id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/9811043 | M. Trucks | M. Trucks | On Bose-Einstein condensation on closed Robertson-Walker spacetimes | 9 pages, 1 figure, uses elsart.cls | Phys.Lett. B445 (1998) 117-122 | 10.1016/S0370-2693(98)01488-9 | null | gr-qc | null | In this letter we summarize our analysis of Bose-Einstein condensation on
closed Robertson-Walker spacetimes. In a previous work we defined an adiabatic
KMS state on the Weyl-algebra of the free massive Klein-Gordon field. This
state describes a free Bose gas on Robertson-Walker spacetimes. We use this
state to analyze the possibility of Bose-Einstein condensation on closed
Robertson-Walker spacetimes. We take into account the effects due to the
finiteness of the spatial volume and show that they are not relevant in the
early universe. Furthermore we show that a critical radius can be defined. The
condensate disappears above the critical radius.
| [
{
"created": "Thu, 12 Nov 1998 23:56:26 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Trucks",
"M.",
""
]
] | In this letter we summarize our analysis of Bose-Einstein condensation on closed Robertson-Walker spacetimes. In a previous work we defined an adiabatic KMS state on the Weyl-algebra of the free massive Klein-Gordon field. This state describes a free Bose gas on Robertson-Walker spacetimes. We use this state to analyze the possibility of Bose-Einstein condensation on closed Robertson-Walker spacetimes. We take into account the effects due to the finiteness of the spatial volume and show that they are not relevant in the early universe. Furthermore we show that a critical radius can be defined. The condensate disappears above the critical radius. |
2109.04486 | Aindri\'u Conroy | Aindri\'u Conroy and Peter Taylor | Response of an Unruh-DeWitt detector near an extremal black hole | 21 pages, 26 figures | null | 10.1103/PhysRevD.105.085001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the response of an Unruh-DeWitt detector near an extremal charged
black hole, modeling the near-horizon region of this extremal spacetime by the
Bertotti-Robinson spacetime. The advantage of employing the Bertotti-Robinson
limit is that the two-point functions for a massless scalar field are
obtainable in closed form for the field in a number of quantum states of
interest. We consider the detector coupled to a massless field in both the
Boulware vacuum state and arbitrary thermal states, including the
Hartle-Hawking state, and analyse the detector's response for a broad range of
trajectories. Particular attention is paid to the thermalization of the
detector, the anti-Unruh and anti-Hawking effect.
| [
{
"created": "Thu, 9 Sep 2021 18:00:07 GMT",
"version": "v1"
}
] | 2022-04-13 | [
[
"Conroy",
"Aindriú",
""
],
[
"Taylor",
"Peter",
""
]
] | We consider the response of an Unruh-DeWitt detector near an extremal charged black hole, modeling the near-horizon region of this extremal spacetime by the Bertotti-Robinson spacetime. The advantage of employing the Bertotti-Robinson limit is that the two-point functions for a massless scalar field are obtainable in closed form for the field in a number of quantum states of interest. We consider the detector coupled to a massless field in both the Boulware vacuum state and arbitrary thermal states, including the Hartle-Hawking state, and analyse the detector's response for a broad range of trajectories. Particular attention is paid to the thermalization of the detector, the anti-Unruh and anti-Hawking effect. |
gr-qc/0312077 | Simone Mercuri | Simone Mercuri and Giovanni Montani | Dualism between Physical Frames and Time in Quantum Gravity | 9 pages, submitted to Mod. Phys. Lett. A, major replacements in
section 3 and 4 | Mod.Phys.Lett. A19 (2004) 1519 | 10.1142/S0217732304014756 | null | gr-qc | null | In this work we present a discussion of the existing links between the
procedures of endowing the quantum gravity with a real time and of including in
the theory a physical reference frame. More precisely, as first step, we
develop the canonical quantum dynamics, starting from the Einstein equations in
presence of a dust fluid and arrive to a Schroedinger evolution. Then, by
fixing the lapse function in the path integral of gravity, we get a
Schroedinger quantum dynamics, of which eigenvalues problem provides the
appearance of a dust fluid in the classical limit. The main issue of our
analysis is to claim that a theory, in which the time displacement invariance,
on a quantum level, is broken, is indistinguishable from a theory for which
this symmetry holds, but a real reference fluid is included.
| [
{
"created": "Wed, 17 Dec 2003 10:44:01 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Feb 2004 15:59:55 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Mercuri",
"Simone",
""
],
[
"Montani",
"Giovanni",
""
]
] | In this work we present a discussion of the existing links between the procedures of endowing the quantum gravity with a real time and of including in the theory a physical reference frame. More precisely, as first step, we develop the canonical quantum dynamics, starting from the Einstein equations in presence of a dust fluid and arrive to a Schroedinger evolution. Then, by fixing the lapse function in the path integral of gravity, we get a Schroedinger quantum dynamics, of which eigenvalues problem provides the appearance of a dust fluid in the classical limit. The main issue of our analysis is to claim that a theory, in which the time displacement invariance, on a quantum level, is broken, is indistinguishable from a theory for which this symmetry holds, but a real reference fluid is included. |
1806.04027 | Shaoqi Hou | Yungui Gong, Shaoqi Hou | The Polarizations of Gravitational Waves | 20 pages, 4 figures, a talk given in International Conference on
Quantum Gravity held in SUSTech, Shenzhen, China | Universe 2018, 4, 85 | 10.3390/universe4080085 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The direct detection of gravitational waves by LIGO/Virgo opened the
possibility to test General Relativity and its alternatives in the high speed,
strong field regime. Alternative theories of gravity generally predict more
polarizations than General Relativity, so it is important to study the
polarization contents of theories of gravity to reveal the nature of gravity.
In this talk, we analyzed the polarizations contents of Horndeski theory and
$f(R)$ gravity. We found out that in addition to the familiar plus and cross
polarizations, a \emph{massless} Horndeski theory predicts an extra transverse
polarization, and there is a mix of the pure longitudinal and transverse
breathing polarizations in the \emph{massive} Horndeski theory and $f(R)$
gravity. It is possible to use pulsar timing arrays to detect the extra
polarizations in these theories. We also pointed out that the classification of
polarizations using Newman-Penrose variables cannot be applied to the massive
modes. It cannot be used to classify polarizations in Einstein-\ae ther theory
or generalized TeVeS theory, either.
| [
{
"created": "Mon, 11 Jun 2018 14:50:04 GMT",
"version": "v1"
}
] | 2018-08-10 | [
[
"Gong",
"Yungui",
""
],
[
"Hou",
"Shaoqi",
""
]
] | The direct detection of gravitational waves by LIGO/Virgo opened the possibility to test General Relativity and its alternatives in the high speed, strong field regime. Alternative theories of gravity generally predict more polarizations than General Relativity, so it is important to study the polarization contents of theories of gravity to reveal the nature of gravity. In this talk, we analyzed the polarizations contents of Horndeski theory and $f(R)$ gravity. We found out that in addition to the familiar plus and cross polarizations, a \emph{massless} Horndeski theory predicts an extra transverse polarization, and there is a mix of the pure longitudinal and transverse breathing polarizations in the \emph{massive} Horndeski theory and $f(R)$ gravity. It is possible to use pulsar timing arrays to detect the extra polarizations in these theories. We also pointed out that the classification of polarizations using Newman-Penrose variables cannot be applied to the massive modes. It cannot be used to classify polarizations in Einstein-\ae ther theory or generalized TeVeS theory, either. |
1901.06785 | Chiara Mingarelli | Chiara M. F. Mingarelli | Probing supermassive black hole mergers and stalling with pulsar timing
arrays | 2 pages, 2 figures, invited comment | Nature Astronomy, volume 3, pages 8-10 (2019) | 10.1038/s41550-018-0666-y | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The observation of gravitational-waves from merging supermassive black holes
will be transformative: the detection of a low-frequency gravitational-wave
background can tell us if and how supermassive black holes merge, inform our
knowledge of galaxy merger rates and supermassive black hole masses, and enable
the possibility of detecting new physics at nanohertz frequencies. All we have
to do is time pulsars.
| [
{
"created": "Mon, 21 Jan 2019 03:55:30 GMT",
"version": "v1"
}
] | 2019-01-23 | [
[
"Mingarelli",
"Chiara M. F.",
""
]
] | The observation of gravitational-waves from merging supermassive black holes will be transformative: the detection of a low-frequency gravitational-wave background can tell us if and how supermassive black holes merge, inform our knowledge of galaxy merger rates and supermassive black hole masses, and enable the possibility of detecting new physics at nanohertz frequencies. All we have to do is time pulsars. |
1111.1856 | Thiago R.P.Caram\^es | T. R. P. Caram\^es, E. R. Bezerra de Mello, M. E. X. Guimar\~aes | On the motion of a test particle around a global monopole in a modified
gravity | 7 pages, 3 figure. New version accepted for publication in Modern
Physics Letters A | Mod. Phys. Lett. A, Vol. 27, No. 30 (2012) 1250177 | 10.1142/S0217732312501775 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we suggest an approach to analyse the motion of a test particle
in the spacetime of a global monopole within a $f(R)$-like modified gravity.
The field equations are written in a more simplified form in terms of
$F(R)=\frac{df(R)}{dR}$. Since we are dealing with a spherically symmetric
problem, $F(R)$ is expressed as a radial function ${\cal F}(r)\equiv{F(R(r))}$.
So, the choice of a specific form for $f(R)$ will be equivalent to adopt an
Ansatz for ${\cal F}(r)$. By choosing an explicit functional form for ${\cal
F}(r)$ we obtain the weak field solutions for the metric tensor, compute the
time-like geodesics and analyse the motion of a massive test particle. An
interesting feature is an emerging attractive force exerted by the monopole on
the particle.
| [
{
"created": "Tue, 8 Nov 2011 10:23:55 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Mar 2012 14:34:11 GMT",
"version": "v2"
},
{
"created": "Mon, 17 Sep 2012 14:53:42 GMT",
"version": "v3"
}
] | 2012-09-19 | [
[
"Caramês",
"T. R. P.",
""
],
[
"de Mello",
"E. R. Bezerra",
""
],
[
"Guimarães",
"M. E. X.",
""
]
] | In this paper we suggest an approach to analyse the motion of a test particle in the spacetime of a global monopole within a $f(R)$-like modified gravity. The field equations are written in a more simplified form in terms of $F(R)=\frac{df(R)}{dR}$. Since we are dealing with a spherically symmetric problem, $F(R)$ is expressed as a radial function ${\cal F}(r)\equiv{F(R(r))}$. So, the choice of a specific form for $f(R)$ will be equivalent to adopt an Ansatz for ${\cal F}(r)$. By choosing an explicit functional form for ${\cal F}(r)$ we obtain the weak field solutions for the metric tensor, compute the time-like geodesics and analyse the motion of a massive test particle. An interesting feature is an emerging attractive force exerted by the monopole on the particle. |
gr-qc/0111003 | Manuel Tiglio | Gioel Calabrese, Luis Lehner, and Manuel Tiglio | Constraint-preserving boundary conditions in numerical relativity | null | Phys.Rev.D65:104031,2002 | 10.1103/PhysRevD.65.104031 | null | gr-qc | null | This is the first paper in a series aimed to implement boundary conditions
consistent with the constraints' propagation in 3D numerical relativity. Here
we consider spherically symmetric black hole spacetimes in vacuum or with a
minimally coupled scalar field, within the Einstein-Christoffel symmetric
hyperbolic formulation of Einstein's equations. By exploiting the
characteristic propagation of the main variables and constraints, we are able
to single out the only free modes at the outer boundary for these problems. In
the vacuum case a single free modes exists which corresponds to a gauge
freedom, while in the matter case an extra mode exists which is associated with
the scalar field. We make use of the fact that the EC formulation has no
superluminal characteristic speeds to excise the singularity. We present a
second-order, finite difference discretization to treat these scenarios, where
we implement these constraint-preserving boundary conditions, and are able to
evolve the system for essentially unlimited times. As a test of the robustness
of our approach, we allow large pulses of gauge and scalar field enter the
domain through the outer boundary. We reproduce expected results, such as
trivial (in the physical sense) evolution in the vacuum case (even in gauge-
dynamical simulations), and the tail decay for the scalar field.
| [
{
"created": "Fri, 2 Nov 2001 18:53:39 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Calabrese",
"Gioel",
""
],
[
"Lehner",
"Luis",
""
],
[
"Tiglio",
"Manuel",
""
]
] | This is the first paper in a series aimed to implement boundary conditions consistent with the constraints' propagation in 3D numerical relativity. Here we consider spherically symmetric black hole spacetimes in vacuum or with a minimally coupled scalar field, within the Einstein-Christoffel symmetric hyperbolic formulation of Einstein's equations. By exploiting the characteristic propagation of the main variables and constraints, we are able to single out the only free modes at the outer boundary for these problems. In the vacuum case a single free modes exists which corresponds to a gauge freedom, while in the matter case an extra mode exists which is associated with the scalar field. We make use of the fact that the EC formulation has no superluminal characteristic speeds to excise the singularity. We present a second-order, finite difference discretization to treat these scenarios, where we implement these constraint-preserving boundary conditions, and are able to evolve the system for essentially unlimited times. As a test of the robustness of our approach, we allow large pulses of gauge and scalar field enter the domain through the outer boundary. We reproduce expected results, such as trivial (in the physical sense) evolution in the vacuum case (even in gauge- dynamical simulations), and the tail decay for the scalar field. |
1701.00883 | Jie-Xiong Mo | Jie-Xiong Mo, Feng Liang and Gu-Qiang Li | Heat engine in the three-dimensional spacetime | Revised version. Discussions added | JHEP 03(2017)010 | 10.1007/JHEP03(2017)010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We define a kind of heat engine via three-dimensional charged BTZ black
holes. This case is quite subtle and needs to be more careful. The heat flow
along the isochores does not equal to zero since the specific heat $C_V\neq0$
and this point completely differs from the cases discussed before whose
isochores and adiabats are identical. So one cannot simply apply the paradigm
in the former literatures. However, if one introduces a new thermodynamic
parameter associated with the renormalization length scale, the above problem
can be solved. We obtain the analytical efficiency expression of the
three-dimensional charged BTZ black hole heat engine for two different schemes.
Moreover, we double check with the exact formula. Our result presents the first
specific example for the sound correctness of the exact efficiency formula. We
argue that the three-dimensional charged BTZ black hole can be viewed as a toy
model for further investigation of holographic heat engine. Furthermore, we
compare our result with that of the Carnot cycle and extend the former result
to three-dimensional spacetime. In this sense, the result in this paper would
be complementary to those obtained in four-dimensional spacetime or ever
higher. Last but not the least, the heat engine efficiency discussed in this
paper may serve as a criterion to discriminate the two thermodynamic approaches
introduced in Ref.[29] and our result seems to support the approach which
introduces a new thermodynamic parameter $R=r_0$.
| [
{
"created": "Wed, 4 Jan 2017 01:55:51 GMT",
"version": "v1"
},
{
"created": "Sat, 4 Mar 2017 05:39:07 GMT",
"version": "v2"
}
] | 2017-03-07 | [
[
"Mo",
"Jie-Xiong",
""
],
[
"Liang",
"Feng",
""
],
[
"Li",
"Gu-Qiang",
""
]
] | We define a kind of heat engine via three-dimensional charged BTZ black holes. This case is quite subtle and needs to be more careful. The heat flow along the isochores does not equal to zero since the specific heat $C_V\neq0$ and this point completely differs from the cases discussed before whose isochores and adiabats are identical. So one cannot simply apply the paradigm in the former literatures. However, if one introduces a new thermodynamic parameter associated with the renormalization length scale, the above problem can be solved. We obtain the analytical efficiency expression of the three-dimensional charged BTZ black hole heat engine for two different schemes. Moreover, we double check with the exact formula. Our result presents the first specific example for the sound correctness of the exact efficiency formula. We argue that the three-dimensional charged BTZ black hole can be viewed as a toy model for further investigation of holographic heat engine. Furthermore, we compare our result with that of the Carnot cycle and extend the former result to three-dimensional spacetime. In this sense, the result in this paper would be complementary to those obtained in four-dimensional spacetime or ever higher. Last but not the least, the heat engine efficiency discussed in this paper may serve as a criterion to discriminate the two thermodynamic approaches introduced in Ref.[29] and our result seems to support the approach which introduces a new thermodynamic parameter $R=r_0$. |
1502.06125 | Vasilis Oikonomou | S.D. Odintsov, V.K. Oikonomou | $\Lambda$CDM Bounce Cosmology without $\Lambda$CDM: the case of modified
gravity | 31 pages, accepted by PRD | null | 10.1103/PhysRevD.91.064036 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide an $F(R)$ gravity description of a $\Lambda$CDM bouncing model,
without the need for matter fluids or for cosmological constant. As we
explicitly demonstrate, the two cosmological eras that constitute the
$\Lambda$CDM bouncing model, can be generated by $F(R)$ gravity which can lead
to accelerating cosmologies. The resulting F(R) gravity has Einstein frame
inflationary properties that have concordance to the latest Planck
observational data. Both the $F(R)$ gravity stability properties are thoroughly
investigated and also, the gravitational particle production, a feature
necessary for the viability of the $\Lambda$CDM bounce scenario, is also
addressed. As we will show, the $\Lambda$CDM bounce model can be successfully
described by pure $F(R)$ gravity, with appealing phenomenological attributes,
which we extensively discuss.
| [
{
"created": "Sat, 21 Feb 2015 18:30:14 GMT",
"version": "v1"
}
] | 2015-06-23 | [
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | We provide an $F(R)$ gravity description of a $\Lambda$CDM bouncing model, without the need for matter fluids or for cosmological constant. As we explicitly demonstrate, the two cosmological eras that constitute the $\Lambda$CDM bouncing model, can be generated by $F(R)$ gravity which can lead to accelerating cosmologies. The resulting F(R) gravity has Einstein frame inflationary properties that have concordance to the latest Planck observational data. Both the $F(R)$ gravity stability properties are thoroughly investigated and also, the gravitational particle production, a feature necessary for the viability of the $\Lambda$CDM bounce scenario, is also addressed. As we will show, the $\Lambda$CDM bounce model can be successfully described by pure $F(R)$ gravity, with appealing phenomenological attributes, which we extensively discuss. |
1708.04566 | Kimet Jusufi | Ayan Banerjee, J. R. Villanueva, Phongpichit Channuie, Kimet Jusufi | Stable Gravastars: Guilfoyle's electrically charged solutions | 12 pages, 6 figures, accepted for publication in Chinese Physics C | Chinese Physics C Vol. 42, No. 11 (2018) 115101 | 10.1088/1674-1137/42/11/115101 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Compelling alternatives to black holes, namely, gravitational vacuum star
({\it gravastar}) models, the multilayered structure compact objects, have been
proposed to avoid a number of theoretical problems associated with event
horizons and singularities. In this work, we construct a spherically symmetric
thin-shell charged gravastar model where the vacuum phase transition between
the de Sitter interior and the external Reissner--Nordstr$\ddot{\text{o}}$m
spacetime (RN) are matched at a junction surface, by using the cut-and-paste
procedure. Gravastar solutions are found among the Guilfoyle exact solutions
where the gravitational potential $W^2$ and the electric potential field $\phi$
obey a particularly relation in a simple form $ a\left(b-\epsilon \phi
\right)^2 +b_1$, where $a$, $b$ and $b_1$ being arbitrary constants. The
simplest ansatz of Guilfoyle's solution is implemented by the following
assumption: that the total energy density $8\pi \rho_m+\frac{Q^2}{ r^4}$ =
constant, where $Q(r)$ is the electric charge up to a certain radius $r$. We
show that, for certain ranges of the parameters, we can avoid the horizon
formation, which allows us to study the linearized spherically symmetric radial
perturbations around static equilibrium solutions. To lend our solution
theoretical support, we also analyze the physical and geometrical properties of
gravastar configurations.
| [
{
"created": "Tue, 15 Aug 2017 15:51:57 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Aug 2018 10:35:56 GMT",
"version": "v2"
}
] | 2018-09-13 | [
[
"Banerjee",
"Ayan",
""
],
[
"Villanueva",
"J. R.",
""
],
[
"Channuie",
"Phongpichit",
""
],
[
"Jusufi",
"Kimet",
""
]
] | Compelling alternatives to black holes, namely, gravitational vacuum star ({\it gravastar}) models, the multilayered structure compact objects, have been proposed to avoid a number of theoretical problems associated with event horizons and singularities. In this work, we construct a spherically symmetric thin-shell charged gravastar model where the vacuum phase transition between the de Sitter interior and the external Reissner--Nordstr$\ddot{\text{o}}$m spacetime (RN) are matched at a junction surface, by using the cut-and-paste procedure. Gravastar solutions are found among the Guilfoyle exact solutions where the gravitational potential $W^2$ and the electric potential field $\phi$ obey a particularly relation in a simple form $ a\left(b-\epsilon \phi \right)^2 +b_1$, where $a$, $b$ and $b_1$ being arbitrary constants. The simplest ansatz of Guilfoyle's solution is implemented by the following assumption: that the total energy density $8\pi \rho_m+\frac{Q^2}{ r^4}$ = constant, where $Q(r)$ is the electric charge up to a certain radius $r$. We show that, for certain ranges of the parameters, we can avoid the horizon formation, which allows us to study the linearized spherically symmetric radial perturbations around static equilibrium solutions. To lend our solution theoretical support, we also analyze the physical and geometrical properties of gravastar configurations. |
1002.4826 | Mark Durkee | Mark Durkee, Vojtech Pravda, Alena Pravdova, Harvey S. Reall | Generalization of the Geroch-Held-Penrose formalism to higher dimensions | 24 pages | Class.Quant.Grav.27:215010,2010 | 10.1088/0264-9381/27/21/215010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Geroch, Held and Penrose invented a formalism for studying spacetimes
admitting one or two preferred null directions. This approach is very useful
for studying algebraically special spacetimes and their perturbations. In the
present paper, the formalism is generalized to higher-dimensional spacetimes.
This new formalism leads to equations that are considerably simpler than those
of the higher-dimensional Newman-Penrose formalism employed previously. The
dynamics of p-form test fields is analyzed using the new formalism and some
results concerning algebraically special p-form fields are proved.
| [
{
"created": "Thu, 25 Feb 2010 16:44:43 GMT",
"version": "v1"
}
] | 2010-10-01 | [
[
"Durkee",
"Mark",
""
],
[
"Pravda",
"Vojtech",
""
],
[
"Pravdova",
"Alena",
""
],
[
"Reall",
"Harvey S.",
""
]
] | Geroch, Held and Penrose invented a formalism for studying spacetimes admitting one or two preferred null directions. This approach is very useful for studying algebraically special spacetimes and their perturbations. In the present paper, the formalism is generalized to higher-dimensional spacetimes. This new formalism leads to equations that are considerably simpler than those of the higher-dimensional Newman-Penrose formalism employed previously. The dynamics of p-form test fields is analyzed using the new formalism and some results concerning algebraically special p-form fields are proved. |
0708.1261 | Nelson Nunes | E. J. Copeland, D. J. Mulryne, N. J. Nunes, M. Shaeri | Super-inflation in Loop Quantum Cosmology | 11 pages, 2 figures. Extended discussion section | Phys.Rev.D77:023510,2008 | 10.1103/PhysRevD.77.023510 | null | gr-qc | null | We investigate the dynamics of super-inflation in two versions of Loop
Quantum Cosmology, one in which the Friedmann equation is modified by the
presence of inverse volume corrections, and one in which quadratic corrections
are important. Computing the tilt of the power spectrum of the perturbed scalar
field in terms of fast-roll parameters, we conclude that the first case leads
to a power spectrum that is scale invariant for steep power law negative
potentials and for the second case, scale invariance is obtained for positive
potentials that asymptote to a constant value for large values of the scalar
field. It is found that in both cases, the horizon problem is solved with only
a few e-folds of super-inflationary evolution.
| [
{
"created": "Thu, 9 Aug 2007 13:01:52 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Oct 2007 20:36:06 GMT",
"version": "v2"
},
{
"created": "Tue, 8 Jan 2008 18:20:22 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Copeland",
"E. J.",
""
],
[
"Mulryne",
"D. J.",
""
],
[
"Nunes",
"N. J.",
""
],
[
"Shaeri",
"M.",
""
]
] | We investigate the dynamics of super-inflation in two versions of Loop Quantum Cosmology, one in which the Friedmann equation is modified by the presence of inverse volume corrections, and one in which quadratic corrections are important. Computing the tilt of the power spectrum of the perturbed scalar field in terms of fast-roll parameters, we conclude that the first case leads to a power spectrum that is scale invariant for steep power law negative potentials and for the second case, scale invariance is obtained for positive potentials that asymptote to a constant value for large values of the scalar field. It is found that in both cases, the horizon problem is solved with only a few e-folds of super-inflationary evolution. |
1612.00266 | Jahed Abedi | Jahed Abedi, Hannah Dykaar, Niayesh Afshordi | Echoes from the Abyss: Tentative evidence for Planck-scale structure at
black hole horizons | 13 pages, 13 figures, 2 tables, Extended discussions, PRD in press | Phys. Rev. D 96, 082004 (2017) | 10.1103/PhysRevD.96.082004 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In classical General Relativity (GR), an observer falling into an
astrophysical black hole is not expected to experience anything dramatic as she
crosses the event horizon. However, tentative resolutions to problems in
quantum gravity, such as the cosmological constant problem, or the black hole
information paradox, invoke significant departures from classicality in the
vicinity of the horizon. It was recently pointed out that such near-horizon
structures can lead to late-time echoes in the black hole merger gravitational
wave signals that are otherwise indistinguishable from GR. We search for
observational signatures of these echoes in the gravitational wave data
released by advanced Laser Interferometer Gravitational-Wave Observatory
(LIGO), following the three black hole merger events GW150914, GW151226, and
LVT151012. In particular, we look for repeating damped echoes with time-delays
of $8 M \log M$ (+spin corrections, in Planck units), corresponding to
Planck-scale departures from GR near their respective horizons. Accounting for
the "look elsewhere" effect due to uncertainty in the echo template, we find
tentative evidence for Planck-scale structure near black hole horizons at false
detection probability of $1\%$ (corresponding to $2.5\sigma$ significance
level). Future observations from interferometric detectors at higher
sensitivity, along with more physical echo templates, will be able to confirm
(or rule out) this finding, providing possible empirical evidence for
alternatives to classical black holes, such as in ${\it firewall}$ or ${\it
fuzzball}$ paradigms.
