhen Pan,
Paolo Pani, George Pappas, Vasileios Paschalidis, Harald P. Pfeiffer, Lorenzo
Pompili, Adam Pound, Geraint Pratten, Hannes R. R\"uter, Milton Ruiz, Zeyd
Sam, Laura Sberna, Stuart L. Shapiro, Deirdre M. Shoemaker, Carlos F.
Sopuerta, Andrew Spiers, Hari Sundar, Nicola Tamanini, Jonathan E. Thompson,
Alexandre Toubiana, Antonios Tsokaros, Samuel D. Upton, Maarten van de Meent,
Daniele Vernieri, Jeremy M. Wachter, Niels Warburton, Barry Wardell, Helvi
Witek, Vojt\v{e}ch Witzany, Huan Yang, Miguel Zilh\~ao, Angelica Albertini,
K. G. Arun, Miguel Bezares, Alexander Bonilla, Christian Chapman-Bird,
Bradley Cownden, Kevin Cunningham, Chris Devitt, Sam Dolan, Francisco Duque,
Conor Dyson, Chris L. Fryer, Jonathan R. Gair, Bruno Giacomazzo, Priti Gupta,
Wen-Biao Han, Roland Haas, Eric W. Hirschmann, E. A. Huerta, Philippe Jetzer,
Bernard Kelly, Mohammed Khalil, Jack Lewis, Nicole Lloyd-Ronning, Sylvain
Marsat, Germano Nardini, Jakob Neef, Adrian Ottewill, Christiana Pantelidou,
Gabriel Andres Piovano, Jaime Redondo-Yuste, Laura Sagunski, Leo C. Stein,
Viktor Skoup\'y, Ulrich Sperhake, Lorenzo Speri, Thomas F.M. Spieksma, Chris
Stevens, David Trestini, Alex Va\~n\'o-Vi\~nuales | Waveform Modelling for the Laser Interferometer Space Antenna | 239 pages, 11 figures, white paper from the LISA Consortium Waveform
Working Group, invited for submission to Living Reviews in Relativity,
updated with comments from community | null | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | LISA, the Laser Interferometer Space Antenna, will usher in a new era in
gravitational-wave astronomy. As the first anticipated space-based
gravitational-wave detector, it will expand our view to the millihertz
gravitational-wave sky, where a spectacular variety of interesting new sources
abound: from millions of ultra-compact binaries in our Galaxy, to mergers of
massive black holes at cosmological distances; from the beginnings of inspirals
that will venture into the ground-based detectors' view to the death spiral of
compact objects into massive black holes, and many sources in between. Central
to realising LISA's discovery potential are waveform models, the theoretical
and phenomenological predictions of the pattern of gravitational waves that
these sources emit. This white paper is presented on behalf of the Waveform
Working Group for the LISA Consortium. It provides a review of the current
state of waveform models for LISA sources, and describes the significant
challenges that must yet be overcome.
| [
{
"created": "Thu, 2 Nov 2023 15:15:33 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Dec 2023 15:13:41 GMT",
"version": "v2"
}
] | 2023-12-21 | [
[
"LISA Consortium Waveform Working Group",
"",
""
],
[
"Afshordi",
"Niayesh",
""
],
[
"Akçay",
"Sarp",
""
],
[
"Seoane",
"Pau Amaro",
""
],
[
"Antonelli",
"Andrea",
""
],
[
"Aurrekoetxea",
"Josu C.",
""
],
[
"Barack... | LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome. |
1805.02854 | Abdulla Al Mamon | Abdulla Al Mamon, Kazuharu Bamba | Observational constraints on the jerk parameter with the data of the
Hubble parameter | 9 pages, 4 figures, 1 table, new references added, version accepted
for publication in the European Physical Journal C | null | null | FU-PCG-32 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the accelerated expansion phase of the universe by using the
{\textit{kinematic approach}}. In particular, the deceleration parameter $q$ is
parametrized in a model-independent way. Considering a generalized
parametrization for $q$, we first obtain the jerk parameter $j$ (a
dimensionless third time derivative of the scale factor) and then confront it
with cosmic observations. We use the latest observational dataset of the Hubble
parameter $H(z)$ consisting of 41 data points in the redshift range of $0.07
\leq z \leq 2.36$, larger than the redshift range that covered by the Type Ia
supernova. We also acquire the current values of the deceleration parameter
$q_0$, jerk parameter $j_0$ and transition redshift $z_t$ (at which the
expansion of the universe switches from being decelerated to accelerated) with
$1\sigma$ errors ($68.3\%$ confidence level). As a result, it is demonstrate
that the universe is indeed undergoing an accelerated expansion phase following
the decelerated one. This is consistent with the present observations.
Moreover, we find the departure for the present model from the standard
$\Lambda$CDM model according to the evolution of $j$. Furthermore, the
evolution of the normalized Hubble parameter is shown for the present model and
it is compared with the dataset of $H(z)$.
| [
{
"created": "Tue, 8 May 2018 06:31:36 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Oct 2018 17:48:27 GMT",
"version": "v2"
}
] | 2018-10-22 | [
[
"Mamon",
"Abdulla Al",
""
],
[
"Bamba",
"Kazuharu",
""
]
] | We study the accelerated expansion phase of the universe by using the {\textit{kinematic approach}}. In particular, the deceleration parameter $q$ is parametrized in a model-independent way. Considering a generalized parametrization for $q$, we first obtain the jerk parameter $j$ (a dimensionless third time derivative of the scale factor) and then confront it with cosmic observations. We use the latest observational dataset of the Hubble parameter $H(z)$ consisting of 41 data points in the redshift range of $0.07 \leq z \leq 2.36$, larger than the redshift range that covered by the Type Ia supernova. We also acquire the current values of the deceleration parameter $q_0$, jerk parameter $j_0$ and transition redshift $z_t$ (at which the expansion of the universe switches from being decelerated to accelerated) with $1\sigma$ errors ($68.3\%$ confidence level). As a result, it is demonstrate that the universe is indeed undergoing an accelerated expansion phase following the decelerated one. This is consistent with the present observations. Moreover, we find the departure for the present model from the standard $\Lambda$CDM model according to the evolution of $j$. Furthermore, the evolution of the normalized Hubble parameter is shown for the present model and it is compared with the dataset of $H(z)$. |
1312.5808 | Alberto Diez-Tejedor | Juan Barranco, Argelia Bernal, Juan Carlos Degollado, Alberto
Diez-Tejedor, Miguel Megevand, Miguel Alcubierre, Dario Nunez and Olivier
Sarbach | Schwarzschild scalar wigs: spectral analysis and late time behavior | 20 pages, 13 figures, 2 tables. Accepted for publication in Phys.
Rev. D | Phys. Rev. D 89, 083006 (2014) | 10.1103/PhysRevD.89.083006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using the Green's function representation technique, the late time behavior
of localized scalar field distributions on Schwarzschild spacetimes is studied.
Assuming arbitrary initial data we perform a spectral analysis, computing the
amplitude of each excited quasi-bound mode without the necessity of performing
dynamical evolutions. The resulting superposition of modes is compared with a
traditional numerical evolution with excellent agreement; therefore, we have an
efficient way to determine final black hole wigs. The astrophysical relevance
of the quasi-bound modes is discussed in the context of scalar field dark
matter models and the axiverse.
| [
{
"created": "Fri, 20 Dec 2013 04:02:23 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Apr 2014 19:14:44 GMT",
"version": "v2"
}
] | 2014-04-23 | [
[
"Barranco",
"Juan",
""
],
[
"Bernal",
"Argelia",
""
],
[
"Degollado",
"Juan Carlos",
""
],
[
"Diez-Tejedor",
"Alberto",
""
],
[
"Megevand",
"Miguel",
""
],
[
"Alcubierre",
"Miguel",
""
],
[
"Nunez",
"Dario",
... | Using the Green's function representation technique, the late time behavior of localized scalar field distributions on Schwarzschild spacetimes is studied. Assuming arbitrary initial data we perform a spectral analysis, computing the amplitude of each excited quasi-bound mode without the necessity of performing dynamical evolutions. The resulting superposition of modes is compared with a traditional numerical evolution with excellent agreement; therefore, we have an efficient way to determine final black hole wigs. The astrophysical relevance of the quasi-bound modes is discussed in the context of scalar field dark matter models and the axiverse. |
0812.2825 | Merced Montesinos | Merced Montesinos, Mercedes Velazquez | Husain-Kuchar model as a constrained BF theory | new version, 5 pages, no figures, LaTeX file | null | 10.1063/1.3284385 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Husain-Kuchar theory is a four-dimensional background-independent model
that has long been viewed as a useful model for addressing several conceptual
and technical problems appearing in the quantization of general relativity
mainly in the loop quantum gravity approach. The model was defined at
Lagrangian level in terms of a su(2)-valued connection one-form $A$ coupled
through its curvature to a su(2)-valued one-form field $e$. We address here the
problem of writing a Lagrangian formulation for the Husain-Kuchar model as a
constrained BF theory motivated by the fact that spin foam models for quantum
gravity are related to action principles of the BF type. The Lagrangian action
principle for the Husain-Kuchar model reported here differs from a previous one
found by Barbero et al in that this description involves a single constrained
BF theory rather than two interacting BF theories. It is, essentially, the
Plebanski action with the condition on the trace of the Lagrange multipliers
removed. Moreover, it can be stated that the relationship between our BF-like
action and the original one for the Husain-Kuchar model is the same
relationship that exists between the Plebanski action and the self-dual
Palatini action for complex general relativity, first because the solution to
the constraint on the two-forms $\Sigma^i$ coming from the BF-like action leads
to the Husain-Kuchar action, and second because the Hamiltonian analysis of the
Husain-Kuchar model is straightforward starting from the BF-like action
principle.
| [
{
"created": "Mon, 15 Dec 2008 14:57:40 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Apr 2009 19:12:04 GMT",
"version": "v2"
}
] | 2015-05-13 | [
[
"Montesinos",
"Merced",
""
],
[
"Velazquez",
"Mercedes",
""
]
] | The Husain-Kuchar theory is a four-dimensional background-independent model that has long been viewed as a useful model for addressing several conceptual and technical problems appearing in the quantization of general relativity mainly in the loop quantum gravity approach. The model was defined at Lagrangian level in terms of a su(2)-valued connection one-form $A$ coupled through its curvature to a su(2)-valued one-form field $e$. We address here the problem of writing a Lagrangian formulation for the Husain-Kuchar model as a constrained BF theory motivated by the fact that spin foam models for quantum gravity are related to action principles of the BF type. The Lagrangian action principle for the Husain-Kuchar model reported here differs from a previous one found by Barbero et al in that this description involves a single constrained BF theory rather than two interacting BF theories. It is, essentially, the Plebanski action with the condition on the trace of the Lagrange multipliers removed. Moreover, it can be stated that the relationship between our BF-like action and the original one for the Husain-Kuchar model is the same relationship that exists between the Plebanski action and the self-dual Palatini action for complex general relativity, first because the solution to the constraint on the two-forms $\Sigma^i$ coming from the BF-like action leads to the Husain-Kuchar action, and second because the Hamiltonian analysis of the Husain-Kuchar model is straightforward starting from the BF-like action principle. |
2401.14048 | Ethan James German Mr. | Ethan James German and Joseph Sultana | Turnaround Radius for charged particles in the Reissner-Nordstr\"{o}m
deSitter spacetime | 22 pages, 7 figures | null | 10.1007/s10714-024-03248-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the turnaround radius of the Reissner-Nordstr\"{o}m deSitter
Spacetime and how the turnaround radius changes if a test particle carries
charge. We also consider the Mart\'{i}nez-Troncoso-Zanelli (MTZ) solution of
conformally coupled gravity and investigate how the turnaround radius changes
for a scalar test charge. In both scalar and electric interaction cases we find
that the Turnaround Radius depends on the particle's energy.
| [
{
"created": "Thu, 25 Jan 2024 10:06:48 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Jan 2024 11:26:11 GMT",
"version": "v2"
}
] | 2024-05-22 | [
[
"German",
"Ethan James",
""
],
[
"Sultana",
"Joseph",
""
]
] | We investigate the turnaround radius of the Reissner-Nordstr\"{o}m deSitter Spacetime and how the turnaround radius changes if a test particle carries charge. We also consider the Mart\'{i}nez-Troncoso-Zanelli (MTZ) solution of conformally coupled gravity and investigate how the turnaround radius changes for a scalar test charge. In both scalar and electric interaction cases we find that the Turnaround Radius depends on the particle's energy. |
0711.2840 | Vladimir Dzhunushaliev | Vladimir Dzhunushaliev and Vladimir Folomeev | 4D static solutions with interacting phantom fields | final version | Int.J.Mod.Phys.D17:2125-2142,2008 | 10.1142/S0218271808013753 | null | gr-qc | null | Three static models with two interacting phantom and ghost scalar fields were
considered: a model of a traversable wormhole, a brane-like model and a
spherically symmetric problem. It was shown numerically that regular solutions
exist for all three cases.
| [
{
"created": "Mon, 19 Nov 2007 04:31:30 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Feb 2008 06:02:58 GMT",
"version": "v2"
}
] | 2009-02-11 | [
[
"Dzhunushaliev",
"Vladimir",
""
],
[
"Folomeev",
"Vladimir",
""
]
] | Three static models with two interacting phantom and ghost scalar fields were considered: a model of a traversable wormhole, a brane-like model and a spherically symmetric problem. It was shown numerically that regular solutions exist for all three cases. |
1604.08706 | Yun Soo Myung | Yun Soo Myung | Comment on Quantum Massive Conformal Gravity | 4 pages, no figures | null | 10.1140/epjc/s10052-016-4165-y | null | gr-qc hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | In a recent paper in EPJC March 2016, Faria has shown that quantum massive
conformal gravity is renormalizable but has ghost states. We comment this paper
on the aspect of renormalizability.
| [
{
"created": "Fri, 29 Apr 2016 07:02:09 GMT",
"version": "v1"
}
] | 2016-07-20 | [
[
"Myung",
"Yun Soo",
""
]
] | In a recent paper in EPJC March 2016, Faria has shown that quantum massive conformal gravity is renormalizable but has ghost states. We comment this paper on the aspect of renormalizability. |
2104.00521 | Enrique Gaztanaga | Enrique Gaztanaga and Pablo Fosalba | A peek outside our Universe | 3 pages. Essay written for the Gravity Research Foundation 2021
Awards for Essays on Gravitation | Symmetry 2022, 14, 285 | 10.3390/sym14020285 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | According to general relativity (GR), a universe with a cosmological constant
$\Lambda$, like ours, is trapped inside an event horizon, $r<
\sqrt{3/\Lambda}$. What is outside? We show, using Israel (1967) junction
conditions, that there could be a different universe outside. Our universe
looks like a black hole for an outside observer. Outgoing radial null geodesics
cannot escape our universe, but incoming photons can enter and leave an imprint
on our CMB sky. We present a picture of such a fossil record from the analysis
of CMB maps that agrees with the black hole universe predictions but challenges
our understanding of the origin of the primordial universe.
| [
{
"created": "Wed, 31 Mar 2021 10:54:01 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Feb 2022 18:42:39 GMT",
"version": "v2"
}
] | 2022-02-03 | [
[
"Gaztanaga",
"Enrique",
""
],
[
"Fosalba",
"Pablo",
""
]
] | According to general relativity (GR), a universe with a cosmological constant $\Lambda$, like ours, is trapped inside an event horizon, $r< \sqrt{3/\Lambda}$. What is outside? We show, using Israel (1967) junction conditions, that there could be a different universe outside. Our universe looks like a black hole for an outside observer. Outgoing radial null geodesics cannot escape our universe, but incoming photons can enter and leave an imprint on our CMB sky. We present a picture of such a fossil record from the analysis of CMB maps that agrees with the black hole universe predictions but challenges our understanding of the origin of the primordial universe. |
gr-qc/0307088 | Kayll Lake | Piotr T. Chru\'sciel and Kayll Lake | Cauchy horizons in Gowdy space times | 25 pages Latex. Further information at http://grtensor.org/gowdy/ | Class.Quant.Grav. 21 (2004) S153-S170 | 10.1088/0264-9381/21/3/010 | null | gr-qc | null | We analyse exhaustively the structure of \emph{non-degenerate} Cauchy
horizons in Gowdy space-times, and we establish existence of a large class of
non-polarized Gowdy space-times with such horizons.
Added in proof: Our results here, together with deep new results of H.
Ringstr\"om (talk at the Miami Waves conference, January 2004), establish
strong cosmic censorship in (toroidal) Gowdy space-times.
| [
{
"created": "Fri, 18 Jul 2003 19:18:55 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jan 2004 20:21:58 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Chruściel",
"Piotr T.",
""
],
[
"Lake",
"Kayll",
""
]
] | We analyse exhaustively the structure of \emph{non-degenerate} Cauchy horizons in Gowdy space-times, and we establish existence of a large class of non-polarized Gowdy space-times with such horizons. Added in proof: Our results here, together with deep new results of H. Ringstr\"om (talk at the Miami Waves conference, January 2004), establish strong cosmic censorship in (toroidal) Gowdy space-times. |
gr-qc/9809037 | Thomas P. Kling | Thomas P. Kling and Ezra T. Newman | Null Cones in Schwarzschild Geometry | 31 pages, 5 figures | Phys.Rev. D59 (1999) 124002 | 10.1103/PhysRevD.59.124002 | null | gr-qc | null | Light cones of Schwarzschild geometry are studied in connection to the Null
Surface Formulation and gravitational lensing. The paper studies the light cone
cut function's singularity structure, gives exact gravitational lensing
equations, and shows that the "pseudo-Minkowski" coordinates are well defined
within the model considered.
| [
{
"created": "Wed, 9 Sep 1998 18:31:23 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Kling",
"Thomas P.",
""
],
[
"Newman",
"Ezra T.",
""
]
] | Light cones of Schwarzschild geometry are studied in connection to the Null Surface Formulation and gravitational lensing. The paper studies the light cone cut function's singularity structure, gives exact gravitational lensing equations, and shows that the "pseudo-Minkowski" coordinates are well defined within the model considered. |
gr-qc/0502073 | Ernesto F. Eiroa | Ernesto F. Eiroa, Claudio Simeone | Thin-shell wormholes in dilaton gravity | 7 pages, 1 figure; v2: shortened and improved. Accepted for
publication in Physical Review D | Phys.Rev. D71 (2005) 127501 | 10.1103/PhysRevD.71.127501 | null | gr-qc hep-th | null | In this work we construct charged thin-shell Lorentzian wormholes in dilaton
gravity. The exotic matter required for the construction is localized in the
shell and the energy conditions are satisfied outside the shell. The total
amount of exotic matter is calculated and its dependence with the parameters of
the model is analysed.
| [
{
"created": "Tue, 15 Feb 2005 16:15:36 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Jun 2005 17:33:34 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Eiroa",
"Ernesto F.",
""
],
[
"Simeone",
"Claudio",
""
]
] | In this work we construct charged thin-shell Lorentzian wormholes in dilaton gravity. The exotic matter required for the construction is localized in the shell and the energy conditions are satisfied outside the shell. The total amount of exotic matter is calculated and its dependence with the parameters of the model is analysed. |
1710.05968 | Nandan Roy | Nandan Roy and Nivedita Bhadra | Dynamical systems analysis of phantom models | 11 pages, 24 figures | null | 10.1088/1475-7516/2018/06/002 | null | gr-qc math.DS | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we study the dynamical systems analysis of phantom dark energy
models considering a general potential. The stability analysis of the system
shows that there is only one fixed point which could be the beginning of the
universe but there could be many options for our future destiny. A detail
numerical analysis of the system is also done using three different schemes and
it shows that the late time behavior of the system is consistent with the
recent observations.
| [
{
"created": "Mon, 16 Oct 2017 19:38:47 GMT",
"version": "v1"
},
{
"created": "Sat, 10 Mar 2018 03:18:30 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Mar 2018 03:03:15 GMT",
"version": "v3"
}
] | 2018-06-13 | [
[
"Roy",
"Nandan",
""
],
[
"Bhadra",
"Nivedita",
""
]
] | In this work, we study the dynamical systems analysis of phantom dark energy models considering a general potential. The stability analysis of the system shows that there is only one fixed point which could be the beginning of the universe but there could be many options for our future destiny. A detail numerical analysis of the system is also done using three different schemes and it shows that the late time behavior of the system is consistent with the recent observations. |
2308.07862 | Kavya N S | V. Venkatesha, Chaitra Chooda Chalavadi, N. S. Kavya, P. K. Sahoo | Wormhole Geometry and Three-Dimensional Embedding in Extended Symmetric
Teleparallel Gravity | New Astronomy published version | New Astronomy, 105 (2024) 102090 | 10.1016/j.newast.2023.102090 | null | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-nd/4.0/ | In the present manuscript, we study traversable wormhole solutions in the
background of extended symmetric teleparallel gravity with matter coupling.
With the anisotropic matter distribution we probe the wormhole geometry for two
different gravity models. Primarily, we consider the linear model $ f(Q,T) =Q +
2 \, \xi \,T$. Firstly, we presume a logarithmic form of shape function and
analyze the scenario for different redshift functions. Secondly, for a specific
form of energy density, we derive a shape function and note its satisfying
behavior. Next, for the non-linear model $f(Q,T) = Q + \alpha ,Q^2 + \beta ,T$
and a specific shape function we examine the wormhole solution. Further, with
the aid of embedding diagrams, we interpreted the geometry of wormhole models.
