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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2312.07237 | Inna Ivanova | Victor Berezin, Inna Ivanova | Conformal invariance, cosmological particle production and imitation of
dark matter | Based on the talk presented at the ICAA-2023 Virtual Conference | null | null | null | gr-qc | http://creativecommons.org/licenses/by-sa/4.0/ | Using a model for an ideal fluid with a variable number of particles, a
phenomenological description of the processes of particle production in strong
external fields is investigated. The conformal invariance of the creation law
is shown, which imposes rather rigorous restrictions on the possible types of
sources. It appears that the combinations with the particle number density can
imitate dark matter within this model.
| [
{
"created": "Tue, 12 Dec 2023 13:06:43 GMT",
"version": "v1"
}
] | 2023-12-13 | [
[
"Berezin",
"Victor",
""
],
[
"Ivanova",
"Inna",
""
]
] | Using a model for an ideal fluid with a variable number of particles, a phenomenological description of the processes of particle production in strong external fields is investigated. The conformal invariance of the creation law is shown, which imposes rather rigorous restrictions on the possible types of sources. It appears that the combinations with the particle number density can imitate dark matter within this model. |
1702.06855 | Ahmadjon Abdujabbarov | Bobir Toshmatov, Cosimo Bambi, Bobomurat Ahmedov, Ahmadjon
Abdujabbarov, Zden\v{e}k Stuchl\'ik | Energy conditions of non-singular black hole spacetimes in conformal
gravity | 10 pages, 9 figures | Eur. Phys. J. C (2017) 77:542 | 10.1140/epjc/s10052-017-5112-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Conformal gravity can elegantly solve the problem of spacetime singularities
present in Einstein's gravity. For every physical spacetime, there is an
infinite family of conformally-equivalent singularity-free metrics. In the
unbroken phase, every non-singular metric is equivalent and can be used to
infer the physical properties of the spacetime. In the broken phase, a
Higgs-like mechanism should select a certain vacuum, which thus becomes the
physical one. However, in the absence of the complete theoretical framework we
do not know how to select the right vacuum. In this paper, we study the energy
conditions of non-singular black hole spacetimes obtained in conformal gravity
assuming they are solutions of Einstein's gravity with an effective
energy-momentum tensor. We check whether such conditions can be helpful to
select the vacuum of the broken phase.
| [
{
"created": "Tue, 21 Feb 2017 13:24:49 GMT",
"version": "v1"
},
{
"created": "Mon, 14 Aug 2017 10:50:55 GMT",
"version": "v2"
}
] | 2017-08-15 | [
[
"Toshmatov",
"Bobir",
""
],
[
"Bambi",
"Cosimo",
""
],
[
"Ahmedov",
"Bobomurat",
""
],
[
"Abdujabbarov",
"Ahmadjon",
""
],
[
"Stuchlík",
"Zdeněk",
""
]
] | Conformal gravity can elegantly solve the problem of spacetime singularities present in Einstein's gravity. For every physical spacetime, there is an infinite family of conformally-equivalent singularity-free metrics. In the unbroken phase, every non-singular metric is equivalent and can be used to infer the physical properties of the spacetime. In the broken phase, a Higgs-like mechanism should select a certain vacuum, which thus becomes the physical one. However, in the absence of the complete theoretical framework we do not know how to select the right vacuum. In this paper, we study the energy conditions of non-singular black hole spacetimes obtained in conformal gravity assuming they are solutions of Einstein's gravity with an effective energy-momentum tensor. We check whether such conditions can be helpful to select the vacuum of the broken phase. |
2407.09591 | Yongqiang Wang | Xin Su, Chen-Hao Hao, Yong-Qiang Wang | Ellis wormhole with nonlinear electromagnetic field | 21 pages, 8 figures. arXiv admin note: text overlap with
arXiv:2311.17557 | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we present the spherically symmetric wormhole in Einstein's
gravity coupling phantom field and nonlinear electromagnetic field. Numerical
results show that this solution violates the Null Energy Condition (NEC), and
as the parameters change, the ADM mass of the entire spacetime changes from
positive to negative. In addition, we analyze the light ring (LR) of the
solution and demonstrate the astronomical observation properties. Especially
when negative mass appears, the general LR will not appear, only a ``special
unstable LR" exists at the throat, which is caused by the repulsive effect of
the negative mass on both sides of the wormhole. Finally, we draw the embedding
diagram to reflect the geometric characteristics of the wormhole.
| [
{
"created": "Fri, 12 Jul 2024 17:31:52 GMT",
"version": "v1"
}
] | 2024-07-16 | [
[
"Su",
"Xin",
""
],
[
"Hao",
"Chen-Hao",
""
],
[
"Wang",
"Yong-Qiang",
""
]
] | In this paper, we present the spherically symmetric wormhole in Einstein's gravity coupling phantom field and nonlinear electromagnetic field. Numerical results show that this solution violates the Null Energy Condition (NEC), and as the parameters change, the ADM mass of the entire spacetime changes from positive to negative. In addition, we analyze the light ring (LR) of the solution and demonstrate the astronomical observation properties. Especially when negative mass appears, the general LR will not appear, only a ``special unstable LR" exists at the throat, which is caused by the repulsive effect of the negative mass on both sides of the wormhole. Finally, we draw the embedding diagram to reflect the geometric characteristics of the wormhole. |
1011.5848 | Amitai Bin-Nun | Amitai Y. Bin-Nun | Strong Gravitational Lensing by Sgr A* | 13 pages, 9 figures. Submitted as invited review article for the GR19
issue of CQG | Class.Quant.Grav.28:114003,2011 | 10.1088/0264-9381/28/11/114003 | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In recent years, there has been increasing recognition of the potential of
the galactic center as a probe of general relativity in the strong field. There
is almost certainly a black hole at Sgr A* in the galactic center, and this
would allow us the opportunity to probe dynamics near the exterior of the black
hole. In the last decade, there has been research into extreme gravitational
lensing in the galactic center. Unlike in most applications of gravitational
lensing, where the bending angle is of the order of several arc seconds, very
large bending angles are possible for light that closely approaches a black
hole. Photons may even loop multiple times around a black hole before reaching
the observer. There have been many proposals to use light's close approach to
the black hole as a probe of the black hole metric. Of particular interest is
the property of light lensed by the S stars orbiting in the galactic center.