| [
{
"created": "Thu, 1 Dec 2016 14:31:12 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Oct 2017 14:31:30 GMT",
"version": "v2"
}
] | 2017-11-01 | [
[
"Abedi",
"Jahed",
""
],
[
"Dykaar",
"Hannah",
""
],
[
"Afshordi",
"Niayesh",
""
]
] | In classical General Relativity (GR), an observer falling into an astrophysical black hole is not expected to experience anything dramatic as she crosses the event horizon. However, tentative resolutions to problems in quantum gravity, such as the cosmological constant problem, or the black hole information paradox, invoke significant departures from classicality in the vicinity of the horizon. It was recently pointed out that such near-horizon structures can lead to late-time echoes in the black hole merger gravitational wave signals that are otherwise indistinguishable from GR. We search for observational signatures of these echoes in the gravitational wave data released by advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), following the three black hole merger events GW150914, GW151226, and LVT151012. In particular, we look for repeating damped echoes with time-delays of $8 M \log M$ (+spin corrections, in Planck units), corresponding to Planck-scale departures from GR near their respective horizons. Accounting for the "look elsewhere" effect due to uncertainty in the echo template, we find tentative evidence for Planck-scale structure near black hole horizons at false detection probability of $1\%$ (corresponding to $2.5\sigma$ significance level). Future observations from interferometric detectors at higher sensitivity, along with more physical echo templates, will be able to confirm (or rule out) this finding, providing possible empirical evidence for alternatives to classical black holes, such as in ${\it firewall}$ or ${\it fuzzball}$ paradigms. |
1710.06299 | Behnam Pourhassan | B. Pourhassan, K. Kokabi, S. Rangyan | Thermodynamics of higher dimensional black holes with higher order
thermal fluctuations | 27 pages, 19 figures | Gen Relativ Gravit 49 (2017) 144 | 10.1007/s10714-017-2315-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we consider higher order corrections of the entropy, which
coming from thermal fluctuations, and find their effect on the thermodynamics
of higher dimensional charged black holes. Leading order thermal fluctuation is
logarithmic term in the entropy while higher order correction is proportional
to the inverse of original entropy. We calculate some thermodynamics quantities
and obtain the effect of logarithmic and higher order corrections of entropy on
them. Validity of the first law of thermodynamics investigated and Van der
Waals equation of state of dual picture studied. We find that five-dimensional
black hole behaves as Van der Waals, but higher dimensional case have not such
behavior. We find that thermal fluctuations are important in stability of black
hole hence affect unstable/stable black hole phase transition.
| [
{
"created": "Sun, 15 Oct 2017 07:49:29 GMT",
"version": "v1"
}
] | 2017-11-29 | [
[
"Pourhassan",
"B.",
""
],
[
"Kokabi",
"K.",
""
],
[
"Rangyan",
"S.",
""
]
] | In this paper, we consider higher order corrections of the entropy, which coming from thermal fluctuations, and find their effect on the thermodynamics of higher dimensional charged black holes. Leading order thermal fluctuation is logarithmic term in the entropy while higher order correction is proportional to the inverse of original entropy. We calculate some thermodynamics quantities and obtain the effect of logarithmic and higher order corrections of entropy on them. Validity of the first law of thermodynamics investigated and Van der Waals equation of state of dual picture studied. We find that five-dimensional black hole behaves as Van der Waals, but higher dimensional case have not such behavior. We find that thermal fluctuations are important in stability of black hole hence affect unstable/stable black hole phase transition. |
1704.00296 | Chopin Soo | Eyo Eyo Ita III, Chopin Soo and Hoi-Lai Yu | Gravitational waves in Intrinsic Time Geometrodynamics | 7 pages; replaced by published version | Eur. Phys. J. C (2018) 78: 723 | 10.1140/epjc/s10052-018-6203-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves are investigated in Intrinsic Time Geometrodynamics. This
theory has a non-vanishing physical Hamiltonian generating intrinsic time
development in our expanding universe, and four-covariance is explicitly broken
by higher spatial curvature terms. Linearization of Hamilton's equations about
the de Sitter solution produces transverse traceless excitations, with the
physics of gravitational waves in Einstein's General Relativity recovered in
the low curvature low frequency limit. A noteworthy feature of the theory is
that gravitational waves always carry positive energy density, even for compact
spatial slicings without any energy contribution from boundary Hamiltonian.
This study of gravitational waves in compact $k= +1$ cosmological de Sitter
spacetime is in contradistinction to, and complements, previous $k= -1$
investigations of Hawking, Hertog and Turok and other more familiar $k=0$
works. In addition, possible non-four-covariant Horava gravity contributions
are considered (hence the use of canonical Hamiltonian, rather than Lagrangian,
methods). Recent explicit $S^3$ transverse-traceless mode spectrum of Lindblom,
Taylor and Zhang are also employed to complete the discussion.
| [
{
"created": "Sun, 2 Apr 2017 13:56:13 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Sep 2018 00:23:04 GMT",
"version": "v2"
}
] | 2018-09-11 | [
[
"Ita",
"Eyo Eyo",
"III"
],
[
"Soo",
"Chopin",
""
],
[
"Yu",
"Hoi-Lai",
""
]
] | Gravitational waves are investigated in Intrinsic Time Geometrodynamics. This theory has a non-vanishing physical Hamiltonian generating intrinsic time development in our expanding universe, and four-covariance is explicitly broken by higher spatial curvature terms. Linearization of Hamilton's equations about the de Sitter solution produces transverse traceless excitations, with the physics of gravitational waves in Einstein's General Relativity recovered in the low curvature low frequency limit. A noteworthy feature of the theory is that gravitational waves always carry positive energy density, even for compact spatial slicings without any energy contribution from boundary Hamiltonian. This study of gravitational waves in compact $k= +1$ cosmological de Sitter spacetime is in contradistinction to, and complements, previous $k= -1$ investigations of Hawking, Hertog and Turok and other more familiar $k=0$ works. In addition, possible non-four-covariant Horava gravity contributions are considered (hence the use of canonical Hamiltonian, rather than Lagrangian, methods). Recent explicit $S^3$ transverse-traceless mode spectrum of Lindblom, Taylor and Zhang are also employed to complete the discussion. |
1909.02698 | Francisco Hernandez Vivanco | Francisco Hernandez Vivanco, Rory Smith, Eric Thrane, Paul D. Lasky,
Colm Talbot, Vivien Raymond | Measuring the neutron star equation of state with gravitational waves:
the first forty binary neutron star mergers | Accepted for publication in Phys. Rev. D. We added Appendix A
following publication of the paper in the journal | Phys. Rev. D 100, 103009 (2019) | 10.1103/PhysRevD.100.103009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves from binary neutron star coalescences contain rich
information about matter at supranuclear densities encoded by the neutron star
equation of state. We can measure the equation of state by analyzing the tidal
interactions between neutron stars, which is quantified by the tidal
deformability. Multiple merger events are required to probe the equation of
state over a range of neutron star masses. The more events included in the
analysis, the stronger the constraints on the equation of state. In this paper,
we build on previous work to explore the constraints that LIGO and Virgo are
likely to place on the neutron star equation of state by combining the first
forty binary neutron star detections, a milestone we project to be reached
during the first year of accumulated design-sensitivity data. We carry out
Bayesian inference on a realistic mock dataset of binaries to obtain posterior
distributions for neutron star tidal parameters. In order to combine posterior
samples from multiple observations, we employ a random forest regressor, which
allows us to efficiently interpolate the likelihood distribution. Assuming a
merger rate of 1540 Gpc$^{-3}$ yr$^{-1}$ and a LIGO-Virgo detector network
operating for one year at the sensitivity of the third-observation run, plus an
additional eight months of design sensitivity, we find that the radius of a 1.4
$M_\odot$ neutron star can be constrained to $\sim 10$% at 90% confidence. At
the same time, the pressure at twice the nuclear saturation density can be
constrained to $\sim 45$ % at 90% confidence. Finally, we add an appendix
following publication of the paper in the journal, showing the posterior
distribution of the maximum neutron star mass allowed by the equation of state.
We find that the maximum mass can be constrained to $\sim 0.3$ $M_\odot$ at 90%
confidence.
| [
{
"created": "Fri, 6 Sep 2019 02:44:32 GMT",
"version": "v1"
},
{
"created": "Thu, 31 Oct 2019 04:05:21 GMT",
"version": "v2"
},
{
"created": "Tue, 26 May 2020 03:55:07 GMT",
"version": "v3"
}
] | 2020-05-27 | [
[
"Vivanco",
"Francisco Hernandez",
""
],
[
"Smith",
"Rory",
""
],
[
"Thrane",
"Eric",
""
],
[
"Lasky",
"Paul D.",
""
],
[
"Talbot",
"Colm",
""
],
[
"Raymond",
"Vivien",
""
]
] | Gravitational waves from binary neutron star coalescences contain rich information about matter at supranuclear densities encoded by the neutron star equation of state. We can measure the equation of state by analyzing the tidal interactions between neutron stars, which is quantified by the tidal deformability. Multiple merger events are required to probe the equation of state over a range of neutron star masses. The more events included in the analysis, the stronger the constraints on the equation of state. In this paper, we build on previous work to explore the constraints that LIGO and Virgo are likely to place on the neutron star equation of state by combining the first forty binary neutron star detections, a milestone we project to be reached during the first year of accumulated design-sensitivity data. We carry out Bayesian inference on a realistic mock dataset of binaries to obtain posterior distributions for neutron star tidal parameters. In order to combine posterior samples from multiple observations, we employ a random forest regressor, which allows us to efficiently interpolate the likelihood distribution. Assuming a merger rate of 1540 Gpc$^{-3}$ yr$^{-1}$ and a LIGO-Virgo detector network operating for one year at the sensitivity of the third-observation run, plus an additional eight months of design sensitivity, we find that the radius of a 1.4 $M_\odot$ neutron star can be constrained to $\sim 10$% at 90% confidence. At the same time, the pressure at twice the nuclear saturation density can be constrained to $\sim 45$ % at 90% confidence. Finally, we add an appendix following publication of the paper in the journal, showing the posterior distribution of the maximum neutron star mass allowed by the equation of state. We find that the maximum mass can be constrained to $\sim 0.3$ $M_\odot$ at 90% confidence. |
2004.03214 | Jacek Jezierski | Jacek Jezierski, Jerzy Kijowski and Marian Wiatr | Localizing Energy in Fierz-Lanczos theory | 25 pages | Phys. Rev. D 102, 024015 (2020) | 10.1103/PhysRevD.102.024015 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We calculate energy carried by the massless spin-2 field using Fierz-Lanczos
representation of the theory. For this purpose Hamiltonian formulation of the
field dynamic is thoroughly analyzed. Final expression for the energy is very
much analogous to the Maxwell energy in electrodynamics (spin-1 field) and
displays the locality property. Known as a ``super-energy'' in gravity theory,
this quantity differs considerably from the well understood gravitational field
energy (represented in linear gravity by the quadratic term in Taylor expansion
of the A.D.M. mass) which cannot be localized.
| [
{
"created": "Tue, 7 Apr 2020 09:09:00 GMT",
"version": "v1"
}
] | 2020-07-15 | [
[
"Jezierski",
"Jacek",
""
],
[
"Kijowski",
"Jerzy",
""
],
[
"Wiatr",
"Marian",
""
]
] | We calculate energy carried by the massless spin-2 field using Fierz-Lanczos representation of the theory. For this purpose Hamiltonian formulation of the field dynamic is thoroughly analyzed. Final expression for the energy is very much analogous to the Maxwell energy in electrodynamics (spin-1 field) and displays the locality property. Known as a ``super-energy'' in gravity theory, this quantity differs considerably from the well understood gravitational field energy (represented in linear gravity by the quadratic term in Taylor expansion of the A.D.M. mass) which cannot be localized. |
gr-qc/9510037 | Vadim V. Zhytnikov | A. O. Barvinsky, A. G. Mirzabekian and V. V. Zhytnikov | Conformal Decomposition of the Effective Action and Covariant Curvature
Expansion | 19 pages, LaTeX, Talk given at 6th Quantum Gravity Seminar Moscow,
June 12-19, 1995 | null | null | null | gr-qc hep-th | null | The class of effective actions exactly reproducing the conformal anomaly in
4D is considered. It is demonstrated that the freedom within this class can be
fixed by the choice of the conformal gauge. The conformal invariant part of the
generic one-loop effective action expanded in the covariant series up to third
order in the curvature is rewritten in the new conformal basis. The possible
applications of the obtained results are discussed.
| [
{
"created": "Wed, 18 Oct 1995 07:54:13 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Barvinsky",
"A. O.",
""
],
[
"Mirzabekian",
"A. G.",
""
],
[
"Zhytnikov",
"V. V.",
""
]
] | The class of effective actions exactly reproducing the conformal anomaly in 4D is considered. It is demonstrated that the freedom within this class can be fixed by the choice of the conformal gauge. The conformal invariant part of the generic one-loop effective action expanded in the covariant series up to third order in the curvature is rewritten in the new conformal basis. The possible applications of the obtained results are discussed. |
1808.00340 | Joel Berg\'e | Joel Berg\'e, Philippe Brax, Martin Pernot-Borr\`as, Jean-Philippe
Uzan | Interpretation of geodesy experiments in non-Newtonian theories of
gravity | submitted to CQG | null | 10.1088/1361-6382/aae9a1 | null | gr-qc astro-ph.CO physics.geo-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The tests of the deviations from Newton's or Einstein's gravity in the Earth
neighbourhood are tied to our knowledge of the shape and mass distribution of
our planet. On the one hand estimators of these "modified" theories of gravity
may be explicitly Earth-model-dependent whilst on the other hand the Earth
gravitational field would act as a systematic error. We revisit deviations from
Newtonian gravity described by a Yukawa interaction that can arise from the
existence of a finite range fifth force. We show that the standard multipolar
expansion of the Earth gravitational potential can be generalised. In
particular, the multipolar coefficients depend on the distance to the centre of
the Earth and are therefore not universal to the Earth system anymore. This
offers new ways of constraining such Yukawa interactions and demonstrates
explicitly the limits of the Newton-based interpretation of geodesy
experiments. In turn, limitations from geodesy data restrict the possibility of
testing gravity in space. The gravitational acceleration is described in terms
of spin-weighted spherical harmonics allowing us to obtain the perturbing force
entering the Lagrange-Gauss secular equations. This is then used to discuss the
correlation between geodesy and modified gravity experiments and the
possibility to break their degeneracy. Finally we show that, given the existing
constraints, a Yukawa fifth force is expected to be sub-dominant in satellite
dynamics and space geodesy experiments, as long as they are performed at
altitudes greater than a few hundred kilometres. Gravity surveys will have to
gain at least two orders of magnitude in instrumental precision before
satellite geodesy could be used to improve the current constraints on modified
gravity.
| [
{
"created": "Wed, 1 Aug 2018 14:33:06 GMT",
"version": "v1"
}
] | 2018-12-05 | [
[
"Bergé",
"Joel",
""
],
[
"Brax",
"Philippe",
""
],
[
"Pernot-Borràs",
"Martin",
""
],
[
"Uzan",
"Jean-Philippe",
""
]
] | The tests of the deviations from Newton's or Einstein's gravity in the Earth neighbourhood are tied to our knowledge of the shape and mass distribution of our planet. On the one hand estimators of these "modified" theories of gravity may be explicitly Earth-model-dependent whilst on the other hand the Earth gravitational field would act as a systematic error. We revisit deviations from Newtonian gravity described by a Yukawa interaction that can arise from the existence of a finite range fifth force. We show that the standard multipolar expansion of the Earth gravitational potential can be generalised. In particular, the multipolar coefficients depend on the distance to the centre of the Earth and are therefore not universal to the Earth system anymore. This offers new ways of constraining such Yukawa interactions and demonstrates explicitly the limits of the Newton-based interpretation of geodesy experiments. In turn, limitations from geodesy data restrict the possibility of testing gravity in space. The gravitational acceleration is described in terms of spin-weighted spherical harmonics allowing us to obtain the perturbing force entering the Lagrange-Gauss secular equations. This is then used to discuss the correlation between geodesy and modified gravity experiments and the possibility to break their degeneracy. Finally we show that, given the existing constraints, a Yukawa fifth force is expected to be sub-dominant in satellite dynamics and space geodesy experiments, as long as they are performed at altitudes greater than a few hundred kilometres. Gravity surveys will have to gain at least two orders of magnitude in instrumental precision before satellite geodesy could be used to improve the current constraints on modified gravity. |
0901.1757 | Dah-Wei Chiou | Dah-Wei Chiou and Li-Fang Li | How loopy is the quantum bounce? A heuristic analysis of higher order
holonomy corrections in LQC | 5 pages, 1 figure; more remarks and references added; version to
appear in PRD | Phys.Rev.D79:063510,2009 | 10.1103/PhysRevD.79.063510 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A well-motivated extension of higher order holonomy corrections in loop
quantum cosmology (LQC) for the $k=0$ Friedmann-Robertson-Walker model is
investigated at the level of heuristic effective dynamics. It reveals that the
quantum bounce is generic, regardless of the order of corrections, and the
matter density remains finite, bounded from above by an upper bound in the
regime of the Planckian density, even if all orders of corrections are
included. This observation provides further evidence that the quantum bounce is
essentially a consequence of the loopy nature (i.e. intrinsic discreteness) of
LQC and LQC is fundamentally different from the Wheeler-DeWitt theory; it also
encourages one to construct the quantum theory of LQC with the higher order
holonomy corrections, which might be understood as related to the higher $j$
representations in the Hamiltonian operator of loop quantum gravity.
| [
{
"created": "Tue, 13 Jan 2009 10:39:50 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Jan 2009 09:07:49 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Mar 2009 07:14:22 GMT",
"version": "v3"
}
] | 2009-03-24 | [
[
"Chiou",
"Dah-Wei",
""
],
[
"Li",
"Li-Fang",
""
]
] | A well-motivated extension of higher order holonomy corrections in loop quantum cosmology (LQC) for the $k=0$ Friedmann-Robertson-Walker model is investigated at the level of heuristic effective dynamics. It reveals that the quantum bounce is generic, regardless of the order of corrections, and the matter density remains finite, bounded from above by an upper bound in the regime of the Planckian density, even if all orders of corrections are included. This observation provides further evidence that the quantum bounce is essentially a consequence of the loopy nature (i.e. intrinsic discreteness) of LQC and LQC is fundamentally different from the Wheeler-DeWitt theory; it also encourages one to construct the quantum theory of LQC with the higher order holonomy corrections, which might be understood as related to the higher $j$ representations in the Hamiltonian operator of loop quantum gravity. |
2110.07194 | Dmitriy Ovchinnikov | Dmitriy Ovchinnikov, Jan Schee, Zdenek Stuchl\'ik, Bobomurat Ahmedov | Light curves of the hot spots on circular orbits around generic regular
black holes related to non-linear electrodynamics with Maxwellian weak-field
Limit | 35 pages, 7 figures, was updated information in acknowledgment, was
added .nb file, the .nb file was moved to auxiliary files | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The combined effect of a strong gravitational field and electromagnetic field
in the vicinity of a generic regular black hole related to non-linear
electrodynamics with Maxwellian weak-field limit on the radiation flux of a hot
spot orbiting the regular black hole on the Keplerian disc has been studied.
The frequency shift due to the strong gravitational field and magnification of
the radiation related to gravitational lensing have been calculated. We compare
the flux related to the Maxwellian regular black hole to the flux of the hot
spots moving with the same orbital period around standard Schwarzschild and
Raissner-Nordstrom black holes to illustrate the role of the effective geometry
governing photon motion around the regular black hole.
| [
{
"created": "Thu, 14 Oct 2021 07:40:17 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Dec 2021 10:37:55 GMT",
"version": "v2"
},
{
"created": "Thu, 9 Dec 2021 08:46:36 GMT",
"version": "v3"
}
] | 2021-12-10 | [
[
"Ovchinnikov",
"Dmitriy",
""
],
[
"Schee",
"Jan",
""
],
[
"Stuchlík",
"Zdenek",
""
],
[
"Ahmedov",
"Bobomurat",
""
]
] | The combined effect of a strong gravitational field and electromagnetic field in the vicinity of a generic regular black hole related to non-linear electrodynamics with Maxwellian weak-field limit on the radiation flux of a hot spot orbiting the regular black hole on the Keplerian disc has been studied. The frequency shift due to the strong gravitational field and magnification of the radiation related to gravitational lensing have been calculated. We compare the flux related to the Maxwellian regular black hole to the flux of the hot spots moving with the same orbital period around standard Schwarzschild and Raissner-Nordstrom black holes to illustrate the role of the effective geometry governing photon motion around the regular black hole. |
gr-qc/9807073 | Luca Lusanna. Sez. Di Firenze. | Luca Lusanna (INFN, Firenze) and Stefano Russo (Lugano) | Tetrad Gravity: I) A New Formulation | 68 pages, revtex, revised version with additions | null | null | null | gr-qc | null | A new version of tetrad gravity in globally hyperbolic, asymptotically flat
at spatial infinity spacetimes with Cauchy surfaces diffeomorphic to $R^3$ is
obtained by using a new parametrization of arbitrary cotetrads to define a set
of configurational variables to be used in the ADM metric action. Seven of the
fourteen first class constraints have the form of the vanishing of canonical
momenta. A comparison is made with other models of tetrad gravity and with the
ADM canonical formalism for metric gravity. The phase space expression of
various 4-tensors is explicitly given.
| [
{
"created": "Tue, 28 Jul 1998 15:02:42 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Jan 1999 16:47:55 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Jul 1999 10:46:38 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Lusanna",
"Luca",
"",
"INFN, Firenze"
],
[
"Russo",
"Stefano",
"",
"Lugano"
]
] | A new version of tetrad gravity in globally hyperbolic, asymptotically flat at spatial infinity spacetimes with Cauchy surfaces diffeomorphic to $R^3$ is obtained by using a new parametrization of arbitrary cotetrads to define a set of configurational variables to be used in the ADM metric action. Seven of the fourteen first class constraints have the form of the vanishing of canonical momenta. A comparison is made with other models of tetrad gravity and with the ADM canonical formalism for metric gravity. The phase space expression of various 4-tensors is explicitly given. |
gr-qc/0605128 | Alan Coley | A.A. Coley, S. Hervik and W.C. Lim | Fluid observers and tilting cosmology | null | Class.Quant.Grav. 23 (2006) 3573-3591 | 10.1088/0264-9381/23/10/021 | null | gr-qc | null | We study perfect fluid cosmological models with a constant equation of state
parameter $\gamma$ in which there are two naturally defined time-like
congruences, a geometrically defined geodesic congruence and a non-geodesic
fluid congruence. We establish an appropriate set of boost formulae relating
the physical variables, and consequently the observed quantities, in the two
frames. We study expanding spatially homogeneous tilted perfect fluid models,
with an emphasis on future evolution with extreme tilt. We show that for
ultra-radiative equations of state (i.e., $\gamma>4/3$), generically the tilt
becomes extreme at late times and the fluid observers will reach infinite
expansion within a finite proper time and experience a singularity similar to
that of the big rip. In addition, we show that for sub-radiative equations of
state (i.e., $\gamma < 4/3$), the tilt can become extreme at late times and
give rise to an effective quintessential equation of state. To establish the
connection with phantom cosmology and quintessence, we calculate the effective
equation of state in the models under consideration and we determine the future
asymptotic behaviour of the tilting models in the fluid frame variables using
the boost formulae. We also discuss spatially inhomogeneous models and tilting
spatially homogeneous models with a cosmological constant.
| [
{
"created": "Wed, 24 May 2006 16:58:11 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Coley",
"A. A.",
""
],
[
"Hervik",
"S.",
""
],
[
"Lim",
"W. C.",
""
]
] | We study perfect fluid cosmological models with a constant equation of state parameter $\gamma$ in which there are two naturally defined time-like congruences, a geometrically defined geodesic congruence and a non-geodesic fluid congruence. We establish an appropriate set of boost formulae relating the physical variables, and consequently the observed quantities, in the two frames. We study expanding spatially homogeneous tilted perfect fluid models, with an emphasis on future evolution with extreme tilt. We show that for ultra-radiative equations of state (i.e., $\gamma>4/3$), generically the tilt becomes extreme at late times and the fluid observers will reach infinite expansion within a finite proper time and experience a singularity similar to that of the big rip. In addition, we show that for sub-radiative equations of state (i.e., $\gamma < 4/3$), the tilt can become extreme at late times and give rise to an effective quintessential equation of state. To establish the connection with phantom cosmology and quintessence, we calculate the effective equation of state in the models under consideration and we determine the future asymptotic behaviour of the tilting models in the fluid frame variables using the boost formulae. We also discuss spatially inhomogeneous models and tilting spatially homogeneous models with a cosmological constant. |
gr-qc/0508095 | Ari Peltola | A. Peltola, J. Makela | Radiation of the Inner Horizon of the Reissner-Nordstr\"om Black Hole | 22 pages, 6 figures. References added, discussion slightly expanded
in Secs. I and V. To appear in IJMPD | Int.J.Mod.Phys. D15 (2006) 817-844 | 10.1142/S0218271806008565 | null | gr-qc | null | Despite of over thirty years of research of the black hole thermodynamics our
understanding of the possible role played by the inner horizons of
Reissner-Nordstr\"om and Kerr-Newman black holes in black hole thermodynamics
is still somewhat incomplete: There are derivations which imply that the
temperature of the inner horizon is negative and it is not quite clear what
this means. Motivated by this problem we perform a detailed analysis of the
radiation emitted by the inner horizon of the Reissner-Nordstr\"om black hole.
