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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1502.00287 | Michael Kunzinger | Michael Kunzinger, Roland Steinbauer, James A. Vickers | The Penrose singularity theorem in regularity $C^{1,1}$ | 13 pages. Final version | Classical Quantum Gravity 32 (2015), no. 15, 155010, 12 pp | 10.1088/0264-9381/32/15/155010 | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We extend the validity of the Penrose singularity theorem to spacetime
metrics of regularity $C^{1,1}$. The proof is based on regularisation
techniques, combined with recent results in low regularity causality theory.
| [
{
"created": "Sun, 1 Feb 2015 17:09:09 GMT",
"version": "v1"
},
{
"created": "Tue, 12 May 2015 20:20:10 GMT",
"version": "v2"
}
] | 2016-09-15 | [
[
"Kunzinger",
"Michael",
""
],
[
"Steinbauer",
"Roland",
""
],
[
"Vickers",
"James A.",
""
]
] | We extend the validity of the Penrose singularity theorem to spacetime metrics of regularity $C^{1,1}$. The proof is based on regularisation techniques, combined with recent results in low regularity causality theory. |
gr-qc/0512140 | H Mohseni Sadjadi | H. Mohseni Sadjadi | Generalized second law in phantom dominated universe | 8 pages, 2 figures. Typos corrected. References added. GSL in the
transition time (from quintessence to phantom phase) discussed. To be
published in Phys. Rev. D | Phys.Rev. D73 (2006) 063525 | null | null | gr-qc | null | We study the conditions of validity of generalized second law in phantom
dominated era.
| [
{
"created": "Fri, 23 Dec 2005 04:43:31 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Feb 2006 18:42:28 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Sadjadi",
"H. Mohseni",
""
]
] | We study the conditions of validity of generalized second law in phantom dominated era. |
gr-qc/0410110 | Lorenzo Iorio | Lorenzo Iorio | Some comments about a recent paper on the measurement of the general
relativistic Lense-Thirring effect in the gravitational field of the Earth
with the laser-ranged LAGEOS and LAGEOS II satellites | Latex2e, 8 pages, no tables, no figures, 17 references. It refers to
the Letter to Nature I. Ciufolini and E.C. Pavlis, Nature, 431, 958-960,
2004. Scientific criticisms on the released error budget presented | null | null | null | gr-qc astro-ph physics.geo-ph physics.space-ph | null | In this brief note some comments about the observable used in a recently
published paper on the measurement of the general relativistic Lense-Thirring
in the gravitational field of the Earth are presented. It turns out that, among
other things, the authors might have yielded an optimistic evaluation of the
error budget because of an underestimation of the impact of the secular
variations of the even zonal harmonics of the geopotential. More realistic
evaluations point towards a 15-45% error at 1-3sigma level, respectively.
| [
{
"created": "Thu, 21 Oct 2004 14:22:51 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Oct 2004 15:56:42 GMT",
"version": "v2"
},
{
"created": "Mon, 25 Oct 2004 00:47:47 GMT",
"version": "v3"
},
{
"created": "Fri, 29 Oct 2004 14:14:04 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Iorio",
"Lorenzo",
""
]
] | In this brief note some comments about the observable used in a recently published paper on the measurement of the general relativistic Lense-Thirring in the gravitational field of the Earth are presented. It turns out that, among other things, the authors might have yielded an optimistic evaluation of the error budget because of an underestimation of the impact of the secular variations of the even zonal harmonics of the geopotential. More realistic evaluations point towards a 15-45% error at 1-3sigma level, respectively. |
gr-qc/9908066 | Richard F. Stark | Leonardo Sigalotti and Richard F. Stark | Test Evolution of Non-Axisymmetric Gravitational Waves | 23 pages including 11 ps figures, TeX, submitted to Class.Quantum
Grav | null | null | null | gr-qc | null | We give a preliminary report on one of the tests we have performed of a full
non-axisymmetric general relativistic code. The test considered here concerns
the numerical evolution of vacuum non-axisymmetric gravitational waves and
their comparison at low amplitudes with theoretical waveforms obtained from
linearised theory.
| [
{
"created": "Wed, 25 Aug 1999 13:44:07 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Sigalotti",
"Leonardo",
""
],
[
"Stark",
"Richard F.",
""
]
] | We give a preliminary report on one of the tests we have performed of a full non-axisymmetric general relativistic code. The test considered here concerns the numerical evolution of vacuum non-axisymmetric gravitational waves and their comparison at low amplitudes with theoretical waveforms obtained from linearised theory. |
gr-qc/0011097 | Luis Anchordoqui | Luis A. Anchordoqui, S. Capozziello, G. Lambiase, and Diego F. Torres | Radiation from a uniformly accelerated charge in the outskirts of a
wormhole throat | 6 pages revtex, 1 eps figure. To be published in Modern Physics
Letters A | Mod.Phys.Lett.A15:2219-2228,2000 | 10.1142/S0217732300002516 | null | gr-qc | null | Using traversable wormholes as theoretical background, we revisit a deep
question of general relativity: Does a uniformly accelerated charged particle
radiate? We particularize to the recently proposed gravitational \v{C}erenkov
radiation, that happens when the spatial part of the Ricci tensor is negative.
If $^{^{(3+1)}}R^i_{\phantom{i}i}< 0$, the matter threading the gravitational
field violates the weak energy condition. In this case, the effective
refractive index for light is bigger than 1, i.e. particles propagates, in that
medium, faster than photons. This leads to a violation of the equivalence
principle.
| [
{
"created": "Mon, 27 Nov 2000 18:20:52 GMT",
"version": "v1"
}
] | 2011-09-12 | [
[
"Anchordoqui",
"Luis A.",
""
],
[
"Capozziello",
"S.",
""
],
[
"Lambiase",
"G.",
""
],
[
"Torres",
"Diego F.",
""
]
] | Using traversable wormholes as theoretical background, we revisit a deep question of general relativity: Does a uniformly accelerated charged particle radiate? We particularize to the recently proposed gravitational \v{C}erenkov radiation, that happens when the spatial part of the Ricci tensor is negative. If $^{^{(3+1)}}R^i_{\phantom{i}i}< 0$, the matter threading the gravitational field violates the weak energy condition. In this case, the effective refractive index for light is bigger than 1, i.e. particles propagates, in that medium, faster than photons. This leads to a violation of the equivalence principle. |
gr-qc/0406026 | Anzhong Wang | R. Chan, M. F. A. da Silva, J. F. Villas da Rocha, and Anzhong Wang | Collapsing Scalar Field with Kinematic Self-Similarity of the Second
Kind in 2+1 Gravity | latex, two figure. To appear in Int. J. Mod. Phys. D | Int.J.Mod.Phys.D14:1049-1062,2005 | 10.1142/S0218271805006882 | CASPER-04-06 | gr-qc | null | All the 2+1-dimensional circularly symmetric solutions with kinematic
self-similarity of the second kind to the Einstein-massless-scalar field
equations are found and their local and global properties are studied. It is
found that some of them represent gravitational collapse of a massless scalar
field, in which black holes are always formed.
| [
{
"created": "Tue, 8 Jun 2004 02:21:49 GMT",
"version": "v1"
}
] | 2009-07-07 | [
[
"Chan",
"R.",
""
],
[
"da Silva",
"M. F. A.",
""
],
[
"da Rocha",
"J. F. Villas",
""
],
[
"Wang",
"Anzhong",
""
]
] | All the 2+1-dimensional circularly symmetric solutions with kinematic self-similarity of the second kind to the Einstein-massless-scalar field equations are found and their local and global properties are studied. It is found that some of them represent gravitational collapse of a massless scalar field, in which black holes are always formed. |
1107.1250 | Alexandre Yale | Alexandre Yale | Simple counterterms for asymptotically AdS spacetimes in Lovelock
gravity | 16 pages. v3: title and presentation updated to match published
version. Explicit expressions for 4th-order Lovelock Lagrangians and
Gibbons-Hawking terms can be found in v2 | Phys. Rev. D 84, 104036 (2011) | 10.1103/PhysRevD.84.104036 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Although gravitational actions diverge in asymptotically AdS spacetimes,
boundary counterterms can be added in order to cancel out those divergences;
such counterterms are known in general to third order in the Riemann tensor for
the Einstein-Hilbert action. Considering foliations of AdS with an $S^m \times
H^{d-m}$ boundary, we discuss a simple algorithm which we use to generate
counterterms up to sixth order in the Riemann tensor, for the Einstein-Hilbert,
Gauss-Bonnet and third-order-Lovelock Lagrangians. We also comment on other
theories such as $F(R)$ gravity.
| [
{
"created": "Wed, 6 Jul 2011 20:29:15 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Jul 2011 15:46:14 GMT",
"version": "v2"
},
{
"created": "Tue, 29 Nov 2011 21:41:45 GMT",
"version": "v3"
}
] | 2011-12-01 | [
[
"Yale",
"Alexandre",
""
]
] | Although gravitational actions diverge in asymptotically AdS spacetimes, boundary counterterms can be added in order to cancel out those divergences; such counterterms are known in general to third order in the Riemann tensor for the Einstein-Hilbert action. Considering foliations of AdS with an $S^m \times H^{d-m}$ boundary, we discuss a simple algorithm which we use to generate counterterms up to sixth order in the Riemann tensor, for the Einstein-Hilbert, Gauss-Bonnet and third-order-Lovelock Lagrangians. We also comment on other theories such as $F(R)$ gravity. |
2204.02138 | Fethi M. Ramazanoglu | Semih Tuna, K{\i}van\c{c} \.I. \"Unl\"ut\"urk, Fethi M.
Ramazano\u{g}lu | Constraining scalar-tensor theories using neutron star mass and radius
measurements | 18 pages, 14 figures. Published version | Phys. Rev. D 105, 124070 (2022) | 10.1103/PhysRevD.105.124070 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | We use neutron star mass and radius measurements to constrain the spontaneous
scalarization phenomenon in scalar-tensor theories using Bayesian analysis.
Neutron star structures in this scenario can be significantly different from
the case of general relativity, which can be used to constrain the theory
parameters. We utilize this idea to obtain lower bounds on the coupling
parameter $\beta$ for the case of massless scalars. These constraints are
currently weaker than the ones coming from binary observations, and they have
relatively low precision due to the approximations in our method. Nevertheless,
our results clearly demonstrate the power of the mass-radius data in testing
gravity, and can be further improved with future observations. The picture is
different for massive scalars, for which the same data is considerably less
effective in constraining the theory parameters in an unexpected manner. We
identify the main reason for this to be a large high-likelihood region in the
parameter space where deviations from general relativity are relatively small.
We hope this initial study to be an invitation to use neutron star structure
measurements more commonly to test alternative theories in general.
| [
{
"created": "Tue, 5 Apr 2022 12:03:01 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Jul 2022 19:22:53 GMT",
"version": "v2"
}
] | 2022-07-06 | [
[
"Tuna",
"Semih",
""
],
[
"Ünlütürk",
"Kıvanç İ.",
""
],
[
"Ramazanoğlu",
"Fethi M.",
""
]
] | We use neutron star mass and radius measurements to constrain the spontaneous scalarization phenomenon in scalar-tensor theories using Bayesian analysis. Neutron star structures in this scenario can be significantly different from the case of general relativity, which can be used to constrain the theory parameters. We utilize this idea to obtain lower bounds on the coupling parameter $\beta$ for the case of massless scalars. These constraints are currently weaker than the ones coming from binary observations, and they have relatively low precision due to the approximations in our method. Nevertheless, our results clearly demonstrate the power of the mass-radius data in testing gravity, and can be further improved with future observations. The picture is different for massive scalars, for which the same data is considerably less effective in constraining the theory parameters in an unexpected manner. We identify the main reason for this to be a large high-likelihood region in the parameter space where deviations from general relativity are relatively small. We hope this initial study to be an invitation to use neutron star structure measurements more commonly to test alternative theories in general. |
1804.06070 | Sajal Mukherjee | Sajal Mukherjee and Rajesh Kumble Nayak | Off-equatorial stable circular orbits for spinning particles | 17 pages, 11 figures, 1 table, Accepted for publication in Physical
Review D | Phys. Rev. D 98, 084023 (2018) | 10.1103/PhysRevD.98.084023 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article, we investigate the motion of a spinning particle at a
constant inclination, different from the equatorial plane, around a Kerr black
hole. We mainly explore the possibilities of stable circular orbits for
different spin supplementary conditions. The Mathission-Papapetrau's equations
are extensively applied and solved within the framework of linear spin
approximation. We explicitly show that for a given spin vector of the form
$S^{a} = \left(0,S^r,S^{\theta},0\right)$ , there exists an unique circular
orbit at $(r_c,\theta_c)$ defined by the simultaneous minima of energy, angular
momentum and Carter constant. This corresponds to the Innermost Stable Circular
Orbit (ISCO) which is located on a non-equatorial plane. We further establish
that the location ($r_c,\theta_c$) of the ISCO for a given spinning particle
depends on the radial component of the spin vector ($S^r$) as well as the
angular momentum of the black hole ($J$). The implications of using different
spin supplementary conditions are investigated.
| [
{
"created": "Tue, 17 Apr 2018 06:47:39 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Sep 2018 04:58:32 GMT",
"version": "v2"
}
] | 2018-10-24 | [
[
"Mukherjee",
"Sajal",
""
],
[
"Nayak",
"Rajesh Kumble",
""
]
] | In this article, we investigate the motion of a spinning particle at a constant inclination, different from the equatorial plane, around a Kerr black hole. We mainly explore the possibilities of stable circular orbits for different spin supplementary conditions. The Mathission-Papapetrau's equations are extensively applied and solved within the framework of linear spin approximation. We explicitly show that for a given spin vector of the form $S^{a} = \left(0,S^r,S^{\theta},0\right)$ , there exists an unique circular orbit at $(r_c,\theta_c)$ defined by the simultaneous minima of energy, angular momentum and Carter constant. This corresponds to the Innermost Stable Circular Orbit (ISCO) which is located on a non-equatorial plane. We further establish that the location ($r_c,\theta_c$) of the ISCO for a given spinning particle depends on the radial component of the spin vector ($S^r$) as well as the angular momentum of the black hole ($J$). The implications of using different spin supplementary conditions are investigated. |
0710.4902 | Robert T. Jantzen | Donato Bini, Christian Cherubini, Robert T. Jantzen | The Lifshitz-Khalatnikov Kasner index parametrization and the Weyl
Tensor | 16 page Latex cimento.cls formatted document with 6 EPS figures annd
2 PicTeX figures; to appear in the Proceedings of the First Italian-Pakistan
Workshop on Relativistic Astrophysics which will be published as a special
issue of Nuovo Cimento B | Nuovo Cim.B122:521-536,2007 | 10.1393/ncb/i2007-10396-4 | null | gr-qc | null | The scale invariant Petrov classification of the Weyl tensor is linked to the
scale invariant combination of the Kasner index constraints, and the
Lifshitz-Khalatnikov Kasner index parametrization scheme turns out to be a
natural way of adapting to this symmetry, while hiding the permutation symmetry
that is instead made manifest by the Misner parametrization scheme. While not
so interesting for the Kasner spacetime by itself, it gives a geometrical
meaning to the famous Kasner map transitioning between Kasner epochs and Kasner
eras, equivalently bouncing between curvature walls, in the BLK-Mixmaster
dynamics exhibited by spatially homogeneous cosmologies approaching the initial
cosmological singularity and the inhomogeneous generalization of this dynamics.
| [
{
"created": "Thu, 25 Oct 2007 15:55:14 GMT",
"version": "v1"
}
] | 2010-11-11 | [
[
"Bini",
"Donato",
""
],
[
"Cherubini",
"Christian",
""
],
[
"Jantzen",
"Robert T.",
""
]
] | The scale invariant Petrov classification of the Weyl tensor is linked to the scale invariant combination of the Kasner index constraints, and the Lifshitz-Khalatnikov Kasner index parametrization scheme turns out to be a natural way of adapting to this symmetry, while hiding the permutation symmetry that is instead made manifest by the Misner parametrization scheme. While not so interesting for the Kasner spacetime by itself, it gives a geometrical meaning to the famous Kasner map transitioning between Kasner epochs and Kasner eras, equivalently bouncing between curvature walls, in the BLK-Mixmaster dynamics exhibited by spatially homogeneous cosmologies approaching the initial cosmological singularity and the inhomogeneous generalization of this dynamics. |
1707.07542 | Cl\'ementine Hauret | Hauret Clementine, Magain Pierre and Biernaux Judith | Cosmological Time, Entropy and Infinity | 11 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1505.02052 | Entropy, 19, 357 (2017) | 10.3390/e19070357 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Time is a parameter playing a central role in our most fundamental modelling
of natural laws. Relativity theory shows that the comparison of times measured
by different clocks depends on their relative motion and on the strength of the
gravitational field in which they are embedded. In standard cosmology, the time
parameter is the one measured by fundamental clocks (i.e., clocks at rest with
respect to the expanding space). This proper time is assumed to flow at a
constant rate throughout the whole history of the universe. We make the
alternative hypothesis that the rate at which the cosmological time flows
depends on the dynamical state of the universe. In thermodynamics, the arrow of
time is strongly related to the second law, which states that the entropy of an
isolated system will always increase with time or, at best, stay constant.
Hence, we assume that the time measured by fundamental clocks is proportional
to the entropy of the region of the universe that is causally connected to
them. Under that simple assumption, we find it possible to build toy
cosmological models that present an acceleration of their expansion without any
need for dark energy while being spatially closed and finite, avoiding the need
to deal with infinite values.
| [
{
"created": "Wed, 19 Jul 2017 13:30:32 GMT",
"version": "v1"
}
] | 2017-07-25 | [
[
"Clementine",
"Hauret",
""
],
[
"Pierre",
"Magain",
""
],
[
"Judith",
"Biernaux",
""
]
] | Time is a parameter playing a central role in our most fundamental modelling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative motion and on the strength of the gravitational field in which they are embedded. In standard cosmology, the time parameter is the one measured by fundamental clocks (i.e., clocks at rest with respect to the expanding space). This proper time is assumed to flow at a constant rate throughout the whole history of the universe. We make the alternative hypothesis that the rate at which the cosmological time flows depends on the dynamical state of the universe. In thermodynamics, the arrow of time is strongly related to the second law, which states that the entropy of an isolated system will always increase with time or, at best, stay constant. Hence, we assume that the time measured by fundamental clocks is proportional to the entropy of the region of the universe that is causally connected to them. Under that simple assumption, we find it possible to build toy cosmological models that present an acceleration of their expansion without any need for dark energy while being spatially closed and finite, avoiding the need to deal with infinite values. |
2304.05609 | Swastik Bhattacharya | Anamika Avinash Pathak, Konka Raviteja, Swastik Bhattacharya,
Sashideep Gutti | Surface Gravity of Dynamical Horizons: A Causal Perspective | 9 pages, no figures, comments welcome | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider marginally trapped surfaces in a spherically symmetric spacetime
evolving due to the presence of a perfect fluid in D-dimensions and look at the
various definitions of the surface gravity for these marginally trapped
surfaces. We show that using Einstein equations it is possible to simplify and
obtain general formulae for the surface gravity in terms of invariant
quantities defined at these marginally trapped surfaces like area radius,
cosmological constant and principal values of the energy-momentum tensor
\r{ho}, p. We then correlate these expressions of surface gravity to the cases
of dynamical horizons and timelike tubes and find which proposals of surface
gravity are causally sensitive as these surfaces undergo causal transitions
from spacelike to timelike and vice versa.
| [
{
"created": "Wed, 12 Apr 2023 05:01:26 GMT",
"version": "v1"
}
] | 2023-04-13 | [
[
"Pathak",
"Anamika Avinash",
""
],
[
"Raviteja",
"Konka",
""
],
[
"Bhattacharya",
"Swastik",
""
],
[
"Gutti",
"Sashideep",
""
]
] | We consider marginally trapped surfaces in a spherically symmetric spacetime evolving due to the presence of a perfect fluid in D-dimensions and look at the various definitions of the surface gravity for these marginally trapped surfaces. We show that using Einstein equations it is possible to simplify and obtain general formulae for the surface gravity in terms of invariant quantities defined at these marginally trapped surfaces like area radius, cosmological constant and principal values of the energy-momentum tensor \r{ho}, p. We then correlate these expressions of surface gravity to the cases of dynamical horizons and timelike tubes and find which proposals of surface gravity are causally sensitive as these surfaces undergo causal transitions from spacelike to timelike and vice versa. |
0709.3314 | Zhong Chao Wu | Zhong Chao Wu | The Cosmological Constant is Probably Zero, and a Proof is Possibly
Right | 6 pages, modified version | Phys.Lett.B659:891-893,2008 | 10.1016/j.physletb.2007.12.019 | ZJUT07-09 | gr-qc astro-ph hep-th | null | Hawking proposed that the cosmological constant is probably zero in quantum
cosmology. Duff claimed that Hawking's proof is invalidated. Using the right
configuration for the wave function of the universe, we provide a complete
proof.
| [
{
"created": "Fri, 21 Sep 2007 16:07:53 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Oct 2007 17:17:18 GMT",
"version": "v2"
},
{
"created": "Sat, 10 Nov 2007 18:24:43 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Wu",
"Zhong Chao",
""
]
] | Hawking proposed that the cosmological constant is probably zero in quantum cosmology. Duff claimed that Hawking's proof is invalidated. Using the right configuration for the wave function of the universe, we provide a complete proof. |
1509.02535 | Andrey Shoom A | Andrey A. Shoom | Synchrotron Radiation From Weakly Magnetized Schwarzschild Black Hole | 7 pages, 4 figures | null | 10.1103/PhysRevD.92.124066 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a synchrotron radiation from a charged particle moving in a bound
orbit around a weakly magnetized Schwarzschild black hole (a static black hole
immersed into a constant uniform magnetic field) in its equatorial plane,
perpendicular to the magnetic field. In particular, we study the case when the
Lorentz force acting on the charged particle is directed outward from the black
hole. The particle is initially moving in a nongeodesic bound orbit which due
to synchrotron radiation decays to a nongeodesic circular orbit. We study this
transition and calculate the radiated power and energy loss of the particle.
| [
{
"created": "Tue, 8 Sep 2015 20:13:12 GMT",
"version": "v1"
}
] | 2016-01-20 | [
[
"Shoom",
"Andrey A.",
""
]
] | We consider a synchrotron radiation from a charged particle moving in a bound orbit around a weakly magnetized Schwarzschild black hole (a static black hole immersed into a constant uniform magnetic field) in its equatorial plane, perpendicular to the magnetic field. In particular, we study the case when the Lorentz force acting on the charged particle is directed outward from the black hole. The particle is initially moving in a nongeodesic bound orbit which due to synchrotron radiation decays to a nongeodesic circular orbit. We study this transition and calculate the radiated power and energy loss of the particle. |
1906.00802 | Jos\'e Crespo | J. A. Crespo and H. P. de Oliveira | Aspects of wave turbulence in preheating III: The case of the two-fields
models | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present work is the continuation of the investigation of aspects of wave
turbulence in preheating we have started in Refs. [1, 2] but considering
several classes of inflationary two-fields models. We exhibit the main elements
of the wave turbulence phase imprinted in the power spectra of relevant
quantities in the time and space domains. As a general feature, the power
spectra resemble in their structure to those obtained using the single
nonminimally coupled scalar field of the previous work. As a consequence, we
obtained an estimate of the temperature corresponding to the thermalized phase
from the power spectrum of the total energy density. Another feature allowed by
the simulations was the determination of the effective equation of state after
taking into account the backreaction of the produced particles.
| [
{
"created": "Mon, 3 Jun 2019 13:41:30 GMT",
"version": "v1"
}
] | 2019-06-04 | [
[
"Crespo",
"J. A.",
""
],
[
"de Oliveira",
"H. P.",
""
]
] | The present work is the continuation of the investigation of aspects of wave turbulence in preheating we have started in Refs. [1, 2] but considering several classes of inflationary two-fields models. We exhibit the main elements of the wave turbulence phase imprinted in the power spectra of relevant quantities in the time and space domains. As a general feature, the power spectra resemble in their structure to those obtained using the single nonminimally coupled scalar field of the previous work. As a consequence, we obtained an estimate of the temperature corresponding to the thermalized phase from the power spectrum of the total energy density. Another feature allowed by the simulations was the determination of the effective equation of state after taking into account the backreaction of the produced particles. |
1402.4779 | Yousef Bisabr | Yousef Bisabr | Notes on the Chameleon Brans-Dicke Gravity | 9 pages, no figure. To appear in Astrophysics and Space Science.
arXiv admin note: text overlap with arXiv:0907.3838, arXiv:1005.5670,
arXiv:1212.2709 | Astrophys Space Sci (2014) 350:407-411 | 10.1007/s10509-013-1751-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a generalized Brans-Dicke model in which the scalar field has a
potential function and is also allowed to couple non-minimally with the matter
sector. This anomalous gravitational coupling can in principle avoid the model
to pass local gravity experiments. One then usually assumes that the scalar
field has a chameleon behavior in the sense that it acquires a
density-dependent effective mass. While it can take a small effective mass in
cosmological (low-density environment) scale, it has a sufficiently heavy mass
in Solar System (large-density environment) and then hides gravity tests. We
will argue that such a chameleon behavior can not be generally realized and
depends significantly on the forms attributed to the potential and the coupling
functions.