This paper will review some of the attempts made to study extreme lensing as
well as extend the analysis of lensing by S stars. In particular, we are
interested in the effect of a Reissner-Nordstrom like 1/r^2 term in the metric
and how this would affect the properties of relativistic images.
| [
{
"created": "Fri, 26 Nov 2010 17:54:43 GMT",
"version": "v1"
}
] | 2011-05-24 | [
[
"Bin-Nun",
"Amitai Y.",
""
]
] | In recent years, there has been increasing recognition of the potential of the galactic center as a probe of general relativity in the strong field. There is almost certainly a black hole at Sgr A* in the galactic center, and this would allow us the opportunity to probe dynamics near the exterior of the black hole. In the last decade, there has been research into extreme gravitational lensing in the galactic center. Unlike in most applications of gravitational lensing, where the bending angle is of the order of several arc seconds, very large bending angles are possible for light that closely approaches a black hole. Photons may even loop multiple times around a black hole before reaching the observer. There have been many proposals to use light's close approach to the black hole as a probe of the black hole metric. Of particular interest is the property of light lensed by the S stars orbiting in the galactic center. This paper will review some of the attempts made to study extreme lensing as well as extend the analysis of lensing by S stars. In particular, we are interested in the effect of a Reissner-Nordstrom like 1/r^2 term in the metric and how this would affect the properties of relativistic images. |
gr-qc/9512046 | Nobuyuki Sakai | Nobuyuki Sakai | Dynamic Monopoles and Spacetime Structure | 2 pages, latex, uuencoded postscript figures; based on gr-qc/9512045,
and presented at 1st RESCUE International Symposium THE COSMOLOGICAL CONSTANT
AND THE EVOLUTION OF THE UNIVERSE, The University of Tokyo, November 7-10,
1995 | null | null | WU-AP/56/95 | gr-qc astro-ph hep-th | null | According to previous work on magnetic monopoles, static regular solutions
are nonexistent if the vacuum expectation value of the Higgs field $\eta$ is
larger than a critical value $\eta_{{\rm cr}}$, which is of the order of the
Planck mass. In order to understand the properties of monopoles for
$\eta>\eta_{{\rm cr}}$, we investigate their dynamics numerically and classify
those dynamical solutions into three types as follows. If $\eta$ is larger than
another critical value $\eta_{{\rm inf}}~(>\eta_{{\rm cr}})$, a monopole
inflates and a wormhole structure appears around it. In the case of $\eta_{{\rm
cr}}<\eta<\eta_{{\rm inf}}$, inflation does not occur and the dynamics depend
on the ratio of the Higgs self coupling constant $\lambda$ and the gauge
coupling constant $e^2$: if $\lambda/e^2\stackrel{<}{\sim}1$, a monopole just
shrinks and becomes a black hole; otherwise, a monopole approaches a stable
configuration.
| [
{
"created": "Thu, 28 Dec 1995 22:04:01 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Jan 1996 07:52:42 GMT",
"version": "v2"
}
] | 2008-02-03 | [
[
"Sakai",
"Nobuyuki",
""
]
] | According to previous work on magnetic monopoles, static regular solutions are nonexistent if the vacuum expectation value of the Higgs field $\eta$ is larger than a critical value $\eta_{{\rm cr}}$, which is of the order of the Planck mass. In order to understand the properties of monopoles for $\eta>\eta_{{\rm cr}}$, we investigate their dynamics numerically and classify those dynamical solutions into three types as follows. If $\eta$ is larger than another critical value $\eta_{{\rm inf}}~(>\eta_{{\rm cr}})$, a monopole inflates and a wormhole structure appears around it. In the case of $\eta_{{\rm cr}}<\eta<\eta_{{\rm inf}}$, inflation does not occur and the dynamics depend on the ratio of the Higgs self coupling constant $\lambda$ and the gauge coupling constant $e^2$: if $\lambda/e^2\stackrel{<}{\sim}1$, a monopole just shrinks and becomes a black hole; otherwise, a monopole approaches a stable configuration. |
2010.06461 | Marios Bounakis | Marios Bounakis, Ian G. Moss, Gerasimos Rigopoulos | Observational constraints on Hyperinflation | 16 pages, 12 figures | null | 10.1088/1475-7516/2021/02/006 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a Hyperinflation model involving a field doublet on a hyperbolic
field-space manifold and an exponential potential, providing a concise
treatment of the evolution of the entropic and adiabatic perturbations around
the homogeneous hyperbolic attractor solution. We find that the adiabatic
spectral index narrows down the admissible values of the potential's slope to a
very small region, severely restricting the state space of the allowed
background solutions.
| [
{
"created": "Tue, 13 Oct 2020 15:14:05 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Feb 2021 16:49:01 GMT",
"version": "v2"
}
] | 2021-02-08 | [
[
"Bounakis",
"Marios",
""
],
[
"Moss",
"Ian G.",
""
],
[
"Rigopoulos",
"Gerasimos",
""
]
] | We study a Hyperinflation model involving a field doublet on a hyperbolic field-space manifold and an exponential potential, providing a concise treatment of the evolution of the entropic and adiabatic perturbations around the homogeneous hyperbolic attractor solution. We find that the adiabatic spectral index narrows down the admissible values of the potential's slope to a very small region, severely restricting the state space of the allowed background solutions. |
gr-qc/9209015 | Juan Garcia-Bellido | Luis J. Garay and Juan Garcia-Bellido | Jordan-Brans-Dicke Quantum Wormholes and Coleman's Mechanism | 22 pp, 1 figure available upon request, LaTeX. Conclusions have been
changed | Nucl.Phys. B400 (1993) 416-434 | 10.1016/0550-3213(93)90411-H | IEM-FT-59/92 | gr-qc hep-th | null | We consider the quantum gravity and cosmology of a Jordan-Brans-Dicke theory,
predicted by string effective actions. We study its canonical formalism and
find that the constraint algebra is that of general relativity, as a
consequence of the general covariance of scalar-tensor theories. We also
analyze the problem of boundary conditions and propose that they must be
imposed in the Jordan frame, in which particles satisfy the strong equivalence
principle. Specifically, we discuss both Hartle-Hawking and wormhole boundary
conditions in the context of quantum cosmology. We find quantum wormhole
solutions for Jordan-Brans-Dicke gravity even in the absence of matter.