As a result we find that in a maximally extended Reissner-Nordstr\"om spacetime
virtual particle-antiparticle pairs are created at the inner horizon of the
Reissner-Nordstr\"om black hole such that real particles with positive energy
and temperature are emitted towards the singularity from the inner horizon and,
as a consequence, antiparticles with negative energy are radiated away from the
singularity through the inner horizon. We show that these antiparticles will
come out from the white hole horizon in the maximally extended
Reissner-Nordstr\"om spacetime, at least when the hole is near extremality. The
energy spectrum of the antiparticles leads to a positive temperature for the
white hole horizon. In other words, our analysis predicts that in addition to
the radiation effects of black hole horizons, also the white hole horizon
radiates. The black hole radiation is caused by the quantum effects at the
outer horizon, whereas the white hole radiation is caused by the quantum
effects at the inner horizon of the Reissner-Nordstr\"om black hole.
| [
{
"created": "Tue, 23 Aug 2005 09:36:48 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Feb 2006 11:27:10 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Peltola",
"A.",
""
],
[
"Makela",
"J.",
""
]
] | Despite of over thirty years of research of the black hole thermodynamics our understanding of the possible role played by the inner horizons of Reissner-Nordstr\"om and Kerr-Newman black holes in black hole thermodynamics is still somewhat incomplete: There are derivations which imply that the temperature of the inner horizon is negative and it is not quite clear what this means. Motivated by this problem we perform a detailed analysis of the radiation emitted by the inner horizon of the Reissner-Nordstr\"om black hole. As a result we find that in a maximally extended Reissner-Nordstr\"om spacetime virtual particle-antiparticle pairs are created at the inner horizon of the Reissner-Nordstr\"om black hole such that real particles with positive energy and temperature are emitted towards the singularity from the inner horizon and, as a consequence, antiparticles with negative energy are radiated away from the singularity through the inner horizon. We show that these antiparticles will come out from the white hole horizon in the maximally extended Reissner-Nordstr\"om spacetime, at least when the hole is near extremality. The energy spectrum of the antiparticles leads to a positive temperature for the white hole horizon. In other words, our analysis predicts that in addition to the radiation effects of black hole horizons, also the white hole horizon radiates. The black hole radiation is caused by the quantum effects at the outer horizon, whereas the white hole radiation is caused by the quantum effects at the inner horizon of the Reissner-Nordstr\"om black hole. |
0706.0981 | Yun-Song Piao | Yun-Song Piao | Primordial Perturbations During a Slow Expansion | 5 pages, 1 eps figure, minor changes and refs. added, to publish in
PRD | Phys.Rev.D76:083505,2007 | 10.1103/PhysRevD.76.083505 | null | gr-qc | null | Recently, it has been showed that a slow expansion, which is asymptotically a
static state in infinite past and may be described as an evolution with
\epsilon \ll -1, of early universe may lead to the generation of primordial
perturbation responsible for the structure formation of observable universe.
However, its feasibility depends on whether the growing mode of Bardeen
potential before phase transition can be inherited by the constant mode of
curvature perturbation after phase transition. In this note, we phenomenally
regard this slow expansion as that driven by multi NEC violating scalar fields.
We calculate the curvature perturbation induced by the entropy perturbation
before phase transition, and find that the spectrum is naturally scale
invariant with a slight red tilt. The result has an interesting similarity to
that of slow roll inflation.
| [
{
"created": "Thu, 7 Jun 2007 10:45:51 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Aug 2007 12:18:17 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Piao",
"Yun-Song",
""
]
] | Recently, it has been showed that a slow expansion, which is asymptotically a static state in infinite past and may be described as an evolution with \epsilon \ll -1, of early universe may lead to the generation of primordial perturbation responsible for the structure formation of observable universe. However, its feasibility depends on whether the growing mode of Bardeen potential before phase transition can be inherited by the constant mode of curvature perturbation after phase transition. In this note, we phenomenally regard this slow expansion as that driven by multi NEC violating scalar fields. We calculate the curvature perturbation induced by the entropy perturbation before phase transition, and find that the spectrum is naturally scale invariant with a slight red tilt. The result has an interesting similarity to that of slow roll inflation. |
1708.01040 | Donato Bini | Donato Bini, Carmen Chicone, Bahram Mashhoon | Anisotropic Gravitational Collapse and Cosmic Jets | 25 pages, 3 figures, revtex macros; v2: slightly expanded version | Phys. Rev. D 96, 084034 (2017) | 10.1103/PhysRevD.96.084034 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Consider a dynamic general relativistic spacetime in which the proper
infinitesimal interval along one spatial coordinate direction decreases
monotonically with time, while the corresponding intervals increase along other
spatial directions. In a system undergoing such complete anisotropic
collapse/expansion, we look for the formation of a cosmic double-jet
configuration: free test particles in the ambient medium, relative to the
collapsing system, gain energy from the gravitational field and asymptotically
line up parallel and antiparallel to the direction of collapse such that their
Lorentz factors approach infinity. A strong burst of electromagnetic radiation
is expected to accompany this event if some of the free test particles carry
electric charge. Previous work in this direction involved mainly Ricci-flat
spacetimes; hence, we concentrate here on inhomogeneous perfect fluid
spacetimes. We briefly explore the possible connection between these
theoretical cosmic jets and astrophysical jets. We also discuss other general
relativistic scenarios for the formation of cosmic jets.
| [
{
"created": "Thu, 3 Aug 2017 08:09:53 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Sep 2017 17:55:43 GMT",
"version": "v2"
}
] | 2022-08-17 | [
[
"Bini",
"Donato",
""
],
[
"Chicone",
"Carmen",
""
],
[
"Mashhoon",
"Bahram",
""
]
] | Consider a dynamic general relativistic spacetime in which the proper infinitesimal interval along one spatial coordinate direction decreases monotonically with time, while the corresponding intervals increase along other spatial directions. In a system undergoing such complete anisotropic collapse/expansion, we look for the formation of a cosmic double-jet configuration: free test particles in the ambient medium, relative to the collapsing system, gain energy from the gravitational field and asymptotically line up parallel and antiparallel to the direction of collapse such that their Lorentz factors approach infinity. A strong burst of electromagnetic radiation is expected to accompany this event if some of the free test particles carry electric charge. Previous work in this direction involved mainly Ricci-flat spacetimes; hence, we concentrate here on inhomogeneous perfect fluid spacetimes. We briefly explore the possible connection between these theoretical cosmic jets and astrophysical jets. We also discuss other general relativistic scenarios for the formation of cosmic jets. |
1601.04420 | Chee Leong Ching | Chee Leong Ching, Cheng Xun Yeo and Wei Khim Ng | Non-Relativistic Anti-Snyder Model and Some Applications | null | International Journal of Modern Physics A, Vol. 32 (2017) 1750009
(28 pages) | 10.1142/S0217751X17500099 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the (2+1)-dimensional Dirac equation in a homogeneous magnetic
field under the non-relativistic anti-Snyder model which is relevant to
deformed special relativity (DSR) since it exhibits an intrinsic upper bound of
the momentum of free particles. After setting up the formalism, exact eigen
solutions are derived in momentum space representation and they are expressed
in terms of finite orthogonal Romanovski polynomials. There is a finite maximum
number of allowable bound states due to the orthogonality of the polynomials
and the maximum energy is truncated at the maximum n. Similar to the minimal
length case, the degeneracy of the Dirac-Landau levels in anti- Snyder model
are modified and there are states that do not exist in the ordinary quantum
mechanics limit. By taking zero mass limit, we explore the motion of effective
zero mass charged Fermions in Graphene like material and obtained a maximum
bound of deformed parameter. Furthermore, we consider the modified energy
dispersion relations and its application in describing the behavior of
neutrinos oscillation under modified commutation relations.
| [
{
"created": "Mon, 18 Jan 2016 07:48:41 GMT",
"version": "v1"
}
] | 2017-01-09 | [
[
"Ching",
"Chee Leong",
""
],
[
"Yeo",
"Cheng Xun",
""
],
[
"Ng",
"Wei Khim",
""
]
] | We examine the (2+1)-dimensional Dirac equation in a homogeneous magnetic field under the non-relativistic anti-Snyder model which is relevant to deformed special relativity (DSR) since it exhibits an intrinsic upper bound of the momentum of free particles. After setting up the formalism, exact eigen solutions are derived in momentum space representation and they are expressed in terms of finite orthogonal Romanovski polynomials. There is a finite maximum number of allowable bound states due to the orthogonality of the polynomials and the maximum energy is truncated at the maximum n. Similar to the minimal length case, the degeneracy of the Dirac-Landau levels in anti- Snyder model are modified and there are states that do not exist in the ordinary quantum mechanics limit. By taking zero mass limit, we explore the motion of effective zero mass charged Fermions in Graphene like material and obtained a maximum bound of deformed parameter. Furthermore, we consider the modified energy dispersion relations and its application in describing the behavior of neutrinos oscillation under modified commutation relations. |
1811.07513 | Avinash Singh | Avinash Singh, Archana Sangwan, H. K. Jassal | Low redshift observational constraints on tachyon models of dark energy | 20 pages, 9 figures, References added, Minor modifications, Published
in JCAP | JCAP04 (2019) 047 | 10.1088/1475-7516/2019/04/047 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The background evolution of an accelerated, dark energy dominated universe is
aptly described by non-canonical tachyon scalar field models. The accelerated
expansion of the universe is determined by the choice of a suitable scalar
field potential; in the case of a tachyon field, a 'runaway' potential. In the
absence of a fundamental theory, dark energy properties are studied in a
phenomenological approach. This includes determining the model parameters using
observations and to probe the allowed deviation from the cosmological constant
model. In this paper, we present constraints on tachyon scalar field parameters
from low redshift data for two different scalar field potentials. These scalar
field potentials have been crucial in tachyon dark energy studies. The datasets
considered in this paper include the supernova type Ia data, independent
measurements of the Hubble parameter and the Baryon Acoustic Oscillation data.
In this paper, we present constraints on tachyon field parameters using these
observations and their combination. A combination of the datasets indicates
that those model parameters are preferred which emulate the cosmological
constant model. The initial value of the scalar field, in the unit of the
Hubble constant, is bounded from below and does not require fine-tuning at
larger values.
| [
{
"created": "Mon, 19 Nov 2018 06:00:36 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Dec 2018 08:31:53 GMT",
"version": "v2"
},
{
"created": "Thu, 9 May 2019 09:21:32 GMT",
"version": "v3"
}
] | 2019-05-10 | [
[
"Singh",
"Avinash",
""
],
[
"Sangwan",
"Archana",
""
],
[
"Jassal",
"H. K.",
""
]
] | The background evolution of an accelerated, dark energy dominated universe is aptly described by non-canonical tachyon scalar field models. The accelerated expansion of the universe is determined by the choice of a suitable scalar field potential; in the case of a tachyon field, a 'runaway' potential. In the absence of a fundamental theory, dark energy properties are studied in a phenomenological approach. This includes determining the model parameters using observations and to probe the allowed deviation from the cosmological constant model. In this paper, we present constraints on tachyon scalar field parameters from low redshift data for two different scalar field potentials. These scalar field potentials have been crucial in tachyon dark energy studies. The datasets considered in this paper include the supernova type Ia data, independent measurements of the Hubble parameter and the Baryon Acoustic Oscillation data. In this paper, we present constraints on tachyon field parameters using these observations and their combination. A combination of the datasets indicates that those model parameters are preferred which emulate the cosmological constant model. The initial value of the scalar field, in the unit of the Hubble constant, is bounded from below and does not require fine-tuning at larger values. |
gr-qc/0609095 | Jason Steffen | P. E. Boynton, R. M. Bonicalzi, A. M. Kalet, A. M. Kleczewski, J. K.
Lingwood, K. J. McKenney, M. W. Moore, J. H. Steffen (University of
Washington, Seattle) E. C. Berg, W. D. Cross, R. D. Newman (University of
California, Irvine) R. E. Gephart (Pacific Northwest National Laboratory) | Gravitation Physics at BGPL | To be published in The Proceedings of the Francesco Melchiorri
Memorial Conference as a special issue of New Astronomy Reviews | New Astron.Rev.51:334-340,2007 | 10.1016/j.newar.2006.11.035 | null | gr-qc | null | We report progress on a program of gravitational physics experiments using
cryogenic torsion pendula undergoing large-amplitude torsion oscillation. This
program includes tests of the gravitational inverse square law and of the weak
equivalence principle. Here we describe our ongoing search for
inverse-square-law violation at a strength down to $10^{-5}$ of standard
gravity. The low-vibration environment provided by the Battelle Gravitation
Physics Laboratory (BGPL) is uniquely suited to this study.
| [
{
"created": "Thu, 21 Sep 2006 22:30:14 GMT",
"version": "v1"
}
] | 2011-04-11 | [
[
"Boynton",
"P. E.",
"",
"University of\n Washington, Seattle"
],
[
"Bonicalzi",
"R. M.",
"",
"University of\n Washington, Seattle"
],
[
"Kalet",
"A. M.",
"",
"University of\n Washington, Seattle"
],
[
"Kleczewski",
"A. M.",
"",
"Univer... | We report progress on a program of gravitational physics experiments using cryogenic torsion pendula undergoing large-amplitude torsion oscillation. This program includes tests of the gravitational inverse square law and of the weak equivalence principle. Here we describe our ongoing search for inverse-square-law violation at a strength down to $10^{-5}$ of standard gravity. The low-vibration environment provided by the Battelle Gravitation Physics Laboratory (BGPL) is uniquely suited to this study. |
gr-qc/0407012 | Andrea Nerozzi Mr | Christopher Beetle, Marco Bruni, Lior M. Burko and Andrea Nerozzi | Towards a novel wave-extraction method for numerical relativity. I.
Foundations and initial-value formulation | 11 pages, 1 figure | Phys.Rev. D72 (2005) 024013 | 10.1103/PhysRevD.72.024013 | null | gr-qc | null | The Teukolsky formalism of black hole perturbation theory describes weak
gravitational radiation generated by a mildly dynamical hole near equilibrium.
A particular null tetrad of the background Kerr geometry, due to Kinnersley,
plays a singularly important role within this formalism. In order to apply the
rich physical intuition of Teukolsky's approach to the results of fully
non-linear numerical simulations, one must approximate this Kinnersley tetrad
using raw numerical data, with no a priori knowledge of a background. This
paper addresses this issue by identifying the directions of the tetrad fields
in a quasi-Kinnersley frame. This frame provides a unique, analytic extension
of Kinnersley's definition for the Kerr geometry to a much broader class of
space-times including not only arbitrary perturbations, but also many examples
which differ non-perturbatively from Kerr. This paper establishes concrete
limits delineating this class and outlines a scheme to calculate the
quasi-Kinnersley frame in numerical codes based on the initial-value
formulation of geometrodynamics.
| [
{
"created": "Fri, 2 Jul 2004 19:39:39 GMT",
"version": "v1"
},
{
"created": "Wed, 11 May 2005 03:42:57 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Beetle",
"Christopher",
""
],
[
"Bruni",
"Marco",
""
],
[
"Burko",
"Lior M.",
""
],
[
"Nerozzi",
"Andrea",
""
]
] | The Teukolsky formalism of black hole perturbation theory describes weak gravitational radiation generated by a mildly dynamical hole near equilibrium. A particular null tetrad of the background Kerr geometry, due to Kinnersley, plays a singularly important role within this formalism. In order to apply the rich physical intuition of Teukolsky's approach to the results of fully non-linear numerical simulations, one must approximate this Kinnersley tetrad using raw numerical data, with no a priori knowledge of a background. This paper addresses this issue by identifying the directions of the tetrad fields in a quasi-Kinnersley frame. This frame provides a unique, analytic extension of Kinnersley's definition for the Kerr geometry to a much broader class of space-times including not only arbitrary perturbations, but also many examples which differ non-perturbatively from Kerr. This paper establishes concrete limits delineating this class and outlines a scheme to calculate the quasi-Kinnersley frame in numerical codes based on the initial-value formulation of geometrodynamics. |
1710.07109 | Oldrich Semerak | P. \v{C}\'i\v{z}ek, O. Semer\'ak | Perturbation of a Schwarzschild black hole due to a rotating thin disc | 24 pages, 4 figures, 2 tables | Phys. Rev. D 97, 084006 (2018) | 10.3847/1538-4365/aa876b | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Will (1974) treated the perturbation of a Schwarzschild black hole due to a
slowly rotating light concentric thin ring by solving the perturbation
equations in terms of a multipole expansion of the mass-and-rotation
perturbation series. In the Schwarzschild background, his approach can be
generalized to the perturbation by a thin disc (which is more relevant
astrophysically), but, due to a rather bad convergence properties, the
resulting expansions are not suitable for specific (numerical) computations.
However, we show that Green's functions represented by the Will's result can be
expressed in a closed form (without multipole expansion) which is more useful.
In particular, they can be integrated out over the source (thin disc in our
case), to yield well converging series both for the gravitational potential and
for the dragging angular velocity. The procedure is demonstrated, in the first
perturbation order, on the simplest case of a constant-density disc, including
physical interpretation of the results in terms of a one-component perfect
fluid or a two-component dust on circular orbits about the central black hole.
Free parameters are chosen in such a way that the resulting black hole has zero
angular momentum but non-zero angular velocity, being just carried along by the
dragging effect of the disc.
| [
{
"created": "Thu, 19 Oct 2017 12:07:29 GMT",
"version": "v1"
}
] | 2018-04-18 | [
[
"Čížek",
"P.",
""
],
[
"Semerák",
"O.",
""
]
] | Will (1974) treated the perturbation of a Schwarzschild black hole due to a slowly rotating light concentric thin ring by solving the perturbation equations in terms of a multipole expansion of the mass-and-rotation perturbation series. In the Schwarzschild background, his approach can be generalized to the perturbation by a thin disc (which is more relevant astrophysically), but, due to a rather bad convergence properties, the resulting expansions are not suitable for specific (numerical) computations. However, we show that Green's functions represented by the Will's result can be expressed in a closed form (without multipole expansion) which is more useful. In particular, they can be integrated out over the source (thin disc in our case), to yield well converging series both for the gravitational potential and for the dragging angular velocity. The procedure is demonstrated, in the first perturbation order, on the simplest case of a constant-density disc, including physical interpretation of the results in terms of a one-component perfect fluid or a two-component dust on circular orbits about the central black hole. Free parameters are chosen in such a way that the resulting black hole has zero angular momentum but non-zero angular velocity, being just carried along by the dragging effect of the disc. |
gr-qc/0412069 | Fernando C. Lombardo | Fernando C. Lombardo | Influence functional approach to decoherence during Inflation | 6 pages, no figures. Contributed talk to the Second International
Workshop DICE2004, Piombino, Italy | Braz.J.Phys. 35 (2005) 391-396 | 10.1590/S0103-97332005000300005 | null | gr-qc | null | We show how the quantum to classical transition of the cosmological
fluctuations produced during inflation can be described by means of the
influence functional and the master equation. We split the inflaton field into
the system-field (long-wavelength modes), and the environment, represented by
its own short-wavelength modes. We compute the decoherence times for the
system-field modes and compare them with the other time scales of the model.
| [
{
"created": "Wed, 15 Dec 2004 15:49:47 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Lombardo",
"Fernando C.",
""
]
] | We show how the quantum to classical transition of the cosmological fluctuations produced during inflation can be described by means of the influence functional and the master equation. We split the inflaton field into the system-field (long-wavelength modes), and the environment, represented by its own short-wavelength modes. We compute the decoherence times for the system-field modes and compare them with the other time scales of the model. |
2306.15355 | Edgar Gasperin | Edgar Gasperin | Polyhomogeneous spin-0 fields in Minkowski spacetime | 17 pages, submitted to Philosophical Transactions A (At the interface
of asymptotics, conformal methods and analysis in general relativity) | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The asymptotic behaviour of massless spin-0 fields close to spatial and null
infinity in Minkowski spacetime is studied by means of Friedrich's cylinder at
spatial infinity. The results are applied to a system of equations called the
good-bad-ugly which serves as a model for the Einstein field equations in
generalised harmonic gauge. The relation between the logarithmic terms
(polyhomogeneity) appearing in the solution obtained using conformal methods
and those obtained by means of a heuristic method based on H\"ormander's
asymptotic system is discussed. This review article is based on Class. Quantum
Grav. 40 055002 and arXiv:2304.11950.
| [
{
"created": "Tue, 27 Jun 2023 10:10:31 GMT",
"version": "v1"
}
] | 2023-06-28 | [
[
"Gasperin",
"Edgar",
""
]
] | The asymptotic behaviour of massless spin-0 fields close to spatial and null infinity in Minkowski spacetime is studied by means of Friedrich's cylinder at spatial infinity. The results are applied to a system of equations called the good-bad-ugly which serves as a model for the Einstein field equations in generalised harmonic gauge. The relation between the logarithmic terms (polyhomogeneity) appearing in the solution obtained using conformal methods and those obtained by means of a heuristic method based on H\"ormander's asymptotic system is discussed. This review article is based on Class. Quantum Grav. 40 055002 and arXiv:2304.11950. |
2209.11184 | Miguel S\'anchez | Miguel S\'anchez | A class of cosmological models with spatially constant sign-changing
curvature | Revised version with some improvements, including an Appendix, two
new references and the simplification of the end of the proof of Th. 4.9. 20
pages, 2 figures. To appear in Portugaliae Matematica | Portugaliae Mathematica. Vol. 80, No. 3/4 (2023) 291-313 | null | null | gr-qc astro-ph.CO math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct globally hyperbolic spacetimes such that each slice $\{t=t_0\}$
of the universal time $t$ is a model space of constant curvature $k(t_0)$ which
may not only vary with $t_0\in\mathbb{R}$ but also change its sign. The metric
is smooth and slightly different to FLRW spacetimes, namely, $g=-dt^2+dr^2+
S_{k(t)}^2(r) g_{\mathbb{S}^{n-1}}$, where $g_{\mathbb{S}^{n-1}}$ is the metric
of the standard sphere, $S_{k(t)}(r)=\sin(\sqrt{k(t)}\, r)/\sqrt{k(t)}$ when
$k(t)\geq 0$ and $S_{k(t)}(r)=\sinh(\sqrt{-k(t)}\, r)/\sqrt{-k(t)}$ when
$k(t)\leq 0$. In the open case, the $t$-slices are (non-compact) Cauchy
hypersurfaces of curvature $k(t)\leq 0$, thus homeomorphic to $\mathbb{R}^n$; a
typical example is $k(t)=-t^2$ (i.e., $S_{k(t)}(r)=\sinh(tr)/t$). In the closed
case, $k(t)>0$ somewhere, a slight extension of the class shows how the
topology of the $t$-slices changes. This makes at least one comoving observer
to disappear in finite time $t$ showing some similarities with an inflationary
expansion. Anyway, the spacetime is foliated by Cauchy hypersurfaces
homeomorphic to spheres, not all of them $t$-slices.
| [
{
"created": "Tue, 20 Sep 2022 16:51:19 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Oct 2022 19:49:48 GMT",
"version": "v2"
},
{
"created": "Thu, 9 Feb 2023 13:35:43 GMT",
"version": "v3"
}
] | 2023-10-09 | [
[
"Sánchez",
"Miguel",
""
]
] | We construct globally hyperbolic spacetimes such that each slice $\{t=t_0\}$ of the universal time $t$ is a model space of constant curvature $k(t_0)$ which may not only vary with $t_0\in\mathbb{R}$ but also change its sign. The metric is smooth and slightly different to FLRW spacetimes, namely, $g=-dt^2+dr^2+ S_{k(t)}^2(r) g_{\mathbb{S}^{n-1}}$, where $g_{\mathbb{S}^{n-1}}$ is the metric of the standard sphere, $S_{k(t)}(r)=\sin(\sqrt{k(t)}\, r)/\sqrt{k(t)}$ when $k(t)\geq 0$ and $S_{k(t)}(r)=\sinh(\sqrt{-k(t)}\, r)/\sqrt{-k(t)}$ when $k(t)\leq 0$. In the open case, the $t$-slices are (non-compact) Cauchy hypersurfaces of curvature $k(t)\leq 0$, thus homeomorphic to $\mathbb{R}^n$; a typical example is $k(t)=-t^2$ (i.e., $S_{k(t)}(r)=\sinh(tr)/t$). In the closed case, $k(t)>0$ somewhere, a slight extension of the class shows how the topology of the $t$-slices changes. This makes at least one comoving observer to disappear in finite time $t$ showing some similarities with an inflationary expansion. Anyway, the spacetime is foliated by Cauchy hypersurfaces homeomorphic to spheres, not all of them $t$-slices. |
1212.0837 | William East | William E. East, Sean T. McWilliams, Janna Levin, Frans Pretorius | Observing complete gravitational wave signals from dynamical capture
binaries | 18 pages, 18 figures; revised to match accepted version, PRD in press | Phys. Rev. D 87, 043004 (2013) | 10.1103/PhysRevD.87.043004 | null | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We assess the detectability of the gravitational wave signals from highly
eccentric compact binaries. We use a simple model for the inspiral, merger, and
ringdown of these systems. The model is based on mapping the binary to an
effective single black hole system described by a Kerr metric, thereby
including certain relativistic effects such as zoom-whirl-type behavior. The
resultant geodesics source quadrupolar radiation and, in turn, are evolved
under its dissipative effects. At the light ring, we attach a merger model that
was previously developed for quasicircular mergers but also performs well for
eccentric mergers with little modification. We apply this model to determine
the detectability of these sources for initial, Enhanced, and Advanced LIGO
across the parameter space of nonspinning close capture compact binaries. We
conclude that, should these systems exist in nature, the vast majority will be
missed by conventional burst searches or by quasicircular waveform templates in
the advanced detector era. Other methods, such as eccentric templates or, more
practically, a stacked excess power search, must be developed to avoid losing
these sources. These systems would also have been missed frequently in the
initial LIGO data analysis. Thus, previous null coincidence results with
detected gamma-ray bursts cannot exclude the possibility of coincident
gravitational wave signals from eccentric binaries.
| [
{
"created": "Tue, 4 Dec 2012 19:43:56 GMT",
"version": "v1"
},
{
"created": "Mon, 11 Feb 2013 21:00:01 GMT",
"version": "v2"
}
] | 2013-02-14 | [
[
"East",
"William E.",
""
],
[
"McWilliams",
"Sean T.",
""
],
[
"Levin",
"Janna",
""
],
[
"Pretorius",
"Frans",
""
]
] | We assess the detectability of the gravitational wave signals from highly eccentric compact binaries. We use a simple model for the inspiral, merger, and ringdown of these systems. The model is based on mapping the binary to an effective single black hole system described by a Kerr metric, thereby including certain relativistic effects such as zoom-whirl-type behavior. The resultant geodesics source quadrupolar radiation and, in turn, are evolved under its dissipative effects. At the light ring, we attach a merger model that was previously developed for quasicircular mergers but also performs well for eccentric mergers with little modification. We apply this model to determine the detectability of these sources for initial, Enhanced, and Advanced LIGO across the parameter space of nonspinning close capture compact binaries. We conclude that, should these systems exist in nature, the vast majority will be missed by conventional burst searches or by quasicircular waveform templates in the advanced detector era. Other methods, such as eccentric templates or, more practically, a stacked excess power search, must be developed to avoid losing these sources. These systems would also have been missed frequently in the initial LIGO data analysis. Thus, previous null coincidence results with detected gamma-ray bursts cannot exclude the possibility of coincident gravitational wave signals from eccentric binaries. |
1904.04471 | Ben David Normann Mr. | Ben David Normann and Chris Clarkson | Recursion relations for gravitational lensing | 18 pages, 1 figure | General Relativity and Gravitation 52 (2020), 3 | 10.1007/s10714-020-02677-z | null | gr-qc astro-ph.CO astro-ph.GA hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The weak gravitational lensing formalism can be extended to the strong
lensing regime by integrating a nonlinear version of the geodesic deviation
equation. The resulting "roulette" expansion generalises the notion of
convergence, shear and flexion to arbitrary order. The independent coefficients
of this expansion are screen space gradients of the optical tidal tensor which
approximates to the usual lensing potential in the weak field limit. From
lensed images, knowledge of the roulette coefficients can in principle be
inverted to reconstruct the mass distribution of a lens. In this paper, we
simplify the roulette expansion and derive a family of recursion relations
between the various coefficients, generalising the Kaiser-Squires relations
beyond the weak-lensing regime.
| [
{
"created": "Tue, 9 Apr 2019 05:35:36 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Oct 2019 06:31:38 GMT",
"version": "v2"
},
{
"created": "Tue, 31 Mar 2020 08:42:04 GMT",
"version": "v3"
}
] | 2020-04-01 | [
[
"Normann",
"Ben David",
""
],
[
"Clarkson",
"Chris",
""
]
] | The weak gravitational lensing formalism can be extended to the strong lensing regime by integrating a nonlinear version of the geodesic deviation equation. The resulting "roulette" expansion generalises the notion of convergence, shear and flexion to arbitrary order. The independent coefficients of this expansion are screen space gradients of the optical tidal tensor which approximates to the usual lensing potential in the weak field limit. From lensed images, knowledge of the roulette coefficients can in principle be inverted to reconstruct the mass distribution of a lens. In this paper, we simplify the roulette expansion and derive a family of recursion relations between the various coefficients, generalising the Kaiser-Squires relations beyond the weak-lensing regime. |
gr-qc/0407010 | Laszlo A. Gergely | L\'aszl\'o \'A. Gergely | No Swiss-cheese universe on the brane | v2: slightly expanded; references added; version to appear Phys. Rev.