| [
{
"created": "Wed, 19 Feb 2014 19:33:16 GMT",
"version": "v1"
}
] | 2015-06-18 | [
[
"Bisabr",
"Yousef",
""
]
] | We consider a generalized Brans-Dicke model in which the scalar field has a potential function and is also allowed to couple non-minimally with the matter sector. This anomalous gravitational coupling can in principle avoid the model to pass local gravity experiments. One then usually assumes that the scalar field has a chameleon behavior in the sense that it acquires a density-dependent effective mass. While it can take a small effective mass in cosmological (low-density environment) scale, it has a sufficiently heavy mass in Solar System (large-density environment) and then hides gravity tests. We will argue that such a chameleon behavior can not be generally realized and depends significantly on the forms attributed to the potential and the coupling functions. |
2103.06771 | Dirk Puetzfeld | Peter A. Hogan, Dirk Puetzfeld | Gravitational Waves with Colliding or Non--Colliding Wave Fronts | 8 pages, 1 figure | Phys. Rev. D 103, 124064 (2021) | 10.1103/PhysRevD.103.124064 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The known exact solutions of Einstein's vacuum field equations modeling the
gravitational fields of pure gravitational radiation involve wave fronts which
are either planar or roughly spherical. We describe a scheme designed to check
explicitly whether or not the wave fronts collide. From the spacetime point of
view the scheme determines whether or not the null hypersurface histories of
the wave fronts intersect and, in particular, allows easy identification of the
cases in which the null hypersurfaces do not intersect.
| [
{
"created": "Thu, 11 Mar 2021 16:31:59 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Jul 2021 14:30:01 GMT",
"version": "v2"
}
] | 2021-07-02 | [
[
"Hogan",
"Peter A.",
""
],
[
"Puetzfeld",
"Dirk",
""
]
] | The known exact solutions of Einstein's vacuum field equations modeling the gravitational fields of pure gravitational radiation involve wave fronts which are either planar or roughly spherical. We describe a scheme designed to check explicitly whether or not the wave fronts collide. From the spacetime point of view the scheme determines whether or not the null hypersurface histories of the wave fronts intersect and, in particular, allows easy identification of the cases in which the null hypersurfaces do not intersect. |
gr-qc/0506003 | Yasushi Mino | Yasushi Mino | Self-Force in the Radiation Reaction Formula -- Adiabatic Approximation
of a Metric Perturbation and an Orbit -- | published in Progress of Theoretical Physics Vol.113 No.4 pp.733 | Prog.Theor.Phys. 113 (2005) 733-761 | 10.1143/PTP.113.733 | null | gr-qc | null | We propose a new metric perturbation scheme under a possible constraint of
the gauge conditions in which we obtain a physically expected prediction of the
orbital evolution caused by the MiSaTaQuWa self-force. In this new scheme of a
metric perturbation, an adiabatic approximation is applied to both the metric
perturbation and the orbit. As a result, we are able to predict the
gravitational evolution of the system in the so-called radiation reaction time
scale, which is longer than the dephasing time scale. However, for
gravitational wave detection by LISA, this may still be insufficient. We
further consider a gauge transformation in this new metric perturbation scheme,
and find a special gauge condition with which we can calculate the
gravitational waveform of a time scale long enough for gravitational wave
detection by LISA.
| [
{
"created": "Tue, 31 May 2005 23:12:03 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Mino",
"Yasushi",
""
]
] | We propose a new metric perturbation scheme under a possible constraint of the gauge conditions in which we obtain a physically expected prediction of the orbital evolution caused by the MiSaTaQuWa self-force. In this new scheme of a metric perturbation, an adiabatic approximation is applied to both the metric perturbation and the orbit. As a result, we are able to predict the gravitational evolution of the system in the so-called radiation reaction time scale, which is longer than the dephasing time scale. However, for gravitational wave detection by LISA, this may still be insufficient. We further consider a gauge transformation in this new metric perturbation scheme, and find a special gauge condition with which we can calculate the gravitational waveform of a time scale long enough for gravitational wave detection by LISA. |
1711.05695 | Klaus Liegener Dr | Thorsten Lang, Klaus Liegener, Thomas Thiemann | Hamiltonian Renormalisation IV. Renormalisation Flow of D+1 dimensional
free scalar fields and Rotation Invariance | 28 pages | Class.Quant.Grav. 35 (2018) no.24, 245014 | 10.1088/1361-6382/aaec43 | null | gr-qc hep-lat hep-th math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we extend the test of Hamiltonian Renormalisation proposed in
this series of articles to the D-dimensional case using a massive free scalar
field. The concepts we introduce are explicitly computed for the D=2 case but
transfer immediately to higher dimensions. In this article we define and verify
a criterion that monitors, at finite resolution defined by a cubic lattice,
whether the flow approaches a rotationally invariant fixed point.
| [
{
"created": "Wed, 15 Nov 2017 17:42:44 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Jul 2019 15:48:42 GMT",
"version": "v2"
}
] | 2019-07-09 | [
[
"Lang",
"Thorsten",
""
],
[
"Liegener",
"Klaus",
""
],
[
"Thiemann",
"Thomas",
""
]
] | In this article we extend the test of Hamiltonian Renormalisation proposed in this series of articles to the D-dimensional case using a massive free scalar field. The concepts we introduce are explicitly computed for the D=2 case but transfer immediately to higher dimensions. In this article we define and verify a criterion that monitors, at finite resolution defined by a cubic lattice, whether the flow approaches a rotationally invariant fixed point. |
1510.08471 | Kenneth Nordtvedt | Kenneth Nordtvedt | Constructing metric gravity's N-body non-linear Lagrangian from
iterative, linear algebraic scaling equations | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A method for constructing metric gravity's N-body Lagrangian is developed
which uses iterative, liner algebraic euqations which enforce invariance
properties of gravity --- exterior effacement, interior effacement, and the
time dilation and Lorentz contraction of matter under boosts. The method is
demonstrated by obtaining the full 1/c^4 order Lagrangian, and a combination of
exterior and interior effacement enforcement permits construction of the full
Schwarzschild temporal and spatial metric potentials.
| [
{
"created": "Wed, 28 Oct 2015 20:19:07 GMT",
"version": "v1"
}
] | 2015-10-30 | [
[
"Nordtvedt",
"Kenneth",
""
]
] | A method for constructing metric gravity's N-body Lagrangian is developed which uses iterative, liner algebraic euqations which enforce invariance properties of gravity --- exterior effacement, interior effacement, and the time dilation and Lorentz contraction of matter under boosts. The method is demonstrated by obtaining the full 1/c^4 order Lagrangian, and a combination of exterior and interior effacement enforcement permits construction of the full Schwarzschild temporal and spatial metric potentials. |
2206.05839 | Georgios Fanaras | Georgios Fanaras, Alexander Vilenkin | The tunneling wavefunction in Kantowski-Sachs quantum cosmology | 31 pages, 4 figures | null | 10.1088/1475-7516/2022/08/069 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use a path-integral approach to study the tunneling wave function in
quantum cosmology with spatial topology $S^{1}\times S^{2}$ and positive
cosmological constant (the Kantowski-Sachs model). If the initial scale factors
of both $S^1$ and $S^2$ are set equal to zero, the wave function describes
(semiclassically) a universe originating at a singularity. This may be
interpreted as indicating that an $S^1\times S^2$ universe cannot nucleate out
of nothing in a non-singular way. Here we explore an alternative suggestion by
Halliwell and Louko that creation from nothing corresponds in this model to
setting the initial volume to zero. We find that the only acceptable version of
this proposal is to fix the radius of $S^1$ to zero, supplementing this with
the condition of smooth closure (absence of a conical singularity). The
resulting wave function predicts an inflating universe of high anisotropy,
which however becomes locally isotropic at late times. Unlike the de Sitter
model, the total nucleation probability is not exponentially suppressed, unless
a Gauss-Bonnet term is added to the action.
| [
{
"created": "Sun, 12 Jun 2022 21:02:55 GMT",
"version": "v1"
}
] | 2022-09-07 | [
[
"Fanaras",
"Georgios",
""
],
[
"Vilenkin",
"Alexander",
""
]
] | We use a path-integral approach to study the tunneling wave function in quantum cosmology with spatial topology $S^{1}\times S^{2}$ and positive cosmological constant (the Kantowski-Sachs model). If the initial scale factors of both $S^1$ and $S^2$ are set equal to zero, the wave function describes (semiclassically) a universe originating at a singularity. This may be interpreted as indicating that an $S^1\times S^2$ universe cannot nucleate out of nothing in a non-singular way. Here we explore an alternative suggestion by Halliwell and Louko that creation from nothing corresponds in this model to setting the initial volume to zero. We find that the only acceptable version of this proposal is to fix the radius of $S^1$ to zero, supplementing this with the condition of smooth closure (absence of a conical singularity). The resulting wave function predicts an inflating universe of high anisotropy, which however becomes locally isotropic at late times. Unlike the de Sitter model, the total nucleation probability is not exponentially suppressed, unless a Gauss-Bonnet term is added to the action. |
2008.04066 | Sourabh Nampalliwar | Sourabh Nampalliwar, Arthur G. Suvorov, Kostas D. Kokkotas | Testing horizon topology with electromagnetic observations | 15 pages, 9 figures. Comments welcome | Phys. Rev. D 102, 104035 (2020) | 10.1103/PhysRevD.102.104035 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In general relativity without a cosmological constant, a classical theorem
due to Hawking states that stationary black holes must be topologically
spherical. This result is one of the several ingredients that collectively
imply the uniqueness of the Kerr metric. If, however, general relativity
describes gravity inexactly at high energies or over cosmological scales,
Hawking's result may not apply, and black holes with non-trivial topology may
be, at least mathematically, permissible. While tests involving electromagnetic
and gravitational-wave data have been used to place tight constraints on
various theoretical departures from a Kerr description of astrophysical black
holes, relatively little attention has been paid to topological alternatives.
In this paper, we derive a new exact solution in an $f(R)$ theory of gravity
which admits topologically non-trivial black holes, and calculate observables
like fluorescent K$\alpha$ iron-line profiles and black hole images from
hypothetical astrophysical systems which house these objects, to provide a
theoretical basis for new tests of black hole nature. On the basis of
qualitative comparisons, we show that topologically non-trivial objects would
leave a strong imprint on electromagnetic observables and can be easily
distinguished from general-relativistic black holes in nearly all cases.
| [
{
"created": "Mon, 10 Aug 2020 12:43:29 GMT",
"version": "v1"
}
] | 2020-11-18 | [
[
"Nampalliwar",
"Sourabh",
""
],
[
"Suvorov",
"Arthur G.",
""
],
[
"Kokkotas",
"Kostas D.",
""
]
] | In general relativity without a cosmological constant, a classical theorem due to Hawking states that stationary black holes must be topologically spherical. This result is one of the several ingredients that collectively imply the uniqueness of the Kerr metric. If, however, general relativity describes gravity inexactly at high energies or over cosmological scales, Hawking's result may not apply, and black holes with non-trivial topology may be, at least mathematically, permissible. While tests involving electromagnetic and gravitational-wave data have been used to place tight constraints on various theoretical departures from a Kerr description of astrophysical black holes, relatively little attention has been paid to topological alternatives. In this paper, we derive a new exact solution in an $f(R)$ theory of gravity which admits topologically non-trivial black holes, and calculate observables like fluorescent K$\alpha$ iron-line profiles and black hole images from hypothetical astrophysical systems which house these objects, to provide a theoretical basis for new tests of black hole nature. On the basis of qualitative comparisons, we show that topologically non-trivial objects would leave a strong imprint on electromagnetic observables and can be easily distinguished from general-relativistic black holes in nearly all cases. |
1104.1908 | Taeyoon Moon | Taeyoon Moon, Yun Soo Myung, and Edwin J. Son | Stability analysis of f(R)-AdS black holes | 17 pages, 1 figure, version to appear in EPJC | null | 10.1140/epjc/s10052-011-1777-0 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the stability of f(R)-AdS (Schwarzschild-AdS) black hole obtained
from f(R) gravity. In order to resolve the difficulty of solving fourth order
linearized equations, we transform f(R) gravity into the scalar-tensor theory
by introducing two auxiliary scalars. In this case, the linearized curvature
scalar becomes a dynamical scalaron, showing that all linearized equations are
second order. Using the positivity of gravitational potentials and S-deformed
technique allows us to guarantee the stability of f(R)-AdS black hole if the
scalaron mass squared satisfies the Breitenlohner-Freedman bound. This is
confirmed by computing quasinormal frequencies of the scalaron for large
f(R)-AdS black hole.
| [
{
"created": "Mon, 11 Apr 2011 11:25:24 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Oct 2011 04:10:48 GMT",
"version": "v2"
}
] | 2015-05-27 | [
[
"Moon",
"Taeyoon",
""
],
[
"Myung",
"Yun Soo",
""
],
[
"Son",
"Edwin J.",
""
]
] | We study the stability of f(R)-AdS (Schwarzschild-AdS) black hole obtained from f(R) gravity. In order to resolve the difficulty of solving fourth order linearized equations, we transform f(R) gravity into the scalar-tensor theory by introducing two auxiliary scalars. In this case, the linearized curvature scalar becomes a dynamical scalaron, showing that all linearized equations are second order. Using the positivity of gravitational potentials and S-deformed technique allows us to guarantee the stability of f(R)-AdS black hole if the scalaron mass squared satisfies the Breitenlohner-Freedman bound. This is confirmed by computing quasinormal frequencies of the scalaron for large f(R)-AdS black hole. |
1401.6862 | Taeyoon Moon | Yun Soo Myung and Taeyoon Moon | Black hole stability in Jordan and Einstein frames | 1+15 pages, 1 figure, version to appear in PRD | Phys. Rev. D 89, 104009 (2014) | 10.1103/PhysRevD.89.104009 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the classical stability of Schwarzschild black hole in Jordan
and Einstein frames which are related by the conformal transformations. For
this purpose, we introduce two models of the Brans-Dicke theory and
Brans-Dicke-Weyl gravity in Jordan frame and two corresponding models in the
Einstein frame. The former model is suitable for studying the massless spin-2
graviton propagating around the Schwarzschild black hole, while the later is
designed for the massive spin-2 graviton propagating around the black hole. It
turns out that the black hole (in)stability is independent of the frame which
shows that the two frames are equivalent to each other.
| [
{
"created": "Mon, 27 Jan 2014 14:21:48 GMT",
"version": "v1"
},
{
"created": "Fri, 18 Apr 2014 08:36:14 GMT",
"version": "v2"
}
] | 2014-05-14 | [
[
"Myung",
"Yun Soo",
""
],
[
"Moon",
"Taeyoon",
""
]
] | We investigate the classical stability of Schwarzschild black hole in Jordan and Einstein frames which are related by the conformal transformations. For this purpose, we introduce two models of the Brans-Dicke theory and Brans-Dicke-Weyl gravity in Jordan frame and two corresponding models in the Einstein frame. The former model is suitable for studying the massless spin-2 graviton propagating around the Schwarzschild black hole, while the later is designed for the massive spin-2 graviton propagating around the black hole. It turns out that the black hole (in)stability is independent of the frame which shows that the two frames are equivalent to each other. |
gr-qc/0202025 | Fernando P. Devecchi | G.M. Kremer and F.P. Devecchi | Thermodynamics and Kinetic Theory of Relativistic Gases in 2-D
Cosmological Models | 23 pages, accepted in PRD | Phys.Rev. D65 (2002) 083515 | 10.1103/PhysRevD.65.083515 | null | gr-qc | null | A kinetic theory of relativistic gases in a two-dimensional space is
developed in order to obtain the equilibrium distribution function and the
expressions for the fields of energy per particle, pressure, entropy per
particle and heat capacities in equilibrium. Furthermore, by using the method
of Chapman and Enskog for a kinetic model of the Boltzmann equation the
non-equilibrium energy-momentum tensor and the entropy production rate are
determined for a universe described by a two-dimensional Robertson-Walker
metric. The solutions of the gravitational field equations that consider the
non-equilibrium energy-momentum tensor - associated with the coefficient of
bulk viscosity - show that opposed to the four-dimensional case, the cosmic
scale factor attains a maximum value at a finite time decreasing to a "big
crunch" and that there exists a solution of the gravitational field equations
corresponding to a "false vacuum". The evolution of the fields of pressure,
energy density and entropy production rate with the time is also discussed.
| [
{
"created": "Thu, 7 Feb 2002 14:56:21 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Kremer",
"G. M.",
""
],
[
"Devecchi",
"F. P.",
""
]
] | A kinetic theory of relativistic gases in a two-dimensional space is developed in order to obtain the equilibrium distribution function and the expressions for the fields of energy per particle, pressure, entropy per particle and heat capacities in equilibrium. Furthermore, by using the method of Chapman and Enskog for a kinetic model of the Boltzmann equation the non-equilibrium energy-momentum tensor and the entropy production rate are determined for a universe described by a two-dimensional Robertson-Walker metric. The solutions of the gravitational field equations that consider the non-equilibrium energy-momentum tensor - associated with the coefficient of bulk viscosity - show that opposed to the four-dimensional case, the cosmic scale factor attains a maximum value at a finite time decreasing to a "big crunch" and that there exists a solution of the gravitational field equations corresponding to a "false vacuum". The evolution of the fields of pressure, energy density and entropy production rate with the time is also discussed. |
2105.07313 | Liu Zhao | Xin Hao, Shaofan Liu and Liu Zhao | Relativistic transformation of thermodynamic parameters and refined Saha
equation | v4: BIG change: the transformation rules in previous versions are
flawed because they were based on the assumption that the form of the first
law remain unchanged under the change of observers, which proves to be false.
The new rules are based on the invariance of Gibbs-Duhem relation | null | null | null | gr-qc cond-mat.stat-mech hep-th | http://creativecommons.org/licenses/by/4.0/ | The relativistic transformation rule for temperature is a subject under
debate for more than 110 years. Several incompatible proposals exist in the
literature, but a final resolution is still missing. In this work, we
reconsider the problem of relativistic transformation rules for a number of
thermodynamic parameters, including temperature, chemical potential, pressure,
entropy and enthalpy densities for a relativistic perfect fluid using
relativistic kinetic theory. The analysis is carried out in a fully
relativistic covariant manner, and the explicit transformation rules for the
above quantities are obtained in both Minkowski and Rindler spacetimes. Our
results suggest that the temperature of a moving fluid appears to be colder,
supporting the proposal by de Broglie, Einstein and Planck in contrast to other
proposals. Moreover, in the case of Rindler fluid, our work indicates that, the
total number of particles and the total entropy of a perfect fluid in a box
whose bottom is parallel to the Rindler horizon are proportional to the area of
the bottom, but are independent of the height of the box, provided the bottom
of the box is sufficiently close to the Rindler horizon. The area dependence of
the particle number implies that the particles tend to be gathered toward the
bottom of the box and hence implicitly determines the distribution of chemical
potential of the system, whereas the area dependence of the entropy indicates
that the entropy is still additive and may find some applications in explaining
the area law of black hole entropy. As a by product, we also obtain a
relativistically refined version of the famous Saha equation which holds in
both Minkowski and Rindler spacetimes.
| [
{
"created": "Sat, 15 May 2021 23:28:12 GMT",
"version": "v1"
},
{
"created": "Wed, 19 May 2021 07:08:43 GMT",
"version": "v2"
},
{
"created": "Mon, 27 Sep 2021 04:07:39 GMT",
"version": "v3"
},
{
"created": "Wed, 22 Dec 2021 13:01:03 GMT",
"version": "v4"
}
] | 2021-12-23 | [
[
"Hao",
"Xin",
""
],
[
"Liu",
"Shaofan",
""
],
[
"Zhao",
"Liu",
""
]
] | The relativistic transformation rule for temperature is a subject under debate for more than 110 years. Several incompatible proposals exist in the literature, but a final resolution is still missing. In this work, we reconsider the problem of relativistic transformation rules for a number of thermodynamic parameters, including temperature, chemical potential, pressure, entropy and enthalpy densities for a relativistic perfect fluid using relativistic kinetic theory. The analysis is carried out in a fully relativistic covariant manner, and the explicit transformation rules for the above quantities are obtained in both Minkowski and Rindler spacetimes. Our results suggest that the temperature of a moving fluid appears to be colder, supporting the proposal by de Broglie, Einstein and Planck in contrast to other proposals. Moreover, in the case of Rindler fluid, our work indicates that, the total number of particles and the total entropy of a perfect fluid in a box whose bottom is parallel to the Rindler horizon are proportional to the area of the bottom, but are independent of the height of the box, provided the bottom of the box is sufficiently close to the Rindler horizon. The area dependence of the particle number implies that the particles tend to be gathered toward the bottom of the box and hence implicitly determines the distribution of chemical potential of the system, whereas the area dependence of the entropy indicates that the entropy is still additive and may find some applications in explaining the area law of black hole entropy. As a by product, we also obtain a relativistically refined version of the famous Saha equation which holds in both Minkowski and Rindler spacetimes. |
2102.12477 | Abdel Nasser Tawfik | Abdel Nasser Tawfik, Carsten Greiner | Early Universe Thermodynamics and Evolution in Nonviscous and Viscous
Strong and Electroweak epochs: Possible Analytical Solutions | 27 pages, 5 figures, accepted for publication in ENTROPY | null | null | ECTP-2019-05, WLCAPP-2019-05 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Based on recent perturbative and non-perturbative lattice calculations with
almost quark flavors and the thermal contributions from photons, neutrinos,
leptons, electroweak particles, and scalar Higgs bosons, various thermodynamic
quantities, at vanishing net-baryon densities, such as pressure, energy
density, bulk viscosity, relaxation time, and temperature have been calculated
up to the TeV-scale, i.e. covering hadron, QGP and electroweak (EW) phases in
the early Universe. This remarkable progress motivated the present study to
determine the possible influence of the bulk viscosity in the early Universe
and to understand how this would vary from epoch to epoch. We have taken into
consideration first- (Eckart) and second-order (Israel-Stewart) theories for
the relativistic cosmic fluid and integrated viscous equations of state in
Friedmann equations. Nonlinear nonhomogeneous differential equations are
obtained as analytical solutions. For Israel-Stewart, the differential
equations are very sophisticated to be solved. They are outlined here as
road-maps for future studies. For Eckart theory, the only possible solution is
the functionality, $H(a(t))$, where $H(t)$ is the Hubble parameter and $a(t)$
is the scale factor, but none of them so far could to be directly expressed in
terms of either proper or cosmic time $t$. For Eckart-type viscous background,
especially at finite cosmological constant, non-singular $H(t)$ and $a(t)$ are
obtained, where $H(t)$ diverges for QCD/EW and asymptotic EoS. For non-viscous
background, the dependence of $H(a(t))$ is monotonic. The same conclusion can
be drawn for an ideal EoS. We also conclude that the rate of decreasing
$H(a(t))$ with increasing $a(t)$ varies from epoch to epoch, at vanishing and
finite cosmological constant. These results obviously help in improving our
understanding of the nucleosynthesis and the cosmological large-scale
structure.
| [
{
"created": "Wed, 24 Feb 2021 12:14:04 GMT",
"version": "v1"
}
] | 2021-02-26 | [
[
"Tawfik",
"Abdel Nasser",
""
],
[
"Greiner",
"Carsten",
""
]
] | Based on recent perturbative and non-perturbative lattice calculations with almost quark flavors and the thermal contributions from photons, neutrinos, leptons, electroweak particles, and scalar Higgs bosons, various thermodynamic quantities, at vanishing net-baryon densities, such as pressure, energy density, bulk viscosity, relaxation time, and temperature have been calculated up to the TeV-scale, i.e. covering hadron, QGP and electroweak (EW) phases in the early Universe. This remarkable progress motivated the present study to determine the possible influence of the bulk viscosity in the early Universe and to understand how this would vary from epoch to epoch. We have taken into consideration first- (Eckart) and second-order (Israel-Stewart) theories for the relativistic cosmic fluid and integrated viscous equations of state in Friedmann equations. Nonlinear nonhomogeneous differential equations are obtained as analytical solutions. For Israel-Stewart, the differential equations are very sophisticated to be solved. They are outlined here as road-maps for future studies. For Eckart theory, the only possible solution is the functionality, $H(a(t))$, where $H(t)$ is the Hubble parameter and $a(t)$ is the scale factor, but none of them so far could to be directly expressed in terms of either proper or cosmic time $t$. For Eckart-type viscous background, especially at finite cosmological constant, non-singular $H(t)$ and $a(t)$ are obtained, where $H(t)$ diverges for QCD/EW and asymptotic EoS. For non-viscous background, the dependence of $H(a(t))$ is monotonic. The same conclusion can be drawn for an ideal EoS. We also conclude that the rate of decreasing $H(a(t))$ with increasing $a(t)$ varies from epoch to epoch, at vanishing and finite cosmological constant. These results obviously help in improving our understanding of the nucleosynthesis and the cosmological large-scale structure. |
gr-qc/0503050 | George E. A. Matsas | Jorge Castineiras, Luis C. B. Crispino, George E. A. Matsas and
Rodrigo Murta | Semiclassical approach to black hole absorption of electromagnetic
radiation emitted by a rotating charge | 8 pages (revtex), 8 figures | Phys.Rev.D71:104013,2005 | 10.1103/PhysRevD.71.104013 | null | gr-qc | null | We consider an electric charge, minimally coupled to the Maxwell field,
rotating around a Schwarzschild black hole. We investigate how much of the
radiation emitted from the swirling charge is absorbed by the black hole and
show that most of the photons escape to infinity. For this purpose we use the
Gupta-Bleuler quantization of the electromagnetic field in the modified Feynman
gauge developed in the context of quantum field theory in Schwarzschild
spacetime. We obtain that the two photon polarizations contribute quite
differently to the emitted power. In addition, we discuss the accurateness of
the results obtained in a full general relativistic approach in comparison with
the ones obtained when the electric charge is assumed to be orbiting a massive
object due to a Newtonian force.
| [
{
"created": "Fri, 11 Mar 2005 12:22:56 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Castineiras",
"Jorge",
""
],
[
"Crispino",
"Luis C. B.",
""
],
[
"Matsas",
"George E. A.",
""
],
[
"Murta",
"Rodrigo",
""
]
] | We consider an electric charge, minimally coupled to the Maxwell field, rotating around a Schwarzschild black hole. We investigate how much of the radiation emitted from the swirling charge is absorbed by the black hole and show that most of the photons escape to infinity. For this purpose we use the Gupta-Bleuler quantization of the electromagnetic field in the modified Feynman gauge developed in the context of quantum field theory in Schwarzschild spacetime. We obtain that the two photon polarizations contribute quite differently to the emitted power. In addition, we discuss the accurateness of the results obtained in a full general relativistic approach in comparison with the ones obtained when the electric charge is assumed to be orbiting a massive object due to a Newtonian force. |
1802.00841 | Zbigniew Haba | Z. Haba | Stabilization of Starobinsky-Vilenkin stochastic inflation by an
environmental noise | 18 pages | INtern.Journ.Modern Phys.D28(2019)1950085 | 10.1142/S0218271819500858 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the inflaton $\phi$ in an interaction with an infinite number of
fields treated as an environment (noise) with a friction $\gamma^{2}>0$. In a
Markovian approximation we obtain a stochastic wave equation (appearing also in
the warm inflation models). After the replacement of the environment by the
white noise, the stochastic wave equation violates the energy conservation if
$\gamma\neq 0$. We introduce a dark energy as a compensation of the inflaton
energy-momentum. We add to the classical wave equation the Starobinsky-Vilenkin
noise which in the slow-roll approximation describes the quantum fluctuations
in an expanding metric. We investigate the resulting consistent
Einstein-Klein-Gordon system in the slow-roll regime. We obtain Fokker-Planck
equation for the probability distribution of the inflaton assuming that the
dependence of the scale factor $a$ and the Hubble variable $ H$ on the field
$\phi$ is known. We obtain explicit stationary solutions of the Fokker-Planck
equation assuming that $a(\phi)$ and $H(\phi)$ can approximately be determined
in a slow-roll regime with the neglect of noise. We extend the results to the
multifield D-dimensional configuration space. We show that in the regime
$a(\phi)^{3}H(\phi)^{5}\rightarrow \infty$ the quantum noise determines the
asymptotic behaviour of the stationary distribution. If
$a(\phi)^{3}H(\phi)^{5}$ stays finite then the environmental noise ensures the
integrability of the stationary probability. In such a case there is no need to
introduce boundary conditions with the purpose to eliminate infinite inflation.