Wormholes may affect the constants of nature and, in particular, the
Brans-Dicke parameter. Following Coleman's mechanism, we find a probability
distribution which is strongly peaked at zero cosmological constant and
infinite Brans-Dicke parameter. That is, we recover general relativity as the
effective low energy theory of gravity.
| [
{
"created": "Wed, 30 Sep 1992 16:58:14 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Oct 1992 18:58:22 GMT",
"version": "v2"
}
] | 2009-10-22 | [
[
"Garay",
"Luis J.",
""
],
[
"Garcia-Bellido",
"Juan",
""
]
] | We consider the quantum gravity and cosmology of a Jordan-Brans-Dicke theory, predicted by string effective actions. We study its canonical formalism and find that the constraint algebra is that of general relativity, as a consequence of the general covariance of scalar-tensor theories. We also analyze the problem of boundary conditions and propose that they must be imposed in the Jordan frame, in which particles satisfy the strong equivalence principle. Specifically, we discuss both Hartle-Hawking and wormhole boundary conditions in the context of quantum cosmology. We find quantum wormhole solutions for Jordan-Brans-Dicke gravity even in the absence of matter. Wormholes may affect the constants of nature and, in particular, the Brans-Dicke parameter. Following Coleman's mechanism, we find a probability distribution which is strongly peaked at zero cosmological constant and infinite Brans-Dicke parameter. That is, we recover general relativity as the effective low energy theory of gravity. |
1412.8195 | Vasilis Oikonomou | V.K. Oikonomou | Loop Quantum Cosmology Matter Bounce Reconstruction from $F(R)$ Gravity
Using an Auxiliary Field | Revised version to appear in GERG | null | 10.1007/s10714-015-1970-9 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using the reconstruction technique with an auxiliary field, we investigate
which $F(R)$ gravities can produce the matter bounce cosmological solutions.
Owing to the specific functional form of the matter bounce Hubble parameter,
the reconstruction technique leads, after some simplifications, to the same
Hubble parameter as in the matter bounce scenario. Focusing the study to the
large and small cosmic time $t$ limits, we were able to find which $F(R)$
gravities can generate the matter bounce Hubble parameter. In the case of small
cosmic time limit, which corresponds to large curvature values, the $F(R)$
gravity is $F(R)\sim R+\alpha R^2$, which is an inflation generating gravity,
and at small curvature, or equivalently, large cosmic time, the $F(R)$ gravity
generating the corresponding limit of the matter bounce Hubble parameter, is
$F(R)\sim \frac{1}{R}$, a gravity known to produce late-time acceleration. Thus
we have the physically appealing picture in which a Jordan frame $F(R)$ gravity
that imitates the matter bounce solution at large and small curvatures, can
generate Starobinsky inflation and late-time acceleration. Moreover, the scale
factor corresponding to the reconstruction technique coincides almost
completely to the matter bounce scenario scale factor, when considered in the
aforementioned limiting curvature cases. This is scrutinized in detail, in
order to examine the validity of the reconstruction method in these limiting
cases, and according to our analysis, exact agreement is achieved.
| [
{
"created": "Sun, 28 Dec 2014 18:35:34 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Oct 2015 13:32:27 GMT",
"version": "v2"
}
] | 2015-11-04 | [
[
"Oikonomou",
"V. K.",
""
]
] | Using the reconstruction technique with an auxiliary field, we investigate which $F(R)$ gravities can produce the matter bounce cosmological solutions. Owing to the specific functional form of the matter bounce Hubble parameter, the reconstruction technique leads, after some simplifications, to the same Hubble parameter as in the matter bounce scenario. Focusing the study to the large and small cosmic time $t$ limits, we were able to find which $F(R)$ gravities can generate the matter bounce Hubble parameter. In the case of small cosmic time limit, which corresponds to large curvature values, the $F(R)$ gravity is $F(R)\sim R+\alpha R^2$, which is an inflation generating gravity, and at small curvature, or equivalently, large cosmic time, the $F(R)$ gravity generating the corresponding limit of the matter bounce Hubble parameter, is $F(R)\sim \frac{1}{R}$, a gravity known to produce late-time acceleration. Thus we have the physically appealing picture in which a Jordan frame $F(R)$ gravity that imitates the matter bounce solution at large and small curvatures, can generate Starobinsky inflation and late-time acceleration. Moreover, the scale factor corresponding to the reconstruction technique coincides almost completely to the matter bounce scenario scale factor, when considered in the aforementioned limiting curvature cases. This is scrutinized in detail, in order to examine the validity of the reconstruction method in these limiting cases, and according to our analysis, exact agreement is achieved. |
1411.0242 | Plamen Fiziev | Plamen Fiziev | Dark Energy and Dark Matter in Stars Physic | Latex file, 7 pages, 11 figures. Symposium "Frontiers of Fundamental
Physics 14", Marseille, France. arXiv admin note: substantial text overlap
with arXiv:1402.2813 | Symposium "Frontiers of Fundamental Physics 14", Marseille,
France, July, 15-18, 2014, PoS(FFP14)080 | null | null | gr-qc astro-ph.CO hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the basic equations and relations for the relativistic static
spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity
(MDG) which is {\em locally} equivalent to the f(R) theories of gravity and
gives an alternative description of the effects of dark matter and dark energy.
The results for the simplest form of the relativistic equation of state (EOS)
of neutron matter are represented. Our approach overcomes the well-known
difficulties of the physics of SSSS in the f(R) theories of gravity introducing
two novel EOS for cosmological energy-pressure densities and dilaton
energy-pressure densities, as well as proper boundary conditions.
| [
{
"created": "Sun, 2 Nov 2014 11:25:19 GMT",
"version": "v1"
}
] | 2014-11-05 | [
[
"Fiziev",
"Plamen",
""
]
] | We present the basic equations and relations for the relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which is {\em locally} equivalent to the f(R) theories of gravity and gives an alternative description of the effects of dark matter and dark energy. The results for the simplest form of the relativistic equation of state (EOS) of neutron matter are represented. Our approach overcomes the well-known difficulties of the physics of SSSS in the f(R) theories of gravity introducing two novel EOS for cosmological energy-pressure densities and dilaton energy-pressure densities, as well as proper boundary conditions. |
2110.15541 | Theo Verwimp | Theo Verwimp | Unified prescription for the generation of electroweak and gravitational
gauge field Lagrangian on a principal fiber bundle | 12 pages, adapted version of the original publication: references
changed, conclusions unchanged | J.Math.Phys.31(12),December 1990,pages 3047-3052 | 10.1063/1.528957 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Glashow-Weinberg-Salam gauge field Lagrangian for electroweak theory and
the Townsend-Zardecki action for gravitation are obtained from the same type of
Yang-Mills Weil form on a principal fiber bundle over space-time, with symmetry
group U(2) and SO(2,3), respectively. The unified geometrical approach given
here shows that fiber bundle reduction and symmetry breaking are essential not
only in electroweak theory but also in the SO(2,3) gauge theory for
gravitation. In fact, the process of symmetry breaking in electroweak theory
and the soldering of the anti-de Sitter bundle, essential in the interpretation
of SO(2,3) gauge theory as a theory for gravitation, are corresponding
geometrical concepts.