D, v3: corrected cf. erratum published in Phys. Rev. D | Phys.Rev.D71:084017,2005; Erratum-ibid.D72:069902,2005 | 10.1103/PhysRevD.71.084017 10.1103/PhysRevD.72.069902 | null | gr-qc | null | We study the possibility of brane-world generalization of the Einstein-Straus
Swiss-cheese cosmological model. We find the modifications induced by the
brane-world scenario. At a first glance only the motion of the boundary is
modified and the fluid in the exterior region is allowed to have pressure. The
general relativistic Einstein-Straus model emerges in the low density limit. By
imposing that the brane is static, a combination of the junction conditions and
modified cosmological evolution leads to the conclusion that the brane is flat.
Thus no static Swiss-cheese universe can exist on the brane. The conclusion is
not altered by the introduction of a cosmological constant in the FLRW regions.
This result mimics a similar general relativistic result: static
Einstein-Straus universes do not exist.
| [
{
"created": "Fri, 2 Jul 2004 13:00:40 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Mar 2005 16:32:29 GMT",
"version": "v2"
},
{
"created": "Thu, 22 Feb 2007 15:08:20 GMT",
"version": "v3"
}
] | 2014-11-17 | [
[
"Gergely",
"László Á.",
""
]
] | We study the possibility of brane-world generalization of the Einstein-Straus Swiss-cheese cosmological model. We find the modifications induced by the brane-world scenario. At a first glance only the motion of the boundary is modified and the fluid in the exterior region is allowed to have pressure. The general relativistic Einstein-Straus model emerges in the low density limit. By imposing that the brane is static, a combination of the junction conditions and modified cosmological evolution leads to the conclusion that the brane is flat. Thus no static Swiss-cheese universe can exist on the brane. The conclusion is not altered by the introduction of a cosmological constant in the FLRW regions. This result mimics a similar general relativistic result: static Einstein-Straus universes do not exist. |
gr-qc/0702103 | Hamid Reza Sepangi | F. Ahmadi, S. Jalalzadeh and H. R. Sepangi | Lorentz violation and the speed of gravitational waves in brane-worlds | 8 pages, to appear in PLB | Phys.Lett.B647:486-492,2007 | 10.1016/j.physletb.2007.02.032 | null | gr-qc hep-th | null | Lorentz violation in a brane-world scenario is presented and used to obtain a
relationship between the speed of gravitational waves in the bulk and that on
the brane. Lorentz violating effects would manifest themselves in gravitational
waves travelling with a greater speed in the bulk than on the brane and this
effect is independent of the signature of the extra dimension.
| [
{
"created": "Mon, 19 Feb 2007 11:26:14 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Ahmadi",
"F.",
""
],
[
"Jalalzadeh",
"S.",
""
],
[
"Sepangi",
"H. R.",
""
]
] | Lorentz violation in a brane-world scenario is presented and used to obtain a relationship between the speed of gravitational waves in the bulk and that on the brane. Lorentz violating effects would manifest themselves in gravitational waves travelling with a greater speed in the bulk than on the brane and this effect is independent of the signature of the extra dimension. |
gr-qc/9906088 | Pedro Marronetti | P. Marronetti, G.J. Mathews, J.R. Wilson | Irrotational binary neutron stars in quasiequilibrium | 4 pages, 2 figures, revtex, accepted for publication in Phys. Rev. D | Phys.Rev. D60 (1999) 087301 | 10.1103/PhysRevD.60.087301 | null | gr-qc | null | We report on numerical results from an independent formalism to describe the
quasi-equilibrium structure of nonsynchronous binary neutron stars in general
relativity. This is an important independent test of controversial numerical
hydrodynamic simulations which suggested that nonsynchronous neutron stars in a
close binary can experience compression prior to the last stable circular
orbit. We show that, for compact enough stars the interior density increases
slightly as irrotational binary neutron stars approach their last orbits. The
magnitude of the effect, however, is much smaller than that reported in
previous hydrodynamic simulations.
| [
{
"created": "Mon, 21 Jun 1999 23:01:50 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Marronetti",
"P.",
""
],
[
"Mathews",
"G. J.",
""
],
[
"Wilson",
"J. R.",
""
]
] | We report on numerical results from an independent formalism to describe the quasi-equilibrium structure of nonsynchronous binary neutron stars in general relativity. This is an important independent test of controversial numerical hydrodynamic simulations which suggested that nonsynchronous neutron stars in a close binary can experience compression prior to the last stable circular orbit. We show that, for compact enough stars the interior density increases slightly as irrotational binary neutron stars approach their last orbits. The magnitude of the effect, however, is much smaller than that reported in previous hydrodynamic simulations. |
1501.04702 | Yongwan Gim | Yongwan Gim and Wontae Kim | Black Hole Complementarity in Gravity's Rainbow | 13 pages, 2 figures added and many improvements, version to appear in
JCAP | JCAP, 05 (2015) 002 | 10.1088/1475-7516/2015/05/002 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | To see how the gravity's rainbow works for black hole complementary, we
evaluate the required energy for duplication of information in the context of
black hole complementarity by calculating the critical value of the rainbow
parameter in the certain class of the rainbow Schwarzschild black hole. The
resultant energy can be written as the well-defined limit for the vanishing
rainbow parameter which characterizes the deformation of the relativistic
dispersion relation in the freely falling frame. It shows that the duplication
of information in quantum mechanics could not be allowed below a certain
critical value of the rainbow parameter; however, it might be possible above
the critical value of the rainbow parameter, so that the consistent formulation
in our model requires additional constraints or any other resolutions for the
latter case.
| [
{
"created": "Tue, 20 Jan 2015 03:01:39 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Apr 2015 07:39:43 GMT",
"version": "v2"
},
{
"created": "Wed, 6 May 2015 01:29:36 GMT",
"version": "v3"
}
] | 2015-05-07 | [
[
"Gim",
"Yongwan",
""
],
[
"Kim",
"Wontae",
""
]
] | To see how the gravity's rainbow works for black hole complementary, we evaluate the required energy for duplication of information in the context of black hole complementarity by calculating the critical value of the rainbow parameter in the certain class of the rainbow Schwarzschild black hole. The resultant energy can be written as the well-defined limit for the vanishing rainbow parameter which characterizes the deformation of the relativistic dispersion relation in the freely falling frame. It shows that the duplication of information in quantum mechanics could not be allowed below a certain critical value of the rainbow parameter; however, it might be possible above the critical value of the rainbow parameter, so that the consistent formulation in our model requires additional constraints or any other resolutions for the latter case. |
gr-qc/0008014 | Yuri N. Obukhov | Yuri N. Obukhov | On a model of an unconstrained hyperfluid | Revtex, 10 pages, no figures | Phys.Lett. A210 (1996) 163-167 | 10.1016/S0375-9601(96)80004-1 | null | gr-qc | null | A hyperfluid is a classical continuous medium carrying hypermomentum. We
modify the earlier developed variational approach to a hyperfluid in such a way
that the Frenkel type constraints imposed on the hypermomentum current are
eliminated. The resulting self-consistent model is different from the
Weyssenhoff type one. The essential point is a conservation of the
hypermomentum current such that the final metrical and canonical
energy-momentum forms coincide.
| [
{
"created": "Mon, 7 Aug 2000 14:14:54 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Obukhov",
"Yuri N.",
""
]
] | A hyperfluid is a classical continuous medium carrying hypermomentum. We modify the earlier developed variational approach to a hyperfluid in such a way that the Frenkel type constraints imposed on the hypermomentum current are eliminated. The resulting self-consistent model is different from the Weyssenhoff type one. The essential point is a conservation of the hypermomentum current such that the final metrical and canonical energy-momentum forms coincide. |
2201.05827 | Joan Sola | Cristian Moreno-Pulido and Joan Sola Peracaula | Renormalizing the vacuum energy in cosmological spacetime: implications
for the cosmological constant problem | Typos corrected, references added | Eur. Phys. J. C82, 551 (2022) | 10.1140/epjc/s10052-022-10484-w | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The renormalization of the vacuum energy in quantum field theory (QFT) is
usually plagued with theoretical conundrums related not only with the
renormalization procedure itself, but also with the fact that the final result
leads usually to very large (finite) contributions incompatible with the
measured value of $\Lambda$ in cosmology. Herein, we compute the zero-point
energy (ZPE) for a nonminimally coupled (massive) scalar field in FLRW
spacetime using the off-shell adiabatic renormalization technique employed in
previous work. The general off-shell result yields a smooth function $\rho_{\rm
vac}(H)$ made out of powers of the Hubble rate and/or of its time derivatives
involving different (even) adiabatic orders $\sim H^N$ ($N=0,2,4,6,...)$, i.e.
it leads, remarkably enough, to the running vacuum model (RVM) structure. We
have verified the same result from the effective action formalism and used it
to find the $\beta$-function of the running quantum vacuum. No undesired
contributions $\sim m^4$ from particle masses appear and hence no fine-tuning
of the parameters is needed in $\rho_{\rm vac}(H)$. Furthermore, we find that
the higher power $\sim H^6$ could naturally drive RVM-inflation in the early
universe. Our calculation also elucidates in detail the equation of state of
the quantum vacuum: it proves to be not exactly $-1$ and is moderately
dynamical. The form of $\rho_{\rm vac}(H)$ at low energies is also
characteristic of the RVM and consists of an additive term (the so-called
`cosmological constant') together with a small dynamical component $\sim \nu
H^2$ ($|\nu|\ll1$). Finally, we predict a slow ($\sim\ln H$) running of
Newton's gravitational coupling $G(H)$. The physical outcome of our
semiclassical QFT calculation is revealing: today's cosmic vacuum and the
gravitational strength should be both mildly dynamical.
| [
{
"created": "Sat, 15 Jan 2022 11:00:43 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Jan 2022 18:56:10 GMT",
"version": "v2"
},
{
"created": "Thu, 3 Feb 2022 18:57:21 GMT",
"version": "v3"
},
{
"created": "Sun, 29 May 2022 11:36:29 GMT",
"version": "v4"
},
{
"cr... | 2023-03-21 | [
[
"Moreno-Pulido",
"Cristian",
""
],
[
"Peracaula",
"Joan Sola",
""
]
] | The renormalization of the vacuum energy in quantum field theory (QFT) is usually plagued with theoretical conundrums related not only with the renormalization procedure itself, but also with the fact that the final result leads usually to very large (finite) contributions incompatible with the measured value of $\Lambda$ in cosmology. Herein, we compute the zero-point energy (ZPE) for a nonminimally coupled (massive) scalar field in FLRW spacetime using the off-shell adiabatic renormalization technique employed in previous work. The general off-shell result yields a smooth function $\rho_{\rm vac}(H)$ made out of powers of the Hubble rate and/or of its time derivatives involving different (even) adiabatic orders $\sim H^N$ ($N=0,2,4,6,...)$, i.e. it leads, remarkably enough, to the running vacuum model (RVM) structure. We have verified the same result from the effective action formalism and used it to find the $\beta$-function of the running quantum vacuum. No undesired contributions $\sim m^4$ from particle masses appear and hence no fine-tuning of the parameters is needed in $\rho_{\rm vac}(H)$. Furthermore, we find that the higher power $\sim H^6$ could naturally drive RVM-inflation in the early universe. Our calculation also elucidates in detail the equation of state of the quantum vacuum: it proves to be not exactly $-1$ and is moderately dynamical. The form of $\rho_{\rm vac}(H)$ at low energies is also characteristic of the RVM and consists of an additive term (the so-called `cosmological constant') together with a small dynamical component $\sim \nu H^2$ ($|\nu|\ll1$). Finally, we predict a slow ($\sim\ln H$) running of Newton's gravitational coupling $G(H)$. The physical outcome of our semiclassical QFT calculation is revealing: today's cosmic vacuum and the gravitational strength should be both mildly dynamical. |
2008.01813 | Vyacheslav Dokuchaev | V. A. Berezin, V. I. Dokuchaev, Yu. N. Eroshenko, A. L. Smirnov | Double layer from least action principle | 15 pages, minor proofs, submitted to CQG | 2021 Class. Quantum Grav. 38 045014 | 10.1088/1361-6382/abd143 | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derived the equations for the double layers in Quadratic Gravity, using
solely the least action principle. The advantage of our approach is that, in
the process of calculation, the $\delta'$-function does not appear at all, and
the $\delta$-functions appear for a moment and are mutually canceled prior to
integration. We revealed the peculiar structure of the obtained equations,
namely, that the surface energy-momentum tensor of the matter fields
(constituents of the thin shells) does not play a role in the determination of
the trajectory of the double layer. Also, we suggested that the space-like
double layers may provide us with the adequate description of the creation of
the universe from the black hole singularity. The related topics, including the
Gauss-Bonnet term and $F(R)$-theories, are shortly discussed.
| [
{
"created": "Tue, 4 Aug 2020 20:19:50 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Jan 2021 10:32:05 GMT",
"version": "v2"
}
] | 2021-01-07 | [
[
"Berezin",
"V. A.",
""
],
[
"Dokuchaev",
"V. I.",
""
],
[
"Eroshenko",
"Yu. N.",
""
],
[
"Smirnov",
"A. L.",
""
]
] | We derived the equations for the double layers in Quadratic Gravity, using solely the least action principle. The advantage of our approach is that, in the process of calculation, the $\delta'$-function does not appear at all, and the $\delta$-functions appear for a moment and are mutually canceled prior to integration. We revealed the peculiar structure of the obtained equations, namely, that the surface energy-momentum tensor of the matter fields (constituents of the thin shells) does not play a role in the determination of the trajectory of the double layer. Also, we suggested that the space-like double layers may provide us with the adequate description of the creation of the universe from the black hole singularity. The related topics, including the Gauss-Bonnet term and $F(R)$-theories, are shortly discussed. |
gr-qc/0703035 | Eric Gourgoulhon | Eric Gourgoulhon (LUTH, CNRS / Observatoire de Paris) | 3+1 Formalism and Bases of Numerical Relativity | Lectures given at the General Relativity Trimester held in the
Institut Henri Poincare (Paris, Sept.-Dec. 2006) and at the VII Mexican
School on Gravitation and Mathematical Physics (Playa del Carmen, Mexico, 26.
Nov. - 2 Dec. 2006), 220 pages, 25 figures. Corrections and suggestions are
welcome | null | null | null | gr-qc astro-ph math.DG | null | These lecture notes provide some introduction to the 3+1 formalism of general
relativity, which is the foundation of most modern numerical relativity. The
text is rather self-contained, with detailed calculations and numerous
examples. Contents: 1. Introduction, 2. Geometry of hypersurfaces, 3. Geometry
of foliations, 4. 3+1 decomposition of Einstein equation, 5. 3+1 equations for
matter and electromagnetic field, 6. Conformal decomposition, 7. Asymptotic
flatness and global quantities, 8. The initial data problem, 9. Choice of
foliation and spatial coordinates, 10. Evolution schemes.
| [
{
"created": "Tue, 6 Mar 2007 13:19:45 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Gourgoulhon",
"Eric",
"",
"LUTH, CNRS / Observatoire de Paris"
]
] | These lecture notes provide some introduction to the 3+1 formalism of general relativity, which is the foundation of most modern numerical relativity. The text is rather self-contained, with detailed calculations and numerous examples. Contents: 1. Introduction, 2. Geometry of hypersurfaces, 3. Geometry of foliations, 4. 3+1 decomposition of Einstein equation, 5. 3+1 equations for matter and electromagnetic field, 6. Conformal decomposition, 7. Asymptotic flatness and global quantities, 8. The initial data problem, 9. Choice of foliation and spatial coordinates, 10. Evolution schemes. |
gr-qc/9608039 | Youngjai Kiem | Dae Sung Hwang, Youngjai Kiem (Sejong Univ.), Dahl Park (KAIST) | Particle dynamics in a class of 2-dimensional gravity theories | 15 pages, LaTeX. The deletion of the repeated portion of the abstract
and the proper line wrapping of the tex file. No other changes | Phys.Rev.D54:4879-4885,1996 | 10.1103/PhysRevD.54.4879 | KAIST-CHEP-95/18 | gr-qc | null | We provide a method to determine the motion of a classical massive particle
in a background geometry of 2-dimensional gravity theories, for which the
Birkhoff theorem holds. In particular, we get the particle trajectory in a
continuous class of 2-dimensional dilaton gravity theories that includes the
Callan-Giddings-Harvey-Strominger (CGHS) model, the Jackiw-Teitelboim (JT)
model, and the $d$-dimensional $s$-wave Einstein gravity. The explicit
trajectory expressions for these theories are given along with the discussions
on the results.
| [
{
"created": "Fri, 16 Aug 1996 17:28:52 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Aug 1996 03:43:20 GMT",
"version": "v2"
}
] | 2011-09-09 | [
[
"Hwang",
"Dae Sung",
"",
"Sejong Univ."
],
[
"Kiem",
"Youngjai",
"",
"Sejong Univ."
],
[
"Park",
"Dahl",
"",
"KAIST"
]
] | We provide a method to determine the motion of a classical massive particle in a background geometry of 2-dimensional gravity theories, for which the Birkhoff theorem holds. In particular, we get the particle trajectory in a continuous class of 2-dimensional dilaton gravity theories that includes the Callan-Giddings-Harvey-Strominger (CGHS) model, the Jackiw-Teitelboim (JT) model, and the $d$-dimensional $s$-wave Einstein gravity. The explicit trajectory expressions for these theories are given along with the discussions on the results. |
2404.08185 | Muhammad Zeeshan Mr | Muhammad Zeeshan, Richard O'Shaughnessy | Eccentricity matters: Impact of eccentricity on inferred binary black
hole populations | null | null | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | Gravitational waves (GW), emanating from binary black holes (BBH), encode
vital information about their source. GW signals enable us to deduce key
properties of the BBH population across the universe, including mass, spin, and
eccentricity distribution. While the masses and spins of binary components are
already recognized for their insights into formation, eccentricity stands out
as a distinct and quantifiable indicator of formation and evolution. Yet,
despite its significance, eccentricity is notably absent from most parameter
estimation (PE) analyses associated with GW signals. To evaluate the precision
with which the eccentricity distribution can be deduced, we generated two
synthetic populations of eccentric binary black holes (EBBH) characterized by
non-spinning, non-precessing dynamics and mass ranges between $10 M_\odot$ and
$50 M_\odot$. This was achieved using an eccentric power law model,
encompassing $100$ events with eccentricity distributions set at
$\sigma_\epsilon = 0.05$ and $\sigma_\epsilon = 0.15$. This synthetic EBBH
ensemble was contrasted against a circular binary black holes (CBBH) collection
to discern how parameter inferences would vary without eccentricity. Employing
Markov Chain Monte Carlo (MCMC) techniques, we constrained vital model
parameters, including the event rate ($\mathcal{R}$), mass distribution,
minimum mass ($m_{min}$), maximum mass ($m_{max}$), and the eccentricity
distribution ($\sigma_\epsilon$). Our analysis demonstrates that eccentric
population inference can identify the signatures of even modest eccentricities,
given sufficiently many events. Conversely, our study shows that an analysis
neglecting eccentricity may draw biased conclusions about population parameters
for populations with the optimistic values of eccentricity distribution used in
our research.
| [
{
"created": "Fri, 12 Apr 2024 01:28:43 GMT",
"version": "v1"
}
] | 2024-04-15 | [
[
"Zeeshan",
"Muhammad",
""
],
[
"O'Shaughnessy",
"Richard",
""
]
] | Gravitational waves (GW), emanating from binary black holes (BBH), encode vital information about their source. GW signals enable us to deduce key properties of the BBH population across the universe, including mass, spin, and eccentricity distribution. While the masses and spins of binary components are already recognized for their insights into formation, eccentricity stands out as a distinct and quantifiable indicator of formation and evolution. Yet, despite its significance, eccentricity is notably absent from most parameter estimation (PE) analyses associated with GW signals. To evaluate the precision with which the eccentricity distribution can be deduced, we generated two synthetic populations of eccentric binary black holes (EBBH) characterized by non-spinning, non-precessing dynamics and mass ranges between $10 M_\odot$ and $50 M_\odot$. This was achieved using an eccentric power law model, encompassing $100$ events with eccentricity distributions set at $\sigma_\epsilon = 0.05$ and $\sigma_\epsilon = 0.15$. This synthetic EBBH ensemble was contrasted against a circular binary black holes (CBBH) collection to discern how parameter inferences would vary without eccentricity. Employing Markov Chain Monte Carlo (MCMC) techniques, we constrained vital model parameters, including the event rate ($\mathcal{R}$), mass distribution, minimum mass ($m_{min}$), maximum mass ($m_{max}$), and the eccentricity distribution ($\sigma_\epsilon$). Our analysis demonstrates that eccentric population inference can identify the signatures of even modest eccentricities, given sufficiently many events. Conversely, our study shows that an analysis neglecting eccentricity may draw biased conclusions about population parameters for populations with the optimistic values of eccentricity distribution used in our research. |
2312.04451 | Vladim\'ir Balek | Vladim\'ir Balek, Barbora Bezd\v{e}kov\'a, Ji\v{r}\'i Bi\v{c}\'ak | Radiation in the black hole - plasma system: propagation in equatorial
plane | 33 pages, 5 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Effect of cold plasma on the form of rays propagating in the equatorial plane
of a rotating black hole is investigated. Two kinds of regions in the
radius-impact parameter plane allowed for the rays are constructed: for
radiation with a given frequency at infinity and for radiation with a given
``telescope frequency'' seen by a local observer. The form of allowed regions
for locally nonrotating observers as well as observers falling freely from
infinity is established. The allowed regions contain rays which directly reach
the horizon, or there exists a ``neck'' connecting the forbidden regions such
that the rays coming from infinity cannot reach the horizon. In case we
considered a set of observers at various radii instead of the neck we find two
different regions -- from one the rays reach the horizon and not infinity and
from the other one they reach infinity, but not the horizon. The results are
analyzed by analytical methods and illustrated by figures constructed
numerically.