Finally, we conclude results.
| [
{
"created": "Tue, 25 Jul 2023 05:32:44 GMT",
"version": "v1"
}
] | 2023-08-16 | [
[
"Venkatesha",
"V.",
""
],
[
"Chalavadi",
"Chaitra Chooda",
""
],
[
"Kavya",
"N. S.",
""
],
[
"Sahoo",
"P. K.",
""
]
] | In the present manuscript, we study traversable wormhole solutions in the background of extended symmetric teleparallel gravity with matter coupling. With the anisotropic matter distribution we probe the wormhole geometry for two different gravity models. Primarily, we consider the linear model $ f(Q,T) =Q + 2 \, \xi \,T$. Firstly, we presume a logarithmic form of shape function and analyze the scenario for different redshift functions. Secondly, for a specific form of energy density, we derive a shape function and note its satisfying behavior. Next, for the non-linear model $f(Q,T) = Q + \alpha ,Q^2 + \beta ,T$ and a specific shape function we examine the wormhole solution. Further, with the aid of embedding diagrams, we interpreted the geometry of wormhole models. Finally, we conclude results. |
gr-qc/0510126 | James B. Hartle | James B. Hartle | Generalizing Quantum Mechanics for Quantum Gravity | 8 pages, LATEX, a very brief abstract of much work | Int.J.Theor.Phys. 45 (2006) 1390-1396 | 10.1007/s10773-006-9134-z | null | gr-qc hep-th quant-ph | null | `How do our ideas about quantum mechanics affect our understanding of
spacetime?' This familiar question leads to quantum gravity. The complementary
question is also important: `How do our ideas about spacetime affect our
understanding of quantum mechanics?' This short abstract of a talk given at the
Gafka2004 conference contains a very brief summary of some of the author's
papers on generalizations of quantum mechanics needed for quantum gravity. The
need for generalization is motivated. The generalized quantum theory framework
for such generalizations is described and illustrated for usual quantum
mechanics and a number of examples to which it does not apply. These include
spacetime alternatives extended over time, time-neutral quantum theory, quantum
field theory in fixed background spacetime not foliable by spacelike surfaces,
and systems with histories that move both forward and backward in time. A fully
four-dimensional, sum-over-histories generalized quantum theory of cosmological
geometries is briefly described. The usual formulation of quantum theory in
terms of states evolving unitarily through spacelike surfaces is an
approximation to this more general framework that is appropriate in the late
universe for coarse-grained descriptions of geometry in which spacetime behaves
classically. This abstract is unlikely to be clear on its own, but references
are provided to the author's works where the ideas can be followed up.
| [
{
"created": "Sun, 30 Oct 2005 18:38:58 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Hartle",
"James B.",
""
]
] | `How do our ideas about quantum mechanics affect our understanding of spacetime?' This familiar question leads to quantum gravity. The complementary question is also important: `How do our ideas about spacetime affect our understanding of quantum mechanics?' This short abstract of a talk given at the Gafka2004 conference contains a very brief summary of some of the author's papers on generalizations of quantum mechanics needed for quantum gravity. The need for generalization is motivated. The generalized quantum theory framework for such generalizations is described and illustrated for usual quantum mechanics and a number of examples to which it does not apply. These include spacetime alternatives extended over time, time-neutral quantum theory, quantum field theory in fixed background spacetime not foliable by spacelike surfaces, and systems with histories that move both forward and backward in time. A fully four-dimensional, sum-over-histories generalized quantum theory of cosmological geometries is briefly described. The usual formulation of quantum theory in terms of states evolving unitarily through spacelike surfaces is an approximation to this more general framework that is appropriate in the late universe for coarse-grained descriptions of geometry in which spacetime behaves classically. This abstract is unlikely to be clear on its own, but references are provided to the author's works where the ideas can be followed up. |
2106.12513 | David Prinz | David Prinz and Alexander Schmeding | Lie Theory for Asymptotic Symmetries in General Relativity: The BMS
Group | 29 pages, article; minor revisions; version to appear in Classical
and Quantum Gravity | Class. Quantum Grav. 39 (2022) 065004 | 10.1088/1361-6382/ac4ae2 | null | gr-qc math-ph math.GR math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the Lie group structure of asymptotic symmetry groups in General
Relativity from the viewpoint of infinite-dimensional geometry. To this end, we
review the geometric definition of asymptotic simplicity and emptiness due to
Penrose and the coordinate-wise definition of asymptotic flatness due to Bondi
et al. Then we construct the Lie group structure of the Bondi--Metzner--Sachs
(BMS) group and discuss its Lie theoretic properties. We find that the BMS
group is regular in the sense of Milnor, but not real analytic. This motivates
us to conjecture that it is not locally exponential. Finally, we verify the
Trotter property as well as the commutator property. As an outlook, we comment
on the situation of related asymptotic symmetry groups. In particular, the much
more involved situation of the Newman--Unti group is highlighted, which will be
studied in future work.
| [
{
"created": "Wed, 23 Jun 2021 16:30:00 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Jan 2022 17:30:00 GMT",
"version": "v2"
}
] | 2022-03-01 | [
[
"Prinz",
"David",
""
],
[
"Schmeding",
"Alexander",
""
]
] | We study the Lie group structure of asymptotic symmetry groups in General Relativity from the viewpoint of infinite-dimensional geometry. To this end, we review the geometric definition of asymptotic simplicity and emptiness due to Penrose and the coordinate-wise definition of asymptotic flatness due to Bondi et al. Then we construct the Lie group structure of the Bondi--Metzner--Sachs (BMS) group and discuss its Lie theoretic properties. We find that the BMS group is regular in the sense of Milnor, but not real analytic. This motivates us to conjecture that it is not locally exponential. Finally, we verify the Trotter property as well as the commutator property. As an outlook, we comment on the situation of related asymptotic symmetry groups. In particular, the much more involved situation of the Newman--Unti group is highlighted, which will be studied in future work. |
2309.10903 | Antonio Enea Romano | Antonio Enea Romano, Mairi Sakellariadou | Constraining the time evolution of the propagation speed of
gravitational waves with multimessenger astronomy | null | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | Several modified gravity theories predict a possible time variation of the
propagation speed of gravitational waves (GW) which could be tested with
multimessenger astronomy. For this purpose we derive the relation between the
redshift dependence of the propagation speed of GWs and the time delay between
the detection of GWs and electromagnetic waves (EMWs) emitted by the same
source. For theories with Einstein frame minimal matter-gravity coupling (EMC)
the propagation speed of GWs can be jointly constrained by the time delay
between GWs and EWs and the GW-EMW luminosity distance ratio, allowing to
derive a consistency relation between these two observables. The event GW
170817 and its EM counterpart satisfy the consistency condition, confirming the
EMC, and allow to set strong constraints on the time variation of the GWs
speed.
| [
{
"created": "Tue, 19 Sep 2023 19:57:10 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Dec 2023 23:58:43 GMT",
"version": "v2"
}
] | 2023-12-08 | [
[
"Romano",
"Antonio Enea",
""
],
[
"Sakellariadou",
"Mairi",
""
]
] | Several modified gravity theories predict a possible time variation of the propagation speed of gravitational waves (GW) which could be tested with multimessenger astronomy. For this purpose we derive the relation between the redshift dependence of the propagation speed of GWs and the time delay between the detection of GWs and electromagnetic waves (EMWs) emitted by the same source. For theories with Einstein frame minimal matter-gravity coupling (EMC) the propagation speed of GWs can be jointly constrained by the time delay between GWs and EWs and the GW-EMW luminosity distance ratio, allowing to derive a consistency relation between these two observables. The event GW 170817 and its EM counterpart satisfy the consistency condition, confirming the EMC, and allow to set strong constraints on the time variation of the GWs speed. |
1911.04487 | Emil M. Prodanov | Rossen I. Ivanov and Emil M. Prodanov | Integrable Cosmological Model with van der Waals Gas and Matter Creation | 25 pages, 21 figures, 1 table | Physical Review D 99, 063501 (2019) | 10.1103/PhysRevD.99.063501 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A cosmological model with van der Waals gas and dust has been studied in the
context of a three-component autonomous non-linear dynamical system involving
the time evolution of the particle number density, the Hubble parameter and the
temperature. Due to the presence of a symmetry of the model, the temperature
evolution law is determined (in terms of the particle number density) and with
this the dynamical system reduces to a two-component one which is fully
integrable. The globally conserved Hamiltonian is identified and, in addition
to it, some special (second) integrals, defined and conserved on a
lower-dimensional manifold, are found. The parameter choices and their
implication for the global dynamics in terms of cosmological relevance are
comprehensively studied and the physically meaningful parameter values are
identified.
| [
{
"created": "Mon, 11 Nov 2019 16:06:10 GMT",
"version": "v1"
}
] | 2019-11-13 | [
[
"Ivanov",
"Rossen I.",
""
],
[
"Prodanov",
"Emil M.",
""
]
] | A cosmological model with van der Waals gas and dust has been studied in the context of a three-component autonomous non-linear dynamical system involving the time evolution of the particle number density, the Hubble parameter and the temperature. Due to the presence of a symmetry of the model, the temperature evolution law is determined (in terms of the particle number density) and with this the dynamical system reduces to a two-component one which is fully integrable. The globally conserved Hamiltonian is identified and, in addition to it, some special (second) integrals, defined and conserved on a lower-dimensional manifold, are found. The parameter choices and their implication for the global dynamics in terms of cosmological relevance are comprehensively studied and the physically meaningful parameter values are identified. |
gr-qc/9509014 | Rafael Vera Mege | Rafael A. Vera | Unified Relativistic Physics from a Standing Wave Particle Model | 17 pages, latex.To appear (5 pages) in Proc.of the 6th Canadian Conf.
on Gen. Rel and Rel. Astroph, with paralel work on the new astrophys. context | null | null | DFUDEC-95-RV9 | gr-qc astro-ph quant-ph | null | An extremely simple and unified base for physics comes out by starting all
over from a single postulate on the common nature of matter and stationary
forms of radiation quanta. Basic relativistic, gravitational (G) and quantum
mechanical properties of a standing wave particle model have been derived. This
has been done from just dual properties of radiation's and strictly homogeneous
relationships for nonlocal cases in G fields. This way reduces the number of
independent variables and puts into relief (and avoid) important inhomogeneity
errors of some G theories. It unifies and accounts for basic principles and
postulates physics. The results for gravity depend on linear radiation
properties but not on arbitrary field relations. They agree with the
conventional tests. However they have some fundamental differences with current
G theories. The particle model, at a difference of the conventional theories,
also fixes well-defined cosmological and astrophysical models that are
different from the rather conventional ones. They have been described and
tested with the astronomical observations. These tests have been resumed in a
separated work to be sent to the astro Archive.
| [
{
"created": "Thu, 7 Sep 1995 16:38:23 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Vera",
"Rafael A.",
""
]
] | An extremely simple and unified base for physics comes out by starting all over from a single postulate on the common nature of matter and stationary forms of radiation quanta. Basic relativistic, gravitational (G) and quantum mechanical properties of a standing wave particle model have been derived. This has been done from just dual properties of radiation's and strictly homogeneous relationships for nonlocal cases in G fields. This way reduces the number of independent variables and puts into relief (and avoid) important inhomogeneity errors of some G theories. It unifies and accounts for basic principles and postulates physics. The results for gravity depend on linear radiation properties but not on arbitrary field relations. They agree with the conventional tests. However they have some fundamental differences with current G theories. The particle model, at a difference of the conventional theories, also fixes well-defined cosmological and astrophysical models that are different from the rather conventional ones. They have been described and tested with the astronomical observations. These tests have been resumed in a separated work to be sent to the astro Archive. |
2109.00357 | Viktor T. Toth | Viktor T. Toth | Gravitoelectromagnetism and stellar orbits in galaxies | 5 pages, no figures (accepted for publication in Int. J. Mod. Phys.
D) | null | 10.1142/S0218271821501029 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Beyond the Newtonian approximation, gravitational fields in general
relativity can be described using a formalism known as gravitoelectromagnetism.
In this formalism a vector potential, the gravitomagnetic potential, arises as
a result of moving masses, in strong analogy with the magnetic force due to
moving charges in Maxwell's theory. Gravitomagnetism can affect orbits in the
gravitational field of a massive, rotating body. This raises the possibility
that gravitomagnetism may serve as the dominant physics behind the anomalous
rotation curves of spiral galaxies, eliminating the need for dark matter. In
this essay, we methodically work out the magnitude of the gravitomagnetic
equivalent of the Lorentz force and apply the result to the Milky Way. We find
that the resulting contribution is too small to produce an observable effect on
these orbits. We also investigate the impact of cosmological boundary
conditions on the result and find that these, too, are negligible.
| [
{
"created": "Tue, 31 Aug 2021 01:21:09 GMT",
"version": "v1"
}
] | 2021-09-02 | [
[
"Toth",
"Viktor T.",
""
]
] | Beyond the Newtonian approximation, gravitational fields in general relativity can be described using a formalism known as gravitoelectromagnetism. In this formalism a vector potential, the gravitomagnetic potential, arises as a result of moving masses, in strong analogy with the magnetic force due to moving charges in Maxwell's theory. Gravitomagnetism can affect orbits in the gravitational field of a massive, rotating body. This raises the possibility that gravitomagnetism may serve as the dominant physics behind the anomalous rotation curves of spiral galaxies, eliminating the need for dark matter. In this essay, we methodically work out the magnitude of the gravitomagnetic equivalent of the Lorentz force and apply the result to the Milky Way. We find that the resulting contribution is too small to produce an observable effect on these orbits. We also investigate the impact of cosmological boundary conditions on the result and find that these, too, are negligible. |
1105.5653 | Neelima Kelkar Dr | D. Batic, N. G. Kelkar, M. Nowakowski | Comment on "Quasinormal modes in Schwarzschild-de Sitter spacetime: A
simple derivation of the level spacing of the frequencies" | null | Phys.Rev.D83:108501,2011 | 10.1103/PhysRevD.83.108501 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown here that the extraction of quasinormal modes (QNMs) within the
first Born approximation of the scattering amplitude is mathematically not well
founded. Indeed, the constraints on the existence of the scattering amplitude
integral lead to inequalities for the imaginary parts of the QNM frequencies.
For instance, in the Schwarzschild case, $0 \leq \omega_I < \kappa$ (where
$\kappa$ is the surface gravity at the horizon) invalidates the poles deduced
from the first Born approximation method, namely, $\omega_n = i n \kappa$.
| [
{
"created": "Fri, 27 May 2011 20:14:16 GMT",
"version": "v1"
}
] | 2011-06-06 | [
[
"Batic",
"D.",
""
],
[
"Kelkar",
"N. G.",
""
],
[
"Nowakowski",
"M.",
""
]
] | It is shown here that the extraction of quasinormal modes (QNMs) within the first Born approximation of the scattering amplitude is mathematically not well founded. Indeed, the constraints on the existence of the scattering amplitude integral lead to inequalities for the imaginary parts of the QNM frequencies. For instance, in the Schwarzschild case, $0 \leq \omega_I < \kappa$ (where $\kappa$ is the surface gravity at the horizon) invalidates the poles deduced from the first Born approximation method, namely, $\omega_n = i n \kappa$. |
2303.06563 | Ohkyung Kwon | Craig Hogan, Ohkyung Kwon, and Nathaniel Selub | Angular spectrum of quantum fluctuations in causal structure | 5 pages, 2 figures. PRD accepted version | Phys. Rev. D 109, 123505 (2024) | 10.1103/PhysRevD.109.123505 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Scaling arguments are used to constrain the angular spectrum of distortions
on boundaries of macroscopic causal diamonds, produced by Planck-scale vacuum
fluctuations of causally-coherent quantum gravity. The small-angle spectrum of
displacement is derived from a form of scale invariance: the variance and
fluctuation rate of distortions normal to the surface of a causal diamond of
radius $R$ at transverse physical separation $c\tau\ll R$ should depend only on
$\tau$, with a normalization set by the Planck time $t_P$, and should not
depend on $R$. For measurements on scale $R$, the principle leads to universal
scaling for variance on angular scale $\Theta$,
$\langle\delta\tau^2\rangle_\Theta\simeq\tau\:\!t_p\sim\Theta R\:\!t_P/c$, and
angular power spectrum $C_\ell\sim (R\:\!l_P)/\ell^3$ at $\ell\gg1$. This
spectrum is consistent with a relational model of holographic noise based on
causally coherent virtual null gravitational shocks, a general picture
conjectured for all $\ell$. The high $\ell$ scaling is contrasted with that
predicted in some other quantum models, which differ by one power of angular
wavenumber $\ell$ and are shown to predict excessive blurring of images from
distant sources.
| [
{
"created": "Sun, 12 Mar 2023 04:05:41 GMT",
"version": "v1"
},
{
"created": "Sun, 12 May 2024 22:00:05 GMT",
"version": "v2"
}
] | 2024-07-02 | [
[
"Hogan",
"Craig",
""
],
[
"Kwon",
"Ohkyung",
""
],
[
"Selub",
"Nathaniel",
""
]
] | Scaling arguments are used to constrain the angular spectrum of distortions on boundaries of macroscopic causal diamonds, produced by Planck-scale vacuum fluctuations of causally-coherent quantum gravity. The small-angle spectrum of displacement is derived from a form of scale invariance: the variance and fluctuation rate of distortions normal to the surface of a causal diamond of radius $R$ at transverse physical separation $c\tau\ll R$ should depend only on $\tau$, with a normalization set by the Planck time $t_P$, and should not depend on $R$. For measurements on scale $R$, the principle leads to universal scaling for variance on angular scale $\Theta$, $\langle\delta\tau^2\rangle_\Theta\simeq\tau\:\!t_p\sim\Theta R\:\!t_P/c$, and angular power spectrum $C_\ell\sim (R\:\!l_P)/\ell^3$ at $\ell\gg1$. This spectrum is consistent with a relational model of holographic noise based on causally coherent virtual null gravitational shocks, a general picture conjectured for all $\ell$. The high $\ell$ scaling is contrasted with that predicted in some other quantum models, which differ by one power of angular wavenumber $\ell$ and are shown to predict excessive blurring of images from distant sources. |
2310.04514 | Misbah Shahzadi | Misbah Shahzadi, Martin Kolos, Rabia Saleem, Yousaf Habib, Adrian
Eduarte-Rojas | Structure-preserving numerical simulations of test particle dynamics
around slowly rotating neutron stars within Hartle-Thorne approach | 21 pages, 12 figures | Physical Review D, 108, 103006 (2023) | 10.1103/PhysRevD.108.103006 | null | gr-qc astro-ph.HE nlin.CD | http://creativecommons.org/licenses/by/4.0/ | In this paper, we explore the chaotic signatures of the geodesic dynamics for
particles moving in the slowly rotating Hartle-Thorne spacetime; an approximate
solution of vacuum Einstein field equations describing the exterior of a
massive, deformed, and slowly rotating compact object. We employ the numerical
study to examine the geodesics of prolate and oblate deformations for generic
orbits and find the plateaus of the rotation curve, which are associated with
the existence of Birkhoff islands in the Poincare surface of the section, where
the ratio of the radial and polar frequency of geodesics remains constant
throughout the island. We investigate various phase space structures, including
hyperbolic points and chaotic regions in the neighborhood of resonant islands.
Moreover, chaotic behavior is observed to be governed by the stickiness
phenomenon, where chaotic orbits remain attached to stable ones for an extended
duration before eventually diverging and are attracted toward the surface of
the neutron star. The precision of the numerical integration used to simulate
the particle's trajectories plays a crucial role in the structures of the
Poincare surface of the section. We present a comparison of several efficient
structure-preserving numerical schemes of order four applied to the considered
non-integrable dynamical system and we investigate which schemes possess the
canonical property of the Hamiltonian flow. Among the class of non-symplectic
integrators, we employ the explicit Runge-Kutta method and explicit general
linear method with a standard projection technique to project the numerical
solution onto the desired manifold. The projection scheme admits the
integration without any drift from the desired manifold and is computationally
cost-effective. We are concerned with two crucial aspects -- long-term
behaviour and CPU time consumption.
| [
{
"created": "Fri, 6 Oct 2023 18:15:51 GMT",
"version": "v1"
}
] | 2024-03-19 | [
[
"Shahzadi",
"Misbah",
""
],
[
"Kolos",
"Martin",
""
],
[
"Saleem",
"Rabia",
""
],
[
"Habib",
"Yousaf",
""
],
[
"Eduarte-Rojas",
"Adrian",
""
]
] | In this paper, we explore the chaotic signatures of the geodesic dynamics for particles moving in the slowly rotating Hartle-Thorne spacetime; an approximate solution of vacuum Einstein field equations describing the exterior of a massive, deformed, and slowly rotating compact object. We employ the numerical study to examine the geodesics of prolate and oblate deformations for generic orbits and find the plateaus of the rotation curve, which are associated with the existence of Birkhoff islands in the Poincare surface of the section, where the ratio of the radial and polar frequency of geodesics remains constant throughout the island. We investigate various phase space structures, including hyperbolic points and chaotic regions in the neighborhood of resonant islands. Moreover, chaotic behavior is observed to be governed by the stickiness phenomenon, where chaotic orbits remain attached to stable ones for an extended duration before eventually diverging and are attracted toward the surface of the neutron star. The precision of the numerical integration used to simulate the particle's trajectories plays a crucial role in the structures of the Poincare surface of the section. We present a comparison of several efficient structure-preserving numerical schemes of order four applied to the considered non-integrable dynamical system and we investigate which schemes possess the canonical property of the Hamiltonian flow. Among the class of non-symplectic integrators, we employ the explicit Runge-Kutta method and explicit general linear method with a standard projection technique to project the numerical solution onto the desired manifold. The projection scheme admits the integration without any drift from the desired manifold and is computationally cost-effective. We are concerned with two crucial aspects -- long-term behaviour and CPU time consumption. |
gr-qc/9604014 | Int. Lab. HTSC and Sse | Sergiu I. Vacaru | Stochastic Processes and Diffusion on Spaces with Local Anisotropy | 45 pages, Revtex, submitted to the Journal of Theoretical Probability | G. Tsagas (ed.) "Global Analysis, Differential Geometry and Lie
Algebras" (Geometry Balkan Press, Thessaloniki, Bucharest, 1997), pp. 123-140 | null | null | gr-qc dg-ga math.DG | null | The purpose of this work is to extend the formalism of stochastic calculus to
the case of spaces with local anisotropy (modeled as vector bundles with
compatible nonlinear and distinguished connections and metric structures and
containing as particular cases different variants of Kaluza--Klein and
generalized Lagrange and Finsler spaces). We shall examine nondegenerate
diffusions on the mentioned spaces and theirs horizontal lifts.
| [
{
"created": "Fri, 5 Apr 1996 14:27:24 GMT",
"version": "v1"
}
] | 2008-02-03 | [
[
"Vacaru",
"Sergiu I.",
""
]
] | The purpose of this work is to extend the formalism of stochastic calculus to the case of spaces with local anisotropy (modeled as vector bundles with compatible nonlinear and distinguished connections and metric structures and containing as particular cases different variants of Kaluza--Klein and generalized Lagrange and Finsler spaces). We shall examine nondegenerate diffusions on the mentioned spaces and theirs horizontal lifts. |
2008.00509 | Geraint Pratten | Geraint Pratten, Alberto Vecchio | Assessing gravitational-wave binary black hole candidates with Bayesian
odds | 23 pages, 11 figures, comments and feedback welcome! | null | 10.1103/PhysRevD.104.124039 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves from the coalescence of binary black holes can be
distinguished from noise transients in a detector network through Bayesian
model selection by exploiting the coherence of the signal across the network.