| [
{
"created": "Fri, 29 Oct 2021 05:12:14 GMT",
"version": "v1"
}
] | 2021-11-03 | [
[
"Verwimp",
"Theo",
""
]
] | The Glashow-Weinberg-Salam gauge field Lagrangian for electroweak theory and the Townsend-Zardecki action for gravitation are obtained from the same type of Yang-Mills Weil form on a principal fiber bundle over space-time, with symmetry group U(2) and SO(2,3), respectively. The unified geometrical approach given here shows that fiber bundle reduction and symmetry breaking are essential not only in electroweak theory but also in the SO(2,3) gauge theory for gravitation. In fact, the process of symmetry breaking in electroweak theory and the soldering of the anti-de Sitter bundle, essential in the interpretation of SO(2,3) gauge theory as a theory for gravitation, are corresponding geometrical concepts. |
gr-qc/9608051 | Jose Wadih Maluf | J. W. Maluf (Universidade de Brasilia) | On the distribution of gravitational energy in the de Sitter space | 18 pages, LaTex file, no figures, to appear in the J. Math. Phys | J.Math.Phys. 37 (1996) 6293-6301 | 10.1063/1.531777 | null | gr-qc | null | We calculate the total gravitational energy and the gravitational energy
density of the de Sitter space using the definition of localized energy that
arises in the framework of the teleparallel equivalent of general relativity.
We find that the gravitational energy can only be defined within the
cosmological horizon and is largely concentrated in regions far from the center
of spherical symmetry, i.e., in the vicinity of the maximal spacelike radial
coordinate $R=\sqrt{ 3 \over \Lambda}$. The smaller the cosmological constant,
the farther the concentration of energy. This result complies with the
phenomenological features of the de Sitter space, namely, the existence of a
radial acceleration directed away from the center of symmetry experienced by a
test particle in the de Sitter space. Einstein already contemplated the de
Sitter solution as a world with a surface distribution of matter, a picture
that is in agreement with the present analysis.
| [
{
"created": "Wed, 21 Aug 1996 16:26:18 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Maluf",
"J. W.",
"",
"Universidade de Brasilia"
]
] | We calculate the total gravitational energy and the gravitational energy density of the de Sitter space using the definition of localized energy that arises in the framework of the teleparallel equivalent of general relativity. We find that the gravitational energy can only be defined within the cosmological horizon and is largely concentrated in regions far from the center of spherical symmetry, i.e., in the vicinity of the maximal spacelike radial coordinate $R=\sqrt{ 3 \over \Lambda}$. The smaller the cosmological constant, the farther the concentration of energy. This result complies with the phenomenological features of the de Sitter space, namely, the existence of a radial acceleration directed away from the center of symmetry experienced by a test particle in the de Sitter space. Einstein already contemplated the de Sitter solution as a world with a surface distribution of matter, a picture that is in agreement with the present analysis. |
0712.0539 | Bernard Linet | Bernard Linet | Electrostatics in a wormhole geometry | latex, 5 pages, a slight correction | null | null | null | gr-qc | null | We determine in closed form the electrostatic potential generated by a point
charge at rest in a simple model of static spherically symmetric wormhole. From
this, we deduce the electrostatic self-energy of this point charge.
| [
{
"created": "Tue, 4 Dec 2007 14:59:24 GMT",
"version": "v1"
},
{
"created": "Mon, 14 Jan 2008 11:50:08 GMT",
"version": "v2"
}
] | 2008-01-14 | [
[
"Linet",
"Bernard",
""
]
] | We determine in closed form the electrostatic potential generated by a point charge at rest in a simple model of static spherically symmetric wormhole. From this, we deduce the electrostatic self-energy of this point charge. |
gr-qc/9608049 | Jose Wadih Maluf | J. W. Maluf, E. F. Martins and A. Kneip (Universidade de Brasilia) | Gravitational energy of rotating black holes | 18 pages, LaTex file, one figure | J.Math.Phys. 37 (1996) 6302-6310 | 10.1063/1.531778 | null | gr-qc | null | In the teleparallel equivalent of general relativity the energy density of
asymptotically flat gravitational fields can be naturaly defined as a scalar
density restricted to a three-dimensional spacelike hypersurface $\Sigma$.
Integration over the whole $\Sigma$ yields the standard ADM energy. After
establishing the reference space with zero gravitational energy we obtain the
expression of the localized energy for a Kerr black hole. The expression of the
energy inside a surface of constant radius can be explicitly calculated in the
limit of small $a$, the specific angular momentum. Such expression turns out to
be exactly the same as the one obtained by means of the method preposed
recently by Brown and York. We also calculate the energy contained within the
outer horizon of the black hole for {\it any} value of $a$. The result is
practically indistinguishable from $E=2M_{ir}$, where $M_{ir}$ is the
irreducible mass of the black hole.
| [
{
"created": "Wed, 21 Aug 1996 16:37:13 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Maluf",
"J. W.",
"",
"Universidade de Brasilia"
],
[
"Martins",
"E. F.",
"",
"Universidade de Brasilia"
],
[
"Kneip",
"A.",
"",
"Universidade de Brasilia"
]
] | In the teleparallel equivalent of general relativity the energy density of asymptotically flat gravitational fields can be naturaly defined as a scalar density restricted to a three-dimensional spacelike hypersurface $\Sigma$. Integration over the whole $\Sigma$ yields the standard ADM energy. After establishing the reference space with zero gravitational energy we obtain the expression of the localized energy for a Kerr black hole. The expression of the energy inside a surface of constant radius can be explicitly calculated in the limit of small $a$, the specific angular momentum. Such expression turns out to be exactly the same as the one obtained by means of the method preposed recently by Brown and York. We also calculate the energy contained within the outer horizon of the black hole for {\it any} value of $a$. The result is practically indistinguishable from $E=2M_{ir}$, where $M_{ir}$ is the irreducible mass of the black hole. |
1904.04101 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Thin-shell wormholes from Kiselev black holes | 9 pages, 3 figures | Turk. J. Phys., vol. 43, 213-220 (2019) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper discusses the theoretical construction of thin-shell wormholes
from Kiselev black holes. We assume a barotropic equation of state for the
exotic matter on the shell. While most of these wormholes are unstable to
linearized radial perturbations, a limit argument is used to show that under
certain conditions, stable solutions can be found.