| [
{
"created": "Thu, 7 Dec 2023 17:19:56 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Dec 2023 15:42:46 GMT",
"version": "v2"
}
] | 2023-12-20 | [
[
"Balek",
"Vladimír",
""
],
[
"Bezděková",
"Barbora",
""
],
[
"Bičák",
"Jiří",
""
]
] | Effect of cold plasma on the form of rays propagating in the equatorial plane of a rotating black hole is investigated. Two kinds of regions in the radius-impact parameter plane allowed for the rays are constructed: for radiation with a given frequency at infinity and for radiation with a given ``telescope frequency'' seen by a local observer. The form of allowed regions for locally nonrotating observers as well as observers falling freely from infinity is established. The allowed regions contain rays which directly reach the horizon, or there exists a ``neck'' connecting the forbidden regions such that the rays coming from infinity cannot reach the horizon. In case we considered a set of observers at various radii instead of the neck we find two different regions -- from one the rays reach the horizon and not infinity and from the other one they reach infinity, but not the horizon. The results are analyzed by analytical methods and illustrated by figures constructed numerically. |
1510.03058 | Andrea Fuster | Andrea Fuster and Cornelia Pabst | Finsler pp-waves | 10 pages, minor corrections, references added | Phys. Rev. D 94, 104072 (2016) | 10.1103/PhysRevD.94.104072 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we present a Finslerian version of the well-known pp-waves,
which generalizes the very special relativity (VSR) line element. Our Finsler
pp-waves are an exact solution of Finslerian Einstein's equations in vacuum.
| [
{
"created": "Sun, 11 Oct 2015 14:36:08 GMT",
"version": "v1"
},
{
"created": "Fri, 20 May 2016 10:15:49 GMT",
"version": "v2"
}
] | 2016-12-07 | [
[
"Fuster",
"Andrea",
""
],
[
"Pabst",
"Cornelia",
""
]
] | In this work we present a Finslerian version of the well-known pp-waves, which generalizes the very special relativity (VSR) line element. Our Finsler pp-waves are an exact solution of Finslerian Einstein's equations in vacuum. |
2301.08032 | Pujian Mao | Pujian Mao, Jun-Bao Wu, Xiaoning Wu | Angular momentum and memory effect | v2: interpretation improved, published version | Phys. Rev. D 107, L101501 (2023) | 10.1103/PhysRevD.107.L101501 | USTC-ICTS/PCFT-23-03 | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | It is a long-standing problem in general relativity that the notion of
angular momentum of an isolated system has supertranslation ambiguity. In this
paper, we argue that the ambiguity is essentially because of the gravitational
wave memory. When properly subtracting the memory effect of the observer, one
can introduce a supertranslation invariant definition of the angular momentum
at null infinity even for dynamical process.
| [
{
"created": "Thu, 19 Jan 2023 12:11:42 GMT",
"version": "v1"
},
{
"created": "Tue, 16 May 2023 00:50:40 GMT",
"version": "v2"
}
] | 2023-05-17 | [
[
"Mao",
"Pujian",
""
],
[
"Wu",
"Jun-Bao",
""
],
[
"Wu",
"Xiaoning",
""
]
] | It is a long-standing problem in general relativity that the notion of angular momentum of an isolated system has supertranslation ambiguity. In this paper, we argue that the ambiguity is essentially because of the gravitational wave memory. When properly subtracting the memory effect of the observer, one can introduce a supertranslation invariant definition of the angular momentum at null infinity even for dynamical process. |
1009.5510 | Tomi Koivisto | Tomi Koivisto, Tomislav Prokopec | Quantum backreaction in evolving FLRW spacetimes | 23 pages, 6 figures | Phys.Rev.D83:044015,2011 | 10.1103/PhysRevD.83.044015 | ITP-UU-10/34, SPIN-10/29 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quantum fluctuations of a nonminimally coupled scalar field in D-dimensional
homogeneous and isotropic background are calculated within the operator
formalism in curved models with time evolutions of the scale factor that allow
smooth transitions between contracting and expanding and between decelerating
and accelerating regimes. The coincident propagator is derived and used to
compute the one-loop backreaction from the scalar field. The inflationary
infrared divergences are absent in Bunch-Davies vacuum when taking into account
a preceding cosmological era or spatial curvature which can be either positive
or negative. It is found that asymptotically, the backreaction energy density
in the minimally coupled case grows logarithmically with the scale factor in
quasi-de Sitter space, and in a class of models decays in slow-roll inflation
and grows as a power-law during super-inflation. The backreaction increases
generically in a contracting phase or in the presence of a negative nonminimal
coupling. The effects of the coupling and renormalization scale upon the
quantum fluctuations together with the novel features due to nontrivial time
evolution and spatial curvature are clarified with exact solutions and
numerical examples.
| [
{
"created": "Tue, 28 Sep 2010 09:57:19 GMT",
"version": "v1"
}
] | 2011-02-18 | [
[
"Koivisto",
"Tomi",
""
],
[
"Prokopec",
"Tomislav",
""
]
] | Quantum fluctuations of a nonminimally coupled scalar field in D-dimensional homogeneous and isotropic background are calculated within the operator formalism in curved models with time evolutions of the scale factor that allow smooth transitions between contracting and expanding and between decelerating and accelerating regimes. The coincident propagator is derived and used to compute the one-loop backreaction from the scalar field. The inflationary infrared divergences are absent in Bunch-Davies vacuum when taking into account a preceding cosmological era or spatial curvature which can be either positive or negative. It is found that asymptotically, the backreaction energy density in the minimally coupled case grows logarithmically with the scale factor in quasi-de Sitter space, and in a class of models decays in slow-roll inflation and grows as a power-law during super-inflation. The backreaction increases generically in a contracting phase or in the presence of a negative nonminimal coupling. The effects of the coupling and renormalization scale upon the quantum fluctuations together with the novel features due to nontrivial time evolution and spatial curvature are clarified with exact solutions and numerical examples. |
1507.06492 | Kevin Ludwick | Kevin J. Ludwick | Examining the Viability of Phantom Dark Energy | 22 pages, 5 figures; emphasized that models with w>-1 can have
negative kinetic energy with perturbations and included a plot showing this | Phys. Rev. D 92, 063019 (2015) | 10.1103/PhysRevD.92.063019 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the standard cosmological framework of the 0th-order FLRW metric and the
use of perfect fluids in the stress-energy tensor, dark energy with an
equation-of-state parameter $w < -1$ (known as phantom dark energy) implies
negative kinetic energy and vacuum instability when modeled as a scalar field.
However, the accepted values for present-day $w$ from Planck and WMAP9 include
a significant range of values less than $-1$. We find that it is not as obvious
as one might think that phantom dark energy has negative kinetic energy
categorically. Analogously, we find that field models of quintessence dark
energy ($w_\phi>-1$) do not necessarily have positive kinetic energy
categorically. Staying within the confines of observational constraints and
general relativity, for which there is good experimental validation, we
consider a few reasonable departures from the standard 0th-order framework in
an attempt to see if negative kinetic energy can be avoided in these settings
despite an apparent $w<-1$. We consider a more accurate description of the
universe through the perturbing of the isotropic and homogeneous FLRW metric
and the components of the stress-energy tensor, and we consider dynamic $w$ and
primordial isocurvature and adiabatic perturbations. We find that phantom dark
energy does not necessarily have negative kinetic energy for all relevant
length scales at all times, and we also find that, by the same token,
quintessence dark energy does not necessarily have positive kinetic energy for
all relevant length scales at all times.
| [
{
"created": "Thu, 23 Jul 2015 13:48:49 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Sep 2015 20:09:29 GMT",
"version": "v2"
}
] | 2015-10-07 | [
[
"Ludwick",
"Kevin J.",
""
]
] | In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter $w < -1$ (known as phantom dark energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the accepted values for present-day $w$ from Planck and WMAP9 include a significant range of values less than $-1$. We find that it is not as obvious as one might think that phantom dark energy has negative kinetic energy categorically. Analogously, we find that field models of quintessence dark energy ($w_\phi>-1$) do not necessarily have positive kinetic energy categorically. Staying within the confines of observational constraints and general relativity, for which there is good experimental validation, we consider a few reasonable departures from the standard 0th-order framework in an attempt to see if negative kinetic energy can be avoided in these settings despite an apparent $w<-1$. We consider a more accurate description of the universe through the perturbing of the isotropic and homogeneous FLRW metric and the components of the stress-energy tensor, and we consider dynamic $w$ and primordial isocurvature and adiabatic perturbations. We find that phantom dark energy does not necessarily have negative kinetic energy for all relevant length scales at all times, and we also find that, by the same token, quintessence dark energy does not necessarily have positive kinetic energy for all relevant length scales at all times. |
1211.1718 | Sebastian Szybka | Piotr T. Chru\'sciel, Christa R. \"Olz, Sebastian J. Szybka | Space-time diagrammatics | 41 pages, minor changes and corrections | Phys.Rev.D86:124041,2012 | 10.1103/PhysRevD.86.124041 | UWThPh-2012-26 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We introduce a new class of two-dimensional diagrams, the \emph{projection
diagrams}, as a tool to visualize the global structure of space-times. We
construct the diagrams for several metrics of interest, including the
Kerr-Newman - (anti) de Sitter family, with or without cosmological constant,
and the Emparan-Reall black rings.
| [
{
"created": "Wed, 7 Nov 2012 22:52:59 GMT",
"version": "v1"
},
{
"created": "Sun, 20 Jan 2013 14:33:54 GMT",
"version": "v2"
}
] | 2013-01-22 | [
[
"Chruściel",
"Piotr T.",
""
],
[
"Ölz",
"Christa R.",
""
],
[
"Szybka",
"Sebastian J.",
""
]
] | We introduce a new class of two-dimensional diagrams, the \emph{projection diagrams}, as a tool to visualize the global structure of space-times. We construct the diagrams for several metrics of interest, including the Kerr-Newman - (anti) de Sitter family, with or without cosmological constant, and the Emparan-Reall black rings. |
2305.01603 | Andreas Wipf | M. Schweizer, N. Straumann, A. Wipf | Post-Newtonian Generation of Gravitational Waves in a Theory of Gravity
with Torsion | Published version: General Relativity and Gravitation, Vol. 12 (1980)
951-961 doi: 10.1007/BF00757366 arXiv-ed February 1980; LaTeX-ed May 1, 2023 | General Relativity and Gravitation, Vol. 12 (1980) 951-961 | 10.1007/BF00757366 | SIN-PR-80-008 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We adapt the post-Newtonian gravitational-radiation methods developed within
general relativity by Epstein and Wagoner to the gravitation theory with
torsion, recently proposed by Hehl et al., and show that the two theories
predict in this approximation the same gravitational radiation losses. Since
they agree also on the first post-Newtonian level, they are at the present time
- observationally - indistinguishable.
| [
{
"created": "Tue, 2 May 2023 17:06:21 GMT",
"version": "v1"
}
] | 2023-05-03 | [
[
"Schweizer",
"M.",
""
],
[
"Straumann",
"N.",
""
],
[
"Wipf",
"A.",
""
]
] | We adapt the post-Newtonian gravitational-radiation methods developed within general relativity by Epstein and Wagoner to the gravitation theory with torsion, recently proposed by Hehl et al., and show that the two theories predict in this approximation the same gravitational radiation losses. Since they agree also on the first post-Newtonian level, they are at the present time - observationally - indistinguishable. |
gr-qc/0309025 | Robert T. Jantzen | Robert T. Jantzen | Higher Dimensional Cosmological Models: the View from Above | 24 latex(2e) article style pages with one EPS figure, from: Proc.
26th Li\`ege Int. Astrophys. Colloq., J. Demaret, ed. (Li\`ege University
Press, Li\`ege, 1987), hard to access proceedings, worth not forgetting | null | null | null | gr-qc | null | A broader perspective is suggested for the study of higher dimensional
cosmological models. [1986: Considerations involving the Einstein constraints
and the Ricci form of the evolution equations for spatially homogeneous
spacetimes in 4 or more dimensions in the Taub time gauge (constant densitized
lapse) are used to show how many of the special exact solutions found at random
fit together into a larger picture in which the Taub spacetime solution plays
an instructive role. Concludes with some remarks on chaos.]
| [
{
"created": "Thu, 4 Sep 2003 14:00:29 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Jantzen",
"Robert T.",
""
]
] | A broader perspective is suggested for the study of higher dimensional cosmological models. [1986: Considerations involving the Einstein constraints and the Ricci form of the evolution equations for spatially homogeneous spacetimes in 4 or more dimensions in the Taub time gauge (constant densitized lapse) are used to show how many of the special exact solutions found at random fit together into a larger picture in which the Taub spacetime solution plays an instructive role. Concludes with some remarks on chaos.] |
gr-qc/0611122 | Sante Carloni | Sante Carloni, Peter K. S. Dunsby | A dynamical system approach to higher order gravity | 6 pages, 1 figure, 2 tables, talk given at IRGAC 2006, July 2006 | J.Phys.A40:6919-6926,2007 | 10.1088/1751-8113/40/25/S40 | null | gr-qc | null | The dynamical system approach has recently acquired great importance in the
investigation on higher order theories of gravity. In this talk I review the
main results and I give brief comments on the perspectives for further
developments.
| [
{
"created": "Thu, 23 Nov 2006 10:45:16 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Carloni",
"Sante",
""
],
[
"Dunsby",
"Peter K. S.",
""
]
] | The dynamical system approach has recently acquired great importance in the investigation on higher order theories of gravity. In this talk I review the main results and I give brief comments on the perspectives for further developments. |
gr-qc/9610061 | Alicia Sintes | A. A. Coley | Kinematic Self-Similarity | 29 pages, AmsTeX | Class.Quant.Grav. 14 (1997) 87-118 | 10.1088/0264-9381/14/1/012 | null | gr-qc | null | Self-similarity in general relativity is briefly reviewed and the differences
between self-similarity of the first kind and generalized self-similarity are
discussed. The covariant notion of a kinematic self-similarity in the context
of relativistic fluid mechanics is defined. Various mathematical and physical
properties of spacetimes admitting a kinematic self-similarity are discussed.
The governing equations for perfect fluid cosmological models are introduced
and a set of integrability conditions for the existence of a proper kinematic
self-similarity in these models is derived. Exact solutions of the irrotational
perfect fluid Einstein field equations admitting a kinematic self-similarity
are then sought in a number of special cases, and it is found that; (1) in the
geodesic case the 3-spaces orthogonal to the fluid velocity vector are
necessarily Ricci-flat and (ii) in the further specialisation to dust the
differential equation governing the expansion can be completely integrated and
the asymptotic properties of these solutions can be determined, (iii) the
solutions in the case of zero-expansion consist of a class of shear-free and
static models and a class of stiff perfect fluid (and non-static) models, and
(iv) solutions in which the kinematic self-similar vector is parallel to the
fluid velocity vector are necessarily Friedmann-Robertson-Walker (FRW) models.
| [
{
"created": "Fri, 25 Oct 1996 20:07:08 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Coley",
"A. A.",
""
]
] | Self-similarity in general relativity is briefly reviewed and the differences between self-similarity of the first kind and generalized self-similarity are discussed. The covariant notion of a kinematic self-similarity in the context of relativistic fluid mechanics is defined. Various mathematical and physical properties of spacetimes admitting a kinematic self-similarity are discussed. The governing equations for perfect fluid cosmological models are introduced and a set of integrability conditions for the existence of a proper kinematic self-similarity in these models is derived. Exact solutions of the irrotational perfect fluid Einstein field equations admitting a kinematic self-similarity are then sought in a number of special cases, and it is found that; (1) in the geodesic case the 3-spaces orthogonal to the fluid velocity vector are necessarily Ricci-flat and (ii) in the further specialisation to dust the differential equation governing the expansion can be completely integrated and the asymptotic properties of these solutions can be determined, (iii) the solutions in the case of zero-expansion consist of a class of shear-free and static models and a class of stiff perfect fluid (and non-static) models, and (iv) solutions in which the kinematic self-similar vector is parallel to the fluid velocity vector are necessarily Friedmann-Robertson-Walker (FRW) models. |
2007.13328 | Salvatore Capozziello | Salvatore Capozziello, Carlo Alberto Mantica, and Luca Guido Molinari | General properties of $\mathbf {f(R)}$ gravity vacuum solutions | 9 pages, accepted for publication in Int. Jou. Mod. Phys. D | null | 10.1142/S0218271820500893 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | General properties of vacuum solutions of $f(R)$ gravity are obtained by the
condition that the divergence of the Weyl tensor is zero and $f''\neq 0$.
Specifically, a theorem states that the gradient of the curvature scalar,
$\nabla R$, is an eigenvector of the Ricci tensor and, if it is time-like, the
space-time is a Generalized Friedman-Robertson-Walker metric; in dimension
four, it is Friedman-Robertson-Walker.
| [
{
"created": "Mon, 27 Jul 2020 07:03:20 GMT",
"version": "v1"
}
] | 2020-11-18 | [
[
"Capozziello",
"Salvatore",
""
],
[
"Mantica",
"Carlo Alberto",
""
],
[
"Molinari",
"Luca Guido",
""
]
] | General properties of vacuum solutions of $f(R)$ gravity are obtained by the condition that the divergence of the Weyl tensor is zero and $f''\neq 0$. Specifically, a theorem states that the gradient of the curvature scalar, $\nabla R$, is an eigenvector of the Ricci tensor and, if it is time-like, the space-time is a Generalized Friedman-Robertson-Walker metric; in dimension four, it is Friedman-Robertson-Walker. |
gr-qc/0612170 | John W. Barrett | John W. Barrett, Ileana Naish-Guzman | The Ponzano-Regge model and Reidemeister torsion | 4 pages. MG11 conference proceedings | null | null | null | gr-qc hep-th math.GT math.QA | null | The Ponzano-Regge model of three-dimensional quantum gravity is well-defined
when the observables satisfy a certain condition involving the twisted
cohomology. In this case, the partition function is defined in terms of the
Reidemeister torsion. Some consequences for the special cases of planar graphs
and knots are given.
| [
{
"created": "Tue, 26 Dec 2006 21:53:13 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Barrett",
"John W.",
""
],
[
"Naish-Guzman",
"Ileana",
""
]
] | The Ponzano-Regge model of three-dimensional quantum gravity is well-defined when the observables satisfy a certain condition involving the twisted cohomology. In this case, the partition function is defined in terms of the Reidemeister torsion. Some consequences for the special cases of planar graphs and knots are given. |
1908.06763 | Sarbari Guha Dr. | Sarbari Guha and Samarjit Chakraborty | On the gravitational entropy of accelerating black holes | 17 pages, 18 figures | International Journal of Modern Physics D, Vol. 29, No. 5 (2020) | 10.1142/S0218271820500340 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we have examined the validity of a proposed definition of
gravitational entropy in the context of accelerating black hole solutions of
the Einstein field equations, which represent the realistic black hole
solutions. We have adopted a phenomenological approach proposed in Rudjord et
al [20] and expanded by Romero et al [21], in which the Weyl curvature
hypothesis is tested against the expressions for the gravitational entropy.
Considering the $C$-metric for the accelerating black holes, we have evaluated
the gravitational entropy and the corresponding entropy density for four
different types of black holes, namely, non-rotating black hole, non-rotating
charged black hole, rotating black hole and rotating charged black hole. We end
up by discussing the merits of such an analysis and the possible reason of
failure in the particular case of rotating charged black hole and comment on
the possible resolution of the problem.
| [
{
"created": "Fri, 16 Aug 2019 15:50:46 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Dec 2019 18:19:10 GMT",
"version": "v2"
}
] | 2021-02-19 | [
[
"Guha",
"Sarbari",
""
],
[
"Chakraborty",
"Samarjit",
""
]
] | In this paper we have examined the validity of a proposed definition of gravitational entropy in the context of accelerating black hole solutions of the Einstein field equations, which represent the realistic black hole solutions. We have adopted a phenomenological approach proposed in Rudjord et al [20] and expanded by Romero et al [21], in which the Weyl curvature hypothesis is tested against the expressions for the gravitational entropy. Considering the $C$-metric for the accelerating black holes, we have evaluated the gravitational entropy and the corresponding entropy density for four different types of black holes, namely, non-rotating black hole, non-rotating charged black hole, rotating black hole and rotating charged black hole. We end up by discussing the merits of such an analysis and the possible reason of failure in the particular case of rotating charged black hole and comment on the possible resolution of the problem. |
gr-qc/0303064 | Alan D. Rendall | P. Noundjeu, N. Noutchegueme, A. D. Rendall | Existence of initial data satisfying the constraints for the spherically
symmetric Einstein-Vlasov-Maxwell system | 12 pages | J.Math.Phys. 45 (2004) 668-676 | 10.1063/1.1637713 | AEI-2003-033 | gr-qc | null | Using ODE techniques we prove the existence of large classes of initial data
satisfying the constraints for the spherically symmetric
Einstein-Vlasov-Maxwell system. These include data for which the ratio of total
charge to total mass is arbitrarily large.
| [
{
"created": "Tue, 18 Mar 2003 14:50:42 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Noundjeu",
"P.",
""
],
[
"Noutchegueme",
"N.",
""
],
[
"Rendall",
"A. D.",
""
]
] | Using ODE techniques we prove the existence of large classes of initial data satisfying the constraints for the spherically symmetric Einstein-Vlasov-Maxwell system. These include data for which the ratio of total charge to total mass is arbitrarily large. |
gr-qc/9811024 | Nobuyuki Sakai | Nobuyuki Sakai, Jun'ichi Yokoyama (YITP, Kyoto U.), Kei-ichi Maeda
(Waseda U.) | Monopole Inflation in Brans-Dicke Theory | 17 pages, revtex, including figures, discussions in more general
theories are added, to appear in Phys. Rev. D | Phys. Rev. D 59, 103504 (1999) | 10.1103/PhysRevD.59.103504 | YITP-98-63, WU-AP/74/98 | gr-qc astro-ph hep-ph hep-th | null | According to previous work, topological defects expand exponentially without
an end if the vacuum expectation value of the Higgs field is of the order of
the Planck mass. We extend the study of inflating topological defects to the
Brans-Dicke gravity. With the help of numerical simulation we investigate the
dynamics and spacetime structure of a global monopole. Contrary to the case of
the Einstein gravity, any inflating monopole eventually shrinks and takes a
stable configuration. We also discuss cosmological constraints on the model
parameters.
| [
{
"created": "Sat, 7 Nov 1998 14:56:57 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Jan 1999 06:55:21 GMT",
"version": "v2"
}
] | 2016-08-25 | [
[
"Sakai",
"Nobuyuki",
"",
"YITP, Kyoto U."
],
[
"Yokoyama",
"Jun'ichi",
"",
"YITP, Kyoto U."
],
[
"Maeda",
"Kei-ichi",
"",
"Waseda U."
]
] | According to previous work, topological defects expand exponentially without an end if the vacuum expectation value of the Higgs field is of the order of the Planck mass. We extend the study of inflating topological defects to the Brans-Dicke gravity. With the help of numerical simulation we investigate the dynamics and spacetime structure of a global monopole. Contrary to the case of the Einstein gravity, any inflating monopole eventually shrinks and takes a stable configuration. We also discuss cosmological constraints on the model parameters. |
2007.04121 | Phongpichit Channuie | Ayan Banerjee (KwaZulu Natal U.), Takol Tangphati (Chulalongkorn U.),
Daris Samart (Khon Kaen U.), Phongpichit Channuie (Walailak U.) | Quark Stars in 4D Einstein-Gauss-Bonnet gravity with an Interacting
Quark Equation of State | v2: regularized scheme to the original 4D EGB theory added, version
accepted by ApJ. arXiv admin note: text overlap with arXiv:2006.00479 | Astrophys. J. 906 (2021) 114 | 10.3847/1538-4357/abc87f | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The detection of gravitational waves (GWs) from the binary neutron star (BNS)
has opened a new window on the gravitational wave astronomy. With current
sensitivities, detectable signals coming from compact objects like neutron
stars turn out to be a crucial ingredient for probing their structure,
composition, and evolution. Moreover, the astronomical observations on the
pulsars and their mass-radius relations put important constraints on the dense
matter equation of state (EoS). In this paper, we consider a homogeneous and
unpaired charge-neutral $3$-flavor interacting quark matter with
$\mathcal{O}(m_s^4)$ corrections that account for the moderately heavy strange
quark instead of the naive MIT bag model. In this article, we perform a
detailed analysis of strange quark star in the context of recently proposed
$4D$ Einstein-Gauss-Bonnet (EGB) theory of gravity. However, this theory does
not have standard four-dimensional field equations. Thus, we thoroughly show
that the equivalence of the actions in the regularized $4D$ EGB theory and in
the original one is satisfied for a spherically symmetric spacetime. We pay
particular attention to the possible existence of massive neutron stars of mass
compatible with $M \sim 2 M_{\odot}$. Our findings suggest that the
fourth-order corrections parameter ($a_4$) of the QCD perturbation and coupling
constant $\alpha$ of the GB term play an important role in the mass-radius
relation as well as the stability of the quark star. Finally, we compare the
results with the well-measured limits of the pulsars and their mass and radius
extracted from the spectra of several X-ray compact sources.
| [
{
"created": "Wed, 8 Jul 2020 13:43:35 GMT",
"version": "v1"
},
{
"created": "Sun, 8 Nov 2020 06:41:52 GMT",
"version": "v2"
}
] | 2021-01-15 | [
[
"Banerjee",
"Ayan",
"",
"KwaZulu Natal U."
],
[
"Tangphati",
"Takol",
"",
"Chulalongkorn U."
],
[
"Samart",
"Daris",
"",
"Khon Kaen U."
],
[
"Channuie",
"Phongpichit",
"",
"Walailak U."