The variation of $a(\phi)^{3}H(\phi)^{5}$ could be interpreted as a sign of a
transition from cold inflation to warm inflation.
| [
{
"created": "Fri, 2 Feb 2018 20:36:54 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Feb 2019 18:43:03 GMT",
"version": "v2"
}
] | 2019-02-18 | [
[
"Haba",
"Z.",
""
]
] | We discuss the inflaton $\phi$ in an interaction with an infinite number of fields treated as an environment (noise) with a friction $\gamma^{2}>0$. In a Markovian approximation we obtain a stochastic wave equation (appearing also in the warm inflation models). After the replacement of the environment by the white noise, the stochastic wave equation violates the energy conservation if $\gamma\neq 0$. We introduce a dark energy as a compensation of the inflaton energy-momentum. We add to the classical wave equation the Starobinsky-Vilenkin noise which in the slow-roll approximation describes the quantum fluctuations in an expanding metric. We investigate the resulting consistent Einstein-Klein-Gordon system in the slow-roll regime. We obtain Fokker-Planck equation for the probability distribution of the inflaton assuming that the dependence of the scale factor $a$ and the Hubble variable $ H$ on the field $\phi$ is known. We obtain explicit stationary solutions of the Fokker-Planck equation assuming that $a(\phi)$ and $H(\phi)$ can approximately be determined in a slow-roll regime with the neglect of noise. We extend the results to the multifield D-dimensional configuration space. We show that in the regime $a(\phi)^{3}H(\phi)^{5}\rightarrow \infty$ the quantum noise determines the asymptotic behaviour of the stationary distribution. If $a(\phi)^{3}H(\phi)^{5}$ stays finite then the environmental noise ensures the integrability of the stationary probability. In such a case there is no need to introduce boundary conditions with the purpose to eliminate infinite inflation. The variation of $a(\phi)^{3}H(\phi)^{5}$ could be interpreted as a sign of a transition from cold inflation to warm inflation. |
1006.2525 | Philippe G. LeFloch | Florian Beyer and Philippe G. LeFloch | Second-order hyperbolic Fuchsian systems. Gowdy spacetimes and the
Fuchsian numerical algorithm | 22 pages. A shortened version is included in: F. Beyer and P.G.
LeFloch, Second-order hyperbolic Fuchsian systems and applications, Class.
Quantum Grav. 27 (2010), 245012 | null | null | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is the second part of a series devoted to the singular initial value
problem for second-order hyperbolic Fuchsian systems. In the first part, we
defined and investigated this general class of systems, and we established a
well-posedness theory in weighted Sobolev spaces. This theory is applied here
to the vacuum Einstein equations for Gowdy spacetimes admitting, by definition,
two Killing fields satisfying certain geometric conditions. We recover, by more
direct and simpler arguments, the well-posedness results established earlier by
Rendall and collaborators. In addition, in this paper we introduce a natural
approximation scheme, which we refer to as the Fuchsian numerical algorithm and
is directly motivated by our general theory. This algorithm provides highly
accurate, numerical approximations of the solution to the singular initial
value problem. In particular, for the class of Gowdy spacetimes under
consideration, various numerical experiments are presented which show the
interest and efficiency of the proposed method. Finally, as an application, we
numerically construct Gowdy spacetimes containing a smooth, incomplete,
non-compact Cauchy horizon.
| [
{
"created": "Sun, 13 Jun 2010 11:03:08 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Jan 2011 20:57:19 GMT",
"version": "v2"
}
] | 2011-01-11 | [
[
"Beyer",
"Florian",
""
],
[
"LeFloch",
"Philippe G.",
""
]
] | This is the second part of a series devoted to the singular initial value problem for second-order hyperbolic Fuchsian systems. In the first part, we defined and investigated this general class of systems, and we established a well-posedness theory in weighted Sobolev spaces. This theory is applied here to the vacuum Einstein equations for Gowdy spacetimes admitting, by definition, two Killing fields satisfying certain geometric conditions. We recover, by more direct and simpler arguments, the well-posedness results established earlier by Rendall and collaborators. In addition, in this paper we introduce a natural approximation scheme, which we refer to as the Fuchsian numerical algorithm and is directly motivated by our general theory. This algorithm provides highly accurate, numerical approximations of the solution to the singular initial value problem. In particular, for the class of Gowdy spacetimes under consideration, various numerical experiments are presented which show the interest and efficiency of the proposed method. Finally, as an application, we numerically construct Gowdy spacetimes containing a smooth, incomplete, non-compact Cauchy horizon. |
gr-qc/9409046 | Sucheta Koshti | Sucheta Koshti and Naresh Dadhich | The General Self-dual solution of the Einstein Equations | 14 Pages, Latex, IUCAA 94/29 | null | null | null | gr-qc | null | We obtain the most general explicit (anti)self-dual solution of the Einstein
equations. We find that any (anti)self-dual solution can be characterised by
three free functions of which one is harmonic. Any stationary (anti)self-dual
solution can be characterised by a harmonic function. It turns out that the
form of the Gibbons and Hawking multi-center metrics is the most general
stationary (anti)self-dual solution. We further note that the stationary
(anti)self-dual Einstein equations can be reinterpreted as the (anti)self-dual
Maxwell equations on the Euclidean background metric.
| [
{
"created": "Wed, 21 Sep 1994 11:51:14 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Koshti",
"Sucheta",
""
],
[
"Dadhich",
"Naresh",
""
]
] | We obtain the most general explicit (anti)self-dual solution of the Einstein equations. We find that any (anti)self-dual solution can be characterised by three free functions of which one is harmonic. Any stationary (anti)self-dual solution can be characterised by a harmonic function. It turns out that the form of the Gibbons and Hawking multi-center metrics is the most general stationary (anti)self-dual solution. We further note that the stationary (anti)self-dual Einstein equations can be reinterpreted as the (anti)self-dual Maxwell equations on the Euclidean background metric. |
0804.0628 | Mark Hannam | Mark Hannam, Sascha Husa, Frank Ohme, Bernd Bruegmann, Niall
O'Murchadha | Wormholes and trumpets: the Schwarzschild spacetime for the
moving-puncture generation | 19 pages, 22 figures | Phys.Rev.D78:064020,2008 | 10.1103/PhysRevD.78.064020 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We expand upon our previous analysis of numerical moving-puncture simulations
of the Schwarzschild spacetime. We present a derivation of the family of
analytic stationary 1+log foliations of the Schwarzschild solution, and outline
a transformation to isotropic-like coordinates. We discuss in detail the
numerical evolution of standard Schwarzschild puncture data, and the new
time-independent 1+log data. Finally, we demonstrate that the moving-puncture
method can locate the appropriate stationary geometry in a robust manner when a
numerical code alternates between two forms of 1+log slicing during a
simulation.
| [
{
"created": "Thu, 3 Apr 2008 21:42:23 GMT",
"version": "v1"
},
{
"created": "Sun, 6 Apr 2008 13:42:32 GMT",
"version": "v2"
}
] | 2009-02-20 | [
[
"Hannam",
"Mark",
""
],
[
"Husa",
"Sascha",
""
],
[
"Ohme",
"Frank",
""
],
[
"Bruegmann",
"Bernd",
""
],
[
"O'Murchadha",
"Niall",
""
]
] | We expand upon our previous analysis of numerical moving-puncture simulations of the Schwarzschild spacetime. We present a derivation of the family of analytic stationary 1+log foliations of the Schwarzschild solution, and outline a transformation to isotropic-like coordinates. We discuss in detail the numerical evolution of standard Schwarzschild puncture data, and the new time-independent 1+log data. Finally, we demonstrate that the moving-puncture method can locate the appropriate stationary geometry in a robust manner when a numerical code alternates between two forms of 1+log slicing during a simulation. |
0812.2581 | Massimo Tinto | Massimo Tinto, George J. Dick, John D. Prestage, and J.W. Armstrong | Improved spacecraft radio science using an on-board atomic clock:
application to gravitational wave searches | 21 pages, 5 figures. Submitted to Phys. Rev. D | Phys.Rev.D79:102003,2009 | 10.1103/PhysRevD.79.102003 | null | gr-qc | http://creativecommons.org/licenses/publicdomain/ | Recent advances in space-qualified atomic clocks (low-mass, low
power-consumption, frequency stability comparable to that of ground-based
clocks) can enable interplanetary spacecraft radio science experiments at
unprecedented Doppler sensitivities. The addition of an on-board digital
receiver would allow the up- and down-link Doppler frequencies to be measured
separately. Such separate, high-quality measurements allow optimal data
combinations that suppress the currently-leading noise sources: phase
scintillation noise from the Earth's atmosphere and Doppler noise caused by
mechanical vibrations of the ground antenna. Here we provide a general
expression for the optimal combination of ground and on-board Doppler data and
compute the sensitivity such a system would have to low-frequency gravitational
waves (GWs). Assuming a plasma scintillation noise calibration comparable to
that already demonstrated with the multi-link CASSINI radio system, the
space-clock/digital-receiver instrumentation enhancements would give GW strain
sensitivity of $2.0 \times 10^{-17}$ for randomly polarized, monochromatic GW
signals over a two-decade ($\sim0.0001-0.01$ Hz) region of the low-frequency
band. This is about an order of magnitude better than currently achieved with
traditional two-way coherent Doppler experiments. The utility of optimally
combining simultaneous up- and down-link observations is not limited to GW
searches. The Doppler tracking technique discussed here could be performed at
minimal incremental cost to also improve other radio science experiments (i.e.
tests of relativistic gravity, planetary and satellite gravity field
measurements, atmospheric and ring occultations) on future interplanetary
missions.
| [
{
"created": "Sat, 13 Dec 2008 20:33:33 GMT",
"version": "v1"
}
] | 2010-04-15 | [
[
"Tinto",
"Massimo",
""
],
[
"Dick",
"George J.",
""
],
[
"Prestage",
"John D.",
""
],
[
"Armstrong",
"J. W.",
""
]
] | Recent advances in space-qualified atomic clocks (low-mass, low power-consumption, frequency stability comparable to that of ground-based clocks) can enable interplanetary spacecraft radio science experiments at unprecedented Doppler sensitivities. The addition of an on-board digital receiver would allow the up- and down-link Doppler frequencies to be measured separately. Such separate, high-quality measurements allow optimal data combinations that suppress the currently-leading noise sources: phase scintillation noise from the Earth's atmosphere and Doppler noise caused by mechanical vibrations of the ground antenna. Here we provide a general expression for the optimal combination of ground and on-board Doppler data and compute the sensitivity such a system would have to low-frequency gravitational waves (GWs). Assuming a plasma scintillation noise calibration comparable to that already demonstrated with the multi-link CASSINI radio system, the space-clock/digital-receiver instrumentation enhancements would give GW strain sensitivity of $2.0 \times 10^{-17}$ for randomly polarized, monochromatic GW signals over a two-decade ($\sim0.0001-0.01$ Hz) region of the low-frequency band. This is about an order of magnitude better than currently achieved with traditional two-way coherent Doppler experiments. The utility of optimally combining simultaneous up- and down-link observations is not limited to GW searches. The Doppler tracking technique discussed here could be performed at minimal incremental cost to also improve other radio science experiments (i.e. tests of relativistic gravity, planetary and satellite gravity field measurements, atmospheric and ring occultations) on future interplanetary missions. |
1209.2680 | Ahmadjon Abdujabbarov | Ahmadjon Abdujabbarov, Arman Tursunov, Bobomurat Ahmedov, and Abdulla
Kuvatov | Acceleration of particles by black hole with gravitomagnetic charge
immersed in magnetic field | 8 pages,7 figures, 1 table, Accepted for publication in Astrophysics
& Space Science | null | 10.1007/s10509-012-1251-y | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The collision of test charged particles in the vicinity of an event horizon
of a weakly magnetized non-rotating black hole with gravitomagnetic charge has
been studied. The presence of the external magnetic field decreases the
innermost stable circular orbits (ISCO) radii of charged particles. The
opposite mechanism occurs when there is nonvanishing gravitomagnetic charge.
For a collision of charged particle moving at ISCO and the neutral particle
falling from infinity the maximal collision energy can be decreased by
gravitomagnetic charge in the presence of external asymptotically uniform
magnetic field.
| [
{
"created": "Wed, 12 Sep 2012 18:16:57 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Dec 2013 10:20:40 GMT",
"version": "v2"
}
] | 2015-06-11 | [
[
"Abdujabbarov",
"Ahmadjon",
""
],
[
"Tursunov",
"Arman",
""
],
[
"Ahmedov",
"Bobomurat",
""
],
[
"Kuvatov",
"Abdulla",
""
]
] | The collision of test charged particles in the vicinity of an event horizon of a weakly magnetized non-rotating black hole with gravitomagnetic charge has been studied. The presence of the external magnetic field decreases the innermost stable circular orbits (ISCO) radii of charged particles. The opposite mechanism occurs when there is nonvanishing gravitomagnetic charge. For a collision of charged particle moving at ISCO and the neutral particle falling from infinity the maximal collision energy can be decreased by gravitomagnetic charge in the presence of external asymptotically uniform magnetic field. |
1701.01039 | Behzad Eslam Panah | S. H. Hendi, G. H. Bordbar, B. Eslam Panah and S. Panahiyan | Neutron stars structure in the context of massive gravity | 17 pages, 6 figures | JCAP 07 (2017) 004 | 10.1088/1475-7516/2017/07/004 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by the recent interests in spin$-2$ massive gravitons, we study the
structure of neutron star in the context of massive gravity. The modifications
of TOV equation in the presence of massive gravity are explored in $4$ and
higher dimensions. Next, by considering the modern equation of state for the
neutron star matter (which is extracted by the lowest order constrained
variational (LOCV) method with the AV$18$ potential), different physical
properties of the neutron star (such as Le Chatelier's principle, stability and
energy conditions) are investigated. It is shown that consideration of the
massive gravity has specific contributions into the structure of neutron star
and introduces new prescriptions for the massive astrophysical objects. The
mass-radius relation is examined and the effects of massive gravity on the
Schwarzschild radius, average density, compactness, gravitational redshift and
dynamical stability are studied. Finally, a relation between mass and radius of
neutron star versus the Planck mass is extracted.
| [
{
"created": "Sun, 1 Jan 2017 17:29:10 GMT",
"version": "v1"
},
{
"created": "Sun, 23 Jul 2017 10:41:03 GMT",
"version": "v2"
}
] | 2017-07-25 | [
[
"Hendi",
"S. H.",
""
],
[
"Bordbar",
"G. H.",
""
],
[
"Panah",
"B. Eslam",
""
],
[
"Panahiyan",
"S.",
""
]
] | Motivated by the recent interests in spin$-2$ massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in $4$ and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV$18$ potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted. |
2212.14843 | Orest Hrycyna | Orest Hrycyna | On the structural stability of a simple cosmological model in $R+\alpha
R^{2}$ theory of gravity | 18 pages, 3 figs | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Theory of gravity with a quadratic contribution of scalar curvature is
investigated in terms of dynamical system approach. The simplest
Friedmann-Robertson-Walker metric is used to formulate dynamics in Jordan frame
as well as in conformally transformed Einstein frame. We show that in both
frames there are stable de Sitter states for which the Hubble function
expansion naturally gives terms corresponding to non-substantial dark matter.
Using invariant centre manifold we show that in the Einstein frame there is a
zero measure set of initial conditions leading from unstable to stable de
Sitter state. Additionally, the initial de Sitter state is plunged with a
parallelly propagated singularity. We show that the Jordan frame and the
Einstein frame formulation of the theory are physically nonequivalent.
| [
{
"created": "Fri, 30 Dec 2022 17:42:18 GMT",
"version": "v1"
}
] | 2023-01-02 | [
[
"Hrycyna",
"Orest",
""
]
] | Theory of gravity with a quadratic contribution of scalar curvature is investigated in terms of dynamical system approach. The simplest Friedmann-Robertson-Walker metric is used to formulate dynamics in Jordan frame as well as in conformally transformed Einstein frame. We show that in both frames there are stable de Sitter states for which the Hubble function expansion naturally gives terms corresponding to non-substantial dark matter. Using invariant centre manifold we show that in the Einstein frame there is a zero measure set of initial conditions leading from unstable to stable de Sitter state. Additionally, the initial de Sitter state is plunged with a parallelly propagated singularity. We show that the Jordan frame and the Einstein frame formulation of the theory are physically nonequivalent. |
2206.05064 | Pasquale Bosso | Pasquale Bosso, Luciano Petruzziello, Fabian Wagner | The minimal length is physical | 4 pages, 1 figure | Phys. Lett. 843 (2022) 137415 | 10.1016/j.physletb.2022.137415 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we clarify a foundational loose end affecting the
phenomenological approach to quantum gravity centered around the generalization
of Heisenberg uncertainty principle. This misconception stems from a series of
recently published works in which perturbative and non-perturbative methods are
confused, thereby resulting in a blurring of the distinction between changes in
the deformed algebra and changes in the representation of operators.
Accordingly, this reasoning would render the existence of a minimal length
representation-dependent, and thus unphysical.
| [
{
"created": "Thu, 9 Jun 2022 17:32:22 GMT",
"version": "v1"
}
] | 2022-10-12 | [
[
"Bosso",
"Pasquale",
""
],
[
"Petruzziello",
"Luciano",
""
],
[
"Wagner",
"Fabian",
""
]
] | In this paper, we clarify a foundational loose end affecting the phenomenological approach to quantum gravity centered around the generalization of Heisenberg uncertainty principle. This misconception stems from a series of recently published works in which perturbative and non-perturbative methods are confused, thereby resulting in a blurring of the distinction between changes in the deformed algebra and changes in the representation of operators. Accordingly, this reasoning would render the existence of a minimal length representation-dependent, and thus unphysical. |
2012.10462 | Baofei Li | Bao-Fei Li, Sahil Saini, Parampreet Singh | Primordial power spectrum from a matter-Ekpyrotic bounce scenario in
loop quantum cosmology | 20 pages, 8 figures, 1 table | Phys. Rev. D 103, 066020 (2021) | 10.1103/PhysRevD.103.066020 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A union of matter bounce and Ekpyrotic scenarios is often studied in an
attempt to combine the most promising features of these two models. Since
non-perturbative quantum geometric effects in loop quantum cosmology (LQC)
result in natural bouncing scenarios without any violation of energy conditions
or fine tuning, an investigation of matter-Ekpyrotic bounce scenario is
interesting to explore in this quantum gravitational setting. In this work, we
explore this unified phenomenological model for a spatially flat
Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe in LQC filled with dust
and a scalar field in an Ekpyrotic scenario like negative potential. Background
dynamics and the power spectrum of the comoving curvature perturbations are
numerically analyzed with various initial conditions and a suitable choice of
the initial states. By varying the initial conditions we consider different
cases of dust and Ekpyrotic field domination in the contracting phase. We use
the dressed metric approach to numerically compute the primordial power
spectrum of the comoving curvature perturbations which turns out to be almost
scale invariant for the modes which exit the horizon in the matter-dominated
phase. But, in contrast with a constant magnitude power spectrum obtained under
approximation of a constant Ekpyrotic equation of state using deformed algebra
approach in an earlier work, we find that the magnitude of power spectrum
changes during evolution. Our analysis shows that the bouncing regime only
leaves imprints on the modes outside the scale-invariant regime. However, an
analysis of the spectral index shows inconsistency with the observational data,
thus making further improvements in such a model necessary.
| [
{
"created": "Fri, 18 Dec 2020 19:00:26 GMT",
"version": "v1"
}
] | 2021-03-31 | [
[
"Li",
"Bao-Fei",
""
],
[
"Saini",
"Sahil",
""
],
[
"Singh",
"Parampreet",
""
]
] | A union of matter bounce and Ekpyrotic scenarios is often studied in an attempt to combine the most promising features of these two models. Since non-perturbative quantum geometric effects in loop quantum cosmology (LQC) result in natural bouncing scenarios without any violation of energy conditions or fine tuning, an investigation of matter-Ekpyrotic bounce scenario is interesting to explore in this quantum gravitational setting. In this work, we explore this unified phenomenological model for a spatially flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe in LQC filled with dust and a scalar field in an Ekpyrotic scenario like negative potential. Background dynamics and the power spectrum of the comoving curvature perturbations are numerically analyzed with various initial conditions and a suitable choice of the initial states. By varying the initial conditions we consider different cases of dust and Ekpyrotic field domination in the contracting phase. We use the dressed metric approach to numerically compute the primordial power spectrum of the comoving curvature perturbations which turns out to be almost scale invariant for the modes which exit the horizon in the matter-dominated phase. But, in contrast with a constant magnitude power spectrum obtained under approximation of a constant Ekpyrotic equation of state using deformed algebra approach in an earlier work, we find that the magnitude of power spectrum changes during evolution. Our analysis shows that the bouncing regime only leaves imprints on the modes outside the scale-invariant regime. However, an analysis of the spectral index shows inconsistency with the observational data, thus making further improvements in such a model necessary. |
gr-qc/0401096 | Matteo Luca Ruggiero | Angelo Tartaglia, Matteo Luca Ruggiero | The Gravitomagnetic measurement of the angular momentum of celestial
bodies | 4 pages, LaTeX, submitted to the Proceedings of the "X Marcel
Grossmann Meeting on General Relativity" in Rio de Janeiro, Brazil, July
20-26 (2003) | null | 10.1142/9789812704030_0230 | null | gr-qc astro-ph | null | The asymmetry in the time delay for light rays propagating on opposite sides
of a spinning body is analyzed. A frequency shift in the perceived signals is
found. A practical procedure is proposed for evidencing the asymmetry, allowing
for a measurement of the specific angular momentum of the rotating mass. Orders
of magnitude are discussed.