| [
{
"created": "Mon, 8 Apr 2019 14:48:06 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Jun 2019 14:58:57 GMT",
"version": "v2"
}
] | 2019-06-06 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | This paper discusses the theoretical construction of thin-shell wormholes from Kiselev black holes. We assume a barotropic equation of state for the exotic matter on the shell. While most of these wormholes are unstable to linearized radial perturbations, a limit argument is used to show that under certain conditions, stable solutions can be found. |
2209.15225 | Hocheol Lee | Bum-Hoon Lee, Hochoel Lee, Wonwoo Lee, Nils A. Nilsson, and Somyadip
Thakur | Induced cosmological anisotropy by a gauge-gravity interaction | 46 pages, 15 figures; title of paper has been changed, added and
clarified discussion of results, added figure, updated references. Accepted
for publication in Physics of the Dark Universe | null | null | CQUeST-2022-0698 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a simple model which generates cosmological anisotropies on top of
standard FLRW geometry. This is in some sense reminiscent of the mean field
approximation, where the mean field cosmological model under consideration
would be the standard FLRW, and the anisotropy is a small perturbative
correction on top of it. Using a supergravity-inspired model, we confirm that
the stable fixed point of our model corresponds to standard FLRW cosmology. We
use a Bianchi VII$_0$-type model supplemented with a scalar and $U(1)$ gauge
fields, and we show that the anisotropies of the geometry are generated by the
non-trivial interaction between the gravity sector and the $U(1)$ gauge sector.
Studying the attractor flow, we show that the anisotropies are present at early
times (high redshift) and decay asymptotically to an FLRW attractor fixed
point. With such a mechanism, observations of non-isotropy are not
contradictory to FLRW geometry or indeed the $\Lambda$CDM model. Such models
could in principle shed some insights on the present cosmological tensions.
| [
{
"created": "Fri, 30 Sep 2022 04:42:47 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Jun 2023 12:07:51 GMT",
"version": "v2"
},
{
"created": "Thu, 21 Mar 2024 12:48:02 GMT",
"version": "v3"
}
] | 2024-03-22 | [
[
"Lee",
"Bum-Hoon",
""
],
[
"Lee",
"Hochoel",
""
],
[
"Lee",
"Wonwoo",
""
],
[
"Nilsson",
"Nils A.",
""
],
[
"Thakur",
"Somyadip",
""
]
] | We present a simple model which generates cosmological anisotropies on top of standard FLRW geometry. This is in some sense reminiscent of the mean field approximation, where the mean field cosmological model under consideration would be the standard FLRW, and the anisotropy is a small perturbative correction on top of it. Using a supergravity-inspired model, we confirm that the stable fixed point of our model corresponds to standard FLRW cosmology. We use a Bianchi VII$_0$-type model supplemented with a scalar and $U(1)$ gauge fields, and we show that the anisotropies of the geometry are generated by the non-trivial interaction between the gravity sector and the $U(1)$ gauge sector. Studying the attractor flow, we show that the anisotropies are present at early times (high redshift) and decay asymptotically to an FLRW attractor fixed point. With such a mechanism, observations of non-isotropy are not contradictory to FLRW geometry or indeed the $\Lambda$CDM model. Such models could in principle shed some insights on the present cosmological tensions. |
gr-qc/0601075 | Anna M. Nobili | G. L. Comandi, M. L. Chiofalo, R. Toncelli, D. Bramanti, E. Polacco,
and A. M. Nobili | Dynamical response of the "GGG" rotor to test the Equivalence Principle:
theory, simulation and experiment. Part I: the normal modes | Accepted for publication by "Review of Scientific Instruments" on Jan
16, 2006. 16 2-column pages, 9 figures | Rev.Sci.Instrum. 77 (2006) 034501 | 10.1063/1.2173075 | null | gr-qc | null | Recent theoretical work suggests that violation of the Equivalence Principle
might be revealed in a measurement of the fractional differential acceleration
$\eta$ between two test bodies -of different composition, falling in the
gravitational field of a source mass- if the measurement is made to the level
of $\eta\simeq 10^{-13}$ or better. This being within the reach of ground based
experiments, gives them a new impetus. However, while slowly rotating torsion
balances in ground laboratories are close to reaching this level, only an
experiment performed in low orbit around the Earth is likely to provide a much
better accuracy.
We report on the progress made with the "Galileo Galilei on the Ground" (GGG)
experiment, which aims to compete with torsion balances using an instrument
design also capable of being converted into a much higher sensitivity space
test.
In the present and following paper (Part I and Part II), we demonstrate that
the dynamical response of the GGG differential accelerometer set into
supercritical rotation -in particular its normal modes (Part I) and rejection
of common mode effects (Part II)- can be predicted by means of a simple but
effective model that embodies all the relevant physics. Analytical solutions
are obtained under special limits, which provide the theoretical understanding.
A simulation environment is set up, obtaining quantitative agreement with the
available experimental data on the frequencies of the normal modes, and on the
whirling behavior. This is a needed and reliable tool for controlling and
separating perturbative effects from the expected signal, as well as for
planning the optimization of the apparatus.