We present a Bayesian framework for calculating the posterior probability that
a signal is of astrophysical origin, agnostic to the specific search strategy,
pipeline or search domain with which a candidate is identified. We apply this
framework under \textit{identical} assumptions to all events reported in the
LIGO-Virgo GWTC-1 catalog, GW190412 and numerous event candidates reported by
independent search pipelines by other authors. With the exception of GW170818,
we find that all GWTC-1 candidates, and GW190412, have odds overwhelmingly in
favour of the astrophysical hypothesis, including GW170729, which was assigned
significantly different astrophysical probabilities by the different search
pipelines used in GWTC-1. GW170818 is de-facto a single detector trigger, and
is therefore of no surprise that it is disfavoured as being produced by an
astrophysical source in our framework. We find \textit{three} additional event
candidates, GW170121, GW170425 and GW170727, that have significant support for
the astrophysical hypothesis, with a probability that the signal is of
astrophysical origin of 0.53, 0.74 and 0.64 respectively. We carry out a
hierarchical population study which includes these three events in addition to
those reported in GWTC-1, finding that the main astrophysical results are
unaffected.
| [
{
"created": "Sun, 2 Aug 2020 16:10:18 GMT",
"version": "v1"
}
] | 2022-01-05 | [
[
"Pratten",
"Geraint",
""
],
[
"Vecchio",
"Alberto",
""
]
] | Gravitational waves from the coalescence of binary black holes can be distinguished from noise transients in a detector network through Bayesian model selection by exploiting the coherence of the signal across the network. We present a Bayesian framework for calculating the posterior probability that a signal is of astrophysical origin, agnostic to the specific search strategy, pipeline or search domain with which a candidate is identified. We apply this framework under \textit{identical} assumptions to all events reported in the LIGO-Virgo GWTC-1 catalog, GW190412 and numerous event candidates reported by independent search pipelines by other authors. With the exception of GW170818, we find that all GWTC-1 candidates, and GW190412, have odds overwhelmingly in favour of the astrophysical hypothesis, including GW170729, which was assigned significantly different astrophysical probabilities by the different search pipelines used in GWTC-1. GW170818 is de-facto a single detector trigger, and is therefore of no surprise that it is disfavoured as being produced by an astrophysical source in our framework. We find \textit{three} additional event candidates, GW170121, GW170425 and GW170727, that have significant support for the astrophysical hypothesis, with a probability that the signal is of astrophysical origin of 0.53, 0.74 and 0.64 respectively. We carry out a hierarchical population study which includes these three events in addition to those reported in GWTC-1, finding that the main astrophysical results are unaffected. |
gr-qc/0005037 | Hiroshi Umetsu | Hiroshi Umetsu | A Conserved Energy Integral for Perturbation Equations in the Kerr-de
Sitter Geometry | 13 pages, LaTeX | Prog.Theor.Phys. 104 (2000) 743-755 | 10.1143/PTP.104.743 | EPHOU 00-004 | gr-qc | null | The analytic proof of mode stability of the Kerr black hole was provided by
Whiting. In his proof, the construction of a conserved quantity for unstable
mode was crucial. We extend the method of the analysis for the Kerr-de Sitter
geometry. The perturbation equations of massless fields in the Kerr-de Sitter
geometry can be transformed into Heun's equations which have four regular
singularities. In this paper we investigate differential and integral
transformations of solutions of the equations. Using those we construct a
conserved quantity for unstable modes in the Kerr-de Sitter geometry, and
discuss its property.
| [
{
"created": "Thu, 11 May 2000 05:46:46 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Umetsu",
"Hiroshi",
""
]
] | The analytic proof of mode stability of the Kerr black hole was provided by Whiting. In his proof, the construction of a conserved quantity for unstable mode was crucial. We extend the method of the analysis for the Kerr-de Sitter geometry. The perturbation equations of massless fields in the Kerr-de Sitter geometry can be transformed into Heun's equations which have four regular singularities. In this paper we investigate differential and integral transformations of solutions of the equations. Using those we construct a conserved quantity for unstable modes in the Kerr-de Sitter geometry, and discuss its property. |
1905.02414 | Jian-Yang Zhu | Yang-yang Wang, Xiao-Min Zhang and Jian-Yang Zhu | Observational Constraints on Two-field Warm Inflation | 13 pages, 6 figures. Accepted for publication in Physical Review D | Phys. Rev. D 99, 103529(2019) | 10.1103/PhysRevD.99.103529 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the two-field warm inflation models with a double quadratic
potential and a linear temperature dependent dissipative coefficient. We
derived the evolution equation of all kinds of perturbations without assuming
slow-roll approximation, and obtained the curvature power spectrum at the end
of inflation with a fully numerical method. Then we compute the scalar spectral
index $n_s$, tensor-to-scalar ratio $r$ for several representative potentials,
and compare our results with observational data. At last, we use Planck data to
constrain the parameters in our models. This work is a natural extension of
single-field warm inflation, and the aim of this work is to present some
features of multi-field warm inflation using a simple two-field model.
| [
{
"created": "Tue, 7 May 2019 08:54:21 GMT",
"version": "v1"
}
] | 2019-05-23 | [
[
"Wang",
"Yang-yang",
""
],
[
"Zhang",
"Xiao-Min",
""
],
[
"Zhu",
"Jian-Yang",
""
]
] | We study the two-field warm inflation models with a double quadratic potential and a linear temperature dependent dissipative coefficient. We derived the evolution equation of all kinds of perturbations without assuming slow-roll approximation, and obtained the curvature power spectrum at the end of inflation with a fully numerical method. Then we compute the scalar spectral index $n_s$, tensor-to-scalar ratio $r$ for several representative potentials, and compare our results with observational data. At last, we use Planck data to constrain the parameters in our models. This work is a natural extension of single-field warm inflation, and the aim of this work is to present some features of multi-field warm inflation using a simple two-field model. |
1611.04569 | Pantelis Apostolopoulos | Pantelis S. Apostolopoulos | Szekeres models: a covariant approach | 16 pages, no figures; (v3) few further amendments and some references
added, final version to appear in Class. Quant. Gravity | Class.Quant.Grav. 34 (2017) no.9, 095013 | 10.1088/1361-6382/aa66df | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We exploit the 1+1+2 formalism to covariantly describe the inhomogeneous and
anisotropic Szekeres models. It is shown that an \emph{average scale length}
can be defined \emph{covariantly} which satisfies a 2d equation of motion
driven from the \emph{effective gravitational mass} (EGM) contained in the dust
cloud. The contributions to the EGM are encoded to the energy density of the
dust fluid and the free gravitational field $E_{ab}$. We show that the
quasi-symmetric property of the Szekeres models is justified through the
existence of 3 independent \emph{Intrinsic Killing Vector Fields (IKVFs)}. In
addition the notions of the Apparent and Absolute Apparent Horizons are briefly
discussed and we give an alternative gauge-invariant form to define them in
terms of the kinematical variables of the spacelike congruences. We argue that
the proposed program can be used in order to express Sachs' optical equations
in a covariant form and analyze the confrontation of a spatially inhomogeneous
irrotational overdense fluid model with the observational data.
| [
{
"created": "Mon, 14 Nov 2016 20:47:08 GMT",
"version": "v1"
},
{
"created": "Mon, 28 Nov 2016 17:38:56 GMT",
"version": "v2"
},
{
"created": "Wed, 15 Mar 2017 06:29:57 GMT",
"version": "v3"
}
] | 2017-04-17 | [
[
"Apostolopoulos",
"Pantelis S.",
""
]
] | We exploit the 1+1+2 formalism to covariantly describe the inhomogeneous and anisotropic Szekeres models. It is shown that an \emph{average scale length} can be defined \emph{covariantly} which satisfies a 2d equation of motion driven from the \emph{effective gravitational mass} (EGM) contained in the dust cloud. The contributions to the EGM are encoded to the energy density of the dust fluid and the free gravitational field $E_{ab}$. We show that the quasi-symmetric property of the Szekeres models is justified through the existence of 3 independent \emph{Intrinsic Killing Vector Fields (IKVFs)}. In addition the notions of the Apparent and Absolute Apparent Horizons are briefly discussed and we give an alternative gauge-invariant form to define them in terms of the kinematical variables of the spacelike congruences. We argue that the proposed program can be used in order to express Sachs' optical equations in a covariant form and analyze the confrontation of a spatially inhomogeneous irrotational overdense fluid model with the observational data. |
gr-qc/0607142 | Sushant Ghosh | S. G. Ghosh and D. W. Deshkar | Higher dimensional dust collapse with a cosmological constant | 7 Pages, no figures | Astrophys.Space Sci.310:111-117,2007 | 10.1007/s10509-007-9485-9 | null | gr-qc | null | The general solution of the Einstein equation for higher dimensional (HD)
spherically symmetric collapse of inhomogeneous dust in presence of a
cosmological term, i.e., exact interior solutions of the Einstein field
equations is presented for the HD Tolman-Bondi metrics imbedded in a de Sitter
background. The solution is then matched to exterior HD Scwarschild-de Sitter.
A brief discussion on the causal structure singularities and horizons is
provided. It turns out that the collapse proceed in the same way as in the
Minkowski background, i.e., the strong curvature naked singularities form and
that the higher dimensions seem to favor black holes rather than naked
singularities.
| [
{
"created": "Mon, 31 Jul 2006 16:46:07 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Ghosh",
"S. G.",
""
],
[
"Deshkar",
"D. W.",
""
]
] | The general solution of the Einstein equation for higher dimensional (HD) spherically symmetric collapse of inhomogeneous dust in presence of a cosmological term, i.e., exact interior solutions of the Einstein field equations is presented for the HD Tolman-Bondi metrics imbedded in a de Sitter background. The solution is then matched to exterior HD Scwarschild-de Sitter. A brief discussion on the causal structure singularities and horizons is provided. It turns out that the collapse proceed in the same way as in the Minkowski background, i.e., the strong curvature naked singularities form and that the higher dimensions seem to favor black holes rather than naked singularities. |
2104.14902 | Yong Xiao | Yong Xiao and Yu Tian | Logarithmic correction to black hole entropy from the nonlocality of
quantum gravity | 9 pages, no figures,latest version accepted by PRD | null | 10.1103/PhysRevD.105.044013 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been known for many years that the leading correction to the black
hole entropy is a logarithmic term, which is universal and closely related to
conformal anomaly. A fully consistent analysis of this issue has to take
quantum backreactions to the black hole geometry into account. However, it was
always unclear how to naturally derive the modified black hole metric
especially from an effective action, because the problem refers to the elusive
non-locality of quantum gravity. In this paper, we show that this problem can
be resolved within an effective field theory (EFT) framework of quantum
gravity. Our work suggests that the EFT approach provides a powerful and
self-consistent tool for studying the quantum gravitational corrections to
black hole geometries and thermodynamics.
| [
{
"created": "Fri, 30 Apr 2021 11:01:05 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jan 2022 09:48:32 GMT",
"version": "v2"
}
] | 2022-02-23 | [
[
"Xiao",
"Yong",
""
],
[
"Tian",
"Yu",
""
]
] | It has been known for many years that the leading correction to the black hole entropy is a logarithmic term, which is universal and closely related to conformal anomaly. A fully consistent analysis of this issue has to take quantum backreactions to the black hole geometry into account. However, it was always unclear how to naturally derive the modified black hole metric especially from an effective action, because the problem refers to the elusive non-locality of quantum gravity. In this paper, we show that this problem can be resolved within an effective field theory (EFT) framework of quantum gravity. Our work suggests that the EFT approach provides a powerful and self-consistent tool for studying the quantum gravitational corrections to black hole geometries and thermodynamics. |
gr-qc/0307101 | Nicolas Arnaud | Nicolas Arnaud, Matteo Barsuglia, Marie-Anne Bizouard, Violette
Brisson, Fabien Cavalier, Michel Davier, Patrice Hello, Stephane
Kreckelbergh, Edward K. Porter | Detection of a close supernova gravitational wave burst in a network of
interferometers, neutrino and optical detectors | Revised version, accepted for publication in Astroparticle Physics | Astropart.Phys. 21 (2004) 201-221 | 10.1016/j.astropartphys.2003.12.005 | null | gr-qc | null | Trying to detect the gravitational wave (GW) signal emitted by a type II
supernova is a main challenge for the GW community. Indeed, the corresponding
waveform is not accurately modeled as the supernova physics is very complex; in
addition, all the existing numerical simulations agree on the weakness of the
GW emission, thus restraining the number of sources potentially detectable.
Consequently, triggering the GW signal with a confidence level high enough to
conclude directly to a detection is very difficult, even with the use of a
network of interferometric detectors. On the other hand, one can hope to take
benefit from the neutrino and optical emissions associated to the supernova
explosion, in order to discover and study GW radiation in an event already
detected independently. This article aims at presenting some realistic
scenarios for the search of the supernova GW bursts, based on the present
knowledge of the emitted signals and on the results of network data analysis
simulations. Both the direct search and the confirmation of the supernova event
are considered. In addition, some physical studies following the discovery of a
supernova GW emission are also mentioned: from the absolute neutrino mass to
the supernova physics or the black hole signature, the potential spectrum of
discoveries is wide.
| [
{
"created": "Wed, 23 Jul 2003 16:14:30 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Sep 2003 12:24:12 GMT",
"version": "v2"
},
{
"created": "Fri, 19 Dec 2003 11:08:40 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Arnaud",
"Nicolas",
""
],
[
"Barsuglia",
"Matteo",
""
],
[
"Bizouard",
"Marie-Anne",
""
],
[
"Brisson",
"Violette",
""
],
[
"Cavalier",
"Fabien",
""
],
[
"Davier",
"Michel",
""
],
[
"Hello",
"Patrice",
""
... | Trying to detect the gravitational wave (GW) signal emitted by a type II supernova is a main challenge for the GW community. Indeed, the corresponding waveform is not accurately modeled as the supernova physics is very complex; in addition, all the existing numerical simulations agree on the weakness of the GW emission, thus restraining the number of sources potentially detectable. Consequently, triggering the GW signal with a confidence level high enough to conclude directly to a detection is very difficult, even with the use of a network of interferometric detectors. On the other hand, one can hope to take benefit from the neutrino and optical emissions associated to the supernova explosion, in order to discover and study GW radiation in an event already detected independently. This article aims at presenting some realistic scenarios for the search of the supernova GW bursts, based on the present knowledge of the emitted signals and on the results of network data analysis simulations. Both the direct search and the confirmation of the supernova event are considered. In addition, some physical studies following the discovery of a supernova GW emission are also mentioned: from the absolute neutrino mass to the supernova physics or the black hole signature, the potential spectrum of discoveries is wide. |
1611.00056 | Gabriel Menezes | G. Menezes | Spontaneous excitation of an atom in a Kerr spacetime | Accepted for publication in Physical Review D | Phys. Rev. D 95, 065015 (2017) | 10.1103/PhysRevD.95.065015 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider radiative processes of an atom in a rotating black-hole
background. We assume the atom, represented by a hypothetical two-level system,
is coupled via a monopole interaction with a massless quantum scalar field
prepared in each one of the usual physical vacuum states of interest. We
constrain ourselves to two different states of motion for the atom, namely a
static situation in which the atom is placed at a fixed radial distance, and
also the case in which it has a stationary motion but with zero angular
momentum. We study the structure of the rate of variation of the atomic energy.
The intention is to clarify in a quantitative way the effect of the
distinguished contributions of vacuum fluctuations and radiation reaction on
spontaneous excitation and on spontaneous emission of atoms. In particular, we
are interested in the comprehension of the combined action of the different
physical processes underlying the Hawking effect in the scenario of rotating
black holes as well as the Unruh-Starobinskii effect. We demonstrate that, in
the case of static atoms, spontaneous excitation is also connected with the
Unruh-Starobinskii effect, but only in the case of the quantum field prepared
in the Frolov-Thorne vacuum state. In addition, we show that, in the ZAMOs
perspective, the Boulware vacuum state contains an outward flux of particles as
a consequence of the black-hole superradiance. The possible relevance of the
findings in the present work is discussed.
| [
{
"created": "Mon, 31 Oct 2016 21:41:15 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Feb 2017 14:50:34 GMT",
"version": "v2"
}
] | 2017-03-29 | [
[
"Menezes",
"G.",
""
]
] | We consider radiative processes of an atom in a rotating black-hole background. We assume the atom, represented by a hypothetical two-level system, is coupled via a monopole interaction with a massless quantum scalar field prepared in each one of the usual physical vacuum states of interest. We constrain ourselves to two different states of motion for the atom, namely a static situation in which the atom is placed at a fixed radial distance, and also the case in which it has a stationary motion but with zero angular momentum. We study the structure of the rate of variation of the atomic energy. The intention is to clarify in a quantitative way the effect of the distinguished contributions of vacuum fluctuations and radiation reaction on spontaneous excitation and on spontaneous emission of atoms. In particular, we are interested in the comprehension of the combined action of the different physical processes underlying the Hawking effect in the scenario of rotating black holes as well as the Unruh-Starobinskii effect. We demonstrate that, in the case of static atoms, spontaneous excitation is also connected with the Unruh-Starobinskii effect, but only in the case of the quantum field prepared in the Frolov-Thorne vacuum state. In addition, we show that, in the ZAMOs perspective, the Boulware vacuum state contains an outward flux of particles as a consequence of the black-hole superradiance. The possible relevance of the findings in the present work is discussed. |
gr-qc/0403013 | Antonio F. Ranada | Antonio F. Ranada | The Pioneer anomaly as an effect of the dynamics of time | 25 pages,2 figures. New text and new figures in this version | null | null | null | gr-qc | null | A model is presented in which the Pioneer anomaly is not related to the
motion of the spaceship, but is a consequence of the acceleration of the
cosmological proper time $\tau$ with respect to the coordinate parametric time
$t$, what is an effect of the background gravitational potential of the entire
universe. The light speed, while being constant if defined with respect to
$\tau$ ({\it i. e.} as ${\rm d}\ell /{\rm d} \tau$), would suffer an adiabatic
secular acceleration, $a_\ell={\rm d}c/{\rm d}t >0$, if defined in terms of $t$
({\it i. e.} as ${\rm d}\ell /{\rm d} t$). Such an adiabatic acceleration of
light, and a small acceleration of the Pioneer towards the Sun $a_{\rm P}$
could be mistaken the one for the other, because they do have the same
fingerprint: a blue shift. However, this shift would be quite unrelated to any
anomalous motion of the Pioneer, being just an observational effect of the
acceleration of light with respect to time $t$. The Pioneer anomaly turns out
then to be an interesting case of the dynamics of time, its explanation
involving the interplay between the two times $\tau$ and $t$.
| [
{
"created": "Tue, 2 Mar 2004 18:07:20 GMT",
"version": "v1"
},
{
"created": "Wed, 5 May 2004 10:06:56 GMT",
"version": "v2"
},
{
"created": "Wed, 28 Jul 2004 11:01:02 GMT",
"version": "v3"
},
{
"created": "Thu, 25 Nov 2004 12:29:04 GMT",
"version": "v4"
}
] | 2009-09-29 | [
[
"Ranada",
"Antonio F.",
""
]
] | A model is presented in which the Pioneer anomaly is not related to the motion of the spaceship, but is a consequence of the acceleration of the cosmological proper time $\tau$ with respect to the coordinate parametric time $t$, what is an effect of the background gravitational potential of the entire universe. The light speed, while being constant if defined with respect to $\tau$ ({\it i. e.} as ${\rm d}\ell /{\rm d} \tau$), would suffer an adiabatic secular acceleration, $a_\ell={\rm d}c/{\rm d}t >0$, if defined in terms of $t$ ({\it i. e.} as ${\rm d}\ell /{\rm d} t$). Such an adiabatic acceleration of light, and a small acceleration of the Pioneer towards the Sun $a_{\rm P}$ could be mistaken the one for the other, because they do have the same fingerprint: a blue shift. However, this shift would be quite unrelated to any anomalous motion of the Pioneer, being just an observational effect of the acceleration of light with respect to time $t$. The Pioneer anomaly turns out then to be an interesting case of the dynamics of time, its explanation involving the interplay between the two times $\tau$ and $t$. |
1908.04406 | Gauranga Samanta | Gauranga C Samanta and Nisha Godani | Validation of Energy Conditions in Wormhole Geometry within Viable
$f(R)$ Gravity | 18 pages, 7 figures | Eur. Phys. J. C (2019) 79: 623 | 10.1140/epjc/s10052-019-7116-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, wormholes, tunnel like structures introduced by Morris \&
Thorne \cite{Morris95}, are explored within the framework of $f(R)$ gravity.