]
] | The detection of gravitational waves (GWs) from the binary neutron star (BNS) has opened a new window on the gravitational wave astronomy. With current sensitivities, detectable signals coming from compact objects like neutron stars turn out to be a crucial ingredient for probing their structure, composition, and evolution. Moreover, the astronomical observations on the pulsars and their mass-radius relations put important constraints on the dense matter equation of state (EoS). In this paper, we consider a homogeneous and unpaired charge-neutral $3$-flavor interacting quark matter with $\mathcal{O}(m_s^4)$ corrections that account for the moderately heavy strange quark instead of the naive MIT bag model. In this article, we perform a detailed analysis of strange quark star in the context of recently proposed $4D$ Einstein-Gauss-Bonnet (EGB) theory of gravity. However, this theory does not have standard four-dimensional field equations. Thus, we thoroughly show that the equivalence of the actions in the regularized $4D$ EGB theory and in the original one is satisfied for a spherically symmetric spacetime. We pay particular attention to the possible existence of massive neutron stars of mass compatible with $M \sim 2 M_{\odot}$. Our findings suggest that the fourth-order corrections parameter ($a_4$) of the QCD perturbation and coupling constant $\alpha$ of the GB term play an important role in the mass-radius relation as well as the stability of the quark star. Finally, we compare the results with the well-measured limits of the pulsars and their mass and radius extracted from the spectra of several X-ray compact sources. |
gr-qc/0503069 | Luca Lusanna | L.Lusanna (INFN, Firenze) and M.Pauri (Parma Univ.) | General covariance and the objectivity of space-time point-events | revtex, 23 pages | null | null | null | gr-qc astro-ph hep-th | null | "The last remnant of physical objectivity of space-time" is disclosed, beyond
the Leibniz equivalence, in the case of a continuous family of spatially
non-compact models of general relativity. The {\it physical individuation} of
point-events is furnished by the intrinsic degrees of freedom of the
gravitational field, (viz, the {\it Dirac observables}) that represent - as it
were - the {\it ontic} part of the metric field. The physical role of the {\it
epistemic} part (viz. the {\it gauge} variables) is likewise clarified. At the
end, a peculiar four-dimensional {\it holistic and structuralist} view of
space-time emerges which includes elements common to the tradition of both {\it
substantivalism} and {\it relationism}. The observables of our models undergo
real {\it temporal change} and thereby provide a counter-example to the thesis
of the {\it frozen-time} picture of evolution.
Invited Contribution to the ESF 2004 Oxford Conference on Space-Time
| [
{
"created": "Wed, 16 Mar 2005 15:46:06 GMT",
"version": "v1"
},
{
"created": "Sat, 3 Sep 2005 16:01:13 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Lusanna",
"L.",
"",
"INFN, Firenze"
],
[
"Pauri",
"M.",
"",
"Parma Univ."
]
] | "The last remnant of physical objectivity of space-time" is disclosed, beyond the Leibniz equivalence, in the case of a continuous family of spatially non-compact models of general relativity. The {\it physical individuation} of point-events is furnished by the intrinsic degrees of freedom of the gravitational field, (viz, the {\it Dirac observables}) that represent - as it were - the {\it ontic} part of the metric field. The physical role of the {\it epistemic} part (viz. the {\it gauge} variables) is likewise clarified. At the end, a peculiar four-dimensional {\it holistic and structuralist} view of space-time emerges which includes elements common to the tradition of both {\it substantivalism} and {\it relationism}. The observables of our models undergo real {\it temporal change} and thereby provide a counter-example to the thesis of the {\it frozen-time} picture of evolution. Invited Contribution to the ESF 2004 Oxford Conference on Space-Time |
2303.07174 | Akhil Uniyal | Akhil Uniyal, Sayan Chakrabarti, Reggie C. Pantig, Ali \"Ovg\"un | Nonlinearly charged black holes: Shadow and Thin-accretion disk | null | New Astronomy 111, 102249 (2024) | 10.1016/j.newast.2024.102249 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we explore the effect of non-linear electrodynamics (NLED)
parameters and magnetic charges on various aspects of black holes, like how
they bend light, how they emit radiation, and how they appear as a shadow by
considering a thin accretion disk model. We initially examine the overall
behavior of the photonsphere and the corresponding shadow silhouette under the
effects of these parameters. Using the EHT data for Sgr. A* and M87*, we aim to
find constraints for $q_m$. Our results indicate that M87* gives better
constraints, and as the value of $\beta$ is varied to increase, the constrained
range for $q_m$ widens. At lower values of $q_m$, we find that the shadow
radius is close to the observed value. Then, we study different things like how
much energy the black hole emits, the temperature of the disk around it, and
the kind of light it gives off. We also look at how the black hole shadow
appears in different situations. We also study how matter falls onto the black
hole from all directions. Finally, we investigate how the magnetic charge
affects all these things when we take into account a theory called NLED along
with gravity. This study helps us understand the complex relationship between
magnetic charge and black holes.
| [
{
"created": "Mon, 13 Mar 2023 15:15:01 GMT",
"version": "v1"
}
] | 2024-06-11 | [
[
"Uniyal",
"Akhil",
""
],
[
"Chakrabarti",
"Sayan",
""
],
[
"Pantig",
"Reggie C.",
""
],
[
"Övgün",
"Ali",
""
]
] | In this paper, we explore the effect of non-linear electrodynamics (NLED) parameters and magnetic charges on various aspects of black holes, like how they bend light, how they emit radiation, and how they appear as a shadow by considering a thin accretion disk model. We initially examine the overall behavior of the photonsphere and the corresponding shadow silhouette under the effects of these parameters. Using the EHT data for Sgr. A* and M87*, we aim to find constraints for $q_m$. Our results indicate that M87* gives better constraints, and as the value of $\beta$ is varied to increase, the constrained range for $q_m$ widens. At lower values of $q_m$, we find that the shadow radius is close to the observed value. Then, we study different things like how much energy the black hole emits, the temperature of the disk around it, and the kind of light it gives off. We also look at how the black hole shadow appears in different situations. We also study how matter falls onto the black hole from all directions. Finally, we investigate how the magnetic charge affects all these things when we take into account a theory called NLED along with gravity. This study helps us understand the complex relationship between magnetic charge and black holes. |
2103.06167 | Gregorio Carullo | Gregorio Carullo, Danny Laghi, John Veitch, Walter Del Pozzo | Bekenstein-Hod Universal Bound on Information Emission Rate Is Obeyed by
LIGO-Virgo Binary Black Hole Remnants | 7 pages, 2 figures, 1 Table | Phys. Rev. Lett. 126, 161102 (2021) | 10.1103/PhysRevLett.126.161102 | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Causality and the generalized laws of black hole thermodynamics imply a
bound, known as the \textit{Bekenstein--Hod universal bound}, on the
information emission rate of a perturbed system. Using a time-domain ringdown
analysis, we investigate whether remnant black holes produced by the
coalescences observed by Advanced LIGO and Advanced Virgo obey this bound. We
find that the bound is verified by the astrophysical black hole population with
$94\%$ probability, providing a first confirmation of the Bekenstein--Hod bound
from black hole systems.
| [
{
"created": "Wed, 10 Mar 2021 16:31:21 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Apr 2021 05:48:34 GMT",
"version": "v2"
}
] | 2021-04-28 | [
[
"Carullo",
"Gregorio",
""
],
[
"Laghi",
"Danny",
""
],
[
"Veitch",
"John",
""
],
[
"Del Pozzo",
"Walter",
""
]
] | Causality and the generalized laws of black hole thermodynamics imply a bound, known as the \textit{Bekenstein--Hod universal bound}, on the information emission rate of a perturbed system. Using a time-domain ringdown analysis, we investigate whether remnant black holes produced by the coalescences observed by Advanced LIGO and Advanced Virgo obey this bound. We find that the bound is verified by the astrophysical black hole population with $94\%$ probability, providing a first confirmation of the Bekenstein--Hod bound from black hole systems. |
1711.02306 | Sanchita Das Ms | Sanchita Das and Somenath Chakraborty | Bose-Einstein Condensation in a uniformly accelerated frame | 8 pages Latex file, one .eps figure | null | null | null | gr-qc astro-ph.SR cond-mat.stat-mech | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we have investigated the possibility of Bose-Einstein
Condensation (BEC) in a frame undergoing uniform acceleration or in other
wards, in Rindler space associated with the uniformly accelerated frame. We
have followed a very simple conventional technique generally used in text book
level studies. It has been observed that the critical temperature for BEC
increases with the increase in magnitude of acceleration of the frame.
Typically the critical temperature in an accelerated frame is of the order of
the Unruh temperature. Hence we have concluded that the increase in the
magnitude of acceleration of the frame facilitates the formation of condensed
phase.
| [
{
"created": "Tue, 7 Nov 2017 06:38:14 GMT",
"version": "v1"
},
{
"created": "Fri, 10 Nov 2017 09:08:31 GMT",
"version": "v2"
}
] | 2017-11-13 | [
[
"Das",
"Sanchita",
""
],
[
"Chakraborty",
"Somenath",
""
]
] | In this article we have investigated the possibility of Bose-Einstein Condensation (BEC) in a frame undergoing uniform acceleration or in other wards, in Rindler space associated with the uniformly accelerated frame. We have followed a very simple conventional technique generally used in text book level studies. It has been observed that the critical temperature for BEC increases with the increase in magnitude of acceleration of the frame. Typically the critical temperature in an accelerated frame is of the order of the Unruh temperature. Hence we have concluded that the increase in the magnitude of acceleration of the frame facilitates the formation of condensed phase. |
1507.07947 | Oihane F Blanco | Oihane F. Blanco and Andrea Moreira | Causal Behaviour on Carter spacetime | 12 pages, 4 figures | Av. Cienc. Ing. (Quito), 2015, Vol. 7, No. 1, Pags. A38-A46 | null | null | gr-qc math-ph math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we will focus on the causal character of Carter Spacetime (see
B. Carter, Causal structure in space-time, Gen. Rel. Grav. 1 4 337-406, 1971).
The importance of this spacetime is the following: for the causally best well
behaved spacetimes (the globally hyperbolic ones), there are several
characterizations or alternative definitions. In some cases, it has been shown
that some of the causal properties required in these characterizations can be
weakened. But Carter spacetime provides a counterexample for an impossible
relaxation in one of them. We studied the possibility of Carter spacetime to be
a counterexample for impossible lessening in another characterization, based on
the previous results.
In particular, we will prove that the time-separation or Lorentzian distance
between two chosen points in Carter spacetime is infinite. Although this
spacetime turned out not to be the counterexample we were looking for, the
found result is interesting per se and provides ideas for alternate approaches
to the possibility of weakening the mentioned characterization.
| [
{
"created": "Tue, 28 Jul 2015 20:29:03 GMT",
"version": "v1"
}
] | 2015-07-30 | [
[
"Blanco",
"Oihane F.",
""
],
[
"Moreira",
"Andrea",
""
]
] | In this work we will focus on the causal character of Carter Spacetime (see B. Carter, Causal structure in space-time, Gen. Rel. Grav. 1 4 337-406, 1971). The importance of this spacetime is the following: for the causally best well behaved spacetimes (the globally hyperbolic ones), there are several characterizations or alternative definitions. In some cases, it has been shown that some of the causal properties required in these characterizations can be weakened. But Carter spacetime provides a counterexample for an impossible relaxation in one of them. We studied the possibility of Carter spacetime to be a counterexample for impossible lessening in another characterization, based on the previous results. In particular, we will prove that the time-separation or Lorentzian distance between two chosen points in Carter spacetime is infinite. Although this spacetime turned out not to be the counterexample we were looking for, the found result is interesting per se and provides ideas for alternate approaches to the possibility of weakening the mentioned characterization. |
1406.0290 | Ganim Gecim | Ganim Gecim and Yusuf Sucu | Hawking Radiation of Topological Massive Warped-AdS3 Black Hole Families | 6 pages, submitted to EPJC | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the Dirac particles tunnelling as a radiation of Warped
AdS$_{3}$ black hole family in Topological Massive Gravity. Using the
Hamilton-Jacobi method, we discuss tunnelling probability and Hawking
temperature of the spin-1/2 particles for the black hole and its extremal
cases. We observe that the Hawking temperature of the non-extremal black hole
higher than the extremal black hole when $\omega <\frac{2\ r_{0}}{3}$, because
the non-extremal black hole become unstable in this case.
| [
{
"created": "Mon, 2 Jun 2014 08:29:00 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Oct 2014 14:51:29 GMT",
"version": "v2"
}
] | 2014-10-16 | [
[
"Gecim",
"Ganim",
""
],
[
"Sucu",
"Yusuf",
""
]
] | We investigate the Dirac particles tunnelling as a radiation of Warped AdS$_{3}$ black hole family in Topological Massive Gravity. Using the Hamilton-Jacobi method, we discuss tunnelling probability and Hawking temperature of the spin-1/2 particles for the black hole and its extremal cases. We observe that the Hawking temperature of the non-extremal black hole higher than the extremal black hole when $\omega <\frac{2\ r_{0}}{3}$, because the non-extremal black hole become unstable in this case. |
2311.13027 | Michail Chabanov | Michail Chabanov and Luciano Rezzolla | Numerical modelling of bulk viscosity in neutron stars | 21 pages, 15 figures | null | null | null | gr-qc astro-ph.HE nucl-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The early post-merger phase of a binary neutron-star coalescence is shaped by
characteristic rotational velocities as well as violent density oscillations
and offers the possibility to constrain the properties of neutron star matter
by observing the gravitational wave emission. One possibility to do so is the
investigation of gravitational wave damping through the bulk viscosity which
originates from violations of weak chemical equilibrium. Motivated by these
prospects, we present a comprehensive report about the implementation of the
self-consistent and second-order formulation of the equations of relativistic
hydrodynamics for dissipative fluids proposed by M\"uller, Israel and Stewart.
Furthermore, we report on the results of two test problems, namely the viscous
damping of linear density oscillations of isolated nonrotating neutron stars
and the viscous migration test, both of which confirm our implementation and
can be used for future code tests. Finally, we present fully
general-relativistic simulations of viscous binary neutron-star mergers. We
explore the structural and thermal properties of binary neutron-star mergers
with a constant bulk viscosity prescription and investigate the impact of bulk
viscosity on dynamical mass ejection. We find that inverse Reynolds numbers of
order $\sim 1\%$ can be achieved for the highest employed viscosity thereby
suppressing the dynamically ejected mass by a factor of $\sim 5$ compared to
the inviscid case.
| [
{
"created": "Tue, 21 Nov 2023 22:26:48 GMT",
"version": "v1"
}
] | 2023-11-23 | [
[
"Chabanov",
"Michail",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | The early post-merger phase of a binary neutron-star coalescence is shaped by characteristic rotational velocities as well as violent density oscillations and offers the possibility to constrain the properties of neutron star matter by observing the gravitational wave emission. One possibility to do so is the investigation of gravitational wave damping through the bulk viscosity which originates from violations of weak chemical equilibrium. Motivated by these prospects, we present a comprehensive report about the implementation of the self-consistent and second-order formulation of the equations of relativistic hydrodynamics for dissipative fluids proposed by M\"uller, Israel and Stewart. Furthermore, we report on the results of two test problems, namely the viscous damping of linear density oscillations of isolated nonrotating neutron stars and the viscous migration test, both of which confirm our implementation and can be used for future code tests. Finally, we present fully general-relativistic simulations of viscous binary neutron-star mergers. We explore the structural and thermal properties of binary neutron-star mergers with a constant bulk viscosity prescription and investigate the impact of bulk viscosity on dynamical mass ejection. We find that inverse Reynolds numbers of order $\sim 1\%$ can be achieved for the highest employed viscosity thereby suppressing the dynamically ejected mass by a factor of $\sim 5$ compared to the inviscid case. |
2306.06279 | Paolo Valtancoli | P. Valtancoli | Euclidean black holes and spin connection | 11 pages, no figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The Euclidean method is usually discussed in the context of the metric
avoiding the typical delta of the conical singularity. We introduce a new way
to calculate the Hawking temperature using the vierbein and spin connection.
The conical singularity is seen globally through an effect on parallel
transport, the so called holonomy of the spin connection. The period of the
Euclidean time is calculated requiring that the holonomy of the spin connection
is trivial at the event horizon.
| [
{
"created": "Fri, 9 Jun 2023 22:06:39 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Sep 2023 09:08:54 GMT",
"version": "v2"
}
] | 2023-09-25 | [
[
"Valtancoli",
"P.",
""
]
] | The Euclidean method is usually discussed in the context of the metric avoiding the typical delta of the conical singularity. We introduce a new way to calculate the Hawking temperature using the vierbein and spin connection. The conical singularity is seen globally through an effect on parallel transport, the so called holonomy of the spin connection. The period of the Euclidean time is calculated requiring that the holonomy of the spin connection is trivial at the event horizon. |
2407.08775 | Aron Kovacs | Pau Figueras, Aaron Held, \'Aron D. Kov\'acs | Well-posed initial value formulation of general effective field theories
of gravity | 5 pages (+ 6 pages of Supplemental Material) | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide a proof that all polynomial higher-derivative effective field
theories of vacuum gravity admit a well-posed initial value formulation when
augmented by suitable regularising terms. These regularising terms can be
obtained by field redefinitions and allow to rewrite the resulting equations of
motion as a system of second-order nonlinear wave equations. For instance, our
result applies to the quadratic, cubic, and quartic truncations of the
effective field theory of gravity that have previously appeared in the
literature. The regularising terms correspond to fiducial massive modes,
however, their masses can be chosen to be non-tachyonic and heavier than the
cutoff scale and hence these modes should not affect the dynamics in the regime
of validity of effective field theory. Our well-posed formulation is not
limited to the weakly coupled regime of these theories, is manifestly covariant
and does neither require fine tuning of free parameters nor involves
prescribing arbitrary equations.
| [
{
"created": "Thu, 11 Jul 2024 18:00:01 GMT",
"version": "v1"
}
] | 2024-07-15 | [
[
"Figueras",
"Pau",
""
],
[
"Held",
"Aaron",
""
],
[
"Kovács",
"Áron D.",
""
]
] | We provide a proof that all polynomial higher-derivative effective field theories of vacuum gravity admit a well-posed initial value formulation when augmented by suitable regularising terms. These regularising terms can be obtained by field redefinitions and allow to rewrite the resulting equations of motion as a system of second-order nonlinear wave equations. For instance, our result applies to the quadratic, cubic, and quartic truncations of the effective field theory of gravity that have previously appeared in the literature. The regularising terms correspond to fiducial massive modes, however, their masses can be chosen to be non-tachyonic and heavier than the cutoff scale and hence these modes should not affect the dynamics in the regime of validity of effective field theory. Our well-posed formulation is not limited to the weakly coupled regime of these theories, is manifestly covariant and does neither require fine tuning of free parameters nor involves prescribing arbitrary equations. |
gr-qc/9810010 | Jiseong Park | Jiseong Park | Static Solutions of the Einstein Equations for Spherically Symmetric
Elastic Bodies | 21 pages, TeX | Gen.Rel.Grav. 32 (2000) 235-252 | 10.1023/A:1001875224949 | AEI-084 | gr-qc | null | The paper is concerned with the Einstein equations for a spherically
symmetric static distribution of anisotropic matter. The equations are cast
into a system of Fuchsian type ODE for certain scalar invariants of the strain.
And then the existence and regularity of this ODE is studied under general
constitutive relation. In the case the constitutive relation is given by a
quadratic form of strain, it is also shown that the solutions stay regular up
to the boundary of the material ball.
| [
{
"created": "Sun, 4 Oct 1998 16:35:47 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Park",
"Jiseong",
""
]
] | The paper is concerned with the Einstein equations for a spherically symmetric static distribution of anisotropic matter. The equations are cast into a system of Fuchsian type ODE for certain scalar invariants of the strain. And then the existence and regularity of this ODE is studied under general constitutive relation. In the case the constitutive relation is given by a quadratic form of strain, it is also shown that the solutions stay regular up to the boundary of the material ball. |
2407.20470 | Isabella Pretto | Isabella G. Pretto, Mark A. Scheel and Saul A. Teukolsky | Automated determination of the end time of junk radiation in binary
black hole simulations | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | When numerically solving Einstein's equations for the evolution of binary
black holes, physical imperfections in the initial data manifest as a
transient, high-frequency pulse of ''junk radiation.'' This unphysical signal
must be removed before the waveform can be used. Improvements in the efficiency
of numerical simulations now allow waveform catalogs containing thousands of
waveforms to be produced. Thus, an automated procedure for identifying junk
radiation is required. To this end, we present a new algorithm based on the
empirical mode decomposition (EMD) from the Hilbert-Huang transform. This
approach allows us to isolate and measure the high-frequency oscillations
present in the measured irreducible masses of the black holes. The decay of
these oscillations allows us to estimate the time from which the junk radiation
can be ignored. To make this procedure more precise, we propose three distinct
threshold criteria that specify how small the contribution of junk radiation
has to be before it can be considered negligible. We apply this algorithm to
3403 BBH simulations from the SXS catalog to find appropriate values for the
thresholds in the three criteria. We find that this approach yields reliable
decay time estimates, i.e., when to consider the simulation physical, for over
98.6% of the simulations studied. This demonstrates the efficacy of the EMD as
a suitable tool to automatically isolate and characterize junk radiation in the
simulation of binary black hole systems.
| [
{
"created": "Tue, 30 Jul 2024 00:14:04 GMT",
"version": "v1"
}
] | 2024-07-31 | [
[
"Pretto",
"Isabella G.",
""
],
[
"Scheel",
"Mark A.",
""
],
[
"Teukolsky",
"Saul A.",
""
]
] | When numerically solving Einstein's equations for the evolution of binary black holes, physical imperfections in the initial data manifest as a transient, high-frequency pulse of ''junk radiation.'' This unphysical signal must be removed before the waveform can be used. Improvements in the efficiency of numerical simulations now allow waveform catalogs containing thousands of waveforms to be produced. Thus, an automated procedure for identifying junk radiation is required. To this end, we present a new algorithm based on the empirical mode decomposition (EMD) from the Hilbert-Huang transform. This approach allows us to isolate and measure the high-frequency oscillations present in the measured irreducible masses of the black holes. The decay of these oscillations allows us to estimate the time from which the junk radiation can be ignored. To make this procedure more precise, we propose three distinct threshold criteria that specify how small the contribution of junk radiation has to be before it can be considered negligible. We apply this algorithm to 3403 BBH simulations from the SXS catalog to find appropriate values for the thresholds in the three criteria. We find that this approach yields reliable decay time estimates, i.e., when to consider the simulation physical, for over 98.6% of the simulations studied. This demonstrates the efficacy of the EMD as a suitable tool to automatically isolate and characterize junk radiation in the simulation of binary black hole systems. |
1101.3171 | Leo Brewin | Leo Brewin | An Einstein-Bianchi system for Smooth Lattice General Relativity. I. The
Schwarzschild spacetime | minor changes to conform with companion paper, new appendix | null | 10.1103/PhysRevD.85.124045 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The second Bianchi identity can be recast as an evolution equation for the
Riemann curvatures. Here we will report on such a system for a vacuum static
spherically symmetric spacetime. This is the first of two papers. In the
following paper we will extend the ideas developed here to general vacuum
spacetimes. In this paper we will demonstrate our ideas on a Schwarzschild
spacetime and give detailed numerical results. For suitable choices of lapse
function we find that the system gives excellent results with long term
stability.
| [
{
"created": "Mon, 17 Jan 2011 10:32:19 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Apr 2011 15:14:06 GMT",
"version": "v2"
}
] | 2013-05-30 | [
[
"Brewin",
"Leo",
""
]
] | The second Bianchi identity can be recast as an evolution equation for the Riemann curvatures. Here we will report on such a system for a vacuum static spherically symmetric spacetime. This is the first of two papers. In the following paper we will extend the ideas developed here to general vacuum spacetimes. In this paper we will demonstrate our ideas on a Schwarzschild spacetime and give detailed numerical results. For suitable choices of lapse function we find that the system gives excellent results with long term stability. |
1005.3778 | Douglas A. Singleton | Douglas Singleton, Elias C. Vagenas, Tao Zhu, Ji-Rong Ren | Insights and possible resolution to the information loss paradox via the
tunneling picture | 16 pages revtex, 4 figures. The formula for temperature is corrected.