| [
{
"created": "Wed, 18 Jan 2006 16:07:06 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Comandi",
"G. L.",
""
],
[
"Chiofalo",
"M. L.",
""
],
[
"Toncelli",
"R.",
""
],
[
"Bramanti",
"D.",
""
],
[
"Polacco",
"E.",
""
],
[
"Nobili",
"A. M.",
""
]
] | Recent theoretical work suggests that violation of the Equivalence Principle might be revealed in a measurement of the fractional differential acceleration $\eta$ between two test bodies -of different composition, falling in the gravitational field of a source mass- if the measurement is made to the level of $\eta\simeq 10^{-13}$ or better. This being within the reach of ground based experiments, gives them a new impetus. However, while slowly rotating torsion balances in ground laboratories are close to reaching this level, only an experiment performed in low orbit around the Earth is likely to provide a much better accuracy. We report on the progress made with the "Galileo Galilei on the Ground" (GGG) experiment, which aims to compete with torsion balances using an instrument design also capable of being converted into a much higher sensitivity space test. In the present and following paper (Part I and Part II), we demonstrate that the dynamical response of the GGG differential accelerometer set into supercritical rotation -in particular its normal modes (Part I) and rejection of common mode effects (Part II)- can be predicted by means of a simple but effective model that embodies all the relevant physics. Analytical solutions are obtained under special limits, which provide the theoretical understanding. A simulation environment is set up, obtaining quantitative agreement with the available experimental data on the frequencies of the normal modes, and on the whirling behavior. This is a needed and reliable tool for controlling and separating perturbative effects from the expected signal, as well as for planning the optimization of the apparatus. |
gr-qc/9911086 | Yungui Gong | Yungui Gong | On Holography in Brans-Dicke Cosmology | talk given at the 9th Midwest Relativity Conference held in
University of Illinois at Urbana-Champaign, November 12-13, 1999. 8 figures | null | null | utexas-hep-20 | gr-qc | null | The holographic bound in Brans-Dicke $k=1$ matter dominated Cosmology is
discussed. In this talk, both the apparent horizon and the particle horizon are
taken for the holographic bound. The covariant entropy conjecture proposed by
Bousso is also discussed.
| [
{
"created": "Mon, 22 Nov 1999 20:25:14 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Gong",
"Yungui",
""
]
] | The holographic bound in Brans-Dicke $k=1$ matter dominated Cosmology is discussed. In this talk, both the apparent horizon and the particle horizon are taken for the holographic bound. The covariant entropy conjecture proposed by Bousso is also discussed. |
gr-qc/0702085 | Andre Fuzfa | A. Fuzfa, J.-M. Alimi | An Awesome Hypothesis for Dark Energy : The Abnormally Weighting Energy | 3 pages, 1 figure, prepared for the Proceedings of the 11th Marcel
Grossmann Conference, held in Berlin, Germany, July 2006 | null | 10.1142/9789812834300_0256 | null | gr-qc astro-ph | null | We introduce the Abnormally Weighting Energy (AWE) hypothesis in which dark
energy (DE) is presented as a consequence of the violation of the weak
equivalence principle (WEP) at cosmological scales by some dark sector. Indeed,
this implies a violation of the strong equivalence principle (SEP) for ordinary
matter and consequent cosmic acceleration in the observable frame as well as
variation of the gravitational constant. The consequent DE mechanism build upon
the AWE hypothesis (i) does not require a violation of the strong energy
condition $p<-\rho c^2/3$, (ii) assumes rather non-negligible direct couplings
to the gravitational scalar field (iii) offers a natural convergence mechanism
toward general relativity (iv) accounts fairly for supernovae data from various
couplings and equations of state of the dark sector as well as density
parameters very close to the ones of the concordance model $\Lambda CDM$.
Finally (v), this AWE mechanism typically ends up with an Einstein-de Sitter
expansion regime once the attractor is reached.
| [
{
"created": "Thu, 15 Feb 2007 09:49:05 GMT",
"version": "v1"
}
] | 2016-11-15 | [
[
"Fuzfa",
"A.",
""
],
[
"Alimi",
"J. -M.",
""
]
] | We introduce the Abnormally Weighting Energy (AWE) hypothesis in which dark energy (DE) is presented as a consequence of the violation of the weak equivalence principle (WEP) at cosmological scales by some dark sector. Indeed, this implies a violation of the strong equivalence principle (SEP) for ordinary matter and consequent cosmic acceleration in the observable frame as well as variation of the gravitational constant. The consequent DE mechanism build upon the AWE hypothesis (i) does not require a violation of the strong energy condition $p<-\rho c^2/3$, (ii) assumes rather non-negligible direct couplings to the gravitational scalar field (iii) offers a natural convergence mechanism toward general relativity (iv) accounts fairly for supernovae data from various couplings and equations of state of the dark sector as well as density parameters very close to the ones of the concordance model $\Lambda CDM$. Finally (v), this AWE mechanism typically ends up with an Einstein-de Sitter expansion regime once the attractor is reached. |
1902.05129 | Kayll Lake | Sheref Nasereldin and Kayll Lake | Boundary Orbits: 1 Static Spacetimes | 4 pages revtex 4.1 Updated and expanded | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The study of circular orbits in spacetime is of astrophysical importance. The
identification and classification of circular orbits in both static and
stationary spacetimes remains an active area of interest. Even in the simplest
static spherically symmetric case, it is well known that the introduction of a
cosmological constant in vacuum leads to the study of quartic polynomials in
order to locate \textit{boundary orbits}, those that straddle between stable
and unstable orbits. These orbits are often referred to as `marginally stable
orbits' or `indifferently stable orbits'. A comprehensive study of texts offers
little clarification as to the stability or instability of these boundary
orbits. Here we argue that the direct use of second order perturbation theory
immediately shows that these boundary orbits are unstable in the perturbative
sense. Our study here includes the two-particle Curzon-Chazy solution.
| [
{
"created": "Wed, 13 Feb 2019 21:02:42 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Jun 2019 19:40:17 GMT",
"version": "v2"
}
] | 2019-06-07 | [
[
"Nasereldin",
"Sheref",
""
],
[
"Lake",
"Kayll",
""
]
] | The study of circular orbits in spacetime is of astrophysical importance. The identification and classification of circular orbits in both static and stationary spacetimes remains an active area of interest. Even in the simplest static spherically symmetric case, it is well known that the introduction of a cosmological constant in vacuum leads to the study of quartic polynomials in order to locate \textit{boundary orbits}, those that straddle between stable and unstable orbits. These orbits are often referred to as `marginally stable orbits' or `indifferently stable orbits'. A comprehensive study of texts offers little clarification as to the stability or instability of these boundary orbits. Here we argue that the direct use of second order perturbation theory immediately shows that these boundary orbits are unstable in the perturbative sense. Our study here includes the two-particle Curzon-Chazy solution. |
1312.1682 | Muhammad Jamil Amir | M. Jamil Amir, Sadia Sattar | Locally Rotationally Symmetric Vacuum Solutions in f(R) Gravity | 22 pages, Accepted for publication in Int. J. Theor. Phys | null | 10.1007/s10773-013-1865-z | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper is devoted to find the Locally Rotationally Symmetric (LRS) vacuum
solutions in the context of f(R) theory of gravity. Actually, we have
considered the three metrics representing the whole family of LRS spacetimes
and solved the field equations by using metric approach as well as the
assumption of constant scalar curvature. It is mention here that R may be zero
or non-zero. In all we found 10 different solutions.