Using the shape function $b(r)=r_0\big(\frac{r}{r_0}\big)^\gamma$, where
$0<\gamma<1$, and the equation of state $p_r=\omega\rho$, the $f(R)$ function
is derived and the field equations are solved. Then null, weak, strong and
dominated energy conditions are analyzed and spherical regions satisfying these
energy conditions are determined. Furthermore, we calculated the range of the
radius of the throat of the wormhole, where the energy conditions are
satisfied.
| [
{
"created": "Tue, 6 Aug 2019 03:09:21 GMT",
"version": "v1"
}
] | 2019-08-14 | [
[
"Samanta",
"Gauranga C",
""
],
[
"Godani",
"Nisha",
""
]
] | In this work, wormholes, tunnel like structures introduced by Morris \& Thorne \cite{Morris95}, are explored within the framework of $f(R)$ gravity. Using the shape function $b(r)=r_0\big(\frac{r}{r_0}\big)^\gamma$, where $0<\gamma<1$, and the equation of state $p_r=\omega\rho$, the $f(R)$ function is derived and the field equations are solved. Then null, weak, strong and dominated energy conditions are analyzed and spherical regions satisfying these energy conditions are determined. Furthermore, we calculated the range of the radius of the throat of the wormhole, where the energy conditions are satisfied. |
gr-qc/0106054 | L. Sriramkumar | L. Sriramkumar | On the response of non-linearly coupled, accelerated detectors in
odd-dimensional flat spacetimes | RevTeX, 8 Pages, 2 Figures | null | null | null | gr-qc | null | In this note, we consider the response of a uniformly accelerated monopole
detector that is coupled non-linearly to the nth power of a quantum scalar
field in (D+1)-dimensional flat spacetime. We show that, when (D+1) is even,
the response of the detector in the Minkowski vacuum is characterized by a
Bose-Einstein factor for all n. Whereas, when (D+1) is odd, we find that a
Fermi-Dirac factor appears in the detector response when n is odd, but a
Bose-Einstein factor arises when n is even.
| [
{
"created": "Fri, 15 Jun 2001 23:25:12 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sriramkumar",
"L.",
""
]
] | In this note, we consider the response of a uniformly accelerated monopole detector that is coupled non-linearly to the nth power of a quantum scalar field in (D+1)-dimensional flat spacetime. We show that, when (D+1) is even, the response of the detector in the Minkowski vacuum is characterized by a Bose-Einstein factor for all n. Whereas, when (D+1) is odd, we find that a Fermi-Dirac factor appears in the detector response when n is odd, but a Bose-Einstein factor arises when n is even. |
gr-qc/9910024 | Takashi Tamaki | Takashi Tamaki, Kei-ichi Maeda | The fate of Reissner-Nortstr\"{o}m black hole in the
Einstein-Yang-Mills-Higgs system | 9 pages, 8 figures | null | 10.1103/PhysRevD.62.084041 | null | gr-qc hep-th | null | We study about an evaporating process of black holes in SO(3)
Einstein-Yang-Mills-Higgs system. We consider a massless scalar field which
couple neither with the Yang-Mills field nor with the Higgs field surrounding
the black hole. We discuss differences in evaporating rate between a monopole
black hole and a Reissner-Nortstr\"{o}m (RN) black hole.
| [
{
"created": "Thu, 7 Oct 1999 10:28:28 GMT",
"version": "v1"
},
{
"created": "Sun, 25 Jun 2000 09:46:34 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Tamaki",
"Takashi",
""
],
[
"Maeda",
"Kei-ichi",
""
]
] | We study about an evaporating process of black holes in SO(3) Einstein-Yang-Mills-Higgs system. We consider a massless scalar field which couple neither with the Yang-Mills field nor with the Higgs field surrounding the black hole. We discuss differences in evaporating rate between a monopole black hole and a Reissner-Nortstr\"{o}m (RN) black hole. |
1407.4875 | Jun-Jin Peng | Jun-Jin Peng | Conserved charges of black holes in Weyl and Einstein-Gauss-Bonnet
gravities | 21 Pages, no figures, references added | null | 10.1140/epjc/s10052-014-3156-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An off-shell generalization of the Abbott-Deser-Tekin (ADT) conserved charge
was recently proposed by Kim et al. They achieved this by introducing off-shell
Noether currents and potentials. In this paper, we construct the crucial
off-shell Noether current by the variation of the Bianchi identity for the
expression of motion equation, with the help of the property of Killing vector.
Our Noether current, which contains an additional term that is just one half of
the Lie derivative of a surface term with respect to the Killing vector, takes
a different form in comparison with the one in their work. Then we employ the
generalized formulation to calculate the quasi-local conserved charges for the
most general charged spherically symmetric and the dyonic rotating black holes
with AdS asymptotics in four-dimensional conformal Weyl gravity, as well as the
charged spherically symmetric black holes in arbitrary dimensional
Einstein-Gauss-Bonnet gravity coupled to Maxwell or nonlinear electrodynamics
in AdS spacetime. Our results confirm those through other methods in the
literature.
| [
{
"created": "Fri, 18 Jul 2014 02:57:40 GMT",
"version": "v1"
},
{
"created": "Sun, 17 Aug 2014 07:01:13 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Peng",
"Jun-Jin",
""
]
] | An off-shell generalization of the Abbott-Deser-Tekin (ADT) conserved charge was recently proposed by Kim et al. They achieved this by introducing off-shell Noether currents and potentials. In this paper, we construct the crucial off-shell Noether current by the variation of the Bianchi identity for the expression of motion equation, with the help of the property of Killing vector. Our Noether current, which contains an additional term that is just one half of the Lie derivative of a surface term with respect to the Killing vector, takes a different form in comparison with the one in their work. Then we employ the generalized formulation to calculate the quasi-local conserved charges for the most general charged spherically symmetric and the dyonic rotating black holes with AdS asymptotics in four-dimensional conformal Weyl gravity, as well as the charged spherically symmetric black holes in arbitrary dimensional Einstein-Gauss-Bonnet gravity coupled to Maxwell or nonlinear electrodynamics in AdS spacetime. Our results confirm those through other methods in the literature. |
gr-qc/9607049 | Reza Mansouri | M. Khorrami, M. Mansouri, M. Mohazzab | A Decrumpling Model of the Universe | 4 pages, Latex file, contribution to Journees Relativistes 96 | Helv.Phys.Acta 69 (1996) 237-240 | null | null | gr-qc | null | Assuming a cellular structure for the space-time, we propose a model in which
the expansion of the universe is understood as a decrumpling process, much like
the one we know from polymeric surfaces. The dimension of space is then a
dynamical real variable. The generalized Friedmann equation, derived from a
Lagrangian, and the generalized equation of continuity for the matter content
of the universe, give the dynamics of our model universe. This leads to an
oscillatory non-singular model with two turning points for the dimension of
space.
| [
{
"created": "Tue, 23 Jul 1996 11:47:10 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Khorrami",
"M.",
""
],
[
"Mansouri",
"M.",
""
],
[
"Mohazzab",
"M.",
""
]
] | Assuming a cellular structure for the space-time, we propose a model in which the expansion of the universe is understood as a decrumpling process, much like the one we know from polymeric surfaces. The dimension of space is then a dynamical real variable. The generalized Friedmann equation, derived from a Lagrangian, and the generalized equation of continuity for the matter content of the universe, give the dynamics of our model universe. This leads to an oscillatory non-singular model with two turning points for the dimension of space. |
1506.04253 | Manuel Hohmann | Manuel Hohmann | Parameterized post-Newtonian limit of Horndeski's gravity theory | 33 pages, no figures; journal version | Phys. Rev. D 92, 064019 (2015) | 10.1103/PhysRevD.92.064019 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the parameterized post-Newtonian (PPN) limit of Horndeski's theory
of gravity, also known under the name generalized G-inflation or
$\text{G}^2$-inflation, which is the most general scalar-tensor theory of
gravity with at most second order field equations in four dimensions. We derive
conditions on the action for the validity of the post-Newtonian limit. For the
most general class of theories consistent with these conditions we calculate
the PPN parameters $\gamma(r)$ and $\beta(r)$, which in general depend on the
interaction distance $r$ between the gravitating mass and the test mass. For a
more restricted class of theories, in which the scalar field is massless, we
calculate the full set of PPN parameters. It turns out that in this restricted
case all parameters are constants and that the only parameters potentially
deviating from observations are $\gamma$ and $\beta$. We finally apply our
results to a number of example theories, including galileons and different
models of Higgs inflation.
| [
{
"created": "Sat, 13 Jun 2015 11:16:54 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Sep 2015 06:40:59 GMT",
"version": "v2"
}
] | 2015-09-17 | [
[
"Hohmann",
"Manuel",
""
]
] | We discuss the parameterized post-Newtonian (PPN) limit of Horndeski's theory of gravity, also known under the name generalized G-inflation or $\text{G}^2$-inflation, which is the most general scalar-tensor theory of gravity with at most second order field equations in four dimensions. We derive conditions on the action for the validity of the post-Newtonian limit. For the most general class of theories consistent with these conditions we calculate the PPN parameters $\gamma(r)$ and $\beta(r)$, which in general depend on the interaction distance $r$ between the gravitating mass and the test mass. For a more restricted class of theories, in which the scalar field is massless, we calculate the full set of PPN parameters. It turns out that in this restricted case all parameters are constants and that the only parameters potentially deviating from observations are $\gamma$ and $\beta$. We finally apply our results to a number of example theories, including galileons and different models of Higgs inflation. |
1712.04226 | Ricardo Landim | Orfeu Bertolami, Ricardo G. Landim | Cosmic Transients, Einstein's Equivalence Principle and Dark Matter
Halos | 6 pages, 4 tables. Published version | Phys.Dark Univ. 21 (2018) 16-20 | 10.1016/j.dark.2018.05.002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cosmic transients, such as gamma-ray bursts and fast radio bursts, have been
used to constrain the Einstein's Equivalence Principle (EEP) through the
parametrized-post-Newtonian (PPN) formalism. In this approach, the time delay
of photons with different energies from these cosmic transients are used to
obtain upper bounds on the difference of the PPN $\gamma$ parameter. In this
work we assume that an important contribution to the time delay is due to the
dark matter halo of the Milky Way and consider the dark matter mass
distribution given by the Navarro--Frenk--White profile. We obtain the upper
limit on the difference of the PPN parameter $\gamma$ for the polarized
gamma-ray emission of GRB 110721A, $\Delta \gamma < 1.06 \times 10^{-28}$, the
most stringent limit to date on the EEP. In addition, we show that a very
similar upper bound is obtained if, instead of having a dark matter component,
a visible matter density profile and a non-minimal gravitational coupling
between curvature and matter are present.
| [
{
"created": "Tue, 12 Dec 2017 10:57:30 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Jan 2018 14:44:51 GMT",
"version": "v2"
},
{
"created": "Sun, 10 Jun 2018 22:47:39 GMT",
"version": "v3"
}
] | 2018-06-12 | [
[
"Bertolami",
"Orfeu",
""
],
[
"Landim",
"Ricardo G.",
""
]
] | Cosmic transients, such as gamma-ray bursts and fast radio bursts, have been used to constrain the Einstein's Equivalence Principle (EEP) through the parametrized-post-Newtonian (PPN) formalism. In this approach, the time delay of photons with different energies from these cosmic transients are used to obtain upper bounds on the difference of the PPN $\gamma$ parameter. In this work we assume that an important contribution to the time delay is due to the dark matter halo of the Milky Way and consider the dark matter mass distribution given by the Navarro--Frenk--White profile. We obtain the upper limit on the difference of the PPN parameter $\gamma$ for the polarized gamma-ray emission of GRB 110721A, $\Delta \gamma < 1.06 \times 10^{-28}$, the most stringent limit to date on the EEP. In addition, we show that a very similar upper bound is obtained if, instead of having a dark matter component, a visible matter density profile and a non-minimal gravitational coupling between curvature and matter are present. |
1010.1846 | Reza Saffari | Robab Hashemi and Reza Saffari | A Well-Behaved f(R) Gravity Model in Planetary Motions | 15 pages, 1 figure, LaTEX, Accepted for publication in Planetary
Space and Science, References added, Minor revision | Planet.Space Sci. 59:338-342,2011 | 10.1016/j.pss.2010.12.011 | null | gr-qc astro-ph.EP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we consider asymptotic behavior of a hybrid action of f(R)
gravity model which proposed by Saffari and Rahvar (2008), in solar system
scale, which can explain Pioneer anomalous acceleration. We use the potential
coming from this hybrid action in weak field limit to test its impacts on Solar
system dynamics, by comparing the theoretical precession of perihelion of a
test particle, $\dot{\varpi}$ with corrections to the standard Newtonian -
Einsteinian precession of perihelia of some planets, recently estimated by
Pitjeva. Here we show that obtained results of the asymptotic behavior of
hybrid action, are in more accordance with observation relative to the other
modifications such as power law and logarithmic corrections Iorio (2008). We
also show that an extra additional lensing of the prediction of General
Relativity is reproduced. Finally we obtain the stability condition of
planetary orbits.
| [
{
"created": "Sat, 9 Oct 2010 13:23:19 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Dec 2010 08:09:15 GMT",
"version": "v2"
},
{
"created": "Sun, 12 Dec 2010 09:34:25 GMT",
"version": "v3"
}
] | 2011-02-18 | [
[
"Hashemi",
"Robab",
""
],
[
"Saffari",
"Reza",
""
]
] | In this paper we consider asymptotic behavior of a hybrid action of f(R) gravity model which proposed by Saffari and Rahvar (2008), in solar system scale, which can explain Pioneer anomalous acceleration. We use the potential coming from this hybrid action in weak field limit to test its impacts on Solar system dynamics, by comparing the theoretical precession of perihelion of a test particle, $\dot{\varpi}$ with corrections to the standard Newtonian - Einsteinian precession of perihelia of some planets, recently estimated by Pitjeva. Here we show that obtained results of the asymptotic behavior of hybrid action, are in more accordance with observation relative to the other modifications such as power law and logarithmic corrections Iorio (2008). We also show that an extra additional lensing of the prediction of General Relativity is reproduced. Finally we obtain the stability condition of planetary orbits. |
2408.06399 | Maurice H. P. M. Van Putten | Maurice H.P.M. van Putten | Galaxy dynamics tracing quantum cosmology beyond $\Lambda$CDM below the
de Sitter scale of acceleration | 8 pages | CJPh 91 (2024) 377-381 | 10.1016/j.cjph.2024.07.040 | null | gr-qc astro-ph.GA | http://creativecommons.org/licenses/by/4.0/ | It is proposed that the baryonic Tully-Fisher relation (bTFR) and JWST
'Impossible galaxies' at cosmic dawn are unified in weak gravity by the trace
$J$ of the Schouten tensor below the Sitter scale of acceleration $a_{dS}=cH$,
where $c$ is the velocity of light and $H$ is the Hubble parameter. Across
$a_{dS}$, $J$ parametrizes short-period galaxy rotation curves and fast
gravitational collapse beyond the predictions of $\Lambda$CDM. The sensitivity
of weak gravitation to $J=\frac{1}{6}R$ is derived in infrared gravitation from
a consistent limit of quantum gravity, reducing to general relativity in the
limit of a small Planck constant, where $R$ is Ricci scalar tensor. For the
first time, it identifies the exact relation $a_0=c^2\sqrt{J}/2\pi$ of the
Milgrom parameter across all redshifts, accounting for the bTFR and early
galaxy formation accelerated by a factor $\sim J^{1/8}$. It predicts
$a_0^\prime(0)<0$ at the present epoch.
| [
{
"created": "Mon, 12 Aug 2024 09:06:35 GMT",
"version": "v1"
}
] | 2024-08-15 | [
[
"van Putten",
"Maurice H. P. M.",
""
]
] | It is proposed that the baryonic Tully-Fisher relation (bTFR) and JWST 'Impossible galaxies' at cosmic dawn are unified in weak gravity by the trace $J$ of the Schouten tensor below the Sitter scale of acceleration $a_{dS}=cH$, where $c$ is the velocity of light and $H$ is the Hubble parameter. Across $a_{dS}$, $J$ parametrizes short-period galaxy rotation curves and fast gravitational collapse beyond the predictions of $\Lambda$CDM. The sensitivity of weak gravitation to $J=\frac{1}{6}R$ is derived in infrared gravitation from a consistent limit of quantum gravity, reducing to general relativity in the limit of a small Planck constant, where $R$ is Ricci scalar tensor. For the first time, it identifies the exact relation $a_0=c^2\sqrt{J}/2\pi$ of the Milgrom parameter across all redshifts, accounting for the bTFR and early galaxy formation accelerated by a factor $\sim J^{1/8}$. It predicts $a_0^\prime(0)<0$ at the present epoch. |
gr-qc/0111040 | Garry Ludwig | Garry Ludwig and S. Brian Edgar | (Conformal) Killing vectors in the Newman-Penrose formalism | 27 pages | Gen.Rel.Grav. 34 (2002) 807-835 | 10.1023/A:1016361729933 | null | gr-qc | null | This paper presents an efficient technique for finding Killing, homothetic,
or even proper conformal Killing vectors in the Newman-Penrose (NP) formalism.
Leaning on, and extending, results previously derived in the GHP formalism we
show that the (conformal) Killing equations can be replaced by a set of
equations involving the commutators of the Lie derivative with the four NP
differential operators applied to the four coordinates.
It is crucial that these operators refer to a preferred tetrad relative to
the (conformal) Killing vectors, a notion to be defined. The equations can then
be readily solved for the Lie derivative of the coordinates, i.e. for the
components of the (conformal) Killing vectors. Some of these equations become
trivial if some coordinates are chosen intrinsically (where possible), i.e. if
they are somehow tied to the Riemann tensor and its covariant derivatives.
If part of the tetrad, i.e. part of null directions and gauge, can be defined
intrinsically then that part is generally preferred relative to any Killing
vector. This is also true relative to a homothetic vector or a proper conformal
Killing vector provided we make a further restriction on that intrinsic part of
the tetrad. If because of null isotropy or gauge isotropy, where part of the
tetrad cannot even in principle be defined intrinsically, the tetrad is defined
only up to (usually) one null rotation parameter and/or a gauge factor, then
the NP-Lie equations become slightly more involved and must be solved for the
Lie derivative of the null rotation parameter and/or of the gauge factor as
well. However, the general method remains the same and is still much more
efficient than conventional methods.
Several explicit examples are given to illustrate the method.
| [
{
"created": "Tue, 13 Nov 2001 22:16:18 GMT",
"version": "v1"
}
] | 2021-10-20 | [
[
"Ludwig",
"Garry",
""
],
[
"Edgar",
"S. Brian",
""
]
] | This paper presents an efficient technique for finding Killing, homothetic, or even proper conformal Killing vectors in the Newman-Penrose (NP) formalism. Leaning on, and extending, results previously derived in the GHP formalism we show that the (conformal) Killing equations can be replaced by a set of equations involving the commutators of the Lie derivative with the four NP differential operators applied to the four coordinates. It is crucial that these operators refer to a preferred tetrad relative to the (conformal) Killing vectors, a notion to be defined. The equations can then be readily solved for the Lie derivative of the coordinates, i.e. for the components of the (conformal) Killing vectors. Some of these equations become trivial if some coordinates are chosen intrinsically (where possible), i.e. if they are somehow tied to the Riemann tensor and its covariant derivatives. If part of the tetrad, i.e. part of null directions and gauge, can be defined intrinsically then that part is generally preferred relative to any Killing vector. This is also true relative to a homothetic vector or a proper conformal Killing vector provided we make a further restriction on that intrinsic part of the tetrad. If because of null isotropy or gauge isotropy, where part of the tetrad cannot even in principle be defined intrinsically, the tetrad is defined only up to (usually) one null rotation parameter and/or a gauge factor, then the NP-Lie equations become slightly more involved and must be solved for the Lie derivative of the null rotation parameter and/or of the gauge factor as well. However, the general method remains the same and is still much more efficient than conventional methods. Several explicit examples are given to illustrate the method. |
gr-qc/0308038 | Kayll Lake | Kayll Lake | Differential Invariants of the Kerr Vacuum | 12 pages 8 figures. Much more information at
http://grtensor.org/diffweyl/ | Gen.Rel.Grav. 36 (2004) 1159 | 10.1023/B:GERG.0000018282.42275.cb | null | gr-qc | null | The norms associated with the gradients of the two non-differential
invariants of the Kerr vacuum are examined. Whereas both locally single out the
horizons, their global behavior is more interesting. Both reflect the
background angular momentum as the volume of space allowing a timelike gradient
decreases with increasing angular momentum becoming zero in the degenerate and
naked cases. These results extend directly to the Kerr-Newman geometry.
| [
{
"created": "Tue, 12 Aug 2003 17:30:47 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Lake",
"Kayll",
""
]
] | The norms associated with the gradients of the two non-differential invariants of the Kerr vacuum are examined. Whereas both locally single out the horizons, their global behavior is more interesting. Both reflect the background angular momentum as the volume of space allowing a timelike gradient decreases with increasing angular momentum becoming zero in the degenerate and naked cases. These results extend directly to the Kerr-Newman geometry. |
1704.08925 | Nelson A. Lima | Georgios Kofinas and Nelson A. Lima | Dynamics of cosmological perturbations in modified Brans-Dicke cosmology
with matter-scalar field interaction | 20 pages, 5 figues. Version 2 with minor revisions to match
manuscript accepted by PRD | Phys. Rev. D 96, 084016 (2017) | 10.1103/PhysRevD.96.084016 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we focus on a novel completion of the well-known Brans-Dicke
theory that introduces an interaction between the dark energy and dark matter
sectors, known as complete Brans-Dicke (CBD) theory. We obtain viable
cosmological accelerating solutions that fit Supernovae observations with great
precision without any scalar potential $V(\phi)$. We use these solutions to
explore the impact of the CBD theory on the large scale structure by studying
the dynamics of its linear perturbations. We observe a growing behavior of the
lensing potential $\Phi_{+}$ at late-times, while the growth rate is actually
suppressed relatively to $\Lambda$CDM, which allows the CBD theory to provide a
competitive fit to current RSD measurements of $f\sigma_{8}$. However, we also
observe that the theory exhibits a pathological change of sign in the effective
gravitational constant concerning the perturbations on sub-horizon scales that
could pose a challenge to its validity.
| [
{
"created": "Thu, 27 Apr 2017 12:59:46 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Sep 2017 10:44:29 GMT",
"version": "v2"
}
] | 2017-10-10 | [
[
"Kofinas",
"Georgios",
""
],
[
"Lima",
"Nelson A.",
""
]
] | In this work we focus on a novel completion of the well-known Brans-Dicke theory that introduces an interaction between the dark energy and dark matter sectors, known as complete Brans-Dicke (CBD) theory. We obtain viable cosmological accelerating solutions that fit Supernovae observations with great precision without any scalar potential $V(\phi)$. We use these solutions to explore the impact of the CBD theory on the large scale structure by studying the dynamics of its linear perturbations. We observe a growing behavior of the lensing potential $\Phi_{+}$ at late-times, while the growth rate is actually suppressed relatively to $\Lambda$CDM, which allows the CBD theory to provide a competitive fit to current RSD measurements of $f\sigma_{8}$. However, we also observe that the theory exhibits a pathological change of sign in the effective gravitational constant concerning the perturbations on sub-horizon scales that could pose a challenge to its validity. |
gr-qc/9501011 | David Scialom | David Scialom and Philippe Jetzer | ASYMPTOTIC BEHAVIOR OF COMPLEX SCALAR FIELDS IN A FRIEDMAN-LEMAITRE
UNIVERSE | uuencoded, compressed tarfile containing a 15 pages Latex file and 2
postscipt figures. Accepted for publication on Phys. Rev. D | Phys.Rev.D51:5698-5706,1995 | 10.1103/PhysRevD.51.5698 | ZU-TH 22/94 | gr-qc astro-ph | null | We study the coupled Einstein-Klein-Gordon equations for a complex scalar
field with and without a quartic self-interaction in a curvatureless
Friedman-Lema\^{\i}\-tre Universe. The equations can be written as a set of
four coupled first order non-linear differential equations, for which we
establish the phase portrait for the time evolution of the scalar field. To
that purpose we find the singular points of the differential equations lying in
the finite region and at infinity of the phase space and study the
corresponding asymptotic behavior of the solutions. This knowledge is of
relevance, since it provides the initial conditions which are needed to solve
numerically the differential equations. For some singular points lying at
infinity we recover the expected emergence of an inflationary stage.
| [
{
"created": "Thu, 12 Jan 1995 16:41:02 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Scialom",
"David",
""
],
[
"Jetzer",
"Philippe",
""
]
] | We study the coupled Einstein-Klein-Gordon equations for a complex scalar field with and without a quartic self-interaction in a curvatureless Friedman-Lema\^{\i}\-tre Universe. The equations can be written as a set of four coupled first order non-linear differential equations, for which we establish the phase portrait for the time evolution of the scalar field. To that purpose we find the singular points of the differential equations lying in the finite region and at infinity of the phase space and study the corresponding asymptotic behavior of the solutions. This knowledge is of relevance, since it provides the initial conditions which are needed to solve numerically the differential equations. For some singular points lying at infinity we recover the expected emergence of an inflationary stage. |
1801.06549 | Jose Natario | Jo\~ao L. Costa, Jos\'e Nat\'ario, Pedro Oliveira | Cosmic no-hair in spherically symmetric black hole spacetimes | 32 pages, 1 figure; v2: minor corrections; v3: a few corrections
added to match the final published version | Ann. Henri Poincar\'e 20 (2019) 3059-3090 | 10.1007/s00023-019-00825-z | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze in detail the geometry and dynamics of the cosmological region
arising in spherically symmetric black hole solutions of the
Einstein-Maxwell-scalar field system with a positive cosmological constant.