| [
{
"created": "Thu, 22 Jan 2004 12:52:20 GMT",
"version": "v1"
}
] | 2016-11-09 | [
[
"Tartaglia",
"Angelo",
""
],
[
"Ruggiero",
"Matteo Luca",
""
]
] | The asymmetry in the time delay for light rays propagating on opposite sides of a spinning body is analyzed. A frequency shift in the perceived signals is found. A practical procedure is proposed for evidencing the asymmetry, allowing for a measurement of the specific angular momentum of the rotating mass. Orders of magnitude are discussed. |
gr-qc/0611004 | Shahar Hod | Shahar Hod | Universal Bound on Dynamical Relaxation Times and Black-Hole Quasinormal
Ringing | 4 pages | Phys.Rev.D75:064013,2007 | 10.1103/PhysRevD.75.064013 | null | gr-qc astro-ph cond-mat.stat-mech hep-th nucl-th quant-ph | null | From information theory and thermodynamic considerations a universal bound on
the relaxation time $\tau$ of a perturbed system is inferred, $\tau \geq
\hbar/\pi T$, where $T$ is the system's temperature. We prove that black holes
comply with the bound; in fact they actually {\it saturate} it. Thus, when
judged by their relaxation properties, black holes are the most extreme objects
in nature, having the maximum relaxation rate which is allowed by quantum
theory.
| [
{
"created": "Wed, 1 Nov 2006 06:43:39 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Hod",
"Shahar",
""
]
] | From information theory and thermodynamic considerations a universal bound on the relaxation time $\tau$ of a perturbed system is inferred, $\tau \geq \hbar/\pi T$, where $T$ is the system's temperature. We prove that black holes comply with the bound; in fact they actually {\it saturate} it. Thus, when judged by their relaxation properties, black holes are the most extreme objects in nature, having the maximum relaxation rate which is allowed by quantum theory. |
1505.05509 | Vitor Cardoso | Vitor Cardoso, Richard Brito, Joao L. Rosa | Superradiance in stars | 5 pages, RevTex 4. Accepted for publication in Physical Review D | Phys.Rev. D91 (2015) 12, 124026 | 10.1103/PhysRevD.91.124026 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has long been known that dissipation is a crucial ingredient in the
superradiant amplification of wavepackets off rotating objects. We show that,
once appropriate dissipation mechanisms are included, stars are also prone to
superradiance and superradiant instabilities. In particular, ultra-light dark
matter with small interaction cross section with the star material or
self-annihilation can trigger a superradiant instability. On long timescales,
the instability strips the star of most of its angular momentum. Whether or not
new stationary configurations surrounded by scalar condensates exist, remains
to be seen.
| [
{
"created": "Wed, 20 May 2015 20:00:35 GMT",
"version": "v1"
}
] | 2015-07-03 | [
[
"Cardoso",
"Vitor",
""
],
[
"Brito",
"Richard",
""
],
[
"Rosa",
"Joao L.",
""
]
] | It has long been known that dissipation is a crucial ingredient in the superradiant amplification of wavepackets off rotating objects. We show that, once appropriate dissipation mechanisms are included, stars are also prone to superradiance and superradiant instabilities. In particular, ultra-light dark matter with small interaction cross section with the star material or self-annihilation can trigger a superradiant instability. On long timescales, the instability strips the star of most of its angular momentum. Whether or not new stationary configurations surrounded by scalar condensates exist, remains to be seen. |
2401.02924 | Jose Barrientos | Jos\'e Barrientos, Adolfo Cisterna, Ivan Kol\'a\v{r}, Keanu M\"uller,
Marcelo Oyarzo, and Konstantinos Pallikaris | Mixing "Magnetic'' and "Electric'' Ehlers--Harrison transformations: The
Electromagnetic Swirling Spacetime and Novel Type I Backgrounds | null | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper, we obtain a complete list of stationary and axisymmetric
spacetimes, generated from a Minkowski spacetime using the Ernst technique. We
do so by operating on the associated seed potentials with a composition of
Ehlers and Harrison transformations. In particular, assigning an additional
``electric'' or ``magnetic'' tag to the transformations, we investigate the new
spacetimes obtained either via a composition of magnetic Ehlers and Harrison
transformations (first part) or via a magnetic-electric combination (second
part). In the first part, the resulting type D spacetime, dubbed
electromagnetic swirling universe, features key properties, separately found in
swirling and (Bonnor--)Melvin spacetimes, the latter recovered in appropriate
limits. A detailed analysis of the geometry is included, and subtle issues are
addressed. A detailed proof that the spacetime belongs to the Kundt family, is
included, and a notable relation to the planar-Reissner-Nordstr\"om-NUT black
hole is also meticulously worked out. This relation is further exploited to
reverse-engineer the form of the solution in the presence of a nontrivial
cosmological constant. A Schwarzschild black hole embedded into the new
background is also discussed. In the second part, we present four novel
stationary and axisymmetric asymptotically nonflat type I spacetimes, which are
naively expected to be extensions of the Melvin or swirling solution including
a NUT parameter or electromagnetic charges. We actually find that they are,
under conditions, free of curvature and topological singularities, with the
physical meaning of the electric transformation parameters in these backgrounds
requiring further investigation.
| [
{
"created": "Fri, 5 Jan 2024 18:05:53 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Jan 2024 18:16:19 GMT",
"version": "v2"
}
] | 2024-01-15 | [
[
"Barrientos",
"José",
""
],
[
"Cisterna",
"Adolfo",
""
],
[
"Kolář",
"Ivan",
""
],
[
"Müller",
"Keanu",
""
],
[
"Oyarzo",
"Marcelo",
""
],
[
"Pallikaris",
"Konstantinos",
""
]
] | In this paper, we obtain a complete list of stationary and axisymmetric spacetimes, generated from a Minkowski spacetime using the Ernst technique. We do so by operating on the associated seed potentials with a composition of Ehlers and Harrison transformations. In particular, assigning an additional ``electric'' or ``magnetic'' tag to the transformations, we investigate the new spacetimes obtained either via a composition of magnetic Ehlers and Harrison transformations (first part) or via a magnetic-electric combination (second part). In the first part, the resulting type D spacetime, dubbed electromagnetic swirling universe, features key properties, separately found in swirling and (Bonnor--)Melvin spacetimes, the latter recovered in appropriate limits. A detailed analysis of the geometry is included, and subtle issues are addressed. A detailed proof that the spacetime belongs to the Kundt family, is included, and a notable relation to the planar-Reissner-Nordstr\"om-NUT black hole is also meticulously worked out. This relation is further exploited to reverse-engineer the form of the solution in the presence of a nontrivial cosmological constant. A Schwarzschild black hole embedded into the new background is also discussed. In the second part, we present four novel stationary and axisymmetric asymptotically nonflat type I spacetimes, which are naively expected to be extensions of the Melvin or swirling solution including a NUT parameter or electromagnetic charges. We actually find that they are, under conditions, free of curvature and topological singularities, with the physical meaning of the electric transformation parameters in these backgrounds requiring further investigation. |
gr-qc/0307092 | Nobuyuki Sakai | Nobuyuki Sakai (Yamagata U./Rome Observatory) | Generality of Topological Inflation | 11 pages, details of numerical method described, discussions added,
to appear in CQG | Class.Quant.Grav. 21 (2004) 281-288 | 10.1088/0264-9381/21/1/020 | null | gr-qc astro-ph hep-ph | null | Many authors claimed that a large initial inhomogeneity prevents the onset of
inflation and therefore inflation takes place only if the scalar field is
homogeneous or appropriately chosen over the horizon scale. We show that those
arguments do not apply to topological inflation. The core of a defect starts
inflation even if it has much smaller size than the horizon and much larger
gradient energy than the potential, as long as the vacuum expectation value is
large enough ($\gtrsim0.3\mpl$) and the core is not contracting initially. This
is due to stability of false vacuum.
| [
{
"created": "Mon, 21 Jul 2003 14:14:23 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Oct 2003 18:29:39 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Sakai",
"Nobuyuki",
"",
"Yamagata U./Rome Observatory"
]
] | Many authors claimed that a large initial inhomogeneity prevents the onset of inflation and therefore inflation takes place only if the scalar field is homogeneous or appropriately chosen over the horizon scale. We show that those arguments do not apply to topological inflation. The core of a defect starts inflation even if it has much smaller size than the horizon and much larger gradient energy than the potential, as long as the vacuum expectation value is large enough ($\gtrsim0.3\mpl$) and the core is not contracting initially. This is due to stability of false vacuum. |
2405.16758 | Kristian Gjorgjieski | Kristian Gjorgjieski and Rog\'erio Capobianco | Geometrically Thick Disks around Kerr Black Holes in a Swirling Universe | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate geometrically thick disks around Kerr black holes in a
swirling universe. This stationary and axisymmetric spacetime is composed of a
Kerr black hole, which is immersed in a swirling background. The swirling
background is characterized by an odd $\mathcal{Z}_2$ symmetry, where the
northern and southern hemispheres are rotating in opposite directions. The Kerr
and swirling rotations can lead to the emergence of complex spin-spin
interactions, which heavily influence the spacetime properties. In order to
study this influence, we analyze prograde as well as retrograde circular orbits
and geometrically thick disks for different spacetime solutions, which are
classified by their Kerr parameter $a$ and the swirling parameter $j$. We find
stabilizing effects on prograde circular orbits and destabilizing effects on
retrograde circular orbits, which originate from the spin-spin interaction and
depend mainly on the Kerr rotation. Furthermore, the background rotation leads
to an emergence of static orbits and the symmetry breaking regarding the
equatorial plane causes a vertical distribution of the circular orbits and
thick torus solutions. Due to the destabilizing effect of the swirling
rotation, an outer marginally stable orbit appears, which heavily downsizes the
parameter space for disk solutions. Dependent on the Keplerian specific angular
momentum distribution of the spacetime and on the disk momentum $\ell_0$,
different types of disk are possible which we classify and which differ in
terms of the complex disk dynamics that could arise due to the presence of an
inner and outer cusp or just an outer cusp.
| [
{
"created": "Mon, 27 May 2024 02:05:50 GMT",
"version": "v1"
}
] | 2024-05-28 | [
[
"Gjorgjieski",
"Kristian",
""
],
[
"Capobianco",
"Rogério",
""
]
] | We investigate geometrically thick disks around Kerr black holes in a swirling universe. This stationary and axisymmetric spacetime is composed of a Kerr black hole, which is immersed in a swirling background. The swirling background is characterized by an odd $\mathcal{Z}_2$ symmetry, where the northern and southern hemispheres are rotating in opposite directions. The Kerr and swirling rotations can lead to the emergence of complex spin-spin interactions, which heavily influence the spacetime properties. In order to study this influence, we analyze prograde as well as retrograde circular orbits and geometrically thick disks for different spacetime solutions, which are classified by their Kerr parameter $a$ and the swirling parameter $j$. We find stabilizing effects on prograde circular orbits and destabilizing effects on retrograde circular orbits, which originate from the spin-spin interaction and depend mainly on the Kerr rotation. Furthermore, the background rotation leads to an emergence of static orbits and the symmetry breaking regarding the equatorial plane causes a vertical distribution of the circular orbits and thick torus solutions. Due to the destabilizing effect of the swirling rotation, an outer marginally stable orbit appears, which heavily downsizes the parameter space for disk solutions. Dependent on the Keplerian specific angular momentum distribution of the spacetime and on the disk momentum $\ell_0$, different types of disk are possible which we classify and which differ in terms of the complex disk dynamics that could arise due to the presence of an inner and outer cusp or just an outer cusp. |
2301.03522 | Galina Weinstein Dr | Galina Weinstein | The Neverending Story of the Eternal Wormhole and the Noisy Sycamore | null | null | null | null | gr-qc hep-th physics.hist-ph quant-ph | http://creativecommons.org/licenses/by/4.0/ | There has been a great buzz surrounding Daniel Jafferis et al.'s latest
Nature paper, "Traversable wormhole dynamics on a quantum processor". The
Nature paper discusses an experiment in which Google's Sycamore quantum
processor is used to simulate a sparse N = 7 SYK model with 5 terms (a learned
Hamiltonian). The Nature paper shows that the learned Hamiltonian preserves the
key gravitational characteristics of an N = 10 SYK model with 210 terms and is
sufficient to produce a traversable wormhole behavior. I will examine the
experiment and discuss some philosophical challenges concerning the experiment
in memory of Ian Hacking. Recently, Norman Yao and two graduate students
discovered multiple flaws in Jafferis et al.'s learned Hamiltonian and uploaded
a comment on the Nature paper. As expected, Jafferis and his team found a
simple way to clarify the misunderstanding. They found a physical justification
that allowed them to avoid the problem. In this paper, I elucidate the main
arguments Yao and his students raised and the way Jafferis et al. found to save
their learned Hamiltonian. I will end this paper with a philosophical comment
on this recent development in the context of the learned Hamiltonian.
| [
{
"created": "Mon, 9 Jan 2023 17:19:19 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Jan 2023 17:51:29 GMT",
"version": "v2"
},
{
"created": "Thu, 18 May 2023 15:52:33 GMT",
"version": "v3"
}
] | 2023-05-19 | [
[
"Weinstein",
"Galina",
""
]
] | There has been a great buzz surrounding Daniel Jafferis et al.'s latest Nature paper, "Traversable wormhole dynamics on a quantum processor". The Nature paper discusses an experiment in which Google's Sycamore quantum processor is used to simulate a sparse N = 7 SYK model with 5 terms (a learned Hamiltonian). The Nature paper shows that the learned Hamiltonian preserves the key gravitational characteristics of an N = 10 SYK model with 210 terms and is sufficient to produce a traversable wormhole behavior. I will examine the experiment and discuss some philosophical challenges concerning the experiment in memory of Ian Hacking. Recently, Norman Yao and two graduate students discovered multiple flaws in Jafferis et al.'s learned Hamiltonian and uploaded a comment on the Nature paper. As expected, Jafferis and his team found a simple way to clarify the misunderstanding. They found a physical justification that allowed them to avoid the problem. In this paper, I elucidate the main arguments Yao and his students raised and the way Jafferis et al. found to save their learned Hamiltonian. I will end this paper with a philosophical comment on this recent development in the context of the learned Hamiltonian. |
gr-qc/9909079 | Hugo A. Morales-Tecotl | Jorge Alfaro (PUC/Santiago), Hugo A. Morales-Tecotl (UAM-I/Mexico
City) and Luis F. Urrutia (ICN-UNAM/Mexico City) | Quantum gravity corrections to neutrino propagation | RevTeX, 5pp, no figures. Notation of a sum in Eq.(2) improved. Slight
modifications in redaction. Final version to appear in Phys. Rev. Lett | Phys.Rev.Lett.84:2318-2321,2000 | 10.1103/PhysRevLett.84.2318 | null | gr-qc astro-ph hep-ph hep-th | null | Massive spin-1/2 fields are studied in the framework of loop quantum gravity
by considering a state approximating, at a length scale $\cal L$ much greater
than Planck length $\ell_P=1.2\times 10^{-33}$cm, a spin-1/2 field in flat
spacetime. The discrete structure of spacetime at $\ell_P$ yields corrections
to the field propagation at scale $\cal L$. Next, Neutrino Bursts (${\bar
p}\approx 10^5$GeV) accompaning Gamma Ray Bursts that have travelled
cosmological distances, $L\approx 10^{10}$l.y., are considered. The dominant
correction is helicity independent and leads to a time delay w.r.t. the speed
of light, $c$, of order $({\bar p} \ell_P) L/c\approx 10^4$s. To next order in
${\bar p} \ell_P$ the correction has the form of the Gambini and Pullin effect
for photons. Its contribution to time delay is comparable to that caused by the
mass term. Finally, a dependence $L_{\rm os}^{-1} \propto {\bar p}^2 \ell_P$ is
found for a two-flavour neutrino oscillation length.
| [
{
"created": "Fri, 24 Sep 1999 23:44:16 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Jan 2000 17:19:55 GMT",
"version": "v2"
}
] | 2011-05-05 | [
[
"Alfaro",
"Jorge",
"",
"PUC/Santiago"
],
[
"Morales-Tecotl",
"Hugo A.",
"",
"UAM-I/Mexico\n City"
],
[
"Urrutia",
"Luis F.",
"",
"ICN-UNAM/Mexico City"
]
] | Massive spin-1/2 fields are studied in the framework of loop quantum gravity by considering a state approximating, at a length scale $\cal L$ much greater than Planck length $\ell_P=1.2\times 10^{-33}$cm, a spin-1/2 field in flat spacetime. The discrete structure of spacetime at $\ell_P$ yields corrections to the field propagation at scale $\cal L$. Next, Neutrino Bursts (${\bar p}\approx 10^5$GeV) accompaning Gamma Ray Bursts that have travelled cosmological distances, $L\approx 10^{10}$l.y., are considered. The dominant correction is helicity independent and leads to a time delay w.r.t. the speed of light, $c$, of order $({\bar p} \ell_P) L/c\approx 10^4$s. To next order in ${\bar p} \ell_P$ the correction has the form of the Gambini and Pullin effect for photons. Its contribution to time delay is comparable to that caused by the mass term. Finally, a dependence $L_{\rm os}^{-1} \propto {\bar p}^2 \ell_P$ is found for a two-flavour neutrino oscillation length. |
1012.5111 | Jonathan R. Gair | Jonathan R. Gair, Eanna E. Flanagan, Steve Drasco, Tanja Hinderer and
Stanislav Babak | Forced motion near black holes | 28 pages, 2 figures, submitted to Phys. Rev. D; v2 has minor changes
for consistency with published version, plus a new section discussing the
relative advantages of the two approaches | Phys.Rev.D83:044037,2011 | 10.1103/PhysRevD.83.044037 | null | gr-qc astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present two methods for integrating forced geodesic equations in the Kerr
spacetime, which can accommodate arbitrary forces. As a test case, we compute
inspirals under a simple drag force, mimicking the presence of gas. We verify
that both methods give the same results for this simple force. We find that
drag generally causes eccentricity to increase throughout the inspiral. This is
a relativistic effect qualitatively opposite to what is seen in
gravitational-radiation-driven inspirals, and similar to what is observed in
hydrodynamic simulations of gaseous binaries. We provide an analytic
explanation by deriving the leading order relativistic correction to the
Newtonian dynamics. If observed, an increasing eccentricity would provide clear
evidence that the inspiral was occurring in a non-vacuum environment. Our two
methods are especially useful for evolving orbits in the adiabatic regime. Both
use the method of osculating orbits, in which each point on the orbit is
characterized by the parameters of the geodesic with the same instantaneous
position and velocity. Both methods describe the orbit in terms of the geodesic
energy, axial angular momentum, Carter constant, azimuthal phase, and two
angular variables that increase monotonically and are relativistic
generalizations of the eccentric anomaly. The two methods differ in their
treatment of the orbital phases and the representation of the force. In one
method the geodesic phase and phase constant are evolved together as a single
orbital phase parameter, and the force is expressed in terms of its components
on the Kinnersley orthonormal tetrad. In the second method, the phase constants
of the geodesic motion are evolved separately and the force is expressed in
terms of its Boyer-Lindquist components. This second approach is a
generalization of earlier work by Pound and Poisson for planar forces in a
Schwarzschild background.
| [
{
"created": "Wed, 22 Dec 2010 21:37:54 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Feb 2011 18:07:54 GMT",
"version": "v2"
}
] | 2011-03-23 | [
[
"Gair",
"Jonathan R.",
""
],
[
"Flanagan",
"Eanna E.",
""
],
[
"Drasco",
"Steve",
""
],
[
"Hinderer",
"Tanja",
""
],
[
"Babak",
"Stanislav",
""
]
] | We present two methods for integrating forced geodesic equations in the Kerr spacetime, which can accommodate arbitrary forces. As a test case, we compute inspirals under a simple drag force, mimicking the presence of gas. We verify that both methods give the same results for this simple force. We find that drag generally causes eccentricity to increase throughout the inspiral. This is a relativistic effect qualitatively opposite to what is seen in gravitational-radiation-driven inspirals, and similar to what is observed in hydrodynamic simulations of gaseous binaries. We provide an analytic explanation by deriving the leading order relativistic correction to the Newtonian dynamics. If observed, an increasing eccentricity would provide clear evidence that the inspiral was occurring in a non-vacuum environment. Our two methods are especially useful for evolving orbits in the adiabatic regime. Both use the method of osculating orbits, in which each point on the orbit is characterized by the parameters of the geodesic with the same instantaneous position and velocity. Both methods describe the orbit in terms of the geodesic energy, axial angular momentum, Carter constant, azimuthal phase, and two angular variables that increase monotonically and are relativistic generalizations of the eccentric anomaly. The two methods differ in their treatment of the orbital phases and the representation of the force. In one method the geodesic phase and phase constant are evolved together as a single orbital phase parameter, and the force is expressed in terms of its components on the Kinnersley orthonormal tetrad. In the second method, the phase constants of the geodesic motion are evolved separately and the force is expressed in terms of its Boyer-Lindquist components. This second approach is a generalization of earlier work by Pound and Poisson for planar forces in a Schwarzschild background. |
gr-qc/9411050 | Serge Droz | A. Bonanno, S. Droz, W.Israel and S.M. Morsink | Structure of the Spherical Black Hole Interior | 11 pages, latex, 2 figures | null | 10.1098/rspa.1995.0100 | Alberta-Thy-35-94 | gr-qc | null | The internal structure of a charged spherical black hole is still a topic of
debate. In a nonrotating but aspherical gravitational collapse to form a
spherical charged black hole, the backscattered gravitational wave tails enter
the black hole and are blueshifted at the Cauchy horizon. This has a
catastrophic effect if combined with an outflux crossing the Cauchy horizon: a
singularity develops at the Cauchy horizon and the effective mass inflates.
Recently a numerical study of a massless scalar field in the \RN background
suggested that a spacelike singularity may form before the Cauchy horizon
forms. We will show that there exists an approximate analytic solution of the
scalar field equations which allows the mass inflation singularity at the
Cauchy horizon to exist. In particular, we see no evidence that the Cauchy
horizon is preceded by a spacelike singularity.
| [
{
"created": "Fri, 18 Nov 1994 21:43:23 GMT",
"version": "v1"
}
] | 2019-08-15 | [
[
"Bonanno",
"A.",
""
],
[
"Droz",
"S.",
""
],
[
"Israel",
"W.",
""
],
[
"Morsink",
"S. M.",
""
]
] | The internal structure of a charged spherical black hole is still a topic of debate. In a nonrotating but aspherical gravitational collapse to form a spherical charged black hole, the backscattered gravitational wave tails enter the black hole and are blueshifted at the Cauchy horizon. This has a catastrophic effect if combined with an outflux crossing the Cauchy horizon: a singularity develops at the Cauchy horizon and the effective mass inflates. Recently a numerical study of a massless scalar field in the \RN background suggested that a spacelike singularity may form before the Cauchy horizon forms. We will show that there exists an approximate analytic solution of the scalar field equations which allows the mass inflation singularity at the Cauchy horizon to exist. In particular, we see no evidence that the Cauchy horizon is preceded by a spacelike singularity. |
1405.3938 | Dario Bettoni | Dario Bettoni | Disformal invariance of second order scalar-tensor theories | 3 pages, to appear in the proceedings of the conference "Rencontres
de Moriond", Cosmology Session, 2014 | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Horndeski action is the most general one involving a metric and a scalar
field that leads to second-order field equations in four dimensions. Being the
natural extension of the well-known scalar-tensor theories, its structure and
properties are worth analyzing along the experience accumulated in the latter
context. Here, we argue that disformal transformations play, for the Horndeski
theory, a similar role to that of conformal transformations for scalar-tensor
theories a la Brans-Dicke.
| [
{
"created": "Mon, 12 May 2014 13:38:03 GMT",
"version": "v1"
}
] | 2014-05-16 | [
[
"Bettoni",
"Dario",
""
]
] | The Horndeski action is the most general one involving a metric and a scalar field that leads to second-order field equations in four dimensions. Being the natural extension of the well-known scalar-tensor theories, its structure and properties are worth analyzing along the experience accumulated in the latter context. Here, we argue that disformal transformations play, for the Horndeski theory, a similar role to that of conformal transformations for scalar-tensor theories a la Brans-Dicke. |
2004.10111 | Tanmoy Paul | Tanmoy Paul and Narayan Banerjee | Cosmological quantum entanglement : A possible testbed for the existence
of Kalb-Ramond field | CQG accepted | null | 10.1088/1361-6382/ab8bb9 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present paper, we explore the possible effects of a second rank
antisymmetric tensor field, known as Kalb-Ramond (KR) field, on cosmological
particle production as well as on quantum entanglement for a massive scalar
field propagating in a four dimensional FRW spacetime evolves through a
symmetric bounce. For this purpose, the scalar field is considered to be
coupled with the KR field and also with the Ricci scalar via the term $\sim \xi
R\Phi^2$ (with $\xi$ be the coupling). The presence of KR field spoils the
conformal symmetry of a massless scalar field even for $\xi = 1/6$ in four
dimensional context, which has interesting consequences on particle production
and consequently on quantum entanglement as we will discuss. In particular, the
presence of KR field in a FRW bouncing universe allows a greater particle
production and consequently the upper bound of the entanglement entropy becomes
larger in comparison to the case when the KR field is absent. This may provide
an interesting testbed for the existence of Kalb-Ramond field in our universe.