| [
{
"created": "Thu, 5 Dec 2013 07:12:51 GMT",
"version": "v1"
}
] | 2015-06-18 | [
[
"Amir",
"M. Jamil",
""
],
[
"Sattar",
"Sadia",
""
]
] | This paper is devoted to find the Locally Rotationally Symmetric (LRS) vacuum solutions in the context of f(R) theory of gravity. Actually, we have considered the three metrics representing the whole family of LRS spacetimes and solved the field equations by using metric approach as well as the assumption of constant scalar curvature. It is mention here that R may be zero or non-zero. In all we found 10 different solutions. |
gr-qc/0405136 | B. S. Sathyaprakash | B.S. Sathyaprakash (Cardiff University) | Gravitational Radiation - Observing the Dark and Dense Universe | 24 pages, invited review at ICRC2003, Tsukuba, Japan | null | null | null | gr-qc | null | Astronomical observations in the electromagnetic window - microwave, radio
and optical - have revealed that most of the Universe is dark. The only reason
we know that dark matter exists is because of its gravitational influence on
luminous matter. It is plausible that a small fraction of that dark matter is
clumped, and strongly gravitating. Such systems are potential sources of
gravitational radiation that can be observed with a world-wide network of
gravitational wave antennas. Electromagnetic astronomy has also revealed
objects and phenomena - supernovae, neutron stars, black holes and the big bang
- that are without doubt extremely strong emitters of the radiation targeted by
the gravitational wave interferometric and resonant bar detectors. In this talk
I will highlight why gravitational waves arise in Einstein's theory, how they
interact with matter, what the chief astronomical sources of the radiation are,
and in which way by observing them we can gain a better understanding of the
dark and dense Universe.
| [
{
"created": "Fri, 28 May 2004 00:05:07 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sathyaprakash",
"B. S.",
"",
"Cardiff University"
]
] | Astronomical observations in the electromagnetic window - microwave, radio and optical - have revealed that most of the Universe is dark. The only reason we know that dark matter exists is because of its gravitational influence on luminous matter. It is plausible that a small fraction of that dark matter is clumped, and strongly gravitating. Such systems are potential sources of gravitational radiation that can be observed with a world-wide network of gravitational wave antennas. Electromagnetic astronomy has also revealed objects and phenomena - supernovae, neutron stars, black holes and the big bang - that are without doubt extremely strong emitters of the radiation targeted by the gravitational wave interferometric and resonant bar detectors. In this talk I will highlight why gravitational waves arise in Einstein's theory, how they interact with matter, what the chief astronomical sources of the radiation are, and in which way by observing them we can gain a better understanding of the dark and dense Universe. |
2110.10667 | Ilkka M\"akinen | Jerzy Lewandowski, Ilkka M\"akinen | Scalar curvature operator for models of loop quantum gravity on a
cubical graph | v3: 43 pages, 5 figures. A few minor corrections. Expanded discussion
in section 5.2. Version accepted for publication. v2: 41 pages, 5 figures.
Major revision correcting an error in the previous version. v1: 30 pages, 3
figures | null | 10.1103/PhysRevD.106.046013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we introduce a new operator representing the
three-dimensional scalar curvature in loop quantum gravity. Our construction
does not apply to the entire kinematical Hilbert space of loop quantum gravity;
instead, the operator is defined on the Hilbert space of a fixed cubical graph.
The starting point of our work is to write the spatial Ricci scalar classically
as a function of the densitized triad and its SU(2)-covariant derivatives. We
pass from the classical expression to a quantum operator through a
regularization procedure, in which covariant derivatives of the triad are
discretized as finite differences of gauge covariant flux variables on the
cubical lattice provided by the graph. While more work is needed in order to
extend our construction to encompass states based on all possible graphs, the
operator presented here can be applied in models such as quantum-reduced loop
gravity and effective dynamics, which are derived from the kinematical
framework of full loop quantum gravity, and are formulated in terms of states
defined on cubical graphs.
| [
{
"created": "Wed, 20 Oct 2021 17:18:46 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Mar 2022 18:25:17 GMT",
"version": "v2"
},
{
"created": "Thu, 1 Jun 2023 12:04:41 GMT",
"version": "v3"
}
] | 2023-06-02 | [
[
"Lewandowski",
"Jerzy",
""
],
[
"Mäkinen",
"Ilkka",
""
]
] | In this article we introduce a new operator representing the three-dimensional scalar curvature in loop quantum gravity. Our construction does not apply to the entire kinematical Hilbert space of loop quantum gravity; instead, the operator is defined on the Hilbert space of a fixed cubical graph. The starting point of our work is to write the spatial Ricci scalar classically as a function of the densitized triad and its SU(2)-covariant derivatives. We pass from the classical expression to a quantum operator through a regularization procedure, in which covariant derivatives of the triad are discretized as finite differences of gauge covariant flux variables on the cubical lattice provided by the graph. While more work is needed in order to extend our construction to encompass states based on all possible graphs, the operator presented here can be applied in models such as quantum-reduced loop gravity and effective dynamics, which are derived from the kinematical framework of full loop quantum gravity, and are formulated in terms of states defined on cubical graphs. |
1709.03798 | Tapobrata Sarkar | Kaushik Bhattacharya, Dipanjan Dey, Arindam Mazumdar, Tapobrata Sarkar | New class of naked singularities and their observational signatures | Substantial modifications in the results. Present version is fully
re-written, and the title is also changed. 24 pages, 10 figures | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | By imposing suitable junction conditions on a space-like hyper-surface, we
obtain a two-parameter family of possible static configurations from
gravitational collapse. These exemplify a new class of naked singularities. We
show that these admit a consistent description via a two-fluid model, one of
which might be dust. We then study lensing and accretion disk properties of our
solution and point out possible differences with black hole scenarios. The
distinctive features of our solution, compared to the existing naked
singularity solutions in the literature are discussed.