More precisely, we solve, for such a system, a characteristic initial value
problem with data emulating a dynamic cosmological horizon. Our assumptions are
fairly weak, in that we only assume that the data approaches that of a
subextremal Reissner-Nordstr\"om-de Sitter black hole, without imposing any
rate of decay. We then show that the radius (of symmetry) blows up along any
null ray parallel to the cosmological horizon ("near" $i^+$), in such a way
that $r=+\infty$ is, in an appropriate sense, a spacelike hypersurface. We also
prove a version of the Cosmic No-Hair Conjecture by showing that in the past of
any causal curve reaching infinity both the metric and the Riemann curvature
tensor asymptote those of a de Sitter spacetime. Finally, we discuss conditions
under which all the previous results can be globalized.
| [
{
"created": "Fri, 19 Jan 2018 19:00:09 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Jul 2018 17:39:59 GMT",
"version": "v2"
},
{
"created": "Wed, 4 Sep 2019 12:48:15 GMT",
"version": "v3"
}
] | 2019-09-05 | [
[
"Costa",
"João L.",
""
],
[
"Natário",
"José",
""
],
[
"Oliveira",
"Pedro",
""
]
] | We analyze in detail the geometry and dynamics of the cosmological region arising in spherically symmetric black hole solutions of the Einstein-Maxwell-scalar field system with a positive cosmological constant. More precisely, we solve, for such a system, a characteristic initial value problem with data emulating a dynamic cosmological horizon. Our assumptions are fairly weak, in that we only assume that the data approaches that of a subextremal Reissner-Nordstr\"om-de Sitter black hole, without imposing any rate of decay. We then show that the radius (of symmetry) blows up along any null ray parallel to the cosmological horizon ("near" $i^+$), in such a way that $r=+\infty$ is, in an appropriate sense, a spacelike hypersurface. We also prove a version of the Cosmic No-Hair Conjecture by showing that in the past of any causal curve reaching infinity both the metric and the Riemann curvature tensor asymptote those of a de Sitter spacetime. Finally, we discuss conditions under which all the previous results can be globalized. |
2403.02852 | Rituparna Mandal | Rituparna Mandal, Soma Sanyal | Asymptotically safe cosmology with non-canonical scalar field | 23 pages, 1 table | null | null | null | gr-qc | http://creativecommons.org/licenses/by-sa/4.0/ | We investigate the quantum modified cosmological dynamical equations in a
Friedmann-Robertson-Walker universe filled with a barotropic fluid and a
general non-canonical scalar field characterized by a Lagrangian similar to
k-essence model but with a potential term. Quantum corrections are incorporated
by considering the running of gravitational and potential couplings, employing
the functional renormalization group approach. Covariant conservation of the
non-canonical scalar field and the background barotropic fluid is considered
separately, imposing a constraint resulting from the Bianchi identity. This
constraint determines the evolution of the cut-off scale with the scale factor
and also reveals cosmic fixed points, depending on whether the flow ceases or
continues to evolve. We explore how the general non-canonical scalar field
parameter affects the different types of cosmic fixed points and how it differs
from the canonical case. Furthermore, we establish a bound on the ratio of the
RG parameters involving the non-canonical parameter for which the universe may
exhibit accelerated expansion for mixed fixed points. This bound indicates the
non-canonical scalar field includes larger sets of RG fixed point which may
give rise to an accelerated universe.
| [
{
"created": "Tue, 5 Mar 2024 10:48:41 GMT",
"version": "v1"
}
] | 2024-03-06 | [
[
"Mandal",
"Rituparna",
""
],
[
"Sanyal",
"Soma",
""
]
] | We investigate the quantum modified cosmological dynamical equations in a Friedmann-Robertson-Walker universe filled with a barotropic fluid and a general non-canonical scalar field characterized by a Lagrangian similar to k-essence model but with a potential term. Quantum corrections are incorporated by considering the running of gravitational and potential couplings, employing the functional renormalization group approach. Covariant conservation of the non-canonical scalar field and the background barotropic fluid is considered separately, imposing a constraint resulting from the Bianchi identity. This constraint determines the evolution of the cut-off scale with the scale factor and also reveals cosmic fixed points, depending on whether the flow ceases or continues to evolve. We explore how the general non-canonical scalar field parameter affects the different types of cosmic fixed points and how it differs from the canonical case. Furthermore, we establish a bound on the ratio of the RG parameters involving the non-canonical parameter for which the universe may exhibit accelerated expansion for mixed fixed points. This bound indicates the non-canonical scalar field includes larger sets of RG fixed point which may give rise to an accelerated universe. |
0905.2464 | Tiberiu Harko | Tiberiu Harko | Matter Accretion by Brane-World Black Holes | 25 pages, accepted for publication in Journal of the Korean Physical
Society | Journal of the Korean Physical Society, 54: 2583-2594, 2009 | 10.3938/jkps.54.2583 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The brane-world description of our universe entails a large extra dimension
and a fundamental scale of gravity that might be lower by several orders of
magnitude compared to the Planck scale. An interesting consequence of the
brane-world scenario is in the nature of spherically symmetric vacuum solutions
to the brane gravitational field equations, with properties quite distinct as
compared to the standard black-hole solutions of general relativity. We
consider the spherically symmetric accretion of matter onto brane-world black
holes in terms of relativistic hydrodynamics by assuming that the inflowing gas
obeys a polytropic equation of state. As a first step in this study, we
consider the accretion process in an arbitrary static, spherically symmetric
space-time, and show that the relativistic equations require a transition to a
supersonic flow in the solution. The velocity, temperature, and density
profiles are obtained for the case of the polytropic equation of state. We
apply the general formalism to the study of the accretion properties of several
classes of brane-world black holes, and we obtain the distribution of the main
physical parameters of the gas. The astrophysical determination of these
physical quantities could discriminate, at least in principle, between the
different brane-world models, and place some constraints on the existence of
the extra dimensions.
| [
{
"created": "Fri, 15 May 2009 03:37:57 GMT",
"version": "v1"
}
] | 2015-05-13 | [
[
"Harko",
"Tiberiu",
""
]
] | The brane-world description of our universe entails a large extra dimension and a fundamental scale of gravity that might be lower by several orders of magnitude compared to the Planck scale. An interesting consequence of the brane-world scenario is in the nature of spherically symmetric vacuum solutions to the brane gravitational field equations, with properties quite distinct as compared to the standard black-hole solutions of general relativity. We consider the spherically symmetric accretion of matter onto brane-world black holes in terms of relativistic hydrodynamics by assuming that the inflowing gas obeys a polytropic equation of state. As a first step in this study, we consider the accretion process in an arbitrary static, spherically symmetric space-time, and show that the relativistic equations require a transition to a supersonic flow in the solution. The velocity, temperature, and density profiles are obtained for the case of the polytropic equation of state. We apply the general formalism to the study of the accretion properties of several classes of brane-world black holes, and we obtain the distribution of the main physical parameters of the gas. The astrophysical determination of these physical quantities could discriminate, at least in principle, between the different brane-world models, and place some constraints on the existence of the extra dimensions. |
2104.14850 | Javier Olmedo | Mercedes Mart\'in-Benito, Rita B. Neves and Javier Olmedo | Non-oscillatory power spectrum from States of Low Energy in kinetically
dominated early universes | 13 pages, 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, States of Low Energy (SLEs) have been proposed as viable vacuum
states of primordial perturbations within Loop Quantum Cosmology (LQC). In this
work we investigate the effect of the high curvature region of LQC on the
definition of SLEs. Shifting the support of the test function that defines them
away from this regime results in primordial power spectra of perturbations
closer to those of the so-called Non-oscillatory (NO) vacuum, which is another
viable choice of initial conditions previously introduced in the LQC context.
Furthermore, through a comparison with the Hadamard-like SLEs, we prove that
the NO vacuum is of Hadamard type as well.
| [
{
"created": "Fri, 30 Apr 2021 09:03:57 GMT",
"version": "v1"
}
] | 2021-05-03 | [
[
"Martín-Benito",
"Mercedes",
""
],
[
"Neves",
"Rita B.",
""
],
[
"Olmedo",
"Javier",
""
]
] | Recently, States of Low Energy (SLEs) have been proposed as viable vacuum states of primordial perturbations within Loop Quantum Cosmology (LQC). In this work we investigate the effect of the high curvature region of LQC on the definition of SLEs. Shifting the support of the test function that defines them away from this regime results in primordial power spectra of perturbations closer to those of the so-called Non-oscillatory (NO) vacuum, which is another viable choice of initial conditions previously introduced in the LQC context. Furthermore, through a comparison with the Hadamard-like SLEs, we prove that the NO vacuum is of Hadamard type as well. |
gr-qc/0608026 | Papantonopoulos Eleftherios | Eleftherios Papantonopoulos and Vassilios Zamarias | Curvaton Dynamics in Brane-worlds | 47 pages, 1 figure, references added, to be published in JCAP | JCAP0611:005,2006 | 10.1088/1475-7516/2006/11/005 | null | gr-qc hep-th | null | We study the curvaton dynamics in brane-world cosmologies. Assuming that the
inflaton field survives without decay after the end of inflation, we apply the
curvaton reheating mechanism to Randall-Sundrum and to its curvature
corrections: Gauss-Bonnet, induced gravity and combined Gauss-Bonnet and
induced gravity cosmological models. In the case of chaotic inflation and
requiring suppression of possible short-wavelength generated gravitational
waves, we constraint the parameters of a successful curvaton brane-world
cosmological model. If density perturbations are also generated by the curvaton
field then, the fundamental five-dimensional mass could be much lower than the
Planck mass
| [
{
"created": "Fri, 4 Aug 2006 12:53:46 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Oct 2006 12:39:21 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Papantonopoulos",
"Eleftherios",
""
],
[
"Zamarias",
"Vassilios",
""
]
] | We study the curvaton dynamics in brane-world cosmologies. Assuming that the inflaton field survives without decay after the end of inflation, we apply the curvaton reheating mechanism to Randall-Sundrum and to its curvature corrections: Gauss-Bonnet, induced gravity and combined Gauss-Bonnet and induced gravity cosmological models. In the case of chaotic inflation and requiring suppression of possible short-wavelength generated gravitational waves, we constraint the parameters of a successful curvaton brane-world cosmological model. If density perturbations are also generated by the curvaton field then, the fundamental five-dimensional mass could be much lower than the Planck mass |
gr-qc/9801063 | Franz Schunck | Eckehard W. Mielke and Franz E. Schunck | Boson Stars: Early History and Recent Prospects | 20 pages, 1 Postscript figure, LaTeX, uses mprocl.sty | Report of parallel session chair in: Proc. 8th M. Grossmann
Meeting, T. Piran (ed.), World Scientific, Singapore 1998, to be published | null | SUSSEX 97/9 | gr-qc | null | Boson stars are descendants of the so-called geons of Wheeler, except that
they are built from scalar particles instead of electromagnetic fields. If
scalar fields exist in nature, such localized configurations kept together by
their self-generated gravitational field can form within Einstein's general
relativity. In the case of complex scalar fields, an absolutely stable branch
of such non-topological solitons with conserved particle number exists. Our
present surge stems from the speculative possibility that these compact objects
could provide a considerable fraction of the non-baryonic part of dark matter.
In any case, they may serve as a convenient "laboratory" for studying
numerically rapidly rotating bodies in general relativity and the generation of
gravitational waves.
| [
{
"created": "Mon, 19 Jan 1998 20:45:57 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mielke",
"Eckehard W.",
""
],
[
"Schunck",
"Franz E.",
""
]
] | Boson stars are descendants of the so-called geons of Wheeler, except that they are built from scalar particles instead of electromagnetic fields. If scalar fields exist in nature, such localized configurations kept together by their self-generated gravitational field can form within Einstein's general relativity. In the case of complex scalar fields, an absolutely stable branch of such non-topological solitons with conserved particle number exists. Our present surge stems from the speculative possibility that these compact objects could provide a considerable fraction of the non-baryonic part of dark matter. In any case, they may serve as a convenient "laboratory" for studying numerically rapidly rotating bodies in general relativity and the generation of gravitational waves. |
2311.07403 | Evgenii Ievlev | Evgenii Ievlev | Moving mirrors and event horizons in non-flat background geometry | 12 pages, 4 figures; overall revision | Class. Quantum Grav. 41 155009 (2024) | 10.1088/1361-6382/ad5bb4 | FTPI-MINN-23-21 | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Moving mirrors have been used for a long time as simple models for studying
various properties of black hole radiation, such as the thermal spectrum and
entanglement entropy. These models are typically constructed to mimic the
collapse of a spherically symmetric distribution of matter in the Minkowski
background. We generalize this correspondence to the case of non-trivial
background geometry and consider two examples, the Schwarzschild -- de Sitter
black hole and the Ba\~nados--Teitelboim--Zanelli (BTZ) black hole. In the BTZ
case we were also able to show that this approach works for the spinning black
hole which has only axial symmetry.
| [
{
"created": "Mon, 13 Nov 2023 15:33:51 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Jul 2024 17:24:21 GMT",
"version": "v2"
}
] | 2024-07-09 | [
[
"Ievlev",
"Evgenii",
""
]
] | Moving mirrors have been used for a long time as simple models for studying various properties of black hole radiation, such as the thermal spectrum and entanglement entropy. These models are typically constructed to mimic the collapse of a spherically symmetric distribution of matter in the Minkowski background. We generalize this correspondence to the case of non-trivial background geometry and consider two examples, the Schwarzschild -- de Sitter black hole and the Ba\~nados--Teitelboim--Zanelli (BTZ) black hole. In the BTZ case we were also able to show that this approach works for the spinning black hole which has only axial symmetry. |
1705.07518 | Orfeu Bertolami | Orfeu Bertolami and Jorge P\'aramos | Using a non-minimal coupling between matter and curvature to sequester
the Cosmological Constant | 8 pages. To match version published at General Relativity and
Gravitation, May 2020 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a novel mechanism for generating a Cosmological Constant and
suitably sequestering the vacuum contribution to it, so that the eponymous
Cosmological Constant problem is avoided.
We do so by resorting to a model endowed with a non-minimal coupling between
curvature and matter in an appropriately defined relaxed regime, and show that
this shares features with both Unimodular gravity as well as a recent proposal
to sequester the vacuum contribution through the use of an external term to the
action functional.
| [
{
"created": "Sun, 21 May 2017 22:40:47 GMT",
"version": "v1"
},
{
"created": "Wed, 16 May 2018 16:11:31 GMT",
"version": "v2"
},
{
"created": "Fri, 8 May 2020 11:36:18 GMT",
"version": "v3"
}
] | 2020-05-11 | [
[
"Bertolami",
"Orfeu",
""
],
[
"Páramos",
"Jorge",
""
]
] | We present a novel mechanism for generating a Cosmological Constant and suitably sequestering the vacuum contribution to it, so that the eponymous Cosmological Constant problem is avoided. We do so by resorting to a model endowed with a non-minimal coupling between curvature and matter in an appropriately defined relaxed regime, and show that this shares features with both Unimodular gravity as well as a recent proposal to sequester the vacuum contribution through the use of an external term to the action functional. |
gr-qc/9810060 | Mihaela Time | Mihaela Time | A Stationary Asymptotically Einstein Static Universe Solution | 7 pages, LaTeX | null | null | null | gr-qc | null | Here I present a stationary cylindrically symmetric asymptotically Einstein
static universe solution with the matter consisting of a cosmological and
rotating dust term which admits predicted black hole event horizon.
| [
{
"created": "Sun, 18 Oct 1998 19:28:14 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Jan 1999 19:00:33 GMT",
"version": "v2"
},
{
"created": "Wed, 27 Jan 1999 18:45:40 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Time",
"Mihaela",
""
]
] | Here I present a stationary cylindrically symmetric asymptotically Einstein static universe solution with the matter consisting of a cosmological and rotating dust term which admits predicted black hole event horizon. |
1203.6185 | Zhoujian Cao Dr | Zhoujian Cao, Jui-Ping Yu, Chun-Yu Lin, Shan Bai and Hwei-Jang Yo | Perturbational Treatment of the Gravitational Potential Effect on Binary
Black Hole Evolution | updated version of Journal of Physics: Conference Series 330 (2011)
012016 | Journal of Physics: Conference Series 330 (2011) 012016 | 10.1088/1742-6596/330/1/012016 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Binary black hole (BBH) systems are usually located in the gravitational
potential well formed by a massive black hole (BH), which is mostly located in
the center of a galaxy. In most existing studies, the BBH systems are treated
as isolated systems, while the effect of the background is ignored. The
validity of the approximation is based on the belief that the background
gravitational field from other sources is extremely weak compared with the
strong gravitational field produced by the BBH itself during the evolution, and
can be neglected in gravitational wave detection. However, it is still
interesting to check how valid this approximation is. In this work, instead of
simulating the three-BH problem with a fully relativistic treatment, we use a
perturbational scheme to investigate the effect of the background gravitational
potential on the evolution of a BBH, especially on the waveform of its
gravitational radiation. Four scenarios are considered including the head-on
collision and the inspiral-to-merger process of a BBH which is either
freefalling towards or circularly orbiting around a third large BH. The head-on
collision and the circular inspiral are two limits of all possible
configurations. The existence of the background gravitational potential changes
the arrival time of the gravitational wavefront of a BH, prolongs the
wavelength, and increases the gravitational radiation energy. And most
interestingly, the background gravitational potential induces the higher-order
modes of the gravitational wave of a BBH. These interesting phenomena can be
explained by the gravitational redshift effect and the change of eccentricity
of a BBH's orbit from the background gravitational potential.
| [
{
"created": "Wed, 28 Mar 2012 07:41:18 GMT",
"version": "v1"
}
] | 2015-06-04 | [
[
"Cao",
"Zhoujian",
""
],
[
"Yu",
"Jui-Ping",
""
],
[
"Lin",
"Chun-Yu",
""
],
[
"Bai",
"Shan",
""
],
[
"Yo",
"Hwei-Jang",
""
]
] | Binary black hole (BBH) systems are usually located in the gravitational potential well formed by a massive black hole (BH), which is mostly located in the center of a galaxy. In most existing studies, the BBH systems are treated as isolated systems, while the effect of the background is ignored. The validity of the approximation is based on the belief that the background gravitational field from other sources is extremely weak compared with the strong gravitational field produced by the BBH itself during the evolution, and can be neglected in gravitational wave detection. However, it is still interesting to check how valid this approximation is. In this work, instead of simulating the three-BH problem with a fully relativistic treatment, we use a perturbational scheme to investigate the effect of the background gravitational potential on the evolution of a BBH, especially on the waveform of its gravitational radiation. Four scenarios are considered including the head-on collision and the inspiral-to-merger process of a BBH which is either freefalling towards or circularly orbiting around a third large BH. The head-on collision and the circular inspiral are two limits of all possible configurations. The existence of the background gravitational potential changes the arrival time of the gravitational wavefront of a BH, prolongs the wavelength, and increases the gravitational radiation energy. And most interestingly, the background gravitational potential induces the higher-order modes of the gravitational wave of a BBH. These interesting phenomena can be explained by the gravitational redshift effect and the change of eccentricity of a BBH's orbit from the background gravitational potential. |
1301.2370 | Yu-ichi Takamizu | Yu-ichi Takamizu and Tsutomu Kobayashi | Nonlinear superhorizon curvature perturbation in generic single-field
inflation | 14 pages, version to appear in PTEP | Prog. Theor. Exp. Phys. 2013, 063E03 | 10.1093/ptep/ptt033 | YITP-13-1, RUP-12-12 | gr-qc astro-ph.CO hep-th nlin.SI | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop a theory of nonlinear cosmological perturbations on superhorizon
scales for generic single-field inflation. Our inflaton is described by the
Lagrangian of the form $W(X,\phi)-G(X,\phi)\Box\phi$ with
$X=-\partial^{\mu}\phi\partial_{\mu}\phi/2$, which is no longer equivalent to a
perfect fluid. This model is more general than k-inflation, and is called
G-inflation. A general nonlinear solution for the metric and the scalar field
is obtained at second order in gradient expansion. We derive a simple master
equation governing the large-scale evolution of the nonlinear curvature
perturbation. It turns out that the nonlinear evolution equation is deduced as
a straightforward extension of the corresponding linear equation for the
curvature perturbation on uniform $\phi$ hypersurfaces.