| [
{
"created": "Tue, 21 Apr 2020 15:39:00 GMT",
"version": "v1"
}
] | 2020-08-26 | [
[
"Paul",
"Tanmoy",
""
],
[
"Banerjee",
"Narayan",
""
]
] | In the present paper, we explore the possible effects of a second rank antisymmetric tensor field, known as Kalb-Ramond (KR) field, on cosmological particle production as well as on quantum entanglement for a massive scalar field propagating in a four dimensional FRW spacetime evolves through a symmetric bounce. For this purpose, the scalar field is considered to be coupled with the KR field and also with the Ricci scalar via the term $\sim \xi R\Phi^2$ (with $\xi$ be the coupling). The presence of KR field spoils the conformal symmetry of a massless scalar field even for $\xi = 1/6$ in four dimensional context, which has interesting consequences on particle production and consequently on quantum entanglement as we will discuss. In particular, the presence of KR field in a FRW bouncing universe allows a greater particle production and consequently the upper bound of the entanglement entropy becomes larger in comparison to the case when the KR field is absent. This may provide an interesting testbed for the existence of Kalb-Ramond field in our universe. |
1602.04021 | Paolo Valtancoli | P. Valtancoli | Scalar field conformally coupled to a charged BTZ black hole | 9 pages, no figures | null | 10.1016/j.aop.2016.03.013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the Klein-Gordon equation of a scalar field conformally coupled to a
charged BTZ black hole. The background metric is obtained by coupling a
non-linear and conformal invariant Maxwell field to (2+1) gravity. We show that
the radial part is generally solved by a Heun function and, in the pure gravity
limit, by a hypergeometric function.
| [
{
"created": "Fri, 12 Feb 2016 11:46:19 GMT",
"version": "v1"
}
] | 2016-05-04 | [
[
"Valtancoli",
"P.",
""
]
] | We study the Klein-Gordon equation of a scalar field conformally coupled to a charged BTZ black hole. The background metric is obtained by coupling a non-linear and conformal invariant Maxwell field to (2+1) gravity. We show that the radial part is generally solved by a Heun function and, in the pure gravity limit, by a hypergeometric function. |
2101.12570 | Dan Vollick | Dan N. Vollick | On the Meaning of Various Mass Definitions for Asymptotically Flat
Spacetimes | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The mass contained in an arbitrary spacetime in general relativity is not
well defined. However, for asymptotically flat spacetimes various definitions
of mass have been proposed. In this paper I consider eight masses and show that
some of them correspond to the active gravitational mass while the others
correspond to the inertial mass. For example, the ADM mass corresponds to the
inertial mass while the M$\o$ller mass corresponds to the active gravitational
mass. In general the inertial and active gravitational masses are not equal. If
the spacetime is vacuum at large $r$ the Einstein equations force the inertial
and active gravitational masses to be the same. The Einstein equations also
force the masses to be the same if any matter that extends out to large $r$
satisfies the weak, strong or dominant energy condition. I also examine the
contributions of the inertial and active gravitational masses to the
gravitational redshift, the deflection of light, the Shapiro time delay, the
precession of perihelia and to the motion of test bodies in the spacetime.
| [
{
"created": "Thu, 28 Jan 2021 17:48:40 GMT",
"version": "v1"
}
] | 2021-02-01 | [
[
"Vollick",
"Dan N.",
""
]
] | The mass contained in an arbitrary spacetime in general relativity is not well defined. However, for asymptotically flat spacetimes various definitions of mass have been proposed. In this paper I consider eight masses and show that some of them correspond to the active gravitational mass while the others correspond to the inertial mass. For example, the ADM mass corresponds to the inertial mass while the M$\o$ller mass corresponds to the active gravitational mass. In general the inertial and active gravitational masses are not equal. If the spacetime is vacuum at large $r$ the Einstein equations force the inertial and active gravitational masses to be the same. The Einstein equations also force the masses to be the same if any matter that extends out to large $r$ satisfies the weak, strong or dominant energy condition. I also examine the contributions of the inertial and active gravitational masses to the gravitational redshift, the deflection of light, the Shapiro time delay, the precession of perihelia and to the motion of test bodies in the spacetime. |
1610.04742 | Benjamin Lackey | Benjamin D. Lackey, Sebastiano Bernuzzi, Chad R. Galley, Jeroen
Meidam, Chris Van Den Broeck | Effective-one-body waveforms for binary neutron stars using surrogate
models | 17 pages, 11 figures, submitted to PRD | Phys. Rev. D 95, 104036 (2017) | 10.1103/PhysRevD.95.104036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational-wave observations of binary neutron star systems can provide
information about the masses, spins, and structure of neutron stars. However,
this requires accurate and computationally efficient waveform models that take
<1s to evaluate for use in Bayesian parameter estimation codes that perform
10^7 - 10^8 waveform evaluations. We present a surrogate model of a nonspinning
effective-one-body waveform model with l = 2, 3, and 4 tidal multipole moments
that reproduces waveforms of binary neutron star numerical simulations up to
merger. The surrogate is built from compact sets of effective-one-body waveform
amplitude and phase data that each form a reduced basis. We find that 12
amplitude and 7 phase basis elements are sufficient to reconstruct any binary
neutron star waveform with a starting frequency of 10Hz. The surrogate has
maximum errors of 3.8% in amplitude (0.04% excluding the last 100M before
merger) and 0.043 radians in phase. The version implemented in the LIGO
Algorithm Library takes ~0.07s to evaluate for a starting frequency of 30Hz and
~0.8s for a starting frequency of 10Hz, resulting in a speed-up factor of ~10^3
- 10^4 relative to the original Matlab code. This allows parameter estimation
codes to run in days to weeks rather than years, and we demonstrate this with a
Nested Sampling run that recovers the masses and tidal parameters of a
simulated binary neutron star system.
| [
{
"created": "Sat, 15 Oct 2016 14:27:31 GMT",
"version": "v1"
}
] | 2017-06-07 | [
[
"Lackey",
"Benjamin D.",
""
],
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Galley",
"Chad R.",
""
],
[
"Meidam",
"Jeroen",
""
],
[
"Broeck",
"Chris Van Den",
""
]
] | Gravitational-wave observations of binary neutron star systems can provide information about the masses, spins, and structure of neutron stars. However, this requires accurate and computationally efficient waveform models that take <1s to evaluate for use in Bayesian parameter estimation codes that perform 10^7 - 10^8 waveform evaluations. We present a surrogate model of a nonspinning effective-one-body waveform model with l = 2, 3, and 4 tidal multipole moments that reproduces waveforms of binary neutron star numerical simulations up to merger. The surrogate is built from compact sets of effective-one-body waveform amplitude and phase data that each form a reduced basis. We find that 12 amplitude and 7 phase basis elements are sufficient to reconstruct any binary neutron star waveform with a starting frequency of 10Hz. The surrogate has maximum errors of 3.8% in amplitude (0.04% excluding the last 100M before merger) and 0.043 radians in phase. The version implemented in the LIGO Algorithm Library takes ~0.07s to evaluate for a starting frequency of 30Hz and ~0.8s for a starting frequency of 10Hz, resulting in a speed-up factor of ~10^3 - 10^4 relative to the original Matlab code. This allows parameter estimation codes to run in days to weeks rather than years, and we demonstrate this with a Nested Sampling run that recovers the masses and tidal parameters of a simulated binary neutron star system. |
0812.4856 | Alberto Rozas-Fernandez | Norman Cruz, Pedro F. Gonzalez-Diaz, Alberto Rozas-Fernandez and
Guillermo Sanchez | Holographic kinetic k-essence model | 6 pages, 4 figures, revised version, accepted for publication in
Phys.Lett.B | Phys.Lett.B679:293-297,2009 | 10.1016/j.physletb.2009.07.028 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a connection between the holographic dark energy density and the
kinetic k-essence energy density in a flat FRW universe. With the choice
$c\geq1$, the holographic dark energy can be described by a kinetic k-essence
scalar field in a certain way. In this paper we show this kinetic k-essential
description of the holographic dark energy with $c\geq1$ and reconstruct the
kinetic k-essence function F(X).
| [
{
"created": "Sun, 28 Dec 2008 21:53:39 GMT",
"version": "v1"
},
{
"created": "Sun, 23 Aug 2009 13:07:32 GMT",
"version": "v2"
}
] | 2009-09-28 | [
[
"Cruz",
"Norman",
""
],
[
"Gonzalez-Diaz",
"Pedro F.",
""
],
[
"Rozas-Fernandez",
"Alberto",
""
],
[
"Sanchez",
"Guillermo",
""
]
] | We consider a connection between the holographic dark energy density and the kinetic k-essence energy density in a flat FRW universe. With the choice $c\geq1$, the holographic dark energy can be described by a kinetic k-essence scalar field in a certain way. In this paper we show this kinetic k-essential description of the holographic dark energy with $c\geq1$ and reconstruct the kinetic k-essence function F(X). |
1505.07017 | N\'estor Ortiz | N\'estor Ortiz, Olivier Sarbach, and Thomas Zannias | Shadow of a naked singularity | 26 pages, 11 figures | Phys. Rev. D 92, 044035 (2015) | 10.1103/PhysRevD.92.044035 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the redshift suffered by photons originating from an external
source, traversing a collapsing dust cloud and finally being received by an
asymptotic observer. In addition, we study the shadow that the collapsing cloud
casts on the sky of the asymptotic observer. We find that the resulting
redshift and properties of the shadow depend crucially on whether the final
outcome of the complete gravitational collapse is a black hole or a naked
singularity. In the black hole case, the shadow is due to the high redshift
acquired by the photons as they approach the event horizon, implying that their
energy is gradually redshifted toward zero within a few crossing times
associated with the event horizon radius. In contrast to this, a naked
singularity not only absorbs photons originating from the source, but it also
emits infinitely redshifted photons with and without angular momenta. This
emission introduces an abrupt cutoff in the frequency shift of the photons
detected in directions close to the radial one, and it is responsible for the
shadow masking the source in the naked singularity case. Furthermore, even
though the shadow forms and begins to grow immediately after the observer
crosses the Cauchy horizon, it takes many more crossing times than in the black
hole case for the source to be occulted from the observer's eyes. We discuss
possible implications of our results for testing the weak cosmic censorship
hypothesis. Even though at late times the image of the source perceived by the
observer looks the same in both cases, the dynamical formation of the shadow
and the redshift images has distinct features and time scales in the black hole
versus the naked singularity case. For stellar collapse, these time scales seem
to be too short to be resolved with existing technology. However, our results
may be relevant for the collapse of seeds leading to supermassive black holes.
| [
{
"created": "Tue, 26 May 2015 15:42:49 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Sep 2015 14:06:53 GMT",
"version": "v2"
}
] | 2015-09-10 | [
[
"Ortiz",
"Néstor",
""
],
[
"Sarbach",
"Olivier",
""
],
[
"Zannias",
"Thomas",
""
]
] | We analyze the redshift suffered by photons originating from an external source, traversing a collapsing dust cloud and finally being received by an asymptotic observer. In addition, we study the shadow that the collapsing cloud casts on the sky of the asymptotic observer. We find that the resulting redshift and properties of the shadow depend crucially on whether the final outcome of the complete gravitational collapse is a black hole or a naked singularity. In the black hole case, the shadow is due to the high redshift acquired by the photons as they approach the event horizon, implying that their energy is gradually redshifted toward zero within a few crossing times associated with the event horizon radius. In contrast to this, a naked singularity not only absorbs photons originating from the source, but it also emits infinitely redshifted photons with and without angular momenta. This emission introduces an abrupt cutoff in the frequency shift of the photons detected in directions close to the radial one, and it is responsible for the shadow masking the source in the naked singularity case. Furthermore, even though the shadow forms and begins to grow immediately after the observer crosses the Cauchy horizon, it takes many more crossing times than in the black hole case for the source to be occulted from the observer's eyes. We discuss possible implications of our results for testing the weak cosmic censorship hypothesis. Even though at late times the image of the source perceived by the observer looks the same in both cases, the dynamical formation of the shadow and the redshift images has distinct features and time scales in the black hole versus the naked singularity case. For stellar collapse, these time scales seem to be too short to be resolved with existing technology. However, our results may be relevant for the collapse of seeds leading to supermassive black holes. |
gr-qc/0210009 | Mauricio Bellini | Mauricio Bellini (IFM, Michoacana University) | Fresh inflation from five-dimensional vacuum state | 8 pages, 1 figure - to appear in Gen. Rel. Grav | Gen.Rel.Grav. 35 (2003) 35-41 | 10.1023/A:1021398710545 | null | gr-qc hep-ph | null | I study fresh inflation from a five-dimensional vacuum state, where the fifth
dimension is constant. In this framework, the universe can be seen as inflating
in a four-dimensional FRW metric embedding in a five-dimensional metric.
Finally, the experimental data $n_s=1$ are consistent with $(p+\rho_t)/\rho_t
\simeq1/3$ in the fresh inflationary scenario.
| [
{
"created": "Wed, 2 Oct 2002 17:23:29 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Bellini",
"Mauricio",
"",
"IFM, Michoacana University"
]
] | I study fresh inflation from a five-dimensional vacuum state, where the fifth dimension is constant. In this framework, the universe can be seen as inflating in a four-dimensional FRW metric embedding in a five-dimensional metric. Finally, the experimental data $n_s=1$ are consistent with $(p+\rho_t)/\rho_t \simeq1/3$ in the fresh inflationary scenario. |
1801.09972 | Ian Harry | Ian Harry, Tanja Hinderer | Observing and measuring the neutron-star equation-of-state in spinning
binary neutron star systems | 29 pages (CQG formatting), 9 figures | null | 10.1088/1361-6382/aac7e3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | LIGO and Virgo recently observed the first binary neutron star merger,
demonstrating that gravitational-waves offer the ability to probe how matter
behaves in one of the most extreme environments in the Universe. However, the
gravitational-wave signal emitted by an inspiraling binary neutron star system
is only weakly dependent on the equation of state and extracting this
information is challenging. Previous studies have focused mainly on binary
systems where the neutron stars are spinning slowly and the main imprint of
neutron star matter in the inspiral signal is due to tidal effects. For
binaries with non-negligible neutron-star spin the deformation of the neutron
star due to its own rotation introduces additional variations in the emitted
gravitational-wave signal. Here we explore whether highly spinning binary
neutron-star systems offer a better chance to measure the equation-of-state
than weakly spinning binary-neutron star systems. We focus on the dominant
adiabatic quadrupolar effects and consider three main questions. First, we show
that equation-of-state effects can be significant in the inspiral waveforms,
and that the spin-quadrupole effect dominates for rapidly rotating neutron
stars. Second, we show that variations in the spin-quadrupole phasing are
strongly degenerate with changes in the component masses and spins, and
neglecting these terms has a negligible impact on the number of observations
with second generation observatories. Finally, we explore the bias in the
masses and spins that would be introduced by using incorrect equation-of-state
terms. Using a novel method to rapidly evaluate an approximation of the
likelihood we show that assuming the incorrect equation-of-state when measuring
source parameters can lead to a significant bias. We also find that the ability
to measure the equation-of-state is improved when considering spinning systems.
| [
{
"created": "Tue, 30 Jan 2018 13:14:39 GMT",
"version": "v1"
}
] | 2018-07-11 | [
[
"Harry",
"Ian",
""
],
[
"Hinderer",
"Tanja",
""
]
] | LIGO and Virgo recently observed the first binary neutron star merger, demonstrating that gravitational-waves offer the ability to probe how matter behaves in one of the most extreme environments in the Universe. However, the gravitational-wave signal emitted by an inspiraling binary neutron star system is only weakly dependent on the equation of state and extracting this information is challenging. Previous studies have focused mainly on binary systems where the neutron stars are spinning slowly and the main imprint of neutron star matter in the inspiral signal is due to tidal effects. For binaries with non-negligible neutron-star spin the deformation of the neutron star due to its own rotation introduces additional variations in the emitted gravitational-wave signal. Here we explore whether highly spinning binary neutron-star systems offer a better chance to measure the equation-of-state than weakly spinning binary-neutron star systems. We focus on the dominant adiabatic quadrupolar effects and consider three main questions. First, we show that equation-of-state effects can be significant in the inspiral waveforms, and that the spin-quadrupole effect dominates for rapidly rotating neutron stars. Second, we show that variations in the spin-quadrupole phasing are strongly degenerate with changes in the component masses and spins, and neglecting these terms has a negligible impact on the number of observations with second generation observatories. Finally, we explore the bias in the masses and spins that would be introduced by using incorrect equation-of-state terms. Using a novel method to rapidly evaluate an approximation of the likelihood we show that assuming the incorrect equation-of-state when measuring source parameters can lead to a significant bias. We also find that the ability to measure the equation-of-state is improved when considering spinning systems. |
2009.11994 | Sai Wang | Zhe Chang, Sai Wang, Qing-Hua Zhu | Gauge Invariant Second Order Gravitational Waves | Major revisions. We further analyze the relation between the gauge
invariant synchronous gravitational waves and the gravitational waves fixed
in the Newtonian gauge. In this way, we could explain why one obtained
correctly the energy density spectrum from the Newtonian gauge in previous
studies (our method is available to other gauge fixings). Additional
citations are added. Typos are corrected | null | null | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the gauge invariance of the second order gravitational waves
induced by the first order scalar perturbations by following the Lie derivative
method. It is shown explicitly that the second order gravitational waves are
gauge invariant in the synchronous frame. In the gauge invariant framework, we
derive the equation of motion of the second order gravitational waves and show
that the second order gravitational waves are sourced from the first order
scalar perturbations described well in the gauge invariant Newtonian frame.
Since the observables of gravitational waves are measured in the synchronous
frame, we define the energy density spectrum of the second order gravitational
waves in terms of the gauge invariant synchronous variables. This way
guarantees no fictitious tensor perturbations. It is shown that the gauge
invariant energy density spectrum of the second order gravitational waves
coincides with the one in the Newtonian gauge.
| [
{
"created": "Fri, 25 Sep 2020 01:38:27 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Sep 2020 08:42:23 GMT",
"version": "v2"
}
] | 2020-09-30 | [
[
"Chang",
"Zhe",
""
],
[
"Wang",
"Sai",
""
],
[
"Zhu",
"Qing-Hua",
""
]
] | We investigate the gauge invariance of the second order gravitational waves induced by the first order scalar perturbations by following the Lie derivative method. It is shown explicitly that the second order gravitational waves are gauge invariant in the synchronous frame. In the gauge invariant framework, we derive the equation of motion of the second order gravitational waves and show that the second order gravitational waves are sourced from the first order scalar perturbations described well in the gauge invariant Newtonian frame. Since the observables of gravitational waves are measured in the synchronous frame, we define the energy density spectrum of the second order gravitational waves in terms of the gauge invariant synchronous variables. This way guarantees no fictitious tensor perturbations. It is shown that the gauge invariant energy density spectrum of the second order gravitational waves coincides with the one in the Newtonian gauge. |
2111.09174 | Pu-Xin Lin | Pu-Xin Lin and Yun-Song Piao | Populating the landscape in an inhomogeneous universe | 11 pages + references and appendix, 8 figures | null | 10.1103/PhysRevD.105.063534 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The primordial Universe might be highly inhomogeneous. We perform the 3+1D
Numerical Relativity simulation for the evolution of scalar field in an initial
inhomogeneous expanding Universe, and investigate how it populates the
landscape with both de Sitter (dS) and AdS vacua. The simulation results show
that eventually either the field in different region separates into different
vacua, so that the expanding dS or AdS bubbles (the bubble wall is expanding
but the spacetime inside AdS bubbles is contracting) come into being with clear
bounderies, or overall region is dS expanding with a few smaller AdS bubbles
(which collapsed into black holes) or inhomogeneously collapsing.
| [
{
"created": "Wed, 17 Nov 2021 15:06:11 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Feb 2022 18:53:43 GMT",
"version": "v2"
}
] | 2022-04-06 | [
[
"Lin",
"Pu-Xin",
""
],
[
"Piao",
"Yun-Song",
""
]
] | The primordial Universe might be highly inhomogeneous. We perform the 3+1D Numerical Relativity simulation for the evolution of scalar field in an initial inhomogeneous expanding Universe, and investigate how it populates the landscape with both de Sitter (dS) and AdS vacua. The simulation results show that eventually either the field in different region separates into different vacua, so that the expanding dS or AdS bubbles (the bubble wall is expanding but the spacetime inside AdS bubbles is contracting) come into being with clear bounderies, or overall region is dS expanding with a few smaller AdS bubbles (which collapsed into black holes) or inhomogeneously collapsing. |
gr-qc/0206058 | Dzhunushaliev Vladimir | V. Dzhunushaliev | Time at the origin of the Universe: fluctuations between two
possibilities | talk given at the NATO ARW "The Nature of Time : Geometry, Physics
and perception", Tatranska Lomnica, Slovak Republic | null | null | null | gr-qc | null | A variation of Hawking's idea about Euclidean origin of a nonsingular birth
of the Universe is considered. It is assumed that near to zero moment $t = 0$
fluctuations of a metric signature are possible.
| [
{
"created": "Thu, 20 Jun 2002 02:34:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Dzhunushaliev",
"V.",
""
]
] | A variation of Hawking's idea about Euclidean origin of a nonsingular birth of the Universe is considered. It is assumed that near to zero moment $t = 0$ fluctuations of a metric signature are possible. |
2203.11031 | Alesandro Santos | A. F. Santos and Faqir C. Khanna | Finite temperature applications in G\"odel space-time | 11 pages, accepted for publication in EPJC | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Temperature effects in a scalar field non-minimally coupled to gravity are
investigated. The Thermo Field Dynamics formalism is used. This is a
topological field theory that allows us to calculate different effects, such as
the Stefan-Boltzmann law and the Casimir effect, on an equal footing. These
phenomena are calculated assuming the G\"odel space-time as a gravitational
background. A possible implication of these results at the beginning of the
universe is discussed.
| [
{
"created": "Mon, 21 Mar 2022 14:50:13 GMT",
"version": "v1"
}
] | 2022-03-22 | [
[
"Santos",
"A. F.",
""
],
[
"Khanna",
"Faqir C.",
""
]
] | Temperature effects in a scalar field non-minimally coupled to gravity are investigated. The Thermo Field Dynamics formalism is used. This is a topological field theory that allows us to calculate different effects, such as the Stefan-Boltzmann law and the Casimir effect, on an equal footing. These phenomena are calculated assuming the G\"odel space-time as a gravitational background. A possible implication of these results at the beginning of the universe is discussed. |
2205.11036 | Silvia Vicentini | Silvia Vicentini | New bounds on vacuum decay in de Sitter space | 26 pages, 9 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Vacuum decay in de Sitter space is a process of great physical interest, as
it allows to rule out cosmological models in the early and current Universe.
Its rate may be described in terms of an instanton in Euclidean space called
bounce and it is usually interpreted as thermally assisted quantum tunneling.
According to analytical and numerical evidence in the literature, a bounce
exists only for certain values of the Hubble parameter in single scalar field
theories with Einstein-Hilbert gravity. In the present paper, we rely on a
novel approach to provide more stringent bounds, which may be easily extended
to theories with non-minimally coupled and quadratic gravity. An additional
restriction is also derived, which specifically applies to the latter.
| [
{
"created": "Mon, 23 May 2022 04:43:27 GMT",
"version": "v1"
}
] | 2022-05-24 | [
[
"Vicentini",
"Silvia",
""
]
] | Vacuum decay in de Sitter space is a process of great physical interest, as it allows to rule out cosmological models in the early and current Universe. Its rate may be described in terms of an instanton in Euclidean space called bounce and it is usually interpreted as thermally assisted quantum tunneling. According to analytical and numerical evidence in the literature, a bounce exists only for certain values of the Hubble parameter in single scalar field theories with Einstein-Hilbert gravity. In the present paper, we rely on a novel approach to provide more stringent bounds, which may be easily extended to theories with non-minimally coupled and quadratic gravity. An additional restriction is also derived, which specifically applies to the latter. |
gr-qc/9707001 | null | S.Ansoldi, A.Aurilia, R.Balbinot, E.Spallucci | Effective dynamics of self-gravitating extended objects | 13 pages, no figures, ReVTeX | Phys.Essays 9 (1996) 556 | 10.4006/1.3029270 | null | gr-qc hep-th | null | We introduce an effective Lagrangian which describes the classical and
semiclassical dynamics of spherically symmetric, self-gravitating objects that
may populate the Universe at large and small (Planck) scale. These include
wormholes, black holes and inflationary bubbles. We speculate that such objects
represent some possible modes of fluctuation in the primordial spacetime foam
out of which our universe was born. Several results obtained by different
methods are encompassed and reinterpreted by our effective approach. As an
example, we discuss: i) the gravitational nucleation coefficient for a pair of
Minkowski bubbles, and ii) the nucleation coefficient of an inflationary vacuum
bubble in a Minkowski background
| [
{
"created": "Tue, 1 Jul 1997 10:22:18 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Ansoldi",
"S.",
""
],
[
"Aurilia",
"A.",
""
],
[
"Balbinot",
"R.",
""
],
[
"Spallucci",
"E.",
""
]
] | We introduce an effective Lagrangian which describes the classical and semiclassical dynamics of spherically symmetric, self-gravitating objects that may populate the Universe at large and small (Planck) scale. These include wormholes, black holes and inflationary bubbles. We speculate that such objects represent some possible modes of fluctuation in the primordial spacetime foam out of which our universe was born. Several results obtained by different methods are encompassed and reinterpreted by our effective approach. As an example, we discuss: i) the gravitational nucleation coefficient for a pair of Minkowski bubbles, and ii) the nucleation coefficient of an inflationary vacuum bubble in a Minkowski background |
1810.10832 | Ayan Chatterjee | Ayan Chatterjee and Ankit Anand | Joining Spacetimes on Fractal Hypersurfaces | 22 pages, 2 figures | null | 10.1016/j.nuclphysb.2019.01.020 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The theory of fractional calculus is attracting a lot of attention from
mathematicians as well as physicists. The fractional generalisation of the
well-known ordinary calculus is being used extensively in many fields,
particularly in understanding stochastic process and fractal dynamics. In this
paper, we apply the techniques of fractional calculus to study some specific
modifications of the geometry of submanifolds. Our generalisation is applied to
extend the Israel formalism which is used to glue together two spacetimes
across a timelike, spacelike or a null hypersurface. In this context, we show
that the fractional extrapolation leads to some striking new results. More
precisely we demonstrate that, in contrast to the original Israel formalism,
where many spacetimes can only be joined together through an intermediate thin
hypersurface of matter satisfying some non- standard energy conditions, the
fractional generalisation allows these spacetimes to be smoothly sewed together
without any such requirements on the stress tensor of the matter fields. We
discuss the ramifications of these results for spacetime structure and the
possible implications for gravitational physics.
| [
{
"created": "Thu, 25 Oct 2018 11:07:46 GMT",
"version": "v1"
}
] | 2019-02-20 | [
[
"Chatterjee",
"Ayan",
""
],
[
"Anand",
"Ankit",
""
]
] | The theory of fractional calculus is attracting a lot of attention from mathematicians as well as physicists. The fractional generalisation of the well-known ordinary calculus is being used extensively in many fields, particularly in understanding stochastic process and fractal dynamics. In this paper, we apply the techniques of fractional calculus to study some specific modifications of the geometry of submanifolds. Our generalisation is applied to extend the Israel formalism which is used to glue together two spacetimes across a timelike, spacelike or a null hypersurface. In this context, we show that the fractional extrapolation leads to some striking new results. More precisely we demonstrate that, in contrast to the original Israel formalism, where many spacetimes can only be joined together through an intermediate thin hypersurface of matter satisfying some non- standard energy conditions, the fractional generalisation allows these spacetimes to be smoothly sewed together without any such requirements on the stress tensor of the matter fields. We discuss the ramifications of these results for spacetime structure and the possible implications for gravitational physics. |
0905.3465 | Eduardo J.S. Villasenor | J. Fernando Barbero G., Jerzy Lewandowski, Eduardo J. S. Villase\~nor | Flux-area operator and black hole entropy | 25 pages | Phys.Rev.D80:044016,2009 | 10.1103/PhysRevD.80.044016 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that, for space-times with inner boundaries, there exists a natural
area operator different from the standard one used in loop quantum gravity.