Main conclusion about the possible resolution to information loss paradox
unchanged. Erratum to be published JHEP | JHEP 1008:089,2010; Erratum-ibid.1101:021,2011 | 10.1007/JHEP08(2010)089 10.1007/JHEP01(2011)021 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper investigates the information loss paradox in the WKB/tunneling
picture of Hawking radiation. In the tunneling picture one can obtain the
tunneling amplitude to all orders in $\hbar$. However all terms beyond the
lowest, semi-classical term involve unknown constants. Despite this we find
that one can still arrive at interesting restrictions on Hawking radiation to
all orders in $\hbar$: (i) Taking into account only quantum corrections the
spectrum remains thermal to all orders. Thus quantum corrections by themselves
will not resolve the information loss paradox. (ii) The first quantum
correction give a temperature for the radiation which goes to zero as the mass
of the black hole goes to zero. Including higher order corrections changes this
nice result of the first order corrections. (iii) Finally we show that by
taking both quantum corrections and back reaction into account it is possible
under specific conditions to solve the information paradox by having the black
hole evaporate completely with the information carried away by the correlations
of the outgoing radiation.
| [
{
"created": "Thu, 20 May 2010 18:17:36 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Jul 2010 06:17:13 GMT",
"version": "v2"
},
{
"created": "Wed, 1 Sep 2010 00:27:10 GMT",
"version": "v3"
},
{
"created": "Fri, 7 Jan 2011 05:24:15 GMT",
"version": "v4"
}
] | 2011-01-17 | [
[
"Singleton",
"Douglas",
""
],
[
"Vagenas",
"Elias C.",
""
],
[
"Zhu",
"Tao",
""
],
[
"Ren",
"Ji-Rong",
""
]
] | This paper investigates the information loss paradox in the WKB/tunneling picture of Hawking radiation. In the tunneling picture one can obtain the tunneling amplitude to all orders in $\hbar$. However all terms beyond the lowest, semi-classical term involve unknown constants. Despite this we find that one can still arrive at interesting restrictions on Hawking radiation to all orders in $\hbar$: (i) Taking into account only quantum corrections the spectrum remains thermal to all orders. Thus quantum corrections by themselves will not resolve the information loss paradox. (ii) The first quantum correction give a temperature for the radiation which goes to zero as the mass of the black hole goes to zero. Including higher order corrections changes this nice result of the first order corrections. (iii) Finally we show that by taking both quantum corrections and back reaction into account it is possible under specific conditions to solve the information paradox by having the black hole evaporate completely with the information carried away by the correlations of the outgoing radiation. |
1408.3553 | Abdul Jawad | M. Sharif and Abdul Jawad | Analysis of Generalized Ghost Version of Pilgrim Dark Energy | 17 pages, 8 figures | Astrophys. Space Sci. 351(2014)321 | 10.1007/s10509-014-1833-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The proposal of pilgrim dark energy is based on the speculation that
phantom-like dark energy possesses enough resistive force to preclude the black
hole formation in the later universe. We explore this phenomenon by assuming
the generalized ghost version of pilgrim dark energy. We find that most of the
values of the interacting ($\xi^2$) as well as pilgrim dark energy ($u$)
parameters push the equation of state parameter towards phantom region. The
squared speed of sound shows that this model remains stable in most of the
cases of $\xi^2$ and $u$. We also develop $\omega_\Lambda-\omega'_\Lambda$
plane and observe that this model corresponds to thawing as well as freezing
regions. Finally, it is shown that the non-interacting and interacting
generalized ghost versions of pilgrim dark energy correspond to $\Lambda$CDM
limit on the statefinder plane.
| [
{
"created": "Fri, 20 Dec 2013 10:37:49 GMT",
"version": "v1"
},
{
"created": "Mon, 18 Aug 2014 05:52:45 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Sharif",
"M.",
""
],
[
"Jawad",
"Abdul",
""
]
] | The proposal of pilgrim dark energy is based on the speculation that phantom-like dark energy possesses enough resistive force to preclude the black hole formation in the later universe. We explore this phenomenon by assuming the generalized ghost version of pilgrim dark energy. We find that most of the values of the interacting ($\xi^2$) as well as pilgrim dark energy ($u$) parameters push the equation of state parameter towards phantom region. The squared speed of sound shows that this model remains stable in most of the cases of $\xi^2$ and $u$. We also develop $\omega_\Lambda-\omega'_\Lambda$ plane and observe that this model corresponds to thawing as well as freezing regions. Finally, it is shown that the non-interacting and interacting generalized ghost versions of pilgrim dark energy correspond to $\Lambda$CDM limit on the statefinder plane. |
2204.08217 | Masato Minamitsuji | Masato Minamitsuji, Antonio De Felice, Shinji Mukohyama, Michele
Oliosi | Static and spherically symmetric general relativity solutions in Minimal
Theory of Bigravity | 19 pages | null | 10.1103/PhysRevD.105.123026 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate static and spherically symmetric solutions in the Minimal
Theory of Bigravity (MTBG). First, we show that a pair of Schwarzschild-de
Sitter spacetimes with different cosmological constants and black hole masses
written in the spatially-flat Gullstrand-Painlev\'e (GP) coordinates is a
solution in the self-accelerating branch of MTBG, while it cannot be a solution
in the normal branch. We then illustrate how Schwarzschild-de Sitter solutions
can become compatible with the normal branch when using different coordinates.
We also confirm that the self-accelerating branch of MTBG admits static and
spherically symmetric general relativity solutions with matter written in the
spatially-flat coordinates, including neutron stars with arbitrary matter
equations of state. Finally, we show that in the self-accelerating branch
nontrivial solutions are given by the Schwarzschild-de Sitter metrics written
in nonstandard coordinates.
| [
{
"created": "Mon, 18 Apr 2022 08:39:54 GMT",
"version": "v1"
}
] | 2022-07-13 | [
[
"Minamitsuji",
"Masato",
""
],
[
"De Felice",
"Antonio",
""
],
[
"Mukohyama",
"Shinji",
""
],
[
"Oliosi",
"Michele",
""
]
] | We investigate static and spherically symmetric solutions in the Minimal Theory of Bigravity (MTBG). First, we show that a pair of Schwarzschild-de Sitter spacetimes with different cosmological constants and black hole masses written in the spatially-flat Gullstrand-Painlev\'e (GP) coordinates is a solution in the self-accelerating branch of MTBG, while it cannot be a solution in the normal branch. We then illustrate how Schwarzschild-de Sitter solutions can become compatible with the normal branch when using different coordinates. We also confirm that the self-accelerating branch of MTBG admits static and spherically symmetric general relativity solutions with matter written in the spatially-flat coordinates, including neutron stars with arbitrary matter equations of state. Finally, we show that in the self-accelerating branch nontrivial solutions are given by the Schwarzschild-de Sitter metrics written in nonstandard coordinates. |
1912.05389 | Connor McIsaac | Connor McIsaac, David Keitel, Thomas Collett, Ian Harry, Simone
Mozzon, Oliver Edy, David Bacon | Search for strongly lensed counterpart images of binary black hole
mergers in the first two LIGO observing runs | 16 pages. Comments welcome. Data release:
https://github.com/icg-gravwaves/lensed-o1-o2-data-release. Version accepted
for publication in PRD. Supplement merged into main paper following PRD
style. Various updates/improvements during review process. Typos corrected | Phys. Rev. D 102, 084031 (2020) | 10.1103/PhysRevD.102.084031 | LIGO-P1900360 | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Strong gravitational lensing can produce multiple images of the same
gravitational-wave signal, each arriving at different times and with different
magnification. Previous work has explored if lensed pairs exist among the known
high-significance events and found no evidence of this. However, the
possibility remains that weaker counterparts of these events are present in the
data, unrecovered by previous searches. We conduct a targeted search
specifically looking for sub-threshold lensed images of known binary black hole
(BBH) observations. We recover candidates matching three of the additional
events first reported by Venumadhav et al. (2019), but find no evidence for
additional BBH events. We also find no evidence that any of the Venumadhav et
al. observations are lensed counterparts. We demonstrate how this type of
counterpart search can constrain hypotheses about the overall source and lens
populations and we rule out at very high confidence the extreme hypothesis that
all heavy BBH detections are in fact lensed systems at high redshift with
intrinsic masses < 15Msun.
| [
{
"created": "Wed, 11 Dec 2019 15:30:42 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Sep 2020 13:57:25 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Oct 2020 14:48:32 GMT",
"version": "v3"
}
] | 2020-10-21 | [
[
"McIsaac",
"Connor",
""
],
[
"Keitel",
"David",
""
],
[
"Collett",
"Thomas",
""
],
[
"Harry",
"Ian",
""
],
[
"Mozzon",
"Simone",
""
],
[
"Edy",
"Oliver",
""
],
[
"Bacon",
"David",
""
]
] | Strong gravitational lensing can produce multiple images of the same gravitational-wave signal, each arriving at different times and with different magnification. Previous work has explored if lensed pairs exist among the known high-significance events and found no evidence of this. However, the possibility remains that weaker counterparts of these events are present in the data, unrecovered by previous searches. We conduct a targeted search specifically looking for sub-threshold lensed images of known binary black hole (BBH) observations. We recover candidates matching three of the additional events first reported by Venumadhav et al. (2019), but find no evidence for additional BBH events. We also find no evidence that any of the Venumadhav et al. observations are lensed counterparts. We demonstrate how this type of counterpart search can constrain hypotheses about the overall source and lens populations and we rule out at very high confidence the extreme hypothesis that all heavy BBH detections are in fact lensed systems at high redshift with intrinsic masses < 15Msun. |
1602.00558 | Xinhe Meng | Deng Wang, Xin-He Meng | Geometric dark energy traversable wormholes constrained by astrophysical
observations | 17ps, 7figs | null | null | null | gr-qc astro-ph.CO hep-ph hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter, we introduce the astrophysical observations into the wormhole
research, which is not meant to general parameters constraints for the dark
energy models, in order to understand more about in which stage of the universe
evolutions wormholes may exist through the investigation of the evolution
behavior of the cosmic equation of state parameter. As a concrete instance, we
investigate the Ricci dark energy (RDE) traversable wormholes constrained by
astrophysical data-sets. Particularly, we can discover from Fig. \ref{fig5} of
the present work, when the effective equation of state parameter $\omega_X<-1$,
namely, the Null Energy conditions (NEC) is violated clearly, the wormholes
will appear (open). Subsequently, six specific solutions of static and
spherically symmetric traversable wormhole supported by the RDE are obtained.
Except for the case of constant redshift function, in which the solution is not
only asymptotically flat but also traversable, the remaining five solutions are
all not asymptotically flat, therefore, the exotic matter from the RDE fluids
is spatially distributed in the vicinity of the throat. Furthermore, we analyze
the physical characteristics and properties of the RDE traversable wormholes.
It is worth noting that, through the astrophysical observations, we get
constraints on the parameters of RDE model, explore the type of exotic RDE
fluids in different stages of the universe changing, limit the number of
available models for wormhole research, reduce the number of the wormholes
corresponding to different parameters for RDE model and provide a more apparent
picture for wormhole investigations from the new perspective of observational
cosmology background
| [
{
"created": "Fri, 29 Jan 2016 13:30:42 GMT",
"version": "v1"
}
] | 2016-02-02 | [
[
"Wang",
"Deng",
""
],
[
"Meng",
"Xin-He",
""
]
] | In this letter, we introduce the astrophysical observations into the wormhole research, which is not meant to general parameters constraints for the dark energy models, in order to understand more about in which stage of the universe evolutions wormholes may exist through the investigation of the evolution behavior of the cosmic equation of state parameter. As a concrete instance, we investigate the Ricci dark energy (RDE) traversable wormholes constrained by astrophysical data-sets. Particularly, we can discover from Fig. \ref{fig5} of the present work, when the effective equation of state parameter $\omega_X<-1$, namely, the Null Energy conditions (NEC) is violated clearly, the wormholes will appear (open). Subsequently, six specific solutions of static and spherically symmetric traversable wormhole supported by the RDE are obtained. Except for the case of constant redshift function, in which the solution is not only asymptotically flat but also traversable, the remaining five solutions are all not asymptotically flat, therefore, the exotic matter from the RDE fluids is spatially distributed in the vicinity of the throat. Furthermore, we analyze the physical characteristics and properties of the RDE traversable wormholes. It is worth noting that, through the astrophysical observations, we get constraints on the parameters of RDE model, explore the type of exotic RDE fluids in different stages of the universe changing, limit the number of available models for wormhole research, reduce the number of the wormholes corresponding to different parameters for RDE model and provide a more apparent picture for wormhole investigations from the new perspective of observational cosmology background |
1111.0418 | Eugen Radu | Eugen Radu and D. H. Tchrakian | Stable black hole solutions with non-Abelian fields | 8 pages, 3 figures | null | 10.1103/PhysRevD.85.084022 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct finite mass, asymptotically flat black hole solutions in d=4
Einstein-Yang-Mills theory augmented with higher order curvature terms of the
gauge field. They possess non-Abelian hair in addition to Coulomb electric
charge, and, below some non-zero critical temperature, they are
thermodynamically preferred over the Reissner-Nordstrom solution. Our results
indicate the existence of hairy non-Abelian black holes which are stable under
linear, spherically symmetric perturbations.
| [
{
"created": "Wed, 2 Nov 2011 08:27:57 GMT",
"version": "v1"
}
] | 2013-05-30 | [
[
"Radu",
"Eugen",
""
],
[
"Tchrakian",
"D. H.",
""
]
] | We construct finite mass, asymptotically flat black hole solutions in d=4 Einstein-Yang-Mills theory augmented with higher order curvature terms of the gauge field. They possess non-Abelian hair in addition to Coulomb electric charge, and, below some non-zero critical temperature, they are thermodynamically preferred over the Reissner-Nordstrom solution. Our results indicate the existence of hairy non-Abelian black holes which are stable under linear, spherically symmetric perturbations. |
1603.05449 | Henrik Zinkernagel | Svend E. Rugh and Henrik Zinkernagel | Limits of time in cosmology | 20 pages, 1 figure. To appear in "The Philosophy of Cosmology";
edited by K. Chamcham, J. Silk, J. Barrow and S. Saunders. Cambridge
University Press, 2016 | null | null | null | gr-qc astro-ph.CO hep-th physics.hist-ph quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide a discussion of some main ideas in our project about the physical
foundation of the time concept in cosmology. It is standard to point to the
Planck scale (located at $\sim 10^{-43}$ seconds after a fictitious "Big Bang"
point) as a limit for how far back we may extrapolate the standard cosmological
model. In our work we have suggested that there are several other (physically
motivated) interesting limits -- located at least thirty orders of magnitude
before the Planck time -- where the physical basis of the cosmological model
and its time concept is progressively weakened. Some of these limits are
connected to phase transitions in the early universe which gradually undermine
the notion of 'standard clocks' widely employed in cosmology. Such
considerations lead to a 'scale problem' for time which becomes particularly
acute above the electroweak phase transition (before $\sim 10^{-11}$ seconds).
Other limits are due to problems of building up a cosmological reference frame,
or even contemplating a sensible notion of proper time, if the early universe
constituents become too quantum. This 'quantum problem' for time arises e.g. if
a pure quantum phase is contemplated at the beginning of inflation at, say,
$\sim 10^{-34}$ seconds.
| [
{
"created": "Thu, 17 Mar 2016 12:28:46 GMT",
"version": "v1"
}
] | 2016-03-18 | [
[
"Rugh",
"Svend E.",
""
],
[
"Zinkernagel",
"Henrik",
""
]
] | We provide a discussion of some main ideas in our project about the physical foundation of the time concept in cosmology. It is standard to point to the Planck scale (located at $\sim 10^{-43}$ seconds after a fictitious "Big Bang" point) as a limit for how far back we may extrapolate the standard cosmological model. In our work we have suggested that there are several other (physically motivated) interesting limits -- located at least thirty orders of magnitude before the Planck time -- where the physical basis of the cosmological model and its time concept is progressively weakened. Some of these limits are connected to phase transitions in the early universe which gradually undermine the notion of 'standard clocks' widely employed in cosmology. Such considerations lead to a 'scale problem' for time which becomes particularly acute above the electroweak phase transition (before $\sim 10^{-11}$ seconds). Other limits are due to problems of building up a cosmological reference frame, or even contemplating a sensible notion of proper time, if the early universe constituents become too quantum. This 'quantum problem' for time arises e.g. if a pure quantum phase is contemplated at the beginning of inflation at, say, $\sim 10^{-34}$ seconds. |
2108.02152 | Nikolaos Mavromatos | Nick E. Mavromatos | Geometrical origins of the Universe dark sector: string-inspired torsion
and anomalies as seeds for inflation and dark matter | 37 pages revtex, 2 pdf figures incorporated | Phil. Trans. R. Soc. A 380: 20210188 (2022) | 10.1098/rsta.2021.0188 | KCL-PH-TH/2021-62 | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a modest attempt to present potentially new paradigms in Cosmology,
including its inflationary epoch, and initiate discussions, I review in this
article some novel, string-inspired cosmological models, which entail a purely
geometrical origin of the Dark sector of the Universe but also of its observed
matter-antimatter asymmetry. The models contain gravitational (string-model
independent, Kalb-Ramond (KR)) axion fields coupled to primordial gravitational
anomalies via CP-violating interactions. The anomaly terms are
four-space-time-dimensional remnants of the Green-Schwarz counterterms
appearing in the definition of the field strength of the spin-one antisymmetric
tensor field of the (bosonic) massless gravitational string multiplet, which
also plays the r\^ole of a totally antisymmetric component of torsion. I show
how in such cosmologies the presence of primordial gravitational waves can lead
to anomaly condensates and dynamical inflation of a "running-vacuum-model"
type, without external inflatons, but also to leptogenesis in the radiation era
due to anomaly-induced Lorentz and CPT Violating KR axion backgrounds. I also
discuss how the torsion-related KR-axion could acquire a mass during the QCD
epoch, thus playing the role of (a component of) Dark Matter. Phenomenological
considerations of the inflationary and post-inflationary (in particular,
modern) eras of the model are briefly discussed, including its potential for
alleviating the observed tensions in the cosmological data of the current
epoch.
| [
{
"created": "Wed, 4 Aug 2021 16:31:30 GMT",
"version": "v1"
}
] | 2022-03-17 | [
[
"Mavromatos",
"Nick E.",
""
]
] | In a modest attempt to present potentially new paradigms in Cosmology, including its inflationary epoch, and initiate discussions, I review in this article some novel, string-inspired cosmological models, which entail a purely geometrical origin of the Dark sector of the Universe but also of its observed matter-antimatter asymmetry. The models contain gravitational (string-model independent, Kalb-Ramond (KR)) axion fields coupled to primordial gravitational anomalies via CP-violating interactions. The anomaly terms are four-space-time-dimensional remnants of the Green-Schwarz counterterms appearing in the definition of the field strength of the spin-one antisymmetric tensor field of the (bosonic) massless gravitational string multiplet, which also plays the r\^ole of a totally antisymmetric component of torsion. I show how in such cosmologies the presence of primordial gravitational waves can lead to anomaly condensates and dynamical inflation of a "running-vacuum-model" type, without external inflatons, but also to leptogenesis in the radiation era due to anomaly-induced Lorentz and CPT Violating KR axion backgrounds. I also discuss how the torsion-related KR-axion could acquire a mass during the QCD epoch, thus playing the role of (a component of) Dark Matter. Phenomenological considerations of the inflationary and post-inflationary (in particular, modern) eras of the model are briefly discussed, including its potential for alleviating the observed tensions in the cosmological data of the current epoch. |
1709.09806 | Zhengcheng Gu | Zheng-Cheng Gu | The emergence of 3+1D Einstein gravity from topological gravity | 5 pages, added references and modified the noncommutative geometry
part | null | null | null | gr-qc cond-mat.str-el hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quantum field theory successfully explains the origin of all fundamental
forces except gravity due to the renormalizability problem. In this paper, we
proposed a topological scenario to understand this puzzle. First, we proposed a
$3+1$D topological (quantum) gravity theory which is renormalizable, and it can
be regarded as a straightforward generalization of Edward Witten's Chern-Simons
theory approach to $2+1$D topological gravity. Then, we showed that the
(vacuum) Einstein-Cartan equation and classical space-time naturally emerge
from topological (quantum) gravity via loop condensation. The second step is a
unique feature in $3+1$D and it might even naturally explain why our space-time
is four dimensional.
| [
{
"created": "Thu, 28 Sep 2017 05:25:17 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Apr 2019 16:28:12 GMT",
"version": "v2"
}
] | 2019-04-11 | [
[
"Gu",
"Zheng-Cheng",
""
]
] | Quantum field theory successfully explains the origin of all fundamental forces except gravity due to the renormalizability problem. In this paper, we proposed a topological scenario to understand this puzzle. First, we proposed a $3+1$D topological (quantum) gravity theory which is renormalizable, and it can be regarded as a straightforward generalization of Edward Witten's Chern-Simons theory approach to $2+1$D topological gravity. Then, we showed that the (vacuum) Einstein-Cartan equation and classical space-time naturally emerge from topological (quantum) gravity via loop condensation. The second step is a unique feature in $3+1$D and it might even naturally explain why our space-time is four dimensional. |
1310.5167 | Flavio Mercati | Julian Barbour, Tim Koslowski and Flavio Mercati | A Gravitational Origin of the Arrows of Time | 44 pages + 14 pages appendices and references. 8 figures and 1 table | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The only widely accepted explanation for the various arrows of time that
everywhere and at all epochs point in the same direction is the `past
hypothesis': the Universe had a very special low-entropy initial state. We
present the first evidence for an alternative conjecture: the arrows exist in
all solutions of the gravitational law that governs the Universe and arise
because the space of its true degrees of freedom (shape space) is asymmetric.
We prove our conjecture for arrows of complexity and information in the
Newtonian N-body problem. Except for a set of measure zero, all of its
solutions for non-negative energy divide at a uniquely defined point into two
halves. In each a well-defined measure of complexity fluctuates but grows
irreversibly between rising bounds from that point. Structures that store
dynamical information are created as the complexity grows. Recognition of the
division is a key novelty of our approach. Each solution can be viewed as
having a single past and two distinct futures emerging from it. Any internal
observer must be in one half of the solution and will only be aware of one past
and one future. The `paradox' of a time-symmetric law that leads to
observationally irreversible behaviour is fully resolved. General Relativity
shares enough architectonic structure with the N-body problem for us to prove
the existence of analogous complexity arrows in the vacuum Bianchi IX model. In
the absence of non-trivial solutions with matter we cannot prove that arrows of
dynamical information will arise in GR, though they have in our Universe.
Finally, we indicate how the other arrows of time could arise.
| [
{
"created": "Fri, 18 Oct 2013 21:19:53 GMT",
"version": "v1"
}
] | 2014-12-11 | [
[
"Barbour",
"Julian",
""
],
[
"Koslowski",
"Tim",
""
],
[
"Mercati",
"Flavio",
""
]
] | The only widely accepted explanation for the various arrows of time that everywhere and at all epochs point in the same direction is the `past hypothesis': the Universe had a very special low-entropy initial state. We present the first evidence for an alternative conjecture: the arrows exist in all solutions of the gravitational law that governs the Universe and arise because the space of its true degrees of freedom (shape space) is asymmetric. We prove our conjecture for arrows of complexity and information in the Newtonian N-body problem. Except for a set of measure zero, all of its solutions for non-negative energy divide at a uniquely defined point into two halves. In each a well-defined measure of complexity fluctuates but grows irreversibly between rising bounds from that point. Structures that store dynamical information are created as the complexity grows. Recognition of the division is a key novelty of our approach. Each solution can be viewed as having a single past and two distinct futures emerging from it. Any internal observer must be in one half of the solution and will only be aware of one past and one future. The `paradox' of a time-symmetric law that leads to observationally irreversible behaviour is fully resolved. General Relativity shares enough architectonic structure with the N-body problem for us to prove the existence of analogous complexity arrows in the vacuum Bianchi IX model. In the absence of non-trivial solutions with matter we cannot prove that arrows of dynamical information will arise in GR, though they have in our Universe. Finally, we indicate how the other arrows of time could arise. |
gr-qc/0010107 | Antonio Teixeira | A.F.F. Teixeira (Centro Brasileiro de Pesquisas Fisicas) | Cosmic crystallography: the hyperbolic isometries | 18 pages, 16 figures included | null | null | null | gr-qc | null | All orientation preserving isometries of the hyperbolic three-space are
studied, and the probability density of conjugate pair separations for each
isometry is presented. The study is relevant for the cosmic crystallography,
and is the theoretical counterpart of the mean histograms arising from computer
simulations of the isometries.
| [
{
"created": "Sun, 29 Oct 2000 13:38:25 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Teixeira",
"A. F. F.",
"",
"Centro Brasileiro de Pesquisas Fisicas"
]
] | All orientation preserving isometries of the hyperbolic three-space are studied, and the probability density of conjugate pair separations for each isometry is presented. The study is relevant for the cosmic crystallography, and is the theoretical counterpart of the mean histograms arising from computer simulations of the isometries. |
1004.3849 | Luca Baiotti | Luca Baiotti, Ian Hawke, Pedro J. Montero, Luciano Rezzolla | A new three-dimensional general-relativistic hydrodynamics code | Published in 2003, this is the first article on the Whisky code. | Mem. S.A.It. Suppl. Vol. 1, 210 (2003) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a new three-dimensional general relativistic hydrodynamics code,
the Whisky code. This code incorporates the expertise developed over the past
years in the numerical solution of Einstein equations and of the hydrodynamics
equations in a curved spacetime, and is the result of a collaboration of
several European Institutes. We here discuss the ability of the code to carry
out long-term accurate evolutions of the linear and nonlinear dynamics of
isolated relativistic stars.
| [
{
"created": "Thu, 22 Apr 2010 07:03:05 GMT",
"version": "v1"
}
] | 2010-04-23 | [
[
"Baiotti",
"Luca",
""
],
[
"Hawke",
"Ian",
""
],
[
"Montero",
"Pedro J.",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | We present a new three-dimensional general relativistic hydrodynamics code, the Whisky code. This code incorporates the expertise developed over the past years in the numerical solution of Einstein equations and of the hydrodynamics equations in a curved spacetime, and is the result of a collaboration of several European Institutes. We here discuss the ability of the code to carry out long-term accurate evolutions of the linear and nonlinear dynamics of isolated relativistic stars. |
2203.16327 | Claudio Nassif Cruz | Cl\'audio Nassif Cruz | Deformed Special Relativity with an invariant minimum speed as an
explanation of the cosmological constant | 9 pages, 2 figures | Pramana J. Phys., 96:55 (2022) | 10.1007/s12043-022-02296-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper shows the need of the emergence of a universal minimum speed in
the space-time by means of a more thorough investigation of Dirac's large
number hypothesis (LNH). We will realize that there should be a minimum speed
$V$ with the same status of the invariance of the speed of light $c$, however
$V$ has gravitational origin. Hence, such a minimum speed forms a new kinematic
basis in the space-time, thus leading to a new Deformed Special Relativity
(DSR) for the quantum world so-called Symmetrical Special Relativity (SSR).