| [
{
"created": "Fri, 11 Jan 2013 01:27:35 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Jun 2013 02:26:35 GMT",
"version": "v2"
}
] | 2013-06-04 | [
[
"Takamizu",
"Yu-ichi",
""
],
[
"Kobayashi",
"Tsutomu",
""
]
] | We develop a theory of nonlinear cosmological perturbations on superhorizon scales for generic single-field inflation. Our inflaton is described by the Lagrangian of the form $W(X,\phi)-G(X,\phi)\Box\phi$ with $X=-\partial^{\mu}\phi\partial_{\mu}\phi/2$, which is no longer equivalent to a perfect fluid. This model is more general than k-inflation, and is called G-inflation. A general nonlinear solution for the metric and the scalar field is obtained at second order in gradient expansion. We derive a simple master equation governing the large-scale evolution of the nonlinear curvature perturbation. It turns out that the nonlinear evolution equation is deduced as a straightforward extension of the corresponding linear equation for the curvature perturbation on uniform $\phi$ hypersurfaces. |
1507.01686 | Eckhard Strobel | Cl\'ement Stahl and Eckhard Strobel and She-Sheng Xue | Fermionic current and Schwinger effect in de Sitter spacetime | 19 pages, 1 figure, V2:small changes and some references added,
version accepted for publication in Phys. Rev. D | Phys. Rev. D 93, 025004 (2016) | 10.1103/PhysRevD.93.025004 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the fermionic Schwinger effect in two dimensional de Sitter
spacetime. To do so we first present a method to semiclassically compute the
number of pairs created per momentum mode for general time dependent fields. In
addition the constant electric field is studied in depth. In this case
solutions for the Dirac equation can be found and the number of pairs can be
computed using the standard Bogoliubov method. This result is shown to agree
with the semiclassical one in the appropriate limit. The solutions are also
used to compute the expectation value of the induced current. Comparing these
results to similar studies for bosons we find that while the results agree in
the semiclassical limit they do not generally. Especially there is no
occurrence of a strong current for small electric fields.
| [
{
"created": "Tue, 7 Jul 2015 06:53:22 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Jan 2016 14:19:34 GMT",
"version": "v2"
}
] | 2016-01-13 | [
[
"Stahl",
"Clément",
""
],
[
"Strobel",
"Eckhard",
""
],
[
"Xue",
"She-Sheng",
""
]
] | We study the fermionic Schwinger effect in two dimensional de Sitter spacetime. To do so we first present a method to semiclassically compute the number of pairs created per momentum mode for general time dependent fields. In addition the constant electric field is studied in depth. In this case solutions for the Dirac equation can be found and the number of pairs can be computed using the standard Bogoliubov method. This result is shown to agree with the semiclassical one in the appropriate limit. The solutions are also used to compute the expectation value of the induced current. Comparing these results to similar studies for bosons we find that while the results agree in the semiclassical limit they do not generally. Especially there is no occurrence of a strong current for small electric fields. |
gr-qc/0602101 | Muxin Han | Muxin Han, Yongge Ma | Dynamics of Scalar Field in Polymer-like Representation | 24 pages, accepted for pubilcation in Class. Quant. Grav | Class.Quant.Grav. 23 (2006) 2741-2760 | 10.1088/0264-9381/23/7/031 | null | gr-qc math-ph math.MP quant-ph | null | In recent twenty years, loop quantum gravity, a background independent
approach to unify general relativity and quantum mechanics, has been widely
investigated. We consider the quantum dynamics of a real massless scalar field
coupled to gravity in this framework. A Hamiltonian operator for the scalar
field can be well defined in the coupled diffeomorphism invariant Hilbert
space, which is both self-adjoint and positive. On the other hand, the
Hamiltonian constraint operator for the scalar field coupled to gravity can be
well defined in the coupled kinematical Hilbert space. There are 1-parameter
ambiguities due to scalar field in the construction of both operators. The
results heighten our confidence that there is no divergence within this
background independent and diffeomorphism invariant quantization approach of
matter coupled to gravity. Moreover, to avoid possible quantum anomaly, the
master constraint programme can be carried out in this coupled system by
employing a self-adjoint master constraint operator on the diffeomorphism
invariant Hilbert space.
| [
{
"created": "Fri, 24 Feb 2006 17:56:08 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Han",
"Muxin",
""
],
[
"Ma",
"Yongge",
""
]
] | In recent twenty years, loop quantum gravity, a background independent approach to unify general relativity and quantum mechanics, has been widely investigated. We consider the quantum dynamics of a real massless scalar field coupled to gravity in this framework. A Hamiltonian operator for the scalar field can be well defined in the coupled diffeomorphism invariant Hilbert space, which is both self-adjoint and positive. On the other hand, the Hamiltonian constraint operator for the scalar field coupled to gravity can be well defined in the coupled kinematical Hilbert space. There are 1-parameter ambiguities due to scalar field in the construction of both operators. The results heighten our confidence that there is no divergence within this background independent and diffeomorphism invariant quantization approach of matter coupled to gravity. Moreover, to avoid possible quantum anomaly, the master constraint programme can be carried out in this coupled system by employing a self-adjoint master constraint operator on the diffeomorphism invariant Hilbert space. |
2111.03827 | Brett McInnes | Brett McInnes | Extremal Instability for Topological Black Holes | 17 pages, no figures; version to appear in Nuclear Physics B | null | 10.1016/j.nuclphysb.2022.115760 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The initial idea underlying the Weak Gravity Conjecture is that extremal
black holes must always be "unstable", in the sense that they should slowly
decay by emitting either particles or smaller black holes. Here we show that,
when this idea is applied to the \emph{planar} asymptotically AdS black holes
which play a central role in applications of holography, the result, via
gauge-gravity duality, is a prediction that there should exist a lower bound on
the possible densities of cold strongly coupled matter. Recent observations of
neutron stars suggest that, in many cases, even the extreme densities in their
cores may not be sufficient to generate quark matter, showing that there is
indeed a (very high) lower bound on the possible density of cold quark matter.
| [
{
"created": "Sat, 6 Nov 2021 08:01:57 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Mar 2022 10:03:37 GMT",
"version": "v2"
}
] | 2022-04-13 | [
[
"McInnes",
"Brett",
""
]
] | The initial idea underlying the Weak Gravity Conjecture is that extremal black holes must always be "unstable", in the sense that they should slowly decay by emitting either particles or smaller black holes. Here we show that, when this idea is applied to the \emph{planar} asymptotically AdS black holes which play a central role in applications of holography, the result, via gauge-gravity duality, is a prediction that there should exist a lower bound on the possible densities of cold strongly coupled matter. Recent observations of neutron stars suggest that, in many cases, even the extreme densities in their cores may not be sufficient to generate quark matter, showing that there is indeed a (very high) lower bound on the possible density of cold quark matter. |
1505.07371 | Alexis Helou | Alexis Helou | Dynamics of the four kinds of Trapping Horizons and Existence of Hawking
Radiation | 22 pages, 4 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We work with the notion of apparent/trapping horizons for spherically
symmetric, dynamical spacetimes: these are quasi-locally defined, simply based
on the behaviour of congruence of light rays. We show that the sign of the
dynamical Hayward-Kodama surface gravity is dictated by the inner/outer nature
of the horizon. Using the tunneling method to compute Hawking Radiation, this
surface gravity is then linked to a notion of temperature, up to a sign that is
dictated by the future/past nature of the horizon. Therefore two sign effects
are conspiring to give a positive temperature for the black hole case and the
expanding cosmology, whereas the same quantity is negative for white holes and
contracting cosmologies. This is consistent with the fact that, in the latter
cases, the horizon does not act as a separating membrane, and Hawking emission
should not occur.
| [
{
"created": "Wed, 27 May 2015 15:20:09 GMT",
"version": "v1"
}
] | 2015-05-28 | [
[
"Helou",
"Alexis",
""
]
] | We work with the notion of apparent/trapping horizons for spherically symmetric, dynamical spacetimes: these are quasi-locally defined, simply based on the behaviour of congruence of light rays. We show that the sign of the dynamical Hayward-Kodama surface gravity is dictated by the inner/outer nature of the horizon. Using the tunneling method to compute Hawking Radiation, this surface gravity is then linked to a notion of temperature, up to a sign that is dictated by the future/past nature of the horizon. Therefore two sign effects are conspiring to give a positive temperature for the black hole case and the expanding cosmology, whereas the same quantity is negative for white holes and contracting cosmologies. This is consistent with the fact that, in the latter cases, the horizon does not act as a separating membrane, and Hawking emission should not occur. |
2007.06907 | Soumya Jana | Soumya Jana, Charles Dalang, Lucas Lombriser | Horndeski theories and beyond from higher dimensions | 29 pages, published version | Class. Quantum Grav. 38 (2021) 025003 | 10.1088/1361-6382/abc272 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Einstein-Hilbert action with a cosmological constant is the most general
local four-dimensional action leading to second-order derivative equations of
motion that are symmetric and divergence free. In higher dimensions, additional
terms can appear. We investigate a generalised metric decomposition involving a
scalar degree of freedom to express the higher-dimensional action as an
effective four-dimensional scalar-tensor theory. From the higher-dimensional
Ricci scalar alone and a subclass of our metric ansatz, we recover the subset
of Horndeski theories with luminal speed of gravitational waves. More
generally, beyond-Horndeski terms appear. When including a Gauss-Bonnet scalar
in the higher-dimensional action, we generate contributions to all cubic-order
second-derivative terms present in the degenerate higher-order scalar-tensor
theory as well as higher-derivative terms beyond that. We discuss this
technique as a way to generate healthy four-dimensional gravity theories with
an extra scalar degree of freedom and outline further generalisations of our
method.
| [
{
"created": "Tue, 14 Jul 2020 08:38:17 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Feb 2021 07:30:32 GMT",
"version": "v2"
}
] | 2021-02-09 | [
[
"Jana",
"Soumya",
""
],
[
"Dalang",
"Charles",
""
],
[
"Lombriser",
"Lucas",
""
]
] | The Einstein-Hilbert action with a cosmological constant is the most general local four-dimensional action leading to second-order derivative equations of motion that are symmetric and divergence free. In higher dimensions, additional terms can appear. We investigate a generalised metric decomposition involving a scalar degree of freedom to express the higher-dimensional action as an effective four-dimensional scalar-tensor theory. From the higher-dimensional Ricci scalar alone and a subclass of our metric ansatz, we recover the subset of Horndeski theories with luminal speed of gravitational waves. More generally, beyond-Horndeski terms appear. When including a Gauss-Bonnet scalar in the higher-dimensional action, we generate contributions to all cubic-order second-derivative terms present in the degenerate higher-order scalar-tensor theory as well as higher-derivative terms beyond that. We discuss this technique as a way to generate healthy four-dimensional gravity theories with an extra scalar degree of freedom and outline further generalisations of our method. |
2205.15277 | Joao G. Rosa | John March-Russell and Jo\~ao G. Rosa | Micro-Bose/Proca dark matter stars from black hole superradiance | 5 pages, 2 figures | null | null | null | gr-qc astro-ph.CO hep-ph | http://creativecommons.org/licenses/by-nc-sa/4.0/ | We study the production of heavy, $\mu \gtrsim 1$ TeV, bosonic spin $s=0,1$
dark matter (DM) via the simultaneous processes of Hawking evaporation and
superradiance (SR) from an initial population of small, $\lesssim 10^6$ kg,
primordial black holes (PBHs). Even for small initial PBH spins the SR process
can produce extremely dense gravitationally-bound DM Bose or Proca soliton
"stars" of radius $\lesssim {\rm pm}$ and mass $\sim 10^{\rm few}$ kg that can
survive to today, well after PBH decay. These solitons can constitute a
significant fraction of the DM density, rising to $\gtrsim 50\%$ in the vector
DM case.
| [
{
"created": "Mon, 30 May 2022 17:38:51 GMT",
"version": "v1"
}
] | 2022-05-31 | [
[
"March-Russell",
"John",
""
],
[
"Rosa",
"João G.",
""
]
] | We study the production of heavy, $\mu \gtrsim 1$ TeV, bosonic spin $s=0,1$ dark matter (DM) via the simultaneous processes of Hawking evaporation and superradiance (SR) from an initial population of small, $\lesssim 10^6$ kg, primordial black holes (PBHs). Even for small initial PBH spins the SR process can produce extremely dense gravitationally-bound DM Bose or Proca soliton "stars" of radius $\lesssim {\rm pm}$ and mass $\sim 10^{\rm few}$ kg that can survive to today, well after PBH decay. These solitons can constitute a significant fraction of the DM density, rising to $\gtrsim 50\%$ in the vector DM case. |
gr-qc/9803072 | Kayll Lake | Kayll Lake | GR 15 Proceedings A5(ii) Computer Methods in GR: Algebraic computing | 7 pages, uses crckapb.sty | null | null | null | gr-qc | null | Algebraic computing in relativity and gravitation dates back more than thirty
years, but only relatively recently has hardware of sufficient power to tackle
large scale calculations become commonplace. Whereas it is generally understood
throughout the relativity community that there are a number of packages
available, the diversity of problems that the available packages can help with
is not so widely appreciated. This session was devoted to computer algebra for
relativity and gravitation from the point of view of developers. In this
summary I expand this to include some background and outline what is available
for users in the field.
| [
{
"created": "Thu, 19 Mar 1998 16:13:18 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Lake",
"Kayll",
""
]
] | Algebraic computing in relativity and gravitation dates back more than thirty years, but only relatively recently has hardware of sufficient power to tackle large scale calculations become commonplace. Whereas it is generally understood throughout the relativity community that there are a number of packages available, the diversity of problems that the available packages can help with is not so widely appreciated. This session was devoted to computer algebra for relativity and gravitation from the point of view of developers. In this summary I expand this to include some background and outline what is available for users in the field. |
gr-qc/9805003 | Ken D. Olum | Ken D. Olum | Superluminal travel requires negative energies | 5 pages, RevTeX, 2 figures with epsf. This paper now contains all the
material of gr-qc/6805003 and gr-qc/9806091 since these became a single
article in Phys. Rev. Lett | Phys.Rev.Lett. 81 (1998) 3567-3570 | 10.1103/PhysRevLett.81.3567 | null | gr-qc | null | I investigate the relationship between faster-than-light travel and
weak-energy-condition violation, i.e., negative energy densities. In a general
spacetime it is difficult to define faster-than-light travel, and I give an
example of a metric which appears to allow superluminal travel, but in fact is
just flat space. To avoid such difficulties, I propose a definition of
superluminal travel which requires that the path to be traveled reach a
destination surface at an earlier time than any neighboring path. With this
definition (and assuming the generic condition) I prove that superluminal
travel requires weak-energy-condition violation.
| [
{
"created": "Fri, 1 May 1998 19:39:39 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Oct 1998 18:55:32 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Olum",
"Ken D.",
""
]
] | I investigate the relationship between faster-than-light travel and weak-energy-condition violation, i.e., negative energy densities. In a general spacetime it is difficult to define faster-than-light travel, and I give an example of a metric which appears to allow superluminal travel, but in fact is just flat space. To avoid such difficulties, I propose a definition of superluminal travel which requires that the path to be traveled reach a destination surface at an earlier time than any neighboring path. With this definition (and assuming the generic condition) I prove that superluminal travel requires weak-energy-condition violation. |
1606.04097 | Supriya Pan | Supriya Pan, Barun Kumar Pal and Souvik Pramanik | Gravitationally influenced particle creation models and late-time cosmic
acceleration | 12 pages, 2 Tables, 5 Figures, title has been changed; published in
Int. J. Geom. Meth. Mod. Phys | Int. J. Geom. Meth. Mod. Phys. 15 (2018), no. 03, 1850042 | 10.1142/S0219887818500421 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we focus on the gravitationally influenced adiabatic particle
creation process, a mechanism that does not need any dark energy or modified
gravity models to explain the current accelerating phase of the universe.
Introducing some particle creation models that generalize some previous models
in the literature, we constrain the cosmological scenarios using the latest
compilation of the Type Ia Supernovae data only, the first indicator of the
accelerating universe. Aside from the observational constraints on the models,
we examine the models using two model independent diagnoses, namely the
cosmography and $Om$. Further, we establish the general conditions to test the
thermodynamic viabilities of any particle creation model. Our analysis shows
that at late-time, the models have close resemblance to that of the
$\Lambda$CDM cosmology, and the models always satisfy the generalized second
law of thermodynamics under certain conditions.
| [
{
"created": "Mon, 13 Jun 2016 15:38:14 GMT",
"version": "v1"
},
{
"created": "Sat, 18 Jun 2016 13:20:27 GMT",
"version": "v2"
},
{
"created": "Fri, 19 Jan 2018 17:49:13 GMT",
"version": "v3"
},
{
"created": "Sun, 8 Apr 2018 07:24:17 GMT",
"version": "v4"
}
] | 2018-04-10 | [
[
"Pan",
"Supriya",
""
],
[
"Pal",
"Barun Kumar",
""
],
[
"Pramanik",
"Souvik",
""
]
] | In this work we focus on the gravitationally influenced adiabatic particle creation process, a mechanism that does not need any dark energy or modified gravity models to explain the current accelerating phase of the universe. Introducing some particle creation models that generalize some previous models in the literature, we constrain the cosmological scenarios using the latest compilation of the Type Ia Supernovae data only, the first indicator of the accelerating universe. Aside from the observational constraints on the models, we examine the models using two model independent diagnoses, namely the cosmography and $Om$. Further, we establish the general conditions to test the thermodynamic viabilities of any particle creation model. Our analysis shows that at late-time, the models have close resemblance to that of the $\Lambda$CDM cosmology, and the models always satisfy the generalized second law of thermodynamics under certain conditions. |
2105.04329 | Lance Williams | L.L. Williams and N. Inan | Inductive rectilinear frame dragging and local coupling to the
gravitational field of the universe | 13 pages, 1 figure | Universe 2021, 7(8), 284 | 10.3390/universe7080284 | null | gr-qc | http://creativecommons.org/licenses/by-nc-nd/4.0/ | There is a drag force on objects moving in the background cosmological
metric, known from galaxy cluster dynamics. The force is quite small over
laboratory timescales, yet it applies in principle to all moving bodies in the
universe. It means it is possible for matter to exchange momentum and energy
with the gravitational field of the universe, and that the cosmological metric
can be determined in principle from local measurements on moving bodies. The
drag force can be understood as inductive rectilinear frame dragging. This
dragging force exists in the rest frame of a moving object, and arises from the
off-diagonal components induced in the boosted-frame metric. Unlike the Kerr
metric or other typical frame-dragging geometries, cosmological inductive
dragging occurs at uniform velocity, along the direction of motion, and
dissipates energy. Proposed gravito-magnetic invariants formed from
contractions of the Riemann tensor do not appear to capture inductive dragging
effects, and this might be the first identification of inductive rectilinear
dragging.
| [
{
"created": "Mon, 10 May 2021 13:05:39 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jul 2021 04:23:30 GMT",
"version": "v2"
}
] | 2021-08-06 | [
[
"Williams",
"L. L.",
""
],
[
"Inan",
"N.",
""
]
] | There is a drag force on objects moving in the background cosmological metric, known from galaxy cluster dynamics. The force is quite small over laboratory timescales, yet it applies in principle to all moving bodies in the universe. It means it is possible for matter to exchange momentum and energy with the gravitational field of the universe, and that the cosmological metric can be determined in principle from local measurements on moving bodies. The drag force can be understood as inductive rectilinear frame dragging. This dragging force exists in the rest frame of a moving object, and arises from the off-diagonal components induced in the boosted-frame metric. Unlike the Kerr metric or other typical frame-dragging geometries, cosmological inductive dragging occurs at uniform velocity, along the direction of motion, and dissipates energy. Proposed gravito-magnetic invariants formed from contractions of the Riemann tensor do not appear to capture inductive dragging effects, and this might be the first identification of inductive rectilinear dragging. |
1912.10015 | Benjamin Elder | Benjamin Elder, Valeri Vardanyan, Yashar Akrami, Philippe Brax,
Anne-Christine Davis, and Ricardo S. Decca | The Classical Symmetron Force in Casimir Experiments | 16 pages, 8 figures | Phys. Rev. D 101, 064065 (2020) | 10.1103/PhysRevD.101.064065 | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The symmetron is a typical example of screened modified gravity, wherein the
symmetron force is dynamically suppressed in dense environments. This allows it
to hide in traditional tests of gravity. However, the past decade has seen
great experimental progress towards measuring screened forces in the laboratory
or in space. Screening relies on nonlinearities in the equation of motion,
which significantly complicates the theoretical analysis of such forces. Here,
we present a calculation of the symmetron force between a dense plate and
sphere surrounded by vacuum. This is done via semi-analytical approaches in two
limiting cases, based on the size of the sphere: large spheres are analyzed via
the proximity force approximation, whilst small spheres are treated as screened
test particles. In the intermediate regime we solve the problem numerically.