This new flux-area operator has equidistant eigenvalues. We discuss the
consequences of substituting the standard area operator in the
Ashtekar-Baez-Corichi-Krasnov definition of black hole entropy by the new one.
Our choice simplifies the definition of the entropy and allows us to consider
only those areas that coincide with the one defined by the value of the level
of the Chern-Simons theory describing the horizon degrees of freedom. We give a
prescription to count the number of relevant horizon states by using spin
components and obtain exact expressions for the black hole entropy. Finally we
derive its asymptotic behavior, discuss several issues related to the
compatibility of our results with the Bekenstein-Hawking area law and the
relation with Schwarzschild quasi-normal modes.
| [
{
"created": "Thu, 21 May 2009 10:19:31 GMT",
"version": "v1"
}
] | 2009-08-19 | [
[
"G.",
"J. Fernando Barbero",
""
],
[
"Lewandowski",
"Jerzy",
""
],
[
"Villaseñor",
"Eduardo J. S.",
""
]
] | We show that, for space-times with inner boundaries, there exists a natural area operator different from the standard one used in loop quantum gravity. This new flux-area operator has equidistant eigenvalues. We discuss the consequences of substituting the standard area operator in the Ashtekar-Baez-Corichi-Krasnov definition of black hole entropy by the new one. Our choice simplifies the definition of the entropy and allows us to consider only those areas that coincide with the one defined by the value of the level of the Chern-Simons theory describing the horizon degrees of freedom. We give a prescription to count the number of relevant horizon states by using spin components and obtain exact expressions for the black hole entropy. Finally we derive its asymptotic behavior, discuss several issues related to the compatibility of our results with the Bekenstein-Hawking area law and the relation with Schwarzschild quasi-normal modes. |
1206.0022 | Marco Cariglia Dr | Marco Cariglia | Hidden symmetries of Eisenhart-Duval lift metrics and the Dirac equation
with flux | 18 pages, no figures. Version 3: some typos corrected, some
discussions clarified, part of the abstract changed | Phys. Rev. D 86, 084050 (2012) | 10.1103/PhysRevD.86.084050 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Eisenhart-Duval lift allows embedding non-relativistic theories into a
Lorentzian geometrical setting. In this paper we study the lift from the point
of view of the Dirac equation and its hidden symmetries. We show that
dimensional reduction of the Dirac equation for the Eisenhart-Duval metric in
general gives rise to the non-relativistic Levy-Leblond equation in lower
dimension. We study in detail in which specific cases the lower dimensional
limit is given by the Dirac equation, with scalar and vector flux, and the
relation between lift, reduction and the hidden symmetries of the Dirac
equation. While there is a precise correspondence in the case of the lower
dimensional massive Dirac equation with no flux, we find that for generic
fluxes it is not possible to lift or reduce all solutions and hidden
symmetries. As a by-product of this analysis we construct new Lorentzian
metrics with special tensors by lifting Killing-Yano and Closed Conformal
Killing-Yano tensors and describe the general Conformal Killing-Yano tensor of
the Eisenhart-Duval lift metrics in terms of lower dimensional forms. Lastly,
we show how dimensionally reducing the higher dimensional operators of the
massless Dirac equation that are associated to shared hidden symmetries it is
possible to recover hidden symmetry operators for the Dirac equation with flux.
| [
{
"created": "Thu, 31 May 2012 20:19:08 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Jun 2012 03:58:05 GMT",
"version": "v2"
},
{
"created": "Thu, 21 Jun 2012 10:37:25 GMT",
"version": "v3"
}
] | 2012-12-07 | [
[
"Cariglia",
"Marco",
""
]
] | The Eisenhart-Duval lift allows embedding non-relativistic theories into a Lorentzian geometrical setting. In this paper we study the lift from the point of view of the Dirac equation and its hidden symmetries. We show that dimensional reduction of the Dirac equation for the Eisenhart-Duval metric in general gives rise to the non-relativistic Levy-Leblond equation in lower dimension. We study in detail in which specific cases the lower dimensional limit is given by the Dirac equation, with scalar and vector flux, and the relation between lift, reduction and the hidden symmetries of the Dirac equation. While there is a precise correspondence in the case of the lower dimensional massive Dirac equation with no flux, we find that for generic fluxes it is not possible to lift or reduce all solutions and hidden symmetries. As a by-product of this analysis we construct new Lorentzian metrics with special tensors by lifting Killing-Yano and Closed Conformal Killing-Yano tensors and describe the general Conformal Killing-Yano tensor of the Eisenhart-Duval lift metrics in terms of lower dimensional forms. Lastly, we show how dimensionally reducing the higher dimensional operators of the massless Dirac equation that are associated to shared hidden symmetries it is possible to recover hidden symmetry operators for the Dirac equation with flux. |
1501.04862 | Christian Corda Prof. | Subenoy Chakraborty, Subhajit Saha and Christian Corda | Quantum corrected non-thermal radiation spectrum from the tunnelling
mechanism | 9 pages, the results of arXiv:1305.4529 have been partially reviewed.
Final version accepted for publication in the Galaxies Special Issue
"Advances in Gravitational Research", Guest Editor Lorenzo Iorio | Galaxies 3, 103 (2015) | 10.3390/galaxies3020103 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Tunnelling mechanism is today considered a popular and widely used method in
describing Hawking radiation. However, in relation to black hole (BH) emission,
this mechanism is mostly used to obtain the Hawking temperature by comparing
the probability of emission of an outgoing particle with the Boltzmann factor.
On the other hand, Banerjee and Majhi reformulated the tunnelling framework
deriving a black body spectrum through the density matrix for the outgoing
modes for both the Bose-Einstein distribution and the Fermi-Dirac distribution.
In contrast, Parikh and Wilczek introduced a correction term performing an
exact calculation of the action for a tunnelling spherically symmetric particle
and, as a result, the probability of emission of an outgoing particle
corresponds to a non-strictly thermal radiation spectrum. Recently, one of us
(C. Corda) introduced a BH effective state and was able to obtain a
non-strictly black body spectrum from the tunnelling mechanism corresponding to
the probability of emission of an outgoing particle found by Parikh and
Wilczek. The present work introduces the quantum corrected effective
temperature and the corresponding quantum corrected effective metric is written
using Hawking's periodicity arguments. Thus, we obtain further corrections to
the non-strictly thermal BH radiation spectrum as the final distributions take
into account both the BH dynamical geometry during the emission of the particle
and the quantum corrections to the semiclassical Hawking temperature.
| [
{
"created": "Fri, 16 Jan 2015 14:20:19 GMT",
"version": "v1"
},
{
"created": "Thu, 28 May 2015 12:22:30 GMT",
"version": "v2"
}
] | 2015-06-15 | [
[
"Chakraborty",
"Subenoy",
""
],
[
"Saha",
"Subhajit",
""
],
[
"Corda",
"Christian",
""
]
] | Tunnelling mechanism is today considered a popular and widely used method in describing Hawking radiation. However, in relation to black hole (BH) emission, this mechanism is mostly used to obtain the Hawking temperature by comparing the probability of emission of an outgoing particle with the Boltzmann factor. On the other hand, Banerjee and Majhi reformulated the tunnelling framework deriving a black body spectrum through the density matrix for the outgoing modes for both the Bose-Einstein distribution and the Fermi-Dirac distribution. In contrast, Parikh and Wilczek introduced a correction term performing an exact calculation of the action for a tunnelling spherically symmetric particle and, as a result, the probability of emission of an outgoing particle corresponds to a non-strictly thermal radiation spectrum. Recently, one of us (C. Corda) introduced a BH effective state and was able to obtain a non-strictly black body spectrum from the tunnelling mechanism corresponding to the probability of emission of an outgoing particle found by Parikh and Wilczek. The present work introduces the quantum corrected effective temperature and the corresponding quantum corrected effective metric is written using Hawking's periodicity arguments. Thus, we obtain further corrections to the non-strictly thermal BH radiation spectrum as the final distributions take into account both the BH dynamical geometry during the emission of the particle and the quantum corrections to the semiclassical Hawking temperature. |
0807.4109 | Keith Hall A | Ka Hall | Exact Results for the Kepler Problem in General Relativity | 7 pages, 0 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Exact results are derived, specifically the perihelion shift and the Kepler
orbit, for a bound test particle in the Schwarzschild metric with cosmological
constant $\Lambda=0$. A series expansion, of $\Delta\phi =
2(2(1-2M/p(3-e))^{-1/2} K((4eM/p)/(1-2M/p(3-e)))-\pi)$, the exact perihelion
shift, admits the standard approximation $\Delta\phi=6M\pi/p$ as the leading
order term. In a similar fashion, a series expansion of the exact Kepler orbit,
represented by a Jacobi elliptic function, gives $u(\phi)=(1+e\cos\phi)/p$ to
first order. The results are valid for $M/p<1/(2(3+e))$ or $r_s<p/(3+e)$.
| [
{
"created": "Fri, 25 Jul 2008 14:35:28 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Jul 2008 18:13:35 GMT",
"version": "v2"
}
] | 2008-07-28 | [
[
"Hall",
"Ka",
""
]
] | Exact results are derived, specifically the perihelion shift and the Kepler orbit, for a bound test particle in the Schwarzschild metric with cosmological constant $\Lambda=0$. A series expansion, of $\Delta\phi = 2(2(1-2M/p(3-e))^{-1/2} K((4eM/p)/(1-2M/p(3-e)))-\pi)$, the exact perihelion shift, admits the standard approximation $\Delta\phi=6M\pi/p$ as the leading order term. In a similar fashion, a series expansion of the exact Kepler orbit, represented by a Jacobi elliptic function, gives $u(\phi)=(1+e\cos\phi)/p$ to first order. The results are valid for $M/p<1/(2(3+e))$ or $r_s<p/(3+e)$. |
1506.02647 | Sumanta Chakraborty | Sumanta Chakraborty | Aspects of Neutrino Oscillation in Alternative Gravity Theories | v2, 36 Pages, 8 figures | JCAP 10(2015)019 | 10.1088/1475-7516/2015/10/019 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Neutrino spin and flavour oscillation in curved spacetime have been studied
for the most general static spherically symmetric configuration. Using the
symmetry properties we have derived spin oscillation frequency for neutrino
moving along a geodesic or in a circular orbit. Starting from the expression of
neutrino spin oscillation frequency we have shown that even in this general
context, in high energy limit the spin oscillation frequency for neutrino
moving along circular orbit vanishes. This finally lends itself to non-zero
probability of neutrino helicity flip. While for neutrino flavour oscillation
we have derived general results for oscillation phase, which subsequently have
been applied to different gravity theories. These include dilaton field coupled
to Maxwell field tensor, generalization of Schwarzschild solution by
introduction of quadratic curvature terms of all possible form to the
Einstein-Hilbert action and finally regular black hole solutions. In all these
cases using the solar neutrino oscillation data we can put bounds on the
parameters of these gravity theories. While for spin oscillation probability,
we have considered two cases, Gauss-Bonnet term added to the Einstein-Hilbert
action and the f(R) gravity theory. In both these cases we could impose bounds
on the parameters which are consistent with previous considerations.
Implications are also discussed.
| [
{
"created": "Mon, 8 Jun 2015 03:49:01 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Oct 2015 11:10:37 GMT",
"version": "v2"
}
] | 2015-10-16 | [
[
"Chakraborty",
"Sumanta",
""
]
] | Neutrino spin and flavour oscillation in curved spacetime have been studied for the most general static spherically symmetric configuration. Using the symmetry properties we have derived spin oscillation frequency for neutrino moving along a geodesic or in a circular orbit. Starting from the expression of neutrino spin oscillation frequency we have shown that even in this general context, in high energy limit the spin oscillation frequency for neutrino moving along circular orbit vanishes. This finally lends itself to non-zero probability of neutrino helicity flip. While for neutrino flavour oscillation we have derived general results for oscillation phase, which subsequently have been applied to different gravity theories. These include dilaton field coupled to Maxwell field tensor, generalization of Schwarzschild solution by introduction of quadratic curvature terms of all possible form to the Einstein-Hilbert action and finally regular black hole solutions. In all these cases using the solar neutrino oscillation data we can put bounds on the parameters of these gravity theories. While for spin oscillation probability, we have considered two cases, Gauss-Bonnet term added to the Einstein-Hilbert action and the f(R) gravity theory. In both these cases we could impose bounds on the parameters which are consistent with previous considerations. Implications are also discussed. |
gr-qc/0311014 | Tomohiro Harada | Tomohiro Harada and Hideki Maeda | Stability criterion for self-similar solutions with a scalar field and
those with a stiff fluid in general relativity | 15 pages, accepted for publication in Classical and Quantum Gravity,
typos corrected | Class.Quant.Grav. 21 (2004) 371-390 | 10.1088/0264-9381/21/2/003 | null | gr-qc astro-ph | null | A stability criterion is derived in general relativity for self-similar
solutions with a scalar field and those with a stiff fluid, which is a perfect
fluid with the equation of state $P=\rho$. A wide class of self-similar
solutions turn out to be unstable against kink mode perturbation. According to
the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be
a critical solution for the spherical collapse of a stiff fluid if we allow
sufficiently small discontinuity in the density gradient field in the initial
data sets. The self-similar scalar-field solution, which was recently found
numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19}
6359), is also unstable. Both the flat Friedmann universe with a scalar field
and that with a stiff fluid suffer from kink instability at the particle
horizon scale.
| [
{
"created": "Wed, 5 Nov 2003 14:24:08 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Nov 2003 12:06:46 GMT",
"version": "v2"
},
{
"created": "Mon, 1 Dec 2003 10:17:13 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Harada",
"Tomohiro",
""
],
[
"Maeda",
"Hideki",
""
]
] | A stability criterion is derived in general relativity for self-similar solutions with a scalar field and those with a stiff fluid, which is a perfect fluid with the equation of state $P=\rho$. A wide class of self-similar solutions turn out to be unstable against kink mode perturbation. According to the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be a critical solution for the spherical collapse of a stiff fluid if we allow sufficiently small discontinuity in the density gradient field in the initial data sets. The self-similar scalar-field solution, which was recently found numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19} 6359), is also unstable. Both the flat Friedmann universe with a scalar field and that with a stiff fluid suffer from kink instability at the particle horizon scale. |
2004.06604 | Jos\'e Domingo Vela Arba\~nil | Jos\'e D. V. Arba\~nil and Pedro H. R. S. Moraes | Stable relativistic polytropic objects with cosmological constant | 11 pages, 7 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The effects of the cosmological constant on the static equilibrium
configurations and stability against small radial perturbations of relativistic
polytropic spheres are investigated. This study numerically solves the
hydrostatic equilibrium equation and the radial stability equation, both of
which are modified from their standard form to introduce the cosmological
constant. For the fluid, we consider a pressure $p$ and an energy density
$\rho$, which are connected through the equation of state
$p=\kappa\delta^{\Gamma}$ with $\delta=\rho-p/(\Gamma-1)$, where $\kappa$,
$\Gamma$ and $\delta$ represent the polytropic constant, adiabatic index and
rest mass density of the fluid, respectively. The dependencies of the mass,
radius and eigenfrequency of oscillations on both the cosmological constant and
the adiabatic index are analyzed. For ranges of both the central rest mass
density $\delta_c$ and the adiabatic index $\Gamma$, we show that the stars
have a larger (lower) mass and radius and a diminished (enhanced) stability
when the cosmological constant $\Lambda>0$ ($\Lambda<0$) is increased
(decreased). In addition, in a sequence of compact objects with fixed $\Gamma$
and $\Lambda$, the regions constructed by stable and unstable static
equilibrium configurations are recognized by the conditions $dM/d\delta_c>0$
and $dM/d\delta_c<0$, respectively.
| [
{
"created": "Tue, 14 Apr 2020 15:39:49 GMT",
"version": "v1"
}
] | 2020-04-15 | [
[
"Arbañil",
"José D. V.",
""
],
[
"Moraes",
"Pedro H. R. S.",
""
]
] | The effects of the cosmological constant on the static equilibrium configurations and stability against small radial perturbations of relativistic polytropic spheres are investigated. This study numerically solves the hydrostatic equilibrium equation and the radial stability equation, both of which are modified from their standard form to introduce the cosmological constant. For the fluid, we consider a pressure $p$ and an energy density $\rho$, which are connected through the equation of state $p=\kappa\delta^{\Gamma}$ with $\delta=\rho-p/(\Gamma-1)$, where $\kappa$, $\Gamma$ and $\delta$ represent the polytropic constant, adiabatic index and rest mass density of the fluid, respectively. The dependencies of the mass, radius and eigenfrequency of oscillations on both the cosmological constant and the adiabatic index are analyzed. For ranges of both the central rest mass density $\delta_c$ and the adiabatic index $\Gamma$, we show that the stars have a larger (lower) mass and radius and a diminished (enhanced) stability when the cosmological constant $\Lambda>0$ ($\Lambda<0$) is increased (decreased). In addition, in a sequence of compact objects with fixed $\Gamma$ and $\Lambda$, the regions constructed by stable and unstable static equilibrium configurations are recognized by the conditions $dM/d\delta_c>0$ and $dM/d\delta_c<0$, respectively. |
0912.2803 | Michael Edmund Tobar | Michael Edmund Tobar, Peter Wolf, Sebastien Bize, Giorgio Santarelli,
Victor Flambaum | Testing Local Lorentz and Position Invariance and Variation of
Fundamental Constants by searching the Derivative of the Comparison Frequency
Between a Cryogenic Sapphire Oscillator and Hydrogen Maser | Fixed typos | Phys.Rev.D81:022003,2010 | 10.1103/PhysRevD.81.022003 | null | gr-qc hep-ph physics.atom-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The cryogenic sapphire oscillator (CSO) at the Paris Observatory has been
continuously compared to various Hydrogen Masers since 2001. The early data
sets were used to test Local Lorentz Invariance in the Robertson-Mansouri-Sexl
(RMS) framework by searching for sidereal modulations with respect to the
Cosmic Microwave Background, and represent the best Kennedy-Thorndike
experiment to date. In this work we present continuous operation over a period
of greater than six years from September 2002 to December 2008 and present a
more precise way to analyze the data by searching the time derivative of the
comparison frequency. Due to the long-term operation we are able to search both
sidereal and annual modulations. The results gives P_{KT} =
\beta_{RMS}-\alpha_{RMS}-1 = -1.7(4.0) \times 10^{-8} for the sidereal and
-23(10) \times 10^{-8} for the annual term, with a weighted mean of -4.8(3.7)
\times 10^{-8}, a factor of 8 better than previous. Also, we analyze the data
with respect to a change in gravitational potential for both diurnal and annual
variations. The result gives \beta_{H-Maser} - \beta_{CSO} = -2.7(1.4) \times
10^{-4} for the annual and -6.9(4.0) \times 10^{-4} for the diurnal terms, with
a weighted mean of -3.2(1.3) \times 10^{-4}. This result is two orders of
magnitude better than other tests that use electromagnetic resonators. With
respect to fundamental constants a limit can be provided on the variation with
ambient gravitational potential and boost of a combination of the fine
structure constant (\alpha), the normalized quark mass (m_q), and the electron
to proton mass ratio (m_e/m_p), setting the first limit on boost dependence of
order 10^{-10}.
| [
{
"created": "Tue, 15 Dec 2009 06:07:48 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Dec 2009 09:50:58 GMT",
"version": "v2"
}
] | 2010-04-21 | [
[
"Tobar",
"Michael Edmund",
""
],
[
"Wolf",
"Peter",
""
],
[
"Bize",
"Sebastien",
""
],
[
"Santarelli",
"Giorgio",
""
],
[
"Flambaum",
"Victor",
""
]
] | The cryogenic sapphire oscillator (CSO) at the Paris Observatory has been continuously compared to various Hydrogen Masers since 2001. The early data sets were used to test Local Lorentz Invariance in the Robertson-Mansouri-Sexl (RMS) framework by searching for sidereal modulations with respect to the Cosmic Microwave Background, and represent the best Kennedy-Thorndike experiment to date. In this work we present continuous operation over a period of greater than six years from September 2002 to December 2008 and present a more precise way to analyze the data by searching the time derivative of the comparison frequency. Due to the long-term operation we are able to search both sidereal and annual modulations. The results gives P_{KT} = \beta_{RMS}-\alpha_{RMS}-1 = -1.7(4.0) \times 10^{-8} for the sidereal and -23(10) \times 10^{-8} for the annual term, with a weighted mean of -4.8(3.7) \times 10^{-8}, a factor of 8 better than previous. Also, we analyze the data with respect to a change in gravitational potential for both diurnal and annual variations. The result gives \beta_{H-Maser} - \beta_{CSO} = -2.7(1.4) \times 10^{-4} for the annual and -6.9(4.0) \times 10^{-4} for the diurnal terms, with a weighted mean of -3.2(1.3) \times 10^{-4}. This result is two orders of magnitude better than other tests that use electromagnetic resonators. With respect to fundamental constants a limit can be provided on the variation with ambient gravitational potential and boost of a combination of the fine structure constant (\alpha), the normalized quark mass (m_q), and the electron to proton mass ratio (m_e/m_p), setting the first limit on boost dependence of order 10^{-10}. |
0801.2883 | Roland Triay | Roland Triay (CPT), Henri-Hugues Fliche (LMMT) | Voids in the distribution of galaxies and the Cosmological constant | 4 pages, 1 figure | Prog.Theor.Phys.Suppl.172:40-43,2008 | 10.1143/PTPS.172.40 | CPT-P002-2008 | gr-qc astro-ph | null | With the motivation in mind to evaluate the contribution of the cosmological
constant $\Lambda$ on the foam like patterns formation process in the
distribution of galaxies, we investigate the Newtonian dynamics of a spherical
void embedded in an uniform medium which undergoes a Hubble expansion. We use a
covariant approach for deriving the evolution with time of the shell (S) acting
as a boundaries condition for the inside and outside media. As a result, with
the usual values for the cosmological parameters, S expands with a huge initial
burst that freezes up to matching Hubble flow. With respect to Friedmann
comoving frame, its magnification increases nonlinearly with $\Lambda$, with a
maximal growth rate at redshift $z\sim 1.7$. The velocity field inside S shows
an interesting feature which enables us to disentangle a spatially closed from
open universe. Namely, the void region are swept out in the first case, what
can be interpreted as a stability criterion.
| [
{
"created": "Fri, 18 Jan 2008 13:37:04 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Triay",
"Roland",
"",
"CPT"
],
[
"Fliche",
"Henri-Hugues",
"",
"LMMT"
]
] | With the motivation in mind to evaluate the contribution of the cosmological constant $\Lambda$ on the foam like patterns formation process in the distribution of galaxies, we investigate the Newtonian dynamics of a spherical void embedded in an uniform medium which undergoes a Hubble expansion. We use a covariant approach for deriving the evolution with time of the shell (S) acting as a boundaries condition for the inside and outside media. As a result, with the usual values for the cosmological parameters, S expands with a huge initial burst that freezes up to matching Hubble flow. With respect to Friedmann comoving frame, its magnification increases nonlinearly with $\Lambda$, with a maximal growth rate at redshift $z\sim 1.7$. The velocity field inside S shows an interesting feature which enables us to disentangle a spatially closed from open universe. Namely, the void region are swept out in the first case, what can be interpreted as a stability criterion. |
1502.02833 | Grasiele Batista Santos | Grasiele Santos, Giulia Gubitosi and Giovanni Amelino-Camelia | On the initial singularity problem in rainbow cosmology | v3: typo in Eq. (9) corrected, results unchanged. 10 pages, 5
figures, v2 matches published version | JCAP 08 (2015) 005 | 10.1088/1475-7516/2015/08/005 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been recently claimed that the initial singularity might be avoided in
the context of rainbow cosmology, where one attempts to account for
quantum-gravitational corrections through an effective-theory description based
on an energy-dependent ("rainbow") space-time metric. We here scrutinize this
exciting hypothesis much more in depth than previous analyses. In particular,
we take into account all requirements for singularity avoidance, while
previously only a subset of these requirements had been considered. Moreover,
we show that the implications of a rainbow metric for thermodynamics are more
significant than previously appreciated. Through the analysis of two
particularly meaningful examples of rainbow metrics we find that our concerns
are not merely important conceptually, but actually change in quantitatively
significant manner the outcome of the analysis. Notably we only find examples
where the singularity is not avoided, though one can have that in the regime
where our semi-classical picture is still reliable the approach to the
singularity is slowed down when compared to the standard classical scenario. We
conclude that the study of rainbow metrics provides tantalizing hints of
singularity avoidance but is inconclusive, since some key questions remain to
be addressed just when the scale factor is very small, a regime which, as here
argued, cannot be reliably described by an effective rainbow-metric picture.
| [
{
"created": "Tue, 10 Feb 2015 10:05:48 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Aug 2015 15:32:02 GMT",
"version": "v2"
},
{
"created": "Mon, 21 Mar 2016 17:43:52 GMT",
"version": "v3"
}
] | 2016-03-22 | [
[
"Santos",
"Grasiele",
""
],
[
"Gubitosi",
"Giulia",
""
],
[
"Amelino-Camelia",
"Giovanni",
""
]
] | It has been recently claimed that the initial singularity might be avoided in the context of rainbow cosmology, where one attempts to account for quantum-gravitational corrections through an effective-theory description based on an energy-dependent ("rainbow") space-time metric. We here scrutinize this exciting hypothesis much more in depth than previous analyses. In particular, we take into account all requirements for singularity avoidance, while previously only a subset of these requirements had been considered. Moreover, we show that the implications of a rainbow metric for thermodynamics are more significant than previously appreciated. Through the analysis of two particularly meaningful examples of rainbow metrics we find that our concerns are not merely important conceptually, but actually change in quantitatively significant manner the outcome of the analysis. Notably we only find examples where the singularity is not avoided, though one can have that in the regime where our semi-classical picture is still reliable the approach to the singularity is slowed down when compared to the standard classical scenario. We conclude that the study of rainbow metrics provides tantalizing hints of singularity avoidance but is inconclusive, since some key questions remain to be addressed just when the scale factor is very small, a regime which, as here argued, cannot be reliably described by an effective rainbow-metric picture. |
2310.11576 | Dennis Philipp | Dennis Philipp, Eva Hackmann, Jan P. Hackstein, Claus L\"ammerzahl | General Relativistic Chronometry with Clocks on Ground and in Space | 15 pages, 4 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | One of geodesy's main tasks is to determine the gravity field of the Earth.