Furthermore, we will show that such a new structure of space-time (SSR) reveals
a connection between $V$ and a preferred reference frame $S_V$ of background
field that leads to the cosmological constant $\Lambda$, which can be
associated with a cosmological anti-gravity. We will also investigate the
effect of the number of baryons $N$ (Eddington number) of the observable
universe on the Hydrogen atom. Finally, we will show that SSR-metric plays the
role of a de-Sitter (dS)-metric with a positive cosmological constant, which
could assume a tiny value.
| [
{
"created": "Tue, 29 Mar 2022 02:55:33 GMT",
"version": "v1"
}
] | 2022-03-31 | [
[
"Cruz",
"Cláudio Nassif",
""
]
] | This paper shows the need of the emergence of a universal minimum speed in the space-time by means of a more thorough investigation of Dirac's large number hypothesis (LNH). We will realize that there should be a minimum speed $V$ with the same status of the invariance of the speed of light $c$, however $V$ has gravitational origin. Hence, such a minimum speed forms a new kinematic basis in the space-time, thus leading to a new Deformed Special Relativity (DSR) for the quantum world so-called Symmetrical Special Relativity (SSR). Furthermore, we will show that such a new structure of space-time (SSR) reveals a connection between $V$ and a preferred reference frame $S_V$ of background field that leads to the cosmological constant $\Lambda$, which can be associated with a cosmological anti-gravity. We will also investigate the effect of the number of baryons $N$ (Eddington number) of the observable universe on the Hydrogen atom. Finally, we will show that SSR-metric plays the role of a de-Sitter (dS)-metric with a positive cosmological constant, which could assume a tiny value. |
gr-qc/0102030 | A. Yeranyan | R. M. Avakyan, E. V. Chubaryan, A. H. Yeranyan | ''Homogeneous'' Gravitational Field in General Relativity ? | 6 pages, 2 figures, LaTeX | null | null | null | gr-qc | null | The gravitation field of the flat plate was investigated. It have been shown
that there exist the internal solution of Einstein equations sewed together
with external one, which described a ''homogeneous'' gravitational field.
| [
{
"created": "Thu, 8 Feb 2001 04:37:38 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Avakyan",
"R. M.",
""
],
[
"Chubaryan",
"E. V.",
""
],
[
"Yeranyan",
"A. H.",
""
]
] | The gravitation field of the flat plate was investigated. It have been shown that there exist the internal solution of Einstein equations sewed together with external one, which described a ''homogeneous'' gravitational field. |
1006.5848 | Henrik Zinkernagel | Svend E. Rugh, Henrik Zinkernagel | Weyl's principle, cosmic time and quantum fundamentalism | To appear in the section on "Physical and philosophical perspectives
on probability and time" in S. Hartmann et al. (eds.) "Explanation,
Prediction and Confirmation", Springer's The Philosophy of Science in a
European Perspective book series | null | null | null | gr-qc astro-ph.CO quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the necessary physical underpinnings for setting up the
cosmological standard model with a global cosmic time parameter. In particular,
we discuss the role of Weyl's principle which asserts that cosmic matter moves
according to certain regularity requirements. After a brief historical
introduction to Weyl's principle we argue that although the principle is often
not explicitly mentioned in modern standard texts on cosmology, it is
implicitly assumed and is, in fact, necessary for a physically well-defined
notion of cosmic time. We finally point out that Weyl's principle might be in
conflict with the wide-spread idea that the universe at some very early stage
can be described exclusively in terms of quantum theory.
| [
{
"created": "Wed, 30 Jun 2010 13:17:22 GMT",
"version": "v1"
}
] | 2010-07-01 | [
[
"Rugh",
"Svend E.",
""
],
[
"Zinkernagel",
"Henrik",
""
]
] | We examine the necessary physical underpinnings for setting up the cosmological standard model with a global cosmic time parameter. In particular, we discuss the role of Weyl's principle which asserts that cosmic matter moves according to certain regularity requirements. After a brief historical introduction to Weyl's principle we argue that although the principle is often not explicitly mentioned in modern standard texts on cosmology, it is implicitly assumed and is, in fact, necessary for a physically well-defined notion of cosmic time. We finally point out that Weyl's principle might be in conflict with the wide-spread idea that the universe at some very early stage can be described exclusively in terms of quantum theory. |
0806.0845 | Jose' P. S. Lemos | Jos\'e P. S. Lemos, Oleg B. Zaslavskii | Black hole mimickers: regular versus singular behavior | 30 pages, 1 figure, references added, minor changes in the revised
version | Phys.Rev.D78:024040,2008 | 10.1103/PhysRevD.78.024040 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black hole mimickers are possible alternatives to black holes, they would
look observationally almost like black holes but would have no horizon. The
properties in the near-horizon region where gravity is strong can be quite
different for both type of objects, but at infinity it could be difficult to
discern black holes from their mimickers. To disentangle this possible
confusion, we examine the near-horizon properties, and their connection with
far away properties, of some candidates to black mimickers. We study
spherically symmetric uncharged or charged but non-extremal objects, as well as
spherically symmetric charged extremal objects. Within the uncharged or charged
but non-extremal black hole mimickers, we study non-extremal
$\epsilon$-wormholes on the threshold of the formation of an event horizon, of
which a subclass are called black foils, and gravastars. Within the charged
extremal black hole mimickers we study extremal $\epsilon$-wormholes on the
threshold of the formation of an event horizon, quasi-black holes, and
wormholes on the basis of quasi-black holes from Bonnor stars. We elucidate,
whether or not the objects belonging to these two classes remain regular in the
near-horizon limit. The requirement of full regularity, i.e., finite curvature
and absence of naked behavior, up to an arbitrary neighborhood of the
gravitational radius of the object enables one to rule out potential mimickers
in most of the cases. A list ranking the best mimickers up to the worse is
given. Since, in observational astrophysics it is difficult to find extremal
configurations (the best mimickers in the ranking), whereas non-extremal
configurations are really bad mimickers, the task of distinguishing black holes
from their mimickers seems to be less difficult than one could think of.
| [
{
"created": "Wed, 4 Jun 2008 19:49:09 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Aug 2008 22:09:39 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Lemos",
"José P. S.",
""
],
[
"Zaslavskii",
"Oleg B.",
""
]
] | Black hole mimickers are possible alternatives to black holes, they would look observationally almost like black holes but would have no horizon. The properties in the near-horizon region where gravity is strong can be quite different for both type of objects, but at infinity it could be difficult to discern black holes from their mimickers. To disentangle this possible confusion, we examine the near-horizon properties, and their connection with far away properties, of some candidates to black mimickers. We study spherically symmetric uncharged or charged but non-extremal objects, as well as spherically symmetric charged extremal objects. Within the uncharged or charged but non-extremal black hole mimickers, we study non-extremal $\epsilon$-wormholes on the threshold of the formation of an event horizon, of which a subclass are called black foils, and gravastars. Within the charged extremal black hole mimickers we study extremal $\epsilon$-wormholes on the threshold of the formation of an event horizon, quasi-black holes, and wormholes on the basis of quasi-black holes from Bonnor stars. We elucidate, whether or not the objects belonging to these two classes remain regular in the near-horizon limit. The requirement of full regularity, i.e., finite curvature and absence of naked behavior, up to an arbitrary neighborhood of the gravitational radius of the object enables one to rule out potential mimickers in most of the cases. A list ranking the best mimickers up to the worse is given. Since, in observational astrophysics it is difficult to find extremal configurations (the best mimickers in the ranking), whereas non-extremal configurations are really bad mimickers, the task of distinguishing black holes from their mimickers seems to be less difficult than one could think of. |
gr-qc/0511018 | David Brown | David Brown | The Midpoint Rule as a Variational--Symplectic Integrator. I.
Hamiltonian Systems | 11 pages, 8 figures, REVTeX | Phys.Rev. D73 (2006) 024001 | 10.1103/PhysRevD.73.024001 | null | gr-qc physics.comp-ph | null | Numerical algorithms based on variational and symplectic integrators exhibit
special features that make them promising candidates for application to general
relativity and other constrained Hamiltonian systems. This paper lays part of
the foundation for such applications. The midpoint rule for Hamilton's
equations is examined from the perspectives of variational and symplectic
integrators. It is shown that the midpoint rule preserves the symplectic form,
conserves Noether charges, and exhibits excellent long--term energy behavior.
The energy behavior is explained by the result, shown here, that the midpoint
rule exactly conserves a phase space function that is close to the Hamiltonian.
The presentation includes several examples.
| [
{
"created": "Thu, 3 Nov 2005 21:23:46 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Brown",
"David",
""
]
] | Numerical algorithms based on variational and symplectic integrators exhibit special features that make them promising candidates for application to general relativity and other constrained Hamiltonian systems. This paper lays part of the foundation for such applications. The midpoint rule for Hamilton's equations is examined from the perspectives of variational and symplectic integrators. It is shown that the midpoint rule preserves the symplectic form, conserves Noether charges, and exhibits excellent long--term energy behavior. The energy behavior is explained by the result, shown here, that the midpoint rule exactly conserves a phase space function that is close to the Hamiltonian. The presentation includes several examples. |
1503.06780 | Boris Latosh | S. O. Alexeyev, B. N. Latosh, A. N. Petrov | Maeda-Dadhich Solutions as Real Black Holes | null | Phys. Rev. D 92, 104046, 2015 | 10.1103/PhysRevD.92.104046 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A four-dimensional static Schwarzschild-like solution obtained in [3]-[6] in
the frames of the Einstein-Gauss-Bonnet gravity at the Kaluza-Klein split is
analyzed. The matter in these solutions is created by auxiliary dimensions. The
main goal of our work is to study physically sensible characteristics, which
could be observable. Study of the perturbed equations demonstrates their
stability under linear perturbations. The specific combinations of the
parameters, permitting to construct black hole-like objects with one or two
horizons or naked singularities are determined. Stable orbits of test particles
around these black holes are presented. We show the exotic thermodynamical
properties of the solution, when the Hawking evaporation law has the behavior
opposite to usual one in General Relativity.
| [
{
"created": "Mon, 23 Mar 2015 19:42:34 GMT",
"version": "v1"
},
{
"created": "Sat, 2 May 2015 16:07:07 GMT",
"version": "v2"
},
{
"created": "Thu, 4 Jun 2015 16:52:27 GMT",
"version": "v3"
},
{
"created": "Tue, 18 Aug 2015 13:14:20 GMT",
"version": "v4"
}
] | 2016-01-07 | [
[
"Alexeyev",
"S. O.",
""
],
[
"Latosh",
"B. N.",
""
],
[
"Petrov",
"A. N.",
""
]
] | A four-dimensional static Schwarzschild-like solution obtained in [3]-[6] in the frames of the Einstein-Gauss-Bonnet gravity at the Kaluza-Klein split is analyzed. The matter in these solutions is created by auxiliary dimensions. The main goal of our work is to study physically sensible characteristics, which could be observable. Study of the perturbed equations demonstrates their stability under linear perturbations. The specific combinations of the parameters, permitting to construct black hole-like objects with one or two horizons or naked singularities are determined. Stable orbits of test particles around these black holes are presented. We show the exotic thermodynamical properties of the solution, when the Hawking evaporation law has the behavior opposite to usual one in General Relativity. |
0705.0080 | Michael Ibison | M. Ibison | Cosmological test of the Yilmaz theory of gravity | null | Class.Quant.Grav.23:577-589,2006 | 10.1088/0264-9381/23/3/001 | null | gr-qc | null | We test the Yilmaz theory of gravitation by working out the corresponding
Friedmann-type equations generated by assuming the Friedmann-Robertson-Walker
cosmological metrics. In the case that space is flat the theory is consistent
only with either a completely empty universe or a negative energy vacuum that
decays to produce a constant density of matter. In both cases the total energy
remains zero at all times, and in the latter case the acceleration of the
expansion is always negative. To obtain a more flexible and potentially more
realistic cosmology, the equation of state relating the pressure and energy
density of the matter creation process must be different from the vacuum, as
for example is the case in the steady-state models of Gold, Bondi, Hoyle and
others. The theory does not support the cosmological principle for curved space
K =/= 0 cosmological metrics.
| [
{
"created": "Tue, 1 May 2007 06:50:20 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Ibison",
"M.",
""
]
] | We test the Yilmaz theory of gravitation by working out the corresponding Friedmann-type equations generated by assuming the Friedmann-Robertson-Walker cosmological metrics. In the case that space is flat the theory is consistent only with either a completely empty universe or a negative energy vacuum that decays to produce a constant density of matter. In both cases the total energy remains zero at all times, and in the latter case the acceleration of the expansion is always negative. To obtain a more flexible and potentially more realistic cosmology, the equation of state relating the pressure and energy density of the matter creation process must be different from the vacuum, as for example is the case in the steady-state models of Gold, Bondi, Hoyle and others. The theory does not support the cosmological principle for curved space K =/= 0 cosmological metrics. |
gr-qc/9908036 | R. S. Bhalerao | B. Ram (New Mexico State University) | The Mass Quantum and Black Hole Entropy | final version which appeared in Phys. Lett. A | Phys.Lett. A265 (2000) 1-4 | 10.1016/S0375-9601(99)00868-3 | null | gr-qc hep-th | null | We give a method in which a quantum of mass equal to twice the Planck mass
arises naturally. Then using Bose-Einstein statistics we derive an expression
for the black hole entropy which physically tends to the Bekenstein-Hawking
formula.
| [
{
"created": "Wed, 11 Aug 1999 07:25:51 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Feb 2000 06:03:10 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Ram",
"B.",
"",
"New Mexico State University"
]
] | We give a method in which a quantum of mass equal to twice the Planck mass arises naturally. Then using Bose-Einstein statistics we derive an expression for the black hole entropy which physically tends to the Bekenstein-Hawking formula. |
0908.4593 | Mikolaj Korzynski | Mikolaj Korzynski | Covariant coarse-graining of inhomogeneous dust flow in General
Relativity | 17 pages, 5 figures. Version accepted in Classical and Quantum
Gravity. | Class.Quant.Grav.27:105015,2010 | 10.1088/0264-9381/27/10/105015 | AEI-2010-031 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new definition of coarse-grained quantities describing the dust flow in
General Relativity is proposed. It assigns the coarse--grained expansion, shear
and vorticity to finite-size comoving domains of fluid in a covariant,
coordinate-independent manner. The coarse--grained quantities are all
quasi-local functionals, depending only on the geometry of the boundary of the
considered domain. They can be thought of as relativistic generalizations of
simple volume averages of local quantities in a flat space. The procedure is
based on the isometric embedding theorem for S^2 surfaces and thus requires the
boundary of the domain in question to have spherical topology and positive
scalar curvature. We prove that in the limit of infinitesimally small volume
the proposed quantities reproduce the local expansion, shear and vorticity. In
case of irrotational flow we derive the time evolution for the coarse-grained
quantities and show that its structure is very similar to the evolution
equation for their local counterparts. Additional terms appearing in it may
serve as a measure of the backreacton of small-scale inhomogeneities of the
flow on the large-scale motion of the fluid inside the domain and therefore the
result may be interesting in the context of the cosmological backreaction
problem. We also consider the application of the proposed coarse-graining
procedure to a number of known exact solutions of Einstein equations with dust
and show that it yields reasonable results.
| [
{
"created": "Mon, 31 Aug 2009 18:20:46 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Sep 2009 12:32:36 GMT",
"version": "v2"
},
{
"created": "Thu, 12 Nov 2009 01:15:18 GMT",
"version": "v3"
},
{
"created": "Fri, 12 Mar 2010 16:54:09 GMT",
"version": "v4"
}
] | 2014-11-20 | [
[
"Korzynski",
"Mikolaj",
""
]
] | A new definition of coarse-grained quantities describing the dust flow in General Relativity is proposed. It assigns the coarse--grained expansion, shear and vorticity to finite-size comoving domains of fluid in a covariant, coordinate-independent manner. The coarse--grained quantities are all quasi-local functionals, depending only on the geometry of the boundary of the considered domain. They can be thought of as relativistic generalizations of simple volume averages of local quantities in a flat space. The procedure is based on the isometric embedding theorem for S^2 surfaces and thus requires the boundary of the domain in question to have spherical topology and positive scalar curvature. We prove that in the limit of infinitesimally small volume the proposed quantities reproduce the local expansion, shear and vorticity. In case of irrotational flow we derive the time evolution for the coarse-grained quantities and show that its structure is very similar to the evolution equation for their local counterparts. Additional terms appearing in it may serve as a measure of the backreacton of small-scale inhomogeneities of the flow on the large-scale motion of the fluid inside the domain and therefore the result may be interesting in the context of the cosmological backreaction problem. We also consider the application of the proposed coarse-graining procedure to a number of known exact solutions of Einstein equations with dust and show that it yields reasonable results. |
2004.05342 | Hrvoje Stefancic | Dalibor Perkovic and Hrvoje Stefancic | Barotropic fluid compatible parametrizations of dark energy | v1: 19 pages, 1 table, 4 figures. v2: minor changes, references
added. v3: version accepted in EPJC | null | 10.1140/epjc/s10052-020-8199-9 | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Parametrizations of Equation of state parameter as a function of the scale
factor or redshift are frequently used in dark energy modeling. The question
investigated in this paper is if parametrizations proposed in the literature
are compatible with the dark energy being a barotropic fluid. The test of this
compatibility is based on the functional form of the speed of sound squared,
which for barotropic fluid dark energy follows directly from the function for
the Equation of state parameter. The requirement that the speed of sound
squared should be between 0 and speed of light squared provides constraints on
model parameters using analytical and numerical methods. It is found that this
fundamental requirement eliminates a large number of parametrizations as
barotropic fluid dark energy models and puts strong constraints on parameters
of other dark energy parametrizations.
| [
{
"created": "Sat, 11 Apr 2020 09:19:07 GMT",
"version": "v1"
},
{
"created": "Fri, 1 May 2020 20:23:09 GMT",
"version": "v2"
},
{
"created": "Wed, 15 Jul 2020 13:19:46 GMT",
"version": "v3"
}
] | 2020-08-26 | [
[
"Perkovic",
"Dalibor",
""
],
[
"Stefancic",
"Hrvoje",
""
]
] | Parametrizations of Equation of state parameter as a function of the scale factor or redshift are frequently used in dark energy modeling. The question investigated in this paper is if parametrizations proposed in the literature are compatible with the dark energy being a barotropic fluid. The test of this compatibility is based on the functional form of the speed of sound squared, which for barotropic fluid dark energy follows directly from the function for the Equation of state parameter. The requirement that the speed of sound squared should be between 0 and speed of light squared provides constraints on model parameters using analytical and numerical methods. It is found that this fundamental requirement eliminates a large number of parametrizations as barotropic fluid dark energy models and puts strong constraints on parameters of other dark energy parametrizations. |
2012.00258 | Pardyumn Kumar Sahoo | Parbati Sahoo, P.H.R.S. Moraes, Marcelo M. Lapola, P.K. Sahoo | Traversable wormholes in the traceless $f(R,T)$ gravity | Revision submitted to IJMPD | International Journal of Modern Physics D, 30 (2021) 2150100 | 10.1142/S0218271821501005 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We present a traversable wormhole solution using the traceless $f(R,T)$
theory of gravity. In the $f(R,T)$ gravity, the Ricci scalar $R$ in the
Einstein-Hilbert action is replaced by a function of $R$ and trace of the
energy momentum tensor $T$. The traceless version of the $f(R,T)$ gravity gives
rise to a possible wormhole geometry without need for "exotic matter", which
violates the principle of causality. Using a physically plausible ansatz for
the wormhole's shape function, the traceless field equations lead to compliance
with the weak energy condition at very well defined intervals of the coupling
constant $\lambda$ in the $f(R,T)=R+2\lambda T$ form. Our solution leads to
other well-behaved energy conditions considering some possible values of the
parameter $\omega$ in the equation of state $p_r=\omega \rho$, with $p_r$ being
the radial pressure and $\rho $ the density. The energy conditions are obeyed
in the ranges $\lambda < -4\pi$ and $\omega > -1$. Through the calculation of
the Volume Integral Quantifier, one sees that this wormholes can be traversable
and respect the causality, since the amount of exotic matter in its interior
can be arbitrarily small.
| [
{
"created": "Tue, 1 Dec 2020 04:22:27 GMT",
"version": "v1"
},
{
"created": "Sun, 30 May 2021 16:58:02 GMT",
"version": "v2"
},
{
"created": "Tue, 13 Jul 2021 07:55:02 GMT",
"version": "v3"
}
] | 2021-09-02 | [
[
"Sahoo",
"Parbati",
""
],
[
"Moraes",
"P. H. R. S.",
""
],
[
"Lapola",
"Marcelo M.",
""
],
[
"Sahoo",
"P. K.",
""
]
] | We present a traversable wormhole solution using the traceless $f(R,T)$ theory of gravity. In the $f(R,T)$ gravity, the Ricci scalar $R$ in the Einstein-Hilbert action is replaced by a function of $R$ and trace of the energy momentum tensor $T$. The traceless version of the $f(R,T)$ gravity gives rise to a possible wormhole geometry without need for "exotic matter", which violates the principle of causality. Using a physically plausible ansatz for the wormhole's shape function, the traceless field equations lead to compliance with the weak energy condition at very well defined intervals of the coupling constant $\lambda$ in the $f(R,T)=R+2\lambda T$ form. Our solution leads to other well-behaved energy conditions considering some possible values of the parameter $\omega$ in the equation of state $p_r=\omega \rho$, with $p_r$ being the radial pressure and $\rho $ the density. The energy conditions are obeyed in the ranges $\lambda < -4\pi$ and $\omega > -1$. Through the calculation of the Volume Integral Quantifier, one sees that this wormholes can be traversable and respect the causality, since the amount of exotic matter in its interior can be arbitrarily small. |
1406.4326 | Emma Jakobsson | Ingemar Bengtsson, S\"oren Holst, Emma Jakobsson | Classics Illustrated: Limits of Spacetimes | 23 pages, 13 figures | Class. Quantum Grav. 31 (2014) 205008 | 10.1088/0264-9381/31/20/205008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We carefully study the $e \rightarrow m$ and $e \rightarrow 0$ limits of the
Reissner-Nordstr\"om spacetime using Geroch's definition of limits of
spacetimes. This is implemented by embedding the one-parameter family of
spacetimes in anti-de Sitter space, and as a result we obtain metrically
correct Penrose diagrams. For $e \rightarrow m$ two distinct limits are
studied.
| [
{
"created": "Tue, 17 Jun 2014 11:31:19 GMT",
"version": "v1"
},
{
"created": "Mon, 6 Oct 2014 15:58:50 GMT",
"version": "v2"
}
] | 2014-10-07 | [
[
"Bengtsson",
"Ingemar",
""
],
[
"Holst",
"Sören",
""
],
[
"Jakobsson",
"Emma",
""
]
] | We carefully study the $e \rightarrow m$ and $e \rightarrow 0$ limits of the Reissner-Nordstr\"om spacetime using Geroch's definition of limits of spacetimes. This is implemented by embedding the one-parameter family of spacetimes in anti-de Sitter space, and as a result we obtain metrically correct Penrose diagrams. For $e \rightarrow m$ two distinct limits are studied. |
1810.08911 | Leo Medeiros Gouvea | R. R. Cuzinatto, L. G. Medeiros, P. J. Pompeia | Higher-order modified Starobinsky inflation | 32 pages, 10 figures, minor changes, new references added | JCAP 02 (2019) 055 | 10.1088/1475-7516/2019/02/055 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An extension of the Starobinsky model is proposed. Besides the usual
Starobinsky Lagrangian, a term proportional to the derivative of the scalar
curvature, $\nabla_{\mu}R\nabla^{\mu}R$, is considered. The analyzis is done in
the Einstein frame with the introduction of a scalar field and a vector field.
We show that inflation is attainable in our model, allowing for a graceful
exit. We also build the cosmological perturbations and obtain the leading-order
curvature power spectrum, scalar and tensor tilts and tensor-to-scalar ratio.
The tensor and curvature power spectrums are compared to the most recent
observations from BICEP2/Keck collaboration. We verify that the
scalar-to-tensor rate $r$ can be expected to be up to three times the values
predicted by Starobinsky model.
| [
{
"created": "Sun, 21 Oct 2018 08:07:57 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Oct 2018 03:25:42 GMT",
"version": "v2"
},
{
"created": "Thu, 31 Jan 2019 19:37:02 GMT",
"version": "v3"
}
] | 2019-03-04 | [
[
"Cuzinatto",
"R. R.",
""
],
[
"Medeiros",
"L. G.",
""
],
[
"Pompeia",
"P. J.",
""
]
] | An extension of the Starobinsky model is proposed. Besides the usual Starobinsky Lagrangian, a term proportional to the derivative of the scalar curvature, $\nabla_{\mu}R\nabla^{\mu}R$, is considered. The analyzis is done in the Einstein frame with the introduction of a scalar field and a vector field. We show that inflation is attainable in our model, allowing for a graceful exit. We also build the cosmological perturbations and obtain the leading-order curvature power spectrum, scalar and tensor tilts and tensor-to-scalar ratio. The tensor and curvature power spectrums are compared to the most recent observations from BICEP2/Keck collaboration. We verify that the scalar-to-tensor rate $r$ can be expected to be up to three times the values predicted by Starobinsky model. |
1807.06263 | Dao-Jun Liu | Yang Huang, Dao-Jun Liu, Xiang-hua Zhai and Xin-zhou Li | On the instability for massive scalar fields in Kerr-Newman spacetime | 8 pages, 5 figures, accepted for publication in PRD | Phys. Rev. D 98, 025021 (2018) | 10.1103/PhysRevD.98.025021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is known that a massive charged scalar field can trigger a superradiant
instability in the background of a Kerr-Newman black hole. In this paper, we
present a numerical study of such an instability by using the continued
fraction method. It is shown that for given a black hole, the unstable scalar
mode with a specific azimuthal index $m$ only occurs in a finite region in the
parameter space of the scalar field. The maximum mass of the scalar cloud is
exactly the upper bound of the mass of the unstable modes. We show that due to
the electromagnetic interaction between the scalar field and the Kerr-Newman
black hole, the growth rate of the instability can be $15.7\%$ larger than that
of a scalar field in Kerr spacetime of the same rotation parameter. In
addition, we find a maximum value of the growth rate $\tau^{-1}=1.788\times
10^{-7}M^{-1}$, which is about $4\%$ larger than that in the Kerr case.
| [
{
"created": "Tue, 17 Jul 2018 07:34:21 GMT",
"version": "v1"
}
] | 2018-08-01 | [
[
"Huang",
"Yang",
""
],
[
"Liu",
"Dao-Jun",
""
],
[
"Zhai",
"Xiang-hua",
""
],
[
"Li",
"Xin-zhou",
""
]
] | It is known that a massive charged scalar field can trigger a superradiant instability in the background of a Kerr-Newman black hole. In this paper, we present a numerical study of such an instability by using the continued fraction method. It is shown that for given a black hole, the unstable scalar mode with a specific azimuthal index $m$ only occurs in a finite region in the parameter space of the scalar field. The maximum mass of the scalar cloud is exactly the upper bound of the mass of the unstable modes. We show that due to the electromagnetic interaction between the scalar field and the Kerr-Newman black hole, the growth rate of the instability can be $15.7\%$ larger than that of a scalar field in Kerr spacetime of the same rotation parameter. In addition, we find a maximum value of the growth rate $\tau^{-1}=1.788\times 10^{-7}M^{-1}$, which is about $4\%$ larger than that in the Kerr case. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.