Our results allow us to make contact with Casimir force experiments, which
often employ a plate and sphere configuration for practical reasons, and may
therefore be used to constrain symmetrons. We use our results to forecast
constraints on the symmetron's parameters for a hypothetical Casimir experiment
that is based on the current state of the art. The forecasts compare favorably
to other leading laboratory tests of gravity, particularly atom interferometry
and bouncing neutrons. We thus conclude that near-future Casimir experiments
will be capable of placing tight new bounds on symmetrons. Our results for the
symmetron force are derived in a scale-invariant way, such that although we
here focus on Casimir experiments, they may be applied to any other
plate-sphere system, ranging from microscopic to astrophysical scales.
| [
{
"created": "Fri, 20 Dec 2019 18:43:31 GMT",
"version": "v1"
}
] | 2020-04-01 | [
[
"Elder",
"Benjamin",
""
],
[
"Vardanyan",
"Valeri",
""
],
[
"Akrami",
"Yashar",
""
],
[
"Brax",
"Philippe",
""
],
[
"Davis",
"Anne-Christine",
""
],
[
"Decca",
"Ricardo S.",
""
]
] | The symmetron is a typical example of screened modified gravity, wherein the symmetron force is dynamically suppressed in dense environments. This allows it to hide in traditional tests of gravity. However, the past decade has seen great experimental progress towards measuring screened forces in the laboratory or in space. Screening relies on nonlinearities in the equation of motion, which significantly complicates the theoretical analysis of such forces. Here, we present a calculation of the symmetron force between a dense plate and sphere surrounded by vacuum. This is done via semi-analytical approaches in two limiting cases, based on the size of the sphere: large spheres are analyzed via the proximity force approximation, whilst small spheres are treated as screened test particles. In the intermediate regime we solve the problem numerically. Our results allow us to make contact with Casimir force experiments, which often employ a plate and sphere configuration for practical reasons, and may therefore be used to constrain symmetrons. We use our results to forecast constraints on the symmetron's parameters for a hypothetical Casimir experiment that is based on the current state of the art. The forecasts compare favorably to other leading laboratory tests of gravity, particularly atom interferometry and bouncing neutrons. We thus conclude that near-future Casimir experiments will be capable of placing tight new bounds on symmetrons. Our results for the symmetron force are derived in a scale-invariant way, such that although we here focus on Casimir experiments, they may be applied to any other plate-sphere system, ranging from microscopic to astrophysical scales. |
0801.4001 | Martin Bojowald | Martin Bojowald | Quantum nature of cosmological bounces | 26 pages | Gen.Rel.Grav.40:2659-2683,2008 | 10.1007/s10714-008-0645-1 | IGC-08/1-3 | gr-qc astro-ph hep-th | null | Several examples are known where quantum gravity effects resolve the
classical big bang singularity by a bounce. The most detailed analysis has
probably occurred for loop quantum cosmology of isotropic models sourced by a
free, massless scalar. Once a bounce has been realized under fairly general
conditions, the central questions are how strongly quantum it behaves, what
influence quantum effects can have on its appearance, and what quantum
space-time beyond the bounce may look like. This, then, has to be taken into
account for effective equations which describe the evolution properly and can
be used for further phenomenological investigations. Here, we provide the first
analysis with interacting matter with new effective equations valid for weak
self-interactions or small masses. They differ from the free scalar equations
by crucial terms and have an important influence on the bounce and the
space-time around it. Especially the role of squeezed states, which have often
been overlooked in this context, is highlighted. The presence of a bounce is
proven for uncorrelated states, but as squeezing is a dynamical property and
may change in time, further work is required for a general conclusion.
| [
{
"created": "Fri, 25 Jan 2008 17:59:45 GMT",
"version": "v1"
}
] | 2008-12-18 | [
[
"Bojowald",
"Martin",
""
]
] | Several examples are known where quantum gravity effects resolve the classical big bang singularity by a bounce. The most detailed analysis has probably occurred for loop quantum cosmology of isotropic models sourced by a free, massless scalar. Once a bounce has been realized under fairly general conditions, the central questions are how strongly quantum it behaves, what influence quantum effects can have on its appearance, and what quantum space-time beyond the bounce may look like. This, then, has to be taken into account for effective equations which describe the evolution properly and can be used for further phenomenological investigations. Here, we provide the first analysis with interacting matter with new effective equations valid for weak self-interactions or small masses. They differ from the free scalar equations by crucial terms and have an important influence on the bounce and the space-time around it. Especially the role of squeezed states, which have often been overlooked in this context, is highlighted. The presence of a bounce is proven for uncorrelated states, but as squeezing is a dynamical property and may change in time, further work is required for a general conclusion. |
1802.08087 | Sergio Ulhoa | A. S. Fernandes, S. C. Ulhoa, R. G. G. Amorim | On Quantum Cosmology in Teleparallel Gravity | null | Journal of Physics: Conf. Series 965 (2018) 012014 | 10.1088/1742-6596/965/1/012014 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A quantum cosmology in teleparallel gravity is presented in this article.
Teleparallel gravity is used to perform such an analysis once in General
Relativity (GR) the concept of gravitational energy is misleading preventing
the establishment of a concise quantum cosmology. The Wheeler-DeWitt like
equation is obtained using the Weyl quantization and the teleparallel
expression of energy.
| [
{
"created": "Wed, 21 Feb 2018 18:59:31 GMT",
"version": "v1"
}
] | 2018-02-23 | [
[
"Fernandes",
"A. S.",
""
],
[
"Ulhoa",
"S. C.",
""
],
[
"Amorim",
"R. G. G.",
""
]
] | A quantum cosmology in teleparallel gravity is presented in this article. Teleparallel gravity is used to perform such an analysis once in General Relativity (GR) the concept of gravitational energy is misleading preventing the establishment of a concise quantum cosmology. The Wheeler-DeWitt like equation is obtained using the Weyl quantization and the teleparallel expression of energy. |
1601.07563 | Dejan Stojkovic | De-Chang Dai, Dejan Stojkovic | Maximal temperature in a simple thermodynamical system | Published in JCAP 1606 (2016) no.06, 040 | JCAP 1606 (2016) no.06, 040 | 10.1088/1475-7516/2016/06/040 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Temperature in a simple thermodynamical system is not limited from above. It
is also widely believed that it does not make sense talking about temperatures
higher than the Planck temperature in the absence of the full theory of quantum
gravity. Here, we demonstrate that there exist a maximal achievable temperature
in a system where particles obey the laws of quantum mechanics and classical
gravity before we reach the realm of quantum gravity. Namely, if two particles
with a given center of mass energy come at the distance shorter than the
Schwarzschild diameter apart, according to classical gravity they will form a
black hole. It is possible to calculate that a simple thermodynamical system
will be dominated by black holes at a critical temperature which is about three
times lower than the Planck temperature. That represents the maximal achievable
temperature in a simple thermodynamical system.
| [
{
"created": "Wed, 27 Jan 2016 21:00:52 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Jul 2016 21:49:31 GMT",
"version": "v2"
}
] | 2016-08-05 | [
[
"Dai",
"De-Chang",
""
],
[
"Stojkovic",
"Dejan",
""
]
] | Temperature in a simple thermodynamical system is not limited from above. It is also widely believed that it does not make sense talking about temperatures higher than the Planck temperature in the absence of the full theory of quantum gravity. Here, we demonstrate that there exist a maximal achievable temperature in a system where particles obey the laws of quantum mechanics and classical gravity before we reach the realm of quantum gravity. Namely, if two particles with a given center of mass energy come at the distance shorter than the Schwarzschild diameter apart, according to classical gravity they will form a black hole. It is possible to calculate that a simple thermodynamical system will be dominated by black holes at a critical temperature which is about three times lower than the Planck temperature. That represents the maximal achievable temperature in a simple thermodynamical system. |
2209.03536 | Kelvin H. M. Chan | Kelvin H. M. Chan and Otto A. Hannuksela | Extracting ultralight boson properties from boson clouds around
post-merger remnants | 12 pages | null | null | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Ultralight bosons are a class of hypothetical particles that could
potentially solve critical problems in fields ranging from cosmology to
astrophysics and fundamental physics. If ultralight bosons exist, they form
clouds around spinning black holes with sizes comparable to their particle
Compton wavelength through superradiance, a well-understood classical wave
amplification process that has been studied for decades. After these clouds
form, they dissipate and emit continuous gravitational waves through the
annihilation of ultralight bosons into gravitons. These gravitons could be
detected with ground-based gravitational-wave detectors using continuous-wave
searches. However, it is conceivable for other continuous-wave sources to mimic
the emission from the clouds, which could lead to false detections. Here we
investigate how one can use continuous waves from clouds formed around known
merger remnants to alleviate this problem. In particular, we simulate a
catalogue of merger remnants that form clouds around them and demonstrate with
select "golden" merger remnants how one can perform a Bayesian
cross-verification of the ultralight boson hypothesis that has the potential to
rule out alternative explanations. Our proof-of-concept study suggest that, in
the future, there is a possibility that a merger remnant exists close enough
for us to perform the analysis and test the boson hypothesis if the bosons
exist in the relevant mass range. Future research will focus on building more
sophisticated continuous-wave tools to perform this analysis in practice.
| [
{
"created": "Thu, 8 Sep 2022 02:35:27 GMT",
"version": "v1"
},
{
"created": "Fri, 9 Sep 2022 00:49:07 GMT",
"version": "v2"
}
] | 2022-09-13 | [
[
"Chan",
"Kelvin H. M.",
""
],
[
"Hannuksela",
"Otto A.",
""
]
] | Ultralight bosons are a class of hypothetical particles that could potentially solve critical problems in fields ranging from cosmology to astrophysics and fundamental physics. If ultralight bosons exist, they form clouds around spinning black holes with sizes comparable to their particle Compton wavelength through superradiance, a well-understood classical wave amplification process that has been studied for decades. After these clouds form, they dissipate and emit continuous gravitational waves through the annihilation of ultralight bosons into gravitons. These gravitons could be detected with ground-based gravitational-wave detectors using continuous-wave searches. However, it is conceivable for other continuous-wave sources to mimic the emission from the clouds, which could lead to false detections. Here we investigate how one can use continuous waves from clouds formed around known merger remnants to alleviate this problem. In particular, we simulate a catalogue of merger remnants that form clouds around them and demonstrate with select "golden" merger remnants how one can perform a Bayesian cross-verification of the ultralight boson hypothesis that has the potential to rule out alternative explanations. Our proof-of-concept study suggest that, in the future, there is a possibility that a merger remnant exists close enough for us to perform the analysis and test the boson hypothesis if the bosons exist in the relevant mass range. Future research will focus on building more sophisticated continuous-wave tools to perform this analysis in practice. |
1406.0840 | Ghulam Abbas | G. Abbas, U. Sabiullah | Geodesic Study of Regular Hayward Black Hole | 14 pages, 7 figures. Accepted for publication in Astrophy. and Space
Sci. This paper is outcome of M.Sc. Thesis of Mr. Sabiullah Supervised by Dr.
Ghulam Abbas | Astrophys. Space Sci. 352(2014)769 | 10.1007/s10509-014-1992-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper is devoted to study the geodesic structure of regular Hayward
black hole. The timelike and null geodesic have been studied explicitly for
radial and non-radial motion. For timelike and null geodesic in radial motion
there exists analytical solution, while for non-radial motion the effective
potential has been plotted, which investigates the position and turning points
of the particle. It has been found that massive particle moving along timelike
geodesics path are dragged towards the BH and continues move around BH in
particular orbits.
| [
{
"created": "Tue, 3 Jun 2014 07:50:47 GMT",
"version": "v1"
}
] | 2015-06-19 | [
[
"Abbas",
"G.",
""
],
[
"Sabiullah",
"U.",
""
]
] | This paper is devoted to study the geodesic structure of regular Hayward black hole. The timelike and null geodesic have been studied explicitly for radial and non-radial motion. For timelike and null geodesic in radial motion there exists analytical solution, while for non-radial motion the effective potential has been plotted, which investigates the position and turning points of the particle. It has been found that massive particle moving along timelike geodesics path are dragged towards the BH and continues move around BH in particular orbits. |
2205.08707 | Vladimir Folomeev | Vladimir Dzhunushaliev, Vladimir Folomeev, and Nassurlla Burtebayev | Rapidly rotating Dirac stars | 12 pages, 4 figures, minor corrections to content, version published
in PRD | Phys. Rev. D 106, 024021 (2022) | 10.1103/PhysRevD.106.024021 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Within general relativity, we construct sequences of rapidly rotating Dirac
stars consisting of a spinor fluid described by an effective equation of state.
We find the physically relevant domain of stable configurations and calculate
their principal characteristics which are completely determined by the central
density of the spinor fluid, the mass of the nonlinear spinor field, and the
velocity of rotation. It is demonstrated that for a certain choice of the
spinor field mass, the main physical characteristics of the Dirac stars are
close to those that are typical of rotating neutron stars.
| [
{
"created": "Wed, 18 May 2022 04:05:48 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Jul 2022 04:01:21 GMT",
"version": "v2"
}
] | 2022-07-15 | [
[
"Dzhunushaliev",
"Vladimir",
""
],
[
"Folomeev",
"Vladimir",
""
],
[
"Burtebayev",
"Nassurlla",
""
]
] | Within general relativity, we construct sequences of rapidly rotating Dirac stars consisting of a spinor fluid described by an effective equation of state. We find the physically relevant domain of stable configurations and calculate their principal characteristics which are completely determined by the central density of the spinor fluid, the mass of the nonlinear spinor field, and the velocity of rotation. It is demonstrated that for a certain choice of the spinor field mass, the main physical characteristics of the Dirac stars are close to those that are typical of rotating neutron stars. |
1808.09202 | Giovanni Acquaviva | Giovanni Acquaviva, Aroonkumar Beesham | Dynamical analysis of a first order theory of bulk viscosity | 18 pages, 11 figures | null | 10.1088/1361-6382/aadb38 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform a global analysis of curved Friedmann-Robertson-Walker cosmologies
in the presence of a viscous fluid. The fluid's bulk viscosity is governed by a
first order theory recently proposed in [M. M. Disconzi, T. W. Kephart, and R.
J. Scherrer, Phys. Rev. D 91, 043532 (2015)], and the analysis is carried out
in a compactified parameter space with dimensionless coordinates. We provide
stability properties, cosmological interpretation and thermodynamic features of
the critical points.
| [
{
"created": "Tue, 28 Aug 2018 09:57:21 GMT",
"version": "v1"
}
] | 2018-08-29 | [
[
"Acquaviva",
"Giovanni",
""
],
[
"Beesham",
"Aroonkumar",
""
]
] | We perform a global analysis of curved Friedmann-Robertson-Walker cosmologies in the presence of a viscous fluid. The fluid's bulk viscosity is governed by a first order theory recently proposed in [M. M. Disconzi, T. W. Kephart, and R. J. Scherrer, Phys. Rev. D 91, 043532 (2015)], and the analysis is carried out in a compactified parameter space with dimensionless coordinates. We provide stability properties, cosmological interpretation and thermodynamic features of the critical points. |
2307.01768 | Hussain Gohar | Hussain Gohar, Vincenzo Salzano | On the foundations of entropic cosmologies: inconsistencies, possible
solutions and dead end signs | 12 pages, added references and explanations | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this letter we explore the foundations of entropic cosmology and highlight
some important flaws which have emerged and adopted in the recent literature.
We argue that, when applying entropy and temperature on the cosmological
horizon by assuming the holographic principle for all thermodynamic approaches
to cosmology and gravity, one must derive the consistent thermodynamic
quantities following Clausius relation. One key assumption which is generally
overlooked, is that in this process one must assume a mass-to-horizon relation,
which is generally taken as a linear one. We show that, regardless of the type
of entropy chosen on the cosmological horizon, when a thermodynamically
consistent corresponding temperature is considered, all modified entropic force
models are equivalent to and indistinguishable from the original entropic force
models based on standard Bekenstein entropy and Hawking temperature. As such,
they are also plagued by the same problems and inability to describe in a
satisfactory qualitative and quantitative way the cosmological dynamics as it
emerges from the probes we have. We also show that the standard accepted
parameterization for Hawking temperature (including a $\gamma$ rescaling) is
actually not correctly applied, namely, it is not related to entropy in a
thermodynamically consistent way. Finally, we clearly state that the explicit
form of the entropic force on cosmological horizons is mostly dictated by the
assumption on the mass-to-horizon relation. As such, we discuss what should be
done in order to fix all such issues, and what conceptually could be implied by
its correct implementation in order to advance in the field.
| [
{
"created": "Tue, 4 Jul 2023 15:15:43 GMT",
"version": "v1"
},
{
"created": "Sat, 8 Jul 2023 00:56:00 GMT",
"version": "v2"
},
{
"created": "Fri, 22 Mar 2024 14:00:09 GMT",
"version": "v3"
}
] | 2024-03-25 | [
[
"Gohar",
"Hussain",
""
],
[
"Salzano",
"Vincenzo",
""
]
] | In this letter we explore the foundations of entropic cosmology and highlight some important flaws which have emerged and adopted in the recent literature. We argue that, when applying entropy and temperature on the cosmological horizon by assuming the holographic principle for all thermodynamic approaches to cosmology and gravity, one must derive the consistent thermodynamic quantities following Clausius relation. One key assumption which is generally overlooked, is that in this process one must assume a mass-to-horizon relation, which is generally taken as a linear one. We show that, regardless of the type of entropy chosen on the cosmological horizon, when a thermodynamically consistent corresponding temperature is considered, all modified entropic force models are equivalent to and indistinguishable from the original entropic force models based on standard Bekenstein entropy and Hawking temperature. As such, they are also plagued by the same problems and inability to describe in a satisfactory qualitative and quantitative way the cosmological dynamics as it emerges from the probes we have. We also show that the standard accepted parameterization for Hawking temperature (including a $\gamma$ rescaling) is actually not correctly applied, namely, it is not related to entropy in a thermodynamically consistent way. Finally, we clearly state that the explicit form of the entropic force on cosmological horizons is mostly dictated by the assumption on the mass-to-horizon relation. As such, we discuss what should be done in order to fix all such issues, and what conceptually could be implied by its correct implementation in order to advance in the field. |
gr-qc/9712032 | S. Droz | Serge Droz and Eric Poisson | Can LIGO see compact binaries? | 4 Pages, Proc. to the 7th Canadian Conference on General Relativity
and Relativistic Astrophysics 1997 | null | null | null | gr-qc | null | The probability that interferometric detectors such as LIGO and VIRGO will
successfully detect inspiraling compact binaries depends in part on our
knowledge of the expected gravitational wave forms.
The best approximations to the true wave forms available today are the
post-Newtonian (PN) templates. In this paper we argue that these 2PN templates
are accurate enough for a successful search for compact binaries with the
advanced LIGO interferometer. Results are presented for the 40-meter Caltech
prototype as well as for the inital and advance LIGO detectors.
| [
{
"created": "Fri, 5 Dec 1997 16:31:37 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Droz",
"Serge",
""
],
[
"Poisson",
"Eric",
""
]
] | The probability that interferometric detectors such as LIGO and VIRGO will successfully detect inspiraling compact binaries depends in part on our knowledge of the expected gravitational wave forms. The best approximations to the true wave forms available today are the post-Newtonian (PN) templates. In this paper we argue that these 2PN templates are accurate enough for a successful search for compact binaries with the advanced LIGO interferometer. Results are presented for the 40-meter Caltech prototype as well as for the inital and advance LIGO detectors. |
2106.05991 | Carlos O. Lousto | Nicole Rosato, Hiroyuki Nakano, Carlos O. Lousto | Local and Approximate classification of spacetimes in the transverse
frames | 18 pages, 11 figures | Phys. Rev. D 104, 044047 (2021) | 10.1103/PhysRevD.104.044047 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revisit the definition of transverse frames and tetrad choices with
regards to its application to numerically generated spacetimes, in particular
those from the merger of binary black holes. We introduce the concept of local
and approximate algebraic Petrov types in the strong field regime. We define an
index $\mathcal{D}=\sqrt{12/I}\left(\Psi_2 - \Psi_3^2/\Psi_4\right)$ able to
discriminate between Petrov types II and D and define regions of spacetime of
those approximate types when used in conjunction with the speciality invariant
$S=27J^2/I^3$. We provide an explicit example applying this method to
Brill-Lindquist initial data corresponding to two nonspinning black holes from
rest at a given initial separation. We find a doughnut-like region that is
approximately of Petrov type II surrounded by an approximately Petrov type D
region. We complete the study by proposing a totally symmetric tetrad fixing of
the transverse frame that can be simply implemented in numerically generated
spacetimes through the computation of spin coefficients ratios. We provide an
application by explicitly deriving the Kerr-perturbative equations in this
tetrad.
| [
{
"created": "Thu, 10 Jun 2021 18:11:33 GMT",
"version": "v1"
},
{
"created": "Sat, 24 Jul 2021 18:10:54 GMT",
"version": "v2"
}
] | 2021-08-25 | [
[
"Rosato",
"Nicole",
""
],
[
"Nakano",
"Hiroyuki",
""
],
[
"Lousto",
"Carlos O.",
""
]
] | We revisit the definition of transverse frames and tetrad choices with regards to its application to numerically generated spacetimes, in particular those from the merger of binary black holes. We introduce the concept of local and approximate algebraic Petrov types in the strong field regime. We define an index $\mathcal{D}=\sqrt{12/I}\left(\Psi_2 - \Psi_3^2/\Psi_4\right)$ able to discriminate between Petrov types II and D and define regions of spacetime of those approximate types when used in conjunction with the speciality invariant $S=27J^2/I^3$. We provide an explicit example applying this method to Brill-Lindquist initial data corresponding to two nonspinning black holes from rest at a given initial separation. We find a doughnut-like region that is approximately of Petrov type II surrounded by an approximately Petrov type D region. We complete the study by proposing a totally symmetric tetrad fixing of the transverse frame that can be simply implemented in numerically generated spacetimes through the computation of spin coefficients ratios. We provide an application by explicitly deriving the Kerr-perturbative equations in this tetrad. |
gr-qc/9411058 | Othmar Brodbeck | Othmar Brodbeck and Norbert Straumann | Instability Proof for Einstein-Yang-Mills Solitons and Black Holes with
Arbitrary Gauge Groups | 26 pages, LATEX, no figures | J.Math.Phys.37:1414-1433,1996 | 10.1063/1.531441 | ZU-TH 38/94 | gr-qc | null | We prove that static, spherically symmetric, asymptotically flat soliton and
black hole solutions of the Einstein-Yang-Mills equations are unstable for
arbitrary gauge groups, at least for the ``generic" case. This conclusion is
derived without explicit knowledge of the possible equilibrium solutions.