High precision clocks have the potential to provide a new tool in a global
determination of the Earth's gravitational potential based on the gravitational
redshift. Towards this clock-based gravimetry or chronometry in stationary
spacetimes, exact expressions for the relativistic redshift and the timing
between observers in various configurations are derived. These observers are
assumed to be equipped with standard clocks and move along arbitrary
worldlines. It is shown that redshift measurements, involving clocks on ground
and/or in space, can be used to determine the (mass) multipole moments of the
underlying spacetime. Results shown here are in agreement with the Newtonian
potential determination from, e.g., the so-called energy approach. The
framework of chronometric geodesy is exemplified in different exact vacuum
spacetimes for illustration and future gravity field recovery missions may use
clock comparisons as an additional data channel for advanced data fusion.
| [
{
"created": "Tue, 17 Oct 2023 20:54:59 GMT",
"version": "v1"
}
] | 2023-10-19 | [
[
"Philipp",
"Dennis",
""
],
[
"Hackmann",
"Eva",
""
],
[
"Hackstein",
"Jan P.",
""
],
[
"Lämmerzahl",
"Claus",
""
]
] | One of geodesy's main tasks is to determine the gravity field of the Earth. High precision clocks have the potential to provide a new tool in a global determination of the Earth's gravitational potential based on the gravitational redshift. Towards this clock-based gravimetry or chronometry in stationary spacetimes, exact expressions for the relativistic redshift and the timing between observers in various configurations are derived. These observers are assumed to be equipped with standard clocks and move along arbitrary worldlines. It is shown that redshift measurements, involving clocks on ground and/or in space, can be used to determine the (mass) multipole moments of the underlying spacetime. Results shown here are in agreement with the Newtonian potential determination from, e.g., the so-called energy approach. The framework of chronometric geodesy is exemplified in different exact vacuum spacetimes for illustration and future gravity field recovery missions may use clock comparisons as an additional data channel for advanced data fusion. |
gr-qc/0612134 | Grigory Volovik | G.E. Volovik | From Quantum Hydrodynamics to Quantum Gravity | 20 pages, 1 figure, rapporteur article for Proceedings of MG11,
session `Analog Models of and for General Relativity', references added | Proceedings of the Eleventh Marcel Grossmann Meeting on General
Relativity, edited by H. Kleinert, R.T. Jantzen and R. Ruffini, World
Scientific, Singapore, 2008, pp. 1404-1423 | null | null | gr-qc cond-mat.soft hep-ph | null | We discuss some lessons from quantum hydrodynamics to quantum gravity.
| [
{
"created": "Thu, 21 Dec 2006 14:22:42 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Dec 2006 18:49:55 GMT",
"version": "v2"
},
{
"created": "Thu, 28 Dec 2006 14:21:41 GMT",
"version": "v3"
},
{
"created": "Sun, 31 Dec 2006 12:53:51 GMT",
"version": "v4"
},
{
"c... | 2008-07-12 | [
[
"Volovik",
"G. E.",
""
]
] | We discuss some lessons from quantum hydrodynamics to quantum gravity. |
gr-qc/0512066 | Volker Perlick | Volker Perlick | On totally umbilic submanifolds of semi-Riemannian manifolds | 7 pages; written version of talk given at World Congress on Nonlinear
Analysis 2004, Orlando, Florida | Nonlinear Analysis 63/5-7 (2005) e511-e518 | null | null | gr-qc | null | The notion of being totally umbilic is considered for non-degenerate and
degenerate submanifolds of semi-Riemanian manifolds. After some remarks on the
general case, timelike and lightlike totally umbilic submanifolds of Lorentzian
manifolds are discussed, along with their physical interpretation in view of
general relativity. In particular, the mathematical notion of totally umbilic
submanifolds is linked to the notions of photon surfaces and of null strings
which have been used in the physics literature.
| [
{
"created": "Sun, 11 Dec 2005 21:57:21 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Perlick",
"Volker",
""
]
] | The notion of being totally umbilic is considered for non-degenerate and degenerate submanifolds of semi-Riemanian manifolds. After some remarks on the general case, timelike and lightlike totally umbilic submanifolds of Lorentzian manifolds are discussed, along with their physical interpretation in view of general relativity. In particular, the mathematical notion of totally umbilic submanifolds is linked to the notions of photon surfaces and of null strings which have been used in the physics literature. |
2311.16775 | Artur Alho | Artur Alho, Claes Uggla, John Wainwright | Tracking Quintessence | 22 pages, 17 figures; v2: comments on previous dynamical systems
analysis of tracking quintessence added v3: References added | null | null | null | gr-qc astro-ph.CO math-ph math.DS math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Tracking quintessence, in a spatially flat and isotropic space-time with a
minimally coupled canonical scalar field and an asymptotically inverse
power-law potential $V(\varphi)\propto\varphi^{-p}$, $p>0$, as
$\varphi\rightarrow0$, is investigated. This is done by introducing a new
three-dimensional \emph{regular} dynamical system, which enables a rigorous
explanation of the tracking feature: 1) The dynamical system has a tracker
fixed point $\mathrm{T}$ with a two-dimensional stable manifold that pushes an
open set of nearby solutions toward a single tracker solution originating from
$\mathrm{T}$. 2) All solutions, including the tracker solution and the
solutions that track/shadow it, end at a common future attractor fixed point
that depends on the potential. Thus, the open set of solutions that shadow the
tracker solution share its properties during the tracking quintessence epoch.
We also discuss similarities and differences of underlying mechanisms for
tracking, thawing and scaling freezing quintessence, and, moreover, we
illustrate with state space pictures that all of these types of quintessence
exist simultaneously for certain potentials.
| [
{
"created": "Tue, 28 Nov 2023 13:34:26 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Jan 2024 10:01:02 GMT",
"version": "v2"
},
{
"created": "Mon, 5 Feb 2024 10:30:46 GMT",
"version": "v3"
}
] | 2024-02-06 | [
[
"Alho",
"Artur",
""
],
[
"Uggla",
"Claes",
""
],
[
"Wainwright",
"John",
""
]
] | Tracking quintessence, in a spatially flat and isotropic space-time with a minimally coupled canonical scalar field and an asymptotically inverse power-law potential $V(\varphi)\propto\varphi^{-p}$, $p>0$, as $\varphi\rightarrow0$, is investigated. This is done by introducing a new three-dimensional \emph{regular} dynamical system, which enables a rigorous explanation of the tracking feature: 1) The dynamical system has a tracker fixed point $\mathrm{T}$ with a two-dimensional stable manifold that pushes an open set of nearby solutions toward a single tracker solution originating from $\mathrm{T}$. 2) All solutions, including the tracker solution and the solutions that track/shadow it, end at a common future attractor fixed point that depends on the potential. Thus, the open set of solutions that shadow the tracker solution share its properties during the tracking quintessence epoch. We also discuss similarities and differences of underlying mechanisms for tracking, thawing and scaling freezing quintessence, and, moreover, we illustrate with state space pictures that all of these types of quintessence exist simultaneously for certain potentials. |
gr-qc/0304019 | Marsha Weaver | James Isenberg and Marsha Weaver | On the area of the symmetry orbits in $T^2$ symmetric spacetimes | The appendix which appears in version 1 has a technical problem (the
inequality appearing as the first stage of (52) is not necessarily true), and
since the appendix is unnecessary for the proof of our results, we leave it
out. version 2 -- clarifications added, version 3 -- reference corrected | Class.Quant.Grav. 20 (2003) 3783-3796 | 10.1088/0264-9381/20/16/316 | null | gr-qc | null | We obtain a global existence result for the Einstein equations. We show that
in the maximal Cauchy development of vacuum $T^2$ symmetric initial data with
nonvanishing twist constant, except for the special case of flat Kasner initial
data, the area of the $T^2$ group orbits takes on all positive values. This
result shows that the areal time coordinate $R$ which covers these spacetimes
runs from zero to infinity, with the singularity occurring at R=0.
| [
{
"created": "Fri, 4 Apr 2003 02:15:46 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Jul 2003 06:15:02 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Feb 2004 05:21:30 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Isenberg",
"James",
""
],
[
"Weaver",
"Marsha",
""
]
] | We obtain a global existence result for the Einstein equations. We show that in the maximal Cauchy development of vacuum $T^2$ symmetric initial data with nonvanishing twist constant, except for the special case of flat Kasner initial data, the area of the $T^2$ group orbits takes on all positive values. This result shows that the areal time coordinate $R$ which covers these spacetimes runs from zero to infinity, with the singularity occurring at R=0. |
2304.03642 | Zhenyu Zhang | Zhenyu Zhang, Yehui Hou, Zezhou Hu, Minyong Guo, Bin Chen | Polarized images of charged particles in vortical motions around a
magnetized Kerr black hole | 25 pages, 8 figures | null | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | In this work, we study the images of a Kerr black hole (BH) immersed in
uniform magnetic fields, illuminated by the synchrotron radiation of charged
particles in the jet. We particularly focus on the spontaneously vortical
motions (SVMs) of charged particles in the jet region and investigate the
polarized images of electromagnetic radiations from the trajectories along
SVMs. We notice that there is a critical value $\omega_c$ for charged particle
released at a given initial position and subjected an outward force, and once
$|qB_0/m|=|\omega_B|>|\omega_c|$ charged particles can move along SVMs in the
jet region. We obtain the polarized images of the electromagnetic radiations
from the trajectories along SVMs. Our simplified model suggests that the SVM
radiations can act as the light source to illuminate the BH and form a photon
ring structure.
| [
{
"created": "Fri, 7 Apr 2023 13:46:36 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Nov 2023 06:06:25 GMT",
"version": "v2"
}
] | 2023-11-15 | [
[
"Zhang",
"Zhenyu",
""
],
[
"Hou",
"Yehui",
""
],
[
"Hu",
"Zezhou",
""
],
[
"Guo",
"Minyong",
""
],
[
"Chen",
"Bin",
""
]
] | In this work, we study the images of a Kerr black hole (BH) immersed in uniform magnetic fields, illuminated by the synchrotron radiation of charged particles in the jet. We particularly focus on the spontaneously vortical motions (SVMs) of charged particles in the jet region and investigate the polarized images of electromagnetic radiations from the trajectories along SVMs. We notice that there is a critical value $\omega_c$ for charged particle released at a given initial position and subjected an outward force, and once $|qB_0/m|=|\omega_B|>|\omega_c|$ charged particles can move along SVMs in the jet region. We obtain the polarized images of the electromagnetic radiations from the trajectories along SVMs. Our simplified model suggests that the SVM radiations can act as the light source to illuminate the BH and form a photon ring structure. |
1810.08343 | Tiberiu Harko | Zolt\'an Kov\'acs, Tiberiu Harko, Shahab Shahidi | Reply to "Comment on 'Can accretion disk properties observationally
distinguish black holes from naked singularities?'" | 3 pages, no figures | Phys. Rev. D 98, 088502 (2018) | 10.1103/PhysRevD.98.088502 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the Comment on "Can accretion disk properties observationally distinguish
black holes from naked singularities?", by Bertrand Chauvineau, Phys. Rev. D
{\bf 98}, 088501 (2018), the author did show that the metric used in Z.
Kov\'{a}cs and T. Harko, Phys. Rev. D {\bf 82}, 124047 (2010), and initially
introduced in K. D. Krori and D. R. Bhattacharjee, J. Math. Phys. \textbf{23},
637 (1982) and K. K. Nandi, P. M. Alsing, J. C. Evans, and T. B. Nayak, Phys.
Rev. D \textbf{63}, 084027 (2001), does not satisfy the Einstein gravitational
field equations with a minimally coupled scalar field. In our reply we would
like to point out that this result is actually not new, but it was already
published in the literature. Moreover, a rotating solution that generalizes the
Kerr metric for a nonminimally coupled scalar field does exist. We briefly
discuss the nature of the singularities for the generalized metric, and point
out that it can be used as a testing ground to differentiate black holes from
naked singularities. We also mention the existence of some other typing or
technical errors existing in the literature.
| [
{
"created": "Fri, 19 Oct 2018 03:12:38 GMT",
"version": "v1"
}
] | 2018-11-14 | [
[
"Kovács",
"Zoltán",
""
],
[
"Harko",
"Tiberiu",
""
],
[
"Shahidi",
"Shahab",
""
]
] | In the Comment on "Can accretion disk properties observationally distinguish black holes from naked singularities?", by Bertrand Chauvineau, Phys. Rev. D {\bf 98}, 088501 (2018), the author did show that the metric used in Z. Kov\'{a}cs and T. Harko, Phys. Rev. D {\bf 82}, 124047 (2010), and initially introduced in K. D. Krori and D. R. Bhattacharjee, J. Math. Phys. \textbf{23}, 637 (1982) and K. K. Nandi, P. M. Alsing, J. C. Evans, and T. B. Nayak, Phys. Rev. D \textbf{63}, 084027 (2001), does not satisfy the Einstein gravitational field equations with a minimally coupled scalar field. In our reply we would like to point out that this result is actually not new, but it was already published in the literature. Moreover, a rotating solution that generalizes the Kerr metric for a nonminimally coupled scalar field does exist. We briefly discuss the nature of the singularities for the generalized metric, and point out that it can be used as a testing ground to differentiate black holes from naked singularities. We also mention the existence of some other typing or technical errors existing in the literature. |
1807.01791 | Richard Woodard | R. P. Woodard (Florida) | The Case for Nonlocal Modifications of Gravity | 30 pages, uses LaTeX 2e, to appear in the proceedings of the
International Conference on Quantum Gravity, SUST, March 26-28,2018 | null | null | UFIFT-QG-18-03 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The huge amounts of undetected and exotic dark matter and dark energy needed
to make general relativity work on large scales argue that we should
investigate modifications of gravity. The only stable, metric-based and
invariant alternative to general relativity is $f(R)$ models. These models can
explain primordial inflation, but they cannot dispense with either dark matter
or dark energy. I advocate nonlocal modifications of gravity, not as new
fundamental theories but rather as the gravitational vacuum polarization
engendered by infrared quanta produced during primordial inflation. I also
discuss some of the many objections which have been raised to this idea.
| [
{
"created": "Wed, 4 Jul 2018 21:34:50 GMT",
"version": "v1"
}
] | 2018-07-06 | [
[
"Woodard",
"R. P.",
"",
"Florida"
]
] | The huge amounts of undetected and exotic dark matter and dark energy needed to make general relativity work on large scales argue that we should investigate modifications of gravity. The only stable, metric-based and invariant alternative to general relativity is $f(R)$ models. These models can explain primordial inflation, but they cannot dispense with either dark matter or dark energy. I advocate nonlocal modifications of gravity, not as new fundamental theories but rather as the gravitational vacuum polarization engendered by infrared quanta produced during primordial inflation. I also discuss some of the many objections which have been raised to this idea. |
gr-qc/0110118 | Takeshi Chiba | Takeshi Chiba | Constancy of the Constants of Nature | 11 pages, based on a talk presented at "Frontier of Cosmology and
Gravitation" (YITP, Kyoto, April 25-27, 2001) | null | null | KUNS-1737 | gr-qc astro-ph hep-ph | null | The current observational and experimental bounds on time variation of the
constants of Nature are briefly reviewed.
| [
{
"created": "Sat, 27 Oct 2001 09:31:29 GMT",
"version": "v1"
},
{
"created": "Sun, 17 Mar 2002 23:52:05 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Chiba",
"Takeshi",
""
]
] | The current observational and experimental bounds on time variation of the constants of Nature are briefly reviewed. |
1401.5262 | Hal Haggard | Goffredo Chirco, Hal M. Haggard, Aldo Riello, Carlo Rovelli | Spacetime thermodynamics without hidden degrees of freedom | 12 pages, 1 figure | Phys. Rev. D 90, 044044 (2014) | 10.1103/PhysRevD.90.044044 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A celebrated result by Jacobson is the derivation of Einstein's equations
from Unruh's temperature, the Bekenstein-Hawking entropy and the Clausius
relation. This has been repeatedly taken as evidence for an interpretation of
Einstein's equations as equations of state for unknown degrees of freedom
underlying the metric. We show that a different interpretation of Jacobson
result is possible, which does not imply the existence of additional degrees of
freedom, and follows only from the quantum properties of gravity. We introduce
the notion of quantum gravitational Hadamard states, which give rise to the
full local thermodynamics of gravity.
| [
{
"created": "Tue, 21 Jan 2014 11:04:36 GMT",
"version": "v1"
}
] | 2014-08-20 | [
[
"Chirco",
"Goffredo",
""
],
[
"Haggard",
"Hal M.",
""
],
[
"Riello",
"Aldo",
""
],
[
"Rovelli",
"Carlo",
""
]
] | A celebrated result by Jacobson is the derivation of Einstein's equations from Unruh's temperature, the Bekenstein-Hawking entropy and the Clausius relation. This has been repeatedly taken as evidence for an interpretation of Einstein's equations as equations of state for unknown degrees of freedom underlying the metric. We show that a different interpretation of Jacobson result is possible, which does not imply the existence of additional degrees of freedom, and follows only from the quantum properties of gravity. We introduce the notion of quantum gravitational Hadamard states, which give rise to the full local thermodynamics of gravity. |
2109.10932 | Maxime Van de Moortel | Maxime Van de Moortel | Violent nonlinear collapse in the interior of charged hairy black holes | Comments welcome! 38 pages, 4 figures | null | null | null | gr-qc hep-th math-ph math.AP math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct a new one-parameter family indexed by $\epsilon$ of two-ended,
spatially-homogeneous black hole interiors solving the
Einstein-Maxwell-Klein-Gordon equations with a (possibly zero) cosmological
constant $\Lambda$ and bifurcating off a Reissner-Nordstr\"om-(dS/AdS) interior
($\epsilon = 0$). For all small $\epsilon \neq 0$, we prove that, although the
black hole is charged, its terminal boundary is an everywhere-spacelike Kasner
singularity foliated by spheres of zero radius $r$.
Moreover, smaller perturbations (i.e. smaller $|\epsilon|$) are more singular
than larger one, in the sense that the Hawking mass and the curvature blow up
following a power law of the form $r^{-O(\epsilon^{-2})}$ at the singularity
$\{r=0\}$. This unusual property originates from a dynamical phenomenon --
violent nonlinear collapse -- caused by the almost formation of a Cauchy
horizon to the past of the spacelike singularity $\{r=0\}$. This phenomenon was
previously described numerically in the physics literature and referred to as
"the collapse of the Einstein-Rosen bridge".
While we cover all values of $\Lambda \in \mathbb{R}$, the case $\Lambda< 0$
is of particular significance to the AdS/CFT correspondence. Our result can
also be viewed in general as a first step towards the understanding of the
interior of hairy black holes.
| [
{
"created": "Wed, 22 Sep 2021 18:01:08 GMT",
"version": "v1"
}
] | 2021-09-24 | [
[
"Van de Moortel",
"Maxime",
""
]
] | We construct a new one-parameter family indexed by $\epsilon$ of two-ended, spatially-homogeneous black hole interiors solving the Einstein-Maxwell-Klein-Gordon equations with a (possibly zero) cosmological constant $\Lambda$ and bifurcating off a Reissner-Nordstr\"om-(dS/AdS) interior ($\epsilon = 0$). For all small $\epsilon \neq 0$, we prove that, although the black hole is charged, its terminal boundary is an everywhere-spacelike Kasner singularity foliated by spheres of zero radius $r$. Moreover, smaller perturbations (i.e. smaller $|\epsilon|$) are more singular than larger one, in the sense that the Hawking mass and the curvature blow up following a power law of the form $r^{-O(\epsilon^{-2})}$ at the singularity $\{r=0\}$. This unusual property originates from a dynamical phenomenon -- violent nonlinear collapse -- caused by the almost formation of a Cauchy horizon to the past of the spacelike singularity $\{r=0\}$. This phenomenon was previously described numerically in the physics literature and referred to as "the collapse of the Einstein-Rosen bridge". While we cover all values of $\Lambda \in \mathbb{R}$, the case $\Lambda< 0$ is of particular significance to the AdS/CFT correspondence. Our result can also be viewed in general as a first step towards the understanding of the interior of hairy black holes. |
2008.04127 | Christian J. Kr\"uger | C. J. Kr\"uger, K. D. Kokkotas | Dynamics of Fast Rotating Neutron Stars: An Approach in the Hilbert
Gauge | 26 pages, 4 figures, revised version | null | 10.1103/PhysRevD.102.064026 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a set of time evolution equations and its numerical
implementation for the investigation of non-axisymmetric oscillations of
rapidly rotating compact objects in full General Relativity, taking into
account the contribution of a dynamic spacetime. We derive the perturbation
equations for the spacetime in the Hilbert gauge, while the hydrodynamical
evolution is based on perturbations of the energy-momentum tensor. In our
numerical implementation, we use Kreiss-Oliger dissipation in order to achieve
a stable time evolution. Our code features high accuracy at comparably low
computational expense and we are able to extract the frequencies of
non-axisymmetric modes of compact objects with rotation rates up to the Kepler
limit.
| [
{
"created": "Mon, 10 Aug 2020 13:39:25 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Sep 2020 11:33:44 GMT",
"version": "v2"
}
] | 2020-09-11 | [
[
"Krüger",
"C. J.",
""
],
[
"Kokkotas",
"K. D.",
""
]
] | We describe a set of time evolution equations and its numerical implementation for the investigation of non-axisymmetric oscillations of rapidly rotating compact objects in full General Relativity, taking into account the contribution of a dynamic spacetime. We derive the perturbation equations for the spacetime in the Hilbert gauge, while the hydrodynamical evolution is based on perturbations of the energy-momentum tensor. In our numerical implementation, we use Kreiss-Oliger dissipation in order to achieve a stable time evolution. Our code features high accuracy at comparably low computational expense and we are able to extract the frequencies of non-axisymmetric modes of compact objects with rotation rates up to the Kepler limit. |
gr-qc/0603020 | Vladimir Dzhunushaliev | Vladimir Dzhunushaliev | Thick brane solution in the presence of two interacting scalar fields | the program for numerical calculations is added | Grav.Cosmol.13:302-307,2007 | null | null | gr-qc hep-th | null | It is shown that two gravitating scalar fields may form a thick brane in 5D
spacetime. The necessary condition for the existence of such a regular solution
is that the scalar fields potential must have local and global minima.
| [
{
"created": "Wed, 8 Mar 2006 03:04:13 GMT",
"version": "v1"
},
{
"created": "Sat, 11 Mar 2006 07:51:30 GMT",
"version": "v2"
},
{
"created": "Wed, 12 Apr 2006 09:52:04 GMT",
"version": "v3"
},
{
"created": "Fri, 14 Apr 2006 03:07:55 GMT",
"version": "v4"
},
{
"cr... | 2008-11-26 | [
[
"Dzhunushaliev",
"Vladimir",
""
]
] | It is shown that two gravitating scalar fields may form a thick brane in 5D spacetime. The necessary condition for the existence of such a regular solution is that the scalar fields potential must have local and global minima. |
1504.05352 | Karim Noui KN | Aurelien Barrau, Xiangyu Cao, Karim Noui and Alejandro Perez | Black hole spectroscopy from Loop Quantum Gravity models | 11 pages, 9 figures | Phys. Rev. D 92, 124046 (2015) | 10.1103/PhysRevD.92.124046 | X11 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using Monte Carlo simulations, we compute the integrated emission spectra of
black holes in the framework of Loop Quantum Gravity (LQG). The black hole
emission rates are governed by the entropy whose value, in recent holographic
loop quantum gravity models, was shown to agree at leading order with the
Bekenstein-Hawking entropy. Quantum corrections depend on the Barbero-Immirzi
parameter $\gamma$. Starting with black holes of initial horizon area $A \sim
10^2$ in Planck units, we present the spectra for different values of $\gamma$.