| [
{
"created": "Tue, 22 Nov 1994 13:07:30 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Brodbeck",
"Othmar",
""
],
[
"Straumann",
"Norbert",
""
]
] | We prove that static, spherically symmetric, asymptotically flat soliton and black hole solutions of the Einstein-Yang-Mills equations are unstable for arbitrary gauge groups, at least for the ``generic" case. This conclusion is derived without explicit knowledge of the possible equilibrium solutions. |
gr-qc/0004081 | Yuri N. Obukhov | Yuri N. Obukhov and Eugen J. Vlachynsky | Einstein--Proca model: spherically symmetric solutions | 20 p., Revtex, 3 Postscript figures | Ann.Phys.8:497-510,1999 | 10.1002/(SICI)1521-3889(199909)8:6<497::AID-ANDP497>3.0.CO;2-5 | null | gr-qc | null | The Proca wave equation describes a classical massive spin 1 particle. We
analyze the gravitational interaction of this vector field. In particular, the
spherically symmetric solutions of the Einstein-Proca coupled system are
obtained numerically. Although at infinity the metric field approaches the
usual Schwarzschild (Reissner-Nordstr\"om) limit, we demonstrate the absence of
black hole type configurations.
| [
{
"created": "Fri, 28 Apr 2000 15:46:39 GMT",
"version": "v1"
}
] | 2017-09-27 | [
[
"Obukhov",
"Yuri N.",
""
],
[
"Vlachynsky",
"Eugen J.",
""
]
] | The Proca wave equation describes a classical massive spin 1 particle. We analyze the gravitational interaction of this vector field. In particular, the spherically symmetric solutions of the Einstein-Proca coupled system are obtained numerically. Although at infinity the metric field approaches the usual Schwarzschild (Reissner-Nordstr\"om) limit, we demonstrate the absence of black hole type configurations. |
1211.2363 | Gabriel Pascu | Gabriel Pascu | Atlas of Coordinate Charts on de Sitter Spacetime | null | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The de Sitter manifold admits a wide variety of interesting
coordinatizations. The 'atlas' is a compilation of the coordinate charts
referenced throughout the literature, and is presented in the form of tables,
the starting point being the embedding in a higher-dimensional Minkowski
spacetime. The metric tensor and the references where the coordinate frame is
discussed or used in applications are noted. Additional information is given
for the entries with significant use: a convenient tetrad and the form taken by
the Killing vectors in the respective coordinate frame.
| [
{
"created": "Sun, 11 Nov 2012 01:08:56 GMT",
"version": "v1"
}
] | 2012-11-13 | [
[
"Pascu",
"Gabriel",
""
]
] | The de Sitter manifold admits a wide variety of interesting coordinatizations. The 'atlas' is a compilation of the coordinate charts referenced throughout the literature, and is presented in the form of tables, the starting point being the embedding in a higher-dimensional Minkowski spacetime. The metric tensor and the references where the coordinate frame is discussed or used in applications are noted. Additional information is given for the entries with significant use: a convenient tetrad and the form taken by the Killing vectors in the respective coordinate frame. |
gr-qc/9905040 | Hiroshi Umetsu | Hisao Suzuki, Eiichi Takasugi and Hiroshi Umetsu | Analytic Solutions of Teukolsky Equation in Kerr-de Sitter and
Kerr-Newman-de Sitter Geometries | 24 pages, LaTeX | Prog.Theor.Phys. 102 (1999) 253-272 | 10.1143/PTP.102.253 | EPHOU 99-007, OU-HET-319 | gr-qc | null | The analytic solution of Teukolsky equation in Kerr-de Sitter and
Kerr-Newman-de Sitter geometries is presented and the properties of the
solution are examined. In particular, we show that our solution satisfies the
Teukolsky-Starobinsky identities explicitly and fix the relative normalization
between solutions with the spin weight $s$ and $-s$.
| [
{
"created": "Thu, 13 May 1999 07:19:18 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Suzuki",
"Hisao",
""
],
[
"Takasugi",
"Eiichi",
""
],
[
"Umetsu",
"Hiroshi",
""
]
] | The analytic solution of Teukolsky equation in Kerr-de Sitter and Kerr-Newman-de Sitter geometries is presented and the properties of the solution are examined. In particular, we show that our solution satisfies the Teukolsky-Starobinsky identities explicitly and fix the relative normalization between solutions with the spin weight $s$ and $-s$. |
1308.3502 | Hirotada Okawa | Hirotada Okawa | Initial Conditions for Numerical Relativity -- Introduction to numerical
methods for solving elliptic PDEs | Lecture notes from the NRHEP spring school held at IST-Lisbon, March
2013. Extra material and notebooks available online at
http://blackholes.ist.utl.pt/nrhep2/ To be published by IJMPA (V. Cardoso, L.
Gualtieri, C. Herdeiro and U. Sperhake, Eds., 2013) | null | 10.1142/S0217751X13400162 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Numerical relativity became a powerful tool to investigate the dynamics of
binary problems with black holes or neutron stars as well as the very structure
of General Relativity. Although public numerical relativity codes are available
to evolve such systems, a proper understanding of the methods involved is quite
important. Here we focus on the numerical solution of elliptic partial
differential equations. Such equations arise when preparing initial data for
numerical relativity, but also for monitoring the evolution of black holes.
Because such elliptic equations play an important role in many branches of
physics, we give an overview of the topic, and show how to numerically solve
them with simple examples and sample codes written in C++ and Fortran90 for
beginners in numerical relativity or other fields requiring numerical
expertise.
| [
{
"created": "Thu, 15 Aug 2013 20:14:33 GMT",
"version": "v1"
}
] | 2015-06-16 | [
[
"Okawa",
"Hirotada",
""
]
] | Numerical relativity became a powerful tool to investigate the dynamics of binary problems with black holes or neutron stars as well as the very structure of General Relativity. Although public numerical relativity codes are available to evolve such systems, a proper understanding of the methods involved is quite important. Here we focus on the numerical solution of elliptic partial differential equations. Such equations arise when preparing initial data for numerical relativity, but also for monitoring the evolution of black holes. Because such elliptic equations play an important role in many branches of physics, we give an overview of the topic, and show how to numerically solve them with simple examples and sample codes written in C++ and Fortran90 for beginners in numerical relativity or other fields requiring numerical expertise. |
2209.04347 | Eleni-Alexandra Kontou | Melanie Graf, Eleni-Alexandra Kontou, Argam Ohanyan, Benedict
Schinnerl | Hawking-type singularity theorems for worldvolume energy inequalities | 30 pages | null | null | null | gr-qc math-ph math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The classical singularity theorems of R. Penrose and S. Hawking from the
1960s show that, given a pointwise energy condition (and some causality as well
as initial assumptions), spacetimes cannot be geodesically complete. Despite
their great success, the theorems leave room for physically relevant
improvements, especially regarding the classical energy conditions as
essentially any quantum field theory necessarily violates them. While
singularity theorems with weakened energy conditions exist for worldline
integral bounds, so called worldvolume bounds are in some cases more applicable
than the worldline ones, such as the case of some massive free fields. In this
paper we study integral Ricci curvature bounds based on worldvolume quantum
strong energy inequalities. Under the additional assumption of a - potentially
very negative - global timelike Ricci curvature bound, a Hawking type
singularity theorem is proven. Finally, we apply the theorem to a cosmological
scenario proving past geodesic incompleteness in cases where the worldline
theorem was inconclusive.
| [
{
"created": "Fri, 9 Sep 2022 15:19:26 GMT",
"version": "v1"
}
] | 2022-09-12 | [
[
"Graf",
"Melanie",
""
],
[
"Kontou",
"Eleni-Alexandra",
""
],
[
"Ohanyan",
"Argam",
""
],
[
"Schinnerl",
"Benedict",
""
]
] | The classical singularity theorems of R. Penrose and S. Hawking from the 1960s show that, given a pointwise energy condition (and some causality as well as initial assumptions), spacetimes cannot be geodesically complete. Despite their great success, the theorems leave room for physically relevant improvements, especially regarding the classical energy conditions as essentially any quantum field theory necessarily violates them. While singularity theorems with weakened energy conditions exist for worldline integral bounds, so called worldvolume bounds are in some cases more applicable than the worldline ones, such as the case of some massive free fields. In this paper we study integral Ricci curvature bounds based on worldvolume quantum strong energy inequalities. Under the additional assumption of a - potentially very negative - global timelike Ricci curvature bound, a Hawking type singularity theorem is proven. Finally, we apply the theorem to a cosmological scenario proving past geodesic incompleteness in cases where the worldline theorem was inconclusive. |
2106.00491 | Pardyumn Kumar Sahoo | Simran Arora, S. K. J. Pacif, Abhishek Parida, P.K. Sahoo | Bulk viscous matter and the cosmic acceleration of the universe in
$f(Q,T)$ gravity | Revised version | Journal of High Energy Astrophysics, 33 (2022) 1-9 | 10.1016/j.jheap.2021.10.001 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We have studied bulk viscosity in the modified $f(Q, T)$ gravity theory
formalism, where $Q$ represents the non-metricity and $T$ denotes the trace of
energy-momentum tensor within a flat Friedmann-Lema\^{i}tre-Robertson-Walker
metric (FLRW). Here, we have explicitly considered the effective equation of
state, which includes a bulk viscosity term, and obtained the exact solutions
by assuming a specific form of $f(Q, T)=\alpha Q+\beta T$, where $\alpha$ and
$\beta$ are constants. Furthermore, we have found constraints on the model
parameters with some external datasets, such as the revised Hubble datasets
consisting of 57 data points, Baryon acoustic oscillations (BAO) datasets, and
the newly published Pantheon samples with 1048 points to obtain the best
fitting values of the model parameters. The obtained model is found to be in
good agreement with observations. In addition, we have analyzed the
cosmological behavior of the density parameter, the equation of state (EoS)
parameter ($\omega$), and the deceleration parameter ($q$). The results are
satisfying to the standard scenario of recent findings of cosmology. The
universe appears to be evolving from a decelerated to an accelerated phase. The
EoS parameter is further in the quintessence phase, indicating that the
universe is accelerating. Finally, we can deduce that the accumulation of bulk
viscosity as effective dark energy supports the current accelerated expansion
of the universe.
| [
{
"created": "Mon, 31 May 2021 06:03:56 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Aug 2021 04:23:13 GMT",
"version": "v2"
},
{
"created": "Mon, 11 Oct 2021 07:43:49 GMT",
"version": "v3"
}
] | 2021-12-01 | [
[
"Arora",
"Simran",
""
],
[
"Pacif",
"S. K. J.",
""
],
[
"Parida",
"Abhishek",
""
],
[
"Sahoo",
"P. K.",
""
]
] | We have studied bulk viscosity in the modified $f(Q, T)$ gravity theory formalism, where $Q$ represents the non-metricity and $T$ denotes the trace of energy-momentum tensor within a flat Friedmann-Lema\^{i}tre-Robertson-Walker metric (FLRW). Here, we have explicitly considered the effective equation of state, which includes a bulk viscosity term, and obtained the exact solutions by assuming a specific form of $f(Q, T)=\alpha Q+\beta T$, where $\alpha$ and $\beta$ are constants. Furthermore, we have found constraints on the model parameters with some external datasets, such as the revised Hubble datasets consisting of 57 data points, Baryon acoustic oscillations (BAO) datasets, and the newly published Pantheon samples with 1048 points to obtain the best fitting values of the model parameters. The obtained model is found to be in good agreement with observations. In addition, we have analyzed the cosmological behavior of the density parameter, the equation of state (EoS) parameter ($\omega$), and the deceleration parameter ($q$). The results are satisfying to the standard scenario of recent findings of cosmology. The universe appears to be evolving from a decelerated to an accelerated phase. The EoS parameter is further in the quintessence phase, indicating that the universe is accelerating. Finally, we can deduce that the accumulation of bulk viscosity as effective dark energy supports the current accelerated expansion of the universe. |
1602.08220 | Crucean Cosmin | Cosmin Crucean and Mihaela-Andreea Baloi | Fermion production in a magnetic field in a de Sitter Universe | 28 pages, 20 figures | Phys. Rev. D 93, 044070 (2016) | 10.1103/PhysRevD.93.044070 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The process of fermion production in the field of a magnetic dipole on a de
Sitter expanding universe is analyzed. The amplitude and probability for
production of massive fermions are obtained using the exact solution of the
Dirac equation written in the momentum-helicity basis. We found that the most
probable transitions are those that generate the fermion pair perpendicular to
the direction of the magnetic field. The behavior of the probability is
graphically studied for large/small values of the expansion factor, and a
detailed analysis of the probability in terms of the angle between the momenta
vectors of the particle and antiparticle is performed. The phenomenon of
fermion production is significant only at large expansion which corresponds to
the conditions from the early Universe. When the expansion factor vanishes we
recover the Minkowski limit where this process is forbidden by the simultaneous
energy-momentum conservation.
| [
{
"created": "Fri, 26 Feb 2016 07:23:37 GMT",
"version": "v1"
}
] | 2016-02-29 | [
[
"Crucean",
"Cosmin",
""
],
[
"Baloi",
"Mihaela-Andreea",
""
]
] | The process of fermion production in the field of a magnetic dipole on a de Sitter expanding universe is analyzed. The amplitude and probability for production of massive fermions are obtained using the exact solution of the Dirac equation written in the momentum-helicity basis. We found that the most probable transitions are those that generate the fermion pair perpendicular to the direction of the magnetic field. The behavior of the probability is graphically studied for large/small values of the expansion factor, and a detailed analysis of the probability in terms of the angle between the momenta vectors of the particle and antiparticle is performed. The phenomenon of fermion production is significant only at large expansion which corresponds to the conditions from the early Universe. When the expansion factor vanishes we recover the Minkowski limit where this process is forbidden by the simultaneous energy-momentum conservation. |
gr-qc/9804030 | Helia Hollmann | P. Breitenlohner (Munich, Max Planck Inst.), H. Hollmann (Cambridge,
DAMTP), D. Maison (Munich, Max Planck Inst.) | Quantization of the Reissner-Nordstr\"{o}m Black Hole | 8 pages, Latex | Phys.Lett. B432 (1998) 293-297 | 10.1016/S0370-2693(98)00663-7 | DAMTP-R-98-12 | gr-qc | null | The Reissner--Nordstr\"{o}m family of solutions can be understood to arise
from the spherically symmetric sector of a nonlinear SO(2,1)/SO(1,1) sigma
model coupled to three dimensional Euclidean gravity. In this context a group
theoretical quantization is performed. We identify the observables of the
theory and calculate their spectra.
| [
{
"created": "Fri, 10 Apr 1998 15:05:02 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Breitenlohner",
"P.",
"",
"Munich, Max Planck Inst."
],
[
"Hollmann",
"H.",
"",
"Cambridge,\n DAMTP"
],
[
"Maison",
"D.",
"",
"Munich, Max Planck Inst."
]
] | The Reissner--Nordstr\"{o}m family of solutions can be understood to arise from the spherically symmetric sector of a nonlinear SO(2,1)/SO(1,1) sigma model coupled to three dimensional Euclidean gravity. In this context a group theoretical quantization is performed. We identify the observables of the theory and calculate their spectra. |
0911.1452 | Antonio Feoli | A. Feoli | The amplitude of the gravitational de Broglie waves | null | Mod.Phys.Lett.A24:2497-2505,2009 | 10.1142/S0217732309031685 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We calculate the amplitude of the de Broglie gravitational waves using the
standard Einstein General Relativity. We find that these waves disappear in the
limit $\hbar \to 0$ and when their source has a large mass and volume. From the
experimental point of view, the knowledge of the amplitude allows to estimate
the magnitude of the effect of the wave on a sphere of test particles. We
propose also to measure a very special shift angle that does not change with
time.
| [
{
"created": "Sat, 7 Nov 2009 19:24:24 GMT",
"version": "v1"
}
] | 2014-11-20 | [
[
"Feoli",
"A.",
""
]
] | We calculate the amplitude of the de Broglie gravitational waves using the standard Einstein General Relativity. We find that these waves disappear in the limit $\hbar \to 0$ and when their source has a large mass and volume. From the experimental point of view, the knowledge of the amplitude allows to estimate the magnitude of the effect of the wave on a sphere of test particles. We propose also to measure a very special shift angle that does not change with time. |
gr-qc/9810020 | Luis Herrera | L. Herrera, A. Di Prisco | The Active Gravitational Mass of a Heat Conducting Sphere Out of
Hydrostatic Equilibrium | To appear in General Relativity and Gravitation | Gen.Rel.Grav.31:301-313,1999 | 10.1023/A:1026684409560 | null | gr-qc astro-ph | null | We obtain an expression for the active gravitational mass of a relativistic
heat conducting fluid, just after its departure from hydrostatic equilibrium,
on a time scale of the order of relaxation time. It is shown that an increase
of a characteristic parameter leads to larger (smaller) values of active
gravitational mass of collapsing (expanding) spheres, enhacing thereby the
instability of the system.
| [
{
"created": "Tue, 6 Oct 1998 03:20:03 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Herrera",
"L.",
""
],
[
"Di Prisco",
"A.",
""
]
] | We obtain an expression for the active gravitational mass of a relativistic heat conducting fluid, just after its departure from hydrostatic equilibrium, on a time scale of the order of relaxation time. It is shown that an increase of a characteristic parameter leads to larger (smaller) values of active gravitational mass of collapsing (expanding) spheres, enhacing thereby the instability of the system. |
gr-qc/9302029 | null | B. L. Hu and Yuhong Zhang | Quantum and Thermal Fluctuations, Uncertainty Principle, Decoherence and
Classicality* | umdpp 93-58, 19 pages, latex. Invited Talk delivered by B. L. Hu at
the Third Workshop on Quantum Nonintegrability, Drexel University,
Philadelphia, May, 1992. To appear in {\it Quantum Dynamics of Chaotic
Systems}, edited by J. M. Yuan, D. H. Feng and G. M. Zaslavsky (Gordon and
Breach, Langhorne 1993) | null | null | null | gr-qc | null | We scrutize the commonly used criteria for classicality and examine their
underlying issues. The two major issues we address here are that of decoherence
and fluctuations. We borrow the insights gained in the study of the
semiclassical limit of quantum cosmology to discuss the three criteria of
classicality for a quantum closed system: adiabaticity, correlation and
decoherence. We then use the Brownian model as a paradigm of quantum open
systems to discuss the relation of quantum and thermal fluctuations and their
role in the transition from quantum to classical. We derive the uncertainty
relation at finite temperature. We study how the fluctuations of a quantum
system evolve after it is brought in contact with a heat bath and analyse the
decoherence and relaxation processes. From the effect of fluctuations on
decoherence we show the relation between these two sets of criteria of
classicality. Finally, we briefly comment on the issue of nonintegrability in
quantum open systems.
| [
{
"created": "Mon, 22 Feb 1993 18:19:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Hu",
"B. L.",
""
],
[
"Zhang",
"Yuhong",
""
]
] | We scrutize the commonly used criteria for classicality and examine their underlying issues. The two major issues we address here are that of decoherence and fluctuations. We borrow the insights gained in the study of the semiclassical limit of quantum cosmology to discuss the three criteria of classicality for a quantum closed system: adiabaticity, correlation and decoherence. We then use the Brownian model as a paradigm of quantum open systems to discuss the relation of quantum and thermal fluctuations and their role in the transition from quantum to classical. We derive the uncertainty relation at finite temperature. We study how the fluctuations of a quantum system evolve after it is brought in contact with a heat bath and analyse the decoherence and relaxation processes. From the effect of fluctuations on decoherence we show the relation between these two sets of criteria of classicality. Finally, we briefly comment on the issue of nonintegrability in quantum open systems. |
2106.14966 | Konstantinos Dimopoulos | Konstantinos Dimopoulos | Jointly modelling Cosmic Inflation and Dark Energy | 9 pages, 3 figures. Contribution to Proceedings of HEP 2021 | null | null | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quintessential inflation utilises a single scalar field to account for the
observations of both cosmic inflation and dark energy. The requirements for
modelling quintessential inflation are described and two explicit successful
models are presented in the context of $\alpha$-attractors and Palatini
modified gravity.
| [
{
"created": "Mon, 28 Jun 2021 20:05:28 GMT",
"version": "v1"
}
] | 2021-06-30 | [
[
"Dimopoulos",
"Konstantinos",
""
]
] | Quintessential inflation utilises a single scalar field to account for the observations of both cosmic inflation and dark energy. The requirements for modelling quintessential inflation are described and two explicit successful models are presented in the context of $\alpha$-attractors and Palatini modified gravity. |
2205.08026 | Deng Wang | Deng Wang | Shaving the Hair of Black Hole with Sagittarius A$^*$ from Event Horizon
Telescope | 4.5 pages, 1 figure | null | null | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, the Event Horizon Telescope collaboration has reported the first
image of the supermassive black hole Sagittarius in the Galactic Center. We
attempt to test the validity of the no-hair theorem of black holes using this
new shadow observation. Considering the Einstein-Maxwell-klein-Gordon theory
with a minimally-coupled scalar field, we find that our numerical result is
consistent with the prediction of the no-hair theorem. However, we can not rule
out the possibility that black holes with scalar hair may exist in some special
cases.
| [
{
"created": "Mon, 16 May 2022 23:56:30 GMT",
"version": "v1"
}
] | 2022-05-18 | [
[
"Wang",
"Deng",
""
]
] | Recently, the Event Horizon Telescope collaboration has reported the first image of the supermassive black hole Sagittarius in the Galactic Center. We attempt to test the validity of the no-hair theorem of black holes using this new shadow observation. Considering the Einstein-Maxwell-klein-Gordon theory with a minimally-coupled scalar field, we find that our numerical result is consistent with the prediction of the no-hair theorem. However, we can not rule out the possibility that black holes with scalar hair may exist in some special cases. |
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