Each spectrum clearly decomposes in two distinct parts: a continuous background
which corresponds to the semi-classical stages of the evaporation and a series
of discrete peaks which constitutes a signature of the deep quantum structure
of the black hole. We show that $\gamma$ has an effect on both parts that we
analyze in details. Finally, we estimate the number of black holes and the
instrumental resolution required to experimentally distinguish between the
considered models.
| [
{
"created": "Tue, 21 Apr 2015 09:33:31 GMT",
"version": "v1"
}
] | 2015-12-30 | [
[
"Barrau",
"Aurelien",
""
],
[
"Cao",
"Xiangyu",
""
],
[
"Noui",
"Karim",
""
],
[
"Perez",
"Alejandro",
""
]
] | Using Monte Carlo simulations, we compute the integrated emission spectra of black holes in the framework of Loop Quantum Gravity (LQG). The black hole emission rates are governed by the entropy whose value, in recent holographic loop quantum gravity models, was shown to agree at leading order with the Bekenstein-Hawking entropy. Quantum corrections depend on the Barbero-Immirzi parameter $\gamma$. Starting with black holes of initial horizon area $A \sim 10^2$ in Planck units, we present the spectra for different values of $\gamma$. Each spectrum clearly decomposes in two distinct parts: a continuous background which corresponds to the semi-classical stages of the evaporation and a series of discrete peaks which constitutes a signature of the deep quantum structure of the black hole. We show that $\gamma$ has an effect on both parts that we analyze in details. Finally, we estimate the number of black holes and the instrumental resolution required to experimentally distinguish between the considered models. |
2206.06963 | Kubantai Ernazarov | K.K. Ernazarov | Examples of exact exponential cosmological solutions with three
isotropic subspaces in the Einstein-Gauss-Bonnet gravity | 18 pages | null | 10.1134/S0202289322040090 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider $(1+ 8)$- and $(1+10)$-dimensional Einstein-Gauss-Bonnet models
with the cosmological $\Lambda$-term. Some new examples of exact solutions with
three constant Hubble-like parameters in this model are obtained, governed by
three non-coinciding Hubble-like parameters: $H \neq 0$, $h_1$ and $h_2$,
obeying $m H + k_1 h_1 + k_2 h_2 \neq 0$, corresponding to factor spaces of
dimensions $m\geqslant 3$, $ k_1 > 1$ and $ k_2\geqslant 1$. In this case, the
multidimensional cosmological model deals with three factor spaces: the
external 3-dimensional "our" world and internal subspaces with dimensions $
(m-3)$, $k_1$ and $k_2$.
| [
{
"created": "Tue, 14 Jun 2022 16:33:43 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Aug 2022 07:52:58 GMT",
"version": "v2"
}
] | 2022-12-07 | [
[
"Ernazarov",
"K. K.",
""
]
] | We consider $(1+ 8)$- and $(1+10)$-dimensional Einstein-Gauss-Bonnet models with the cosmological $\Lambda$-term. Some new examples of exact solutions with three constant Hubble-like parameters in this model are obtained, governed by three non-coinciding Hubble-like parameters: $H \neq 0$, $h_1$ and $h_2$, obeying $m H + k_1 h_1 + k_2 h_2 \neq 0$, corresponding to factor spaces of dimensions $m\geqslant 3$, $ k_1 > 1$ and $ k_2\geqslant 1$. In this case, the multidimensional cosmological model deals with three factor spaces: the external 3-dimensional "our" world and internal subspaces with dimensions $ (m-3)$, $k_1$ and $k_2$. |
gr-qc/0203030 | Alessandra Buonanno | Alessandra Buonanno | Gravitational waves from inspiraling binary black holes | References added and updated; few typos corrected | Class.Quant.Grav. 19 (2002) 1267-1278 | 10.1088/0264-9381/19/7/305 | null | gr-qc | null | Binary black holes are the most promising candidate sources for the first
generation of earth-based interferometric gravitational-wave detectors. We
summarize and discuss the state-of-the-art analytic techniques developed during
the last years to better describe the late dynamical evolution of binary black
holes of comparable masses.
| [
{
"created": "Sun, 10 Mar 2002 02:33:57 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Mar 2002 18:22:12 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Buonanno",
"Alessandra",
""
]
] | Binary black holes are the most promising candidate sources for the first generation of earth-based interferometric gravitational-wave detectors. We summarize and discuss the state-of-the-art analytic techniques developed during the last years to better describe the late dynamical evolution of binary black holes of comparable masses. |
2101.02848 | Karthik Rajeev | Karthik Rajeev, Vikramaditya Mondal and Sumanta Chakraborty | No-boundary Wave Function, Wheeler-DeWitt Equation and Path Integral
Analysis of the Bouncing `Quantum' Cosmology | version published in PRD, 32 pages, 6 figures and 1 table | Phys. Rev. D 103, 106008 (2021) | 10.1103/PhysRevD.103.106008 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Bouncing models are alternatives to inflationary cosmology that replace the
initial Big-Bang singularity by a `bouncing' phase. A deeper understanding of
the initial conditions of the universe, in these scenarios, requires knowledge
of quantum aspects of bouncing models. In this work, we propose two classes of
bouncing models that can be studied with great analytical ease and hence,
provide test-bed for investigating more profound problems in quantum cosmology
of bouncing universes. Our model's two key ingredients enable us to do
straightforward analytical calculations: (i) a convenient parametrization of
the minisuperspace of FRLW spacetimes and (ii) two distinct choices of the
effective perfect fluids that source the background geometry of the bouncing
universe. We study the quantum cosmology of these models using both the
Wheeler-de Witt equations and the path integral approach. In particular, we
found a bouncing model analogue of the no-boundary wavefunction and presented a
Lorentzian path integral representation for the same. We also discuss the
introduction of real scalar perturbations.
| [
{
"created": "Fri, 8 Jan 2021 04:46:39 GMT",
"version": "v1"
},
{
"created": "Tue, 25 May 2021 19:46:53 GMT",
"version": "v2"
}
] | 2021-05-27 | [
[
"Rajeev",
"Karthik",
""
],
[
"Mondal",
"Vikramaditya",
""
],
[
"Chakraborty",
"Sumanta",
""
]
] | Bouncing models are alternatives to inflationary cosmology that replace the initial Big-Bang singularity by a `bouncing' phase. A deeper understanding of the initial conditions of the universe, in these scenarios, requires knowledge of quantum aspects of bouncing models. In this work, we propose two classes of bouncing models that can be studied with great analytical ease and hence, provide test-bed for investigating more profound problems in quantum cosmology of bouncing universes. Our model's two key ingredients enable us to do straightforward analytical calculations: (i) a convenient parametrization of the minisuperspace of FRLW spacetimes and (ii) two distinct choices of the effective perfect fluids that source the background geometry of the bouncing universe. We study the quantum cosmology of these models using both the Wheeler-de Witt equations and the path integral approach. In particular, we found a bouncing model analogue of the no-boundary wavefunction and presented a Lorentzian path integral representation for the same. We also discuss the introduction of real scalar perturbations. |
1610.07865 | Suddhasattwa Brahma | Suddhasattwa Brahma, Michele Ronco, Giovanni Amelino-Camelia and
Antonino Marciano | Linking loop quantum gravity quantization ambiguities with phenomenology | 12 pages, 3 figures | Phys. Rev. D 95, 044005 (2017) | 10.1103/PhysRevD.95.044005 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Fundamental quantum gravity theories are known to be notoriously difficult to
extract viable testable predictions out of. In this paper, we aim to
incorporate putative quantum corrections coming from loop quantum gravity in
deriving modified dispersion relations for particles on a deformed Minkowski
spacetime. We show how different choices of the Immirzi parameter can, in some
cases, serendipitously lead to different outcomes for such modifications,
depending on the quantization scheme chosen. This allows one to differentiate
between these quantization choices via testable phenomenological predictions.
| [
{
"created": "Tue, 25 Oct 2016 13:32:25 GMT",
"version": "v1"
}
] | 2017-02-15 | [
[
"Brahma",
"Suddhasattwa",
""
],
[
"Ronco",
"Michele",
""
],
[
"Amelino-Camelia",
"Giovanni",
""
],
[
"Marciano",
"Antonino",
""
]
] | Fundamental quantum gravity theories are known to be notoriously difficult to extract viable testable predictions out of. In this paper, we aim to incorporate putative quantum corrections coming from loop quantum gravity in deriving modified dispersion relations for particles on a deformed Minkowski spacetime. We show how different choices of the Immirzi parameter can, in some cases, serendipitously lead to different outcomes for such modifications, depending on the quantization scheme chosen. This allows one to differentiate between these quantization choices via testable phenomenological predictions. |
1907.06919 | Polina Dyadina | P.I. Dyadina, S.P. Labazova, S.O. Alexeyev | Post-Newtonian limit of hybrid metric-Palatini f(R)-gravity | 13 pages, 2 figures | JETP, vol.156, number 5, pp. 905-917 (2019) | 10.1134/S0044451019110087 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using the latest most accurate values of post-Newtonian parameters $\gamma$
and $\beta$ obtained by MESSENGER we impose restrictions on the recently
proposed hybrid f(R)-gravity model in its scalar-tensor representation. We show
that the presence of a light scalar field in this theory does not contradict
the experimental data based not only on the $ \gamma $ parameter (as was shown
earlier), but also on all other PPN parameters. The application of
parameterized post-Newtonian formalism to gravitational theories with massive
fields is also discussed.
| [
{
"created": "Tue, 16 Jul 2019 09:47:40 GMT",
"version": "v1"
}
] | 2019-10-08 | [
[
"Dyadina",
"P. I.",
""
],
[
"Labazova",
"S. P.",
""
],
[
"Alexeyev",
"S. O.",
""
]
] | Using the latest most accurate values of post-Newtonian parameters $\gamma$ and $\beta$ obtained by MESSENGER we impose restrictions on the recently proposed hybrid f(R)-gravity model in its scalar-tensor representation. We show that the presence of a light scalar field in this theory does not contradict the experimental data based not only on the $ \gamma $ parameter (as was shown earlier), but also on all other PPN parameters. The application of parameterized post-Newtonian formalism to gravitational theories with massive fields is also discussed. |
1803.03255 | Ernesto Contreras | Ernesto Contreras, Angel Rincon, Benjamin Koch and Pedro Bargue\~no | Scale-dependent polytropic black hole | Eur. Phys. J. C (Accepted) | Eur. Phys. J. C (2018) 78:246 | 10.1140/epjc/s10052-018-5709-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present work we study the scale--dependence of polytropic non-charged
black holes in (3+1)-dimensional space--times assuming a cosmological constant.
We allow for scale--dependence of the gravitational and cosmological couplings,
and we solve the corresponding generalized field equations imposing the null
energy condition. Besides, some properties, such as horizon structure and
thermodynamics, are discussed in detail.
| [
{
"created": "Thu, 8 Mar 2018 18:53:25 GMT",
"version": "v1"
}
] | 2019-04-01 | [
[
"Contreras",
"Ernesto",
""
],
[
"Rincon",
"Angel",
""
],
[
"Koch",
"Benjamin",
""
],
[
"Bargueño",
"Pedro",
""
]
] | In the present work we study the scale--dependence of polytropic non-charged black holes in (3+1)-dimensional space--times assuming a cosmological constant. We allow for scale--dependence of the gravitational and cosmological couplings, and we solve the corresponding generalized field equations imposing the null energy condition. Besides, some properties, such as horizon structure and thermodynamics, are discussed in detail. |
2404.16599 | Anjali B Yelikar | A. B. Yelikar, R. O' Shaughnessy, J. Lange, and A. Z. Jan | Waveform systematics in gravitational-wave inference of signals from
binary neutron star merger models incorporating higher order modes
information | 7 pages, 6 figures | null | null | LIGO DCC P2400138 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Accurate information from gravitational wave signals from coalescing binary
neutron stars provides essential input to downstream interpretations, including
inference of the neutron star population and equation of state. However, even
adopting the currently most accurate and physically motivated models available
for parameter estimation (PE) of BNSs, these models remain subject to waveform
modeling uncertainty: differences between these models may introduce biases in
recovered source properties. In this work, we describe injection studies
investigating these systematic differences between the two best waveform models
available for BNS currently, NRHybSur3dq8Tidal and TEOBResumS. We demonstrate
that for BNS sources observable by current second-generation detectors,
differences for low-amplitude signals are significant for certain sources.
| [
{
"created": "Thu, 25 Apr 2024 13:26:17 GMT",
"version": "v1"
}
] | 2024-04-26 | [
[
"Yelikar",
"A. B.",
""
],
[
"Shaughnessy",
"R. O'",
""
],
[
"Lange",
"J.",
""
],
[
"Jan",
"A. Z.",
""
]
] | Accurate information from gravitational wave signals from coalescing binary neutron stars provides essential input to downstream interpretations, including inference of the neutron star population and equation of state. However, even adopting the currently most accurate and physically motivated models available for parameter estimation (PE) of BNSs, these models remain subject to waveform modeling uncertainty: differences between these models may introduce biases in recovered source properties. In this work, we describe injection studies investigating these systematic differences between the two best waveform models available for BNS currently, NRHybSur3dq8Tidal and TEOBResumS. We demonstrate that for BNS sources observable by current second-generation detectors, differences for low-amplitude signals are significant for certain sources. |
2004.14395 | Hong Lu | Hai-Shan Liu, H. Lu, Zi-Yu Tang and Bin Wang | Black Hole Scalarization in Gauss-Bonnet Extended Starobinsky Gravity | Latex, 11 pages, reference added | Phys. Rev. D 103, 084043 (2021) | 10.1103/PhysRevD.103.084043 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a class of higher-derivative gravities that can be viewed as the
Gauss-Bonnet extension of the Starobinsky model. The theory admits the
Minkowski spacetime vacuum whose linear spectrum consists of the graviton and a
massive scalar mode. In addition to the usual Schwarzschild black hole, we use
numerical analysis to establish that in some suitable mass range, new black
holes carrying the massive scalar hair can emerge. The new black hole serves as
a "wall" separating the naked spacetime singularity and wormholes in the
parameter space of the scalar hair. Our numerical results also indicate that
although the new hairy black hole and the Schwarzschild have different
spacetime geometry, their entropy and temperature are same for the same mass.
| [
{
"created": "Wed, 29 Apr 2020 18:00:02 GMT",
"version": "v1"
},
{
"created": "Sun, 10 May 2020 12:59:44 GMT",
"version": "v2"
}
] | 2021-04-28 | [
[
"Liu",
"Hai-Shan",
""
],
[
"Lu",
"H.",
""
],
[
"Tang",
"Zi-Yu",
""
],
[
"Wang",
"Bin",
""
]
] | We propose a class of higher-derivative gravities that can be viewed as the Gauss-Bonnet extension of the Starobinsky model. The theory admits the Minkowski spacetime vacuum whose linear spectrum consists of the graviton and a massive scalar mode. In addition to the usual Schwarzschild black hole, we use numerical analysis to establish that in some suitable mass range, new black holes carrying the massive scalar hair can emerge. The new black hole serves as a "wall" separating the naked spacetime singularity and wormholes in the parameter space of the scalar hair. Our numerical results also indicate that although the new hairy black hole and the Schwarzschild have different spacetime geometry, their entropy and temperature are same for the same mass. |
gr-qc/9802048 | David Hochberg | David Hochberg (LAEFF) and Matt Visser (Washington University) | The null energy condition in dynamic wormholes | 4 pages in RevTex; some textual changes made, references added and
some key definitions refined | Phys.Rev.Lett. 81 (1998) 746-749 | 10.1103/PhysRevLett.81.746 | LAEFF-98/02 | gr-qc | null | We extend previous proofs that violations of the null energy condition (NEC)
are a generic and universal feature of traversable wormholes to completely
non-symmetric time-dependent wormholes. We show that the analysis can be
phrased purely in terms of local geometry at and near the wormhole throat, and
do not have to make any technical assumptions about asymptotic flatness or
other global properties. A key aspect of the analysis is the demonstration that
time-dependent wormholes have two throats, one for each direction through the
wormhole, and that the two throats coalesce only for the case of a static
wormhole.
| [
{
"created": "Wed, 18 Feb 1998 10:23:20 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Feb 1998 17:54:51 GMT",
"version": "v2"
},
{
"created": "Thu, 18 Jun 1998 09:28:10 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Hochberg",
"David",
"",
"LAEFF"
],
[
"Visser",
"Matt",
"",
"Washington University"
]
] | We extend previous proofs that violations of the null energy condition (NEC) are a generic and universal feature of traversable wormholes to completely non-symmetric time-dependent wormholes. We show that the analysis can be phrased purely in terms of local geometry at and near the wormhole throat, and do not have to make any technical assumptions about asymptotic flatness or other global properties. A key aspect of the analysis is the demonstration that time-dependent wormholes have two throats, one for each direction through the wormhole, and that the two throats coalesce only for the case of a static wormhole. |
2311.05710 | S\'ergio Mittmann dos Santos | Jo\~ao Victor Chaves, S\'ergio Mittmann dos Santos | Spinning cosmic strings in Brans-Dicke gravity as the generators of the
rotational curves of the galaxies | 11 pages, 2 figures, text in Portuguese, work presented at the 23a.
Mostra de Ensino, Pesquisa e Extens\~ao, IFRS, C\^ampus Porto Alegre, 2023 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Only 5% of what makes up the Universe is well understood, and it consists of
baryonic matter and radiation. Dark matter and energy correspond to the
remaining 95% of the Universe, and their origin and evolution have not yet been
satisfactorily explained. Dark matter, supposedly present in the galaxies' halo
region, appears to be the mechanism that causes the unusual behavior of the
stars' tangential velocity, which is higher than that predicted by the
interaction with visible matter. With the solutions of the equations of motion
for spacetime generated by a spinning cosmic string with an internal structure
in Brans-Dicke gravitation, the present work aimed to evaluate whether this
type of string can play the role currently defined as that of dark matter,
which is to originate the typical rotational curves of galaxies, responsible
for maintaining the tangential velocities of the stars that form these
galaxies, whose behavior cannot be justified solely by the observed baryonic
matter. For this, the model was used to obtain the velocities of the stars of 4
Sc-type galaxies, to be compared with their respective experimentally observed
values.
| [
{
"created": "Thu, 9 Nov 2023 19:36:32 GMT",
"version": "v1"
}
] | 2023-11-13 | [
[
"Chaves",
"João Victor",
""
],
[
"Santos",
"Sérgio Mittmann dos",
""
]
] | Only 5% of what makes up the Universe is well understood, and it consists of baryonic matter and radiation. Dark matter and energy correspond to the remaining 95% of the Universe, and their origin and evolution have not yet been satisfactorily explained. Dark matter, supposedly present in the galaxies' halo region, appears to be the mechanism that causes the unusual behavior of the stars' tangential velocity, which is higher than that predicted by the interaction with visible matter. With the solutions of the equations of motion for spacetime generated by a spinning cosmic string with an internal structure in Brans-Dicke gravitation, the present work aimed to evaluate whether this type of string can play the role currently defined as that of dark matter, which is to originate the typical rotational curves of galaxies, responsible for maintaining the tangential velocities of the stars that form these galaxies, whose behavior cannot be justified solely by the observed baryonic matter. For this, the model was used to obtain the velocities of the stars of 4 Sc-type galaxies, to be compared with their respective experimentally observed values. |
1907.10057 | Jackson Levi Said | Sebastian Bahamonde, Konstantinos F. Dialektopoulos, Viktor Gakis,
Jackson Levi Said | Reviving Horndeski Theory using Teleparallel Gravity after GW170817 | 12 pages, 0 figures | Phys. Rev. D 101, 084060 (2020) | 10.1103/PhysRevD.101.084060 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Horndeski gravity was highly constrained from the recent gravitational wave
observations by the LIGO Collaboration down to $|c_{g}/c-1|\gtrsim 10^{-15}$.
In this Letter we study the tensorial perturbations in a flat cosmological
background for an analogue version of Horndenki gravity which is based in
Teleparallel Gravity constructed from a flat manifold with a nonvanishing
torsion tensor. It is found that in this approach, one can construct a more
general Horndeski theory satisfying $c_T=c_g/c=1$ without eliminating the
coupling functions $G_5(\phi,X)$ and $G_4(\phi,X)$ that were highly constrained
in standard Horndeski theory. Hence, in the Teleparallel approach one is able
to restore these terms, creating an interesting way to revive Horndeski
gravity.
| [
{
"created": "Tue, 23 Jul 2019 13:55:04 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Apr 2020 05:48:37 GMT",
"version": "v2"
}
] | 2020-05-01 | [
[
"Bahamonde",
"Sebastian",
""
],
[
"Dialektopoulos",
"Konstantinos F.",
""
],
[
"Gakis",
"Viktor",
""
],
[
"Said",
"Jackson Levi",
""
]
] | Horndeski gravity was highly constrained from the recent gravitational wave observations by the LIGO Collaboration down to $|c_{g}/c-1|\gtrsim 10^{-15}$. In this Letter we study the tensorial perturbations in a flat cosmological background for an analogue version of Horndenki gravity which is based in Teleparallel Gravity constructed from a flat manifold with a nonvanishing torsion tensor. It is found that in this approach, one can construct a more general Horndeski theory satisfying $c_T=c_g/c=1$ without eliminating the coupling functions $G_5(\phi,X)$ and $G_4(\phi,X)$ that were highly constrained in standard Horndeski theory. Hence, in the Teleparallel approach one is able to restore these terms, creating an interesting way to revive Horndeski gravity. |
2109.03191 | Valentin Rudenko | A. V. Belonenko, A. V. Gusev, V. N. Rudenko | Precision measurement of gravitational frequency shift of radio signals
using Rao-Cramer estimates | null | null | 10.1134/S0202289321040022 | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | A method has been developed for precision measurement of the gravitational
frequency shift of communication radio signals between the spacecraft and the
ground tracking station based on the maximum likelihood principle, using the
Rao-Cramer limit estimates for the kinematic parameters associated with orbital
motion. Numerical illustrations of the efficiency of the method are presented
using the example of data obtained in experiments with the Spectr-R satellite
as part of the VLBI system in the "Radioastron" mission. A compensatory
"on-line" technique for suppressing Doppler and atmospheric noise has been
implemented due to the presence of two modes of communication in gravity
sessions: unidirectional (1w) and looped (2w). Recipes for reducing the
magnitude of systematic errors are discussed.
| [
{
"created": "Tue, 7 Sep 2021 16:56:00 GMT",
"version": "v1"
}
] | 2021-12-22 | [
[
"Belonenko",
"A. V.",
""
],
[
"Gusev",
"A. V.",
""
],
[
"Rudenko",
"V. N.",
""
]
] | A method has been developed for precision measurement of the gravitational frequency shift of communication radio signals between the spacecraft and the ground tracking station based on the maximum likelihood principle, using the Rao-Cramer limit estimates for the kinematic parameters associated with orbital motion. Numerical illustrations of the efficiency of the method are presented using the example of data obtained in experiments with the Spectr-R satellite as part of the VLBI system in the "Radioastron" mission. A compensatory "on-line" technique for suppressing Doppler and atmospheric noise has been implemented due to the presence of two modes of communication in gravity sessions: unidirectional (1w) and looped (2w). Recipes for reducing the magnitude of systematic errors are discussed. |
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