| [
{
"created": "Tue, 12 Sep 2017 12:19:01 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Sep 2017 14:07:14 GMT",
"version": "v2"
},
{
"created": "Tue, 2 Jan 2018 12:07:52 GMT",
"version": "v3"
},
{
"created": "Sat, 8 Feb 2020 12:48:52 GMT",
"version": "v4"
}
] | 2020-02-11 | [
[
"Bhattacharya",
"Kaushik",
""
],
[
"Dey",
"Dipanjan",
""
],
[
"Mazumdar",
"Arindam",
""
],
[
"Sarkar",
"Tapobrata",
""
]
] | By imposing suitable junction conditions on a space-like hyper-surface, we obtain a two-parameter family of possible static configurations from gravitational collapse. These exemplify a new class of naked singularities. We show that these admit a consistent description via a two-fluid model, one of which might be dust. We then study lensing and accretion disk properties of our solution and point out possible differences with black hole scenarios. The distinctive features of our solution, compared to the existing naked singularity solutions in the literature are discussed. |
gr-qc/9612036 | Arvind Borde | Arvind Borde and Alexander Vilenkin | Singularities in Inflationary Cosmology: A Review | Plain TeX. Twelve pages, five figures (that will automatically appear
if you use "dvips" to print the file) | Int.J.Mod.Phys.D5:813-824,1996 | 10.1142/S0218271896000497 | null | gr-qc | null | We review here some recent results that show that inflationary cosmological
models must contain initial singularities. We also present a new singularity
theorem. The question of the initial singularity re-emerges in inflationary
cosmology because inflation is known to be generically future-eternal. It is
natural to ask, therefore, if inflationary models can be continued into the
infinite past in a non-singular way. The results that we discuss show that the
answer to the question is ``no.'' This means that we cannot use inflation as a
way of avoiding the question of the birth of the Universe. We also argue that
our new theorem suggests - in a sense that we explain in the paper - that the
Universe cannot be infinitely old.
| [
{
"created": "Sun, 15 Dec 1996 00:29:07 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Borde",
"Arvind",
""
],
[
"Vilenkin",
"Alexander",
""
]
] | We review here some recent results that show that inflationary cosmological models must contain initial singularities. We also present a new singularity theorem. The question of the initial singularity re-emerges in inflationary cosmology because inflation is known to be generically future-eternal. It is natural to ask, therefore, if inflationary models can be continued into the infinite past in a non-singular way. The results that we discuss show that the answer to the question is ``no.'' This means that we cannot use inflation as a way of avoiding the question of the birth of the Universe. We also argue that our new theorem suggests - in a sense that we explain in the paper - that the Universe cannot be infinitely old. |
gr-qc/9604056 | null | Masayuki Tanimoto, Tatsuhiko Koike, and Akio Hosoya | Dynamics of compact homogeneous universes | 32 pages with 2 figures (LaTeX with epsf macro package) | J.Math.Phys. 38 (1997) 350-368 | 10.1063/1.531853 | TIT/HEP-322/COSMO-68 | gr-qc | null | A complete description of dynamics of compact locally homogeneous universes
is given, which, in particular, includes explicit calculations of Teichm\"uller
deformations and careful counting of dynamical degrees of freedom. We regard
each of the universes as a simply connected four dimensional spacetime with
identifications by the action of a discrete subgroup of the isometry group. We
then reduce the identifications defined by the spacetime isometries to ones in
a homogeneous section, and find a condition that such spatial identifications
must satisfy. This is essential for explicit construction of compact
homogenoeus universes. Some examples are demonstrated for Bianchi II, VI${}_0$,
VII${}_0$, and I universal covers.
| [
{
"created": "Wed, 1 May 1996 09:59:26 GMT",
"version": "v1"
},
{
"created": "Sat, 27 Jul 1996 17:04:47 GMT",
"version": "v2"
}
] | 2009-10-28 | [
[
"Tanimoto",
"Masayuki",
""
],
[
"Koike",
"Tatsuhiko",
""
],
[
"Hosoya",
"Akio",
""
]
] | A complete description of dynamics of compact locally homogeneous universes is given, which, in particular, includes explicit calculations of Teichm\"uller deformations and careful counting of dynamical degrees of freedom. We regard each of the universes as a simply connected four dimensional spacetime with identifications by the action of a discrete subgroup of the isometry group. We then reduce the identifications defined by the spacetime isometries to ones in a homogeneous section, and find a condition that such spatial identifications must satisfy. This is essential for explicit construction of compact homogenoeus universes. Some examples are demonstrated for Bianchi II, VI${}_0$, VII${}_0$, and I universal covers. |
gr-qc/0104035 | S. Antoci | S. Antoci, D.-E. Liebscher and L. Mihich | Revisiting Weyl's calculation of the gravitational pull in Bach's
two-body solution | 11 pages, 2 figures. Text to appear in Classical and Quantum Gravity | Class.Quant.Grav. 18 (2001) 3463-3472 | 10.1088/0264-9381/18/17/307 | null | gr-qc | null | When the mass of one of the two bodies tends to zero, Weyl's definition of
the gravitational force in an axially symmetric, static two-body solution can
be given an invariant formulation in terms of a force four-vector. The norm of
this force is calculated for Bach's two-body solution, that is known to be in
one-to-one correspondence with Schwarzschild's original solution when one of
the two masses l, l' is made to vanish. In the limit when, say, l' goes to
zero, the norm of the force divided by l' and calculated at the position of the
vanishing mass is found to coincide with the norm of the acceleration of a test
body kept at rest in Schwarzschild's field. Both norms happen thus to grow
without limit when the test body (respectively the vanishing mass l') is kept
at rest in a position closer and closer to Schwarzschild's two-surface.
| [
{
"created": "Thu, 12 Apr 2001 13:24:50 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Jul 2001 09:05:26 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Antoci",
"S.",
""
],
[
"Liebscher",
"D. -E.",
""
],
[
"Mihich",
"L.",
""
]
] | When the mass of one of the two bodies tends to zero, Weyl's definition of the gravitational force in an axially symmetric, static two-body solution can be given an invariant formulation in terms of a force four-vector. The norm of this force is calculated for Bach's two-body solution, that is known to be in one-to-one correspondence with Schwarzschild's original solution when one of the two masses l, l' is made to vanish. In the limit when, say, l' goes to zero, the norm of the force divided by l' and calculated at the position of the vanishing mass is found to coincide with the norm of the acceleration of a test body kept at rest in Schwarzschild's field. Both norms happen thus to grow without limit when the test body (respectively the vanishing mass l') is kept at rest in a position closer and closer to Schwarzschild's two-surface. |
gr-qc/9510033 | Nicholas Landsman | N.P. Landsman (DAMTP, Cambridge) | Against the Wheeler-DeWitt equation | 12 pages, LaTeX; revised version corrects treatment of open
minisuperspace model. No conclusions are affected by this | Class.Quant.Grav. 12 (1995) L119-L124 | 10.1088/0264-9381/12/12/003 | null | gr-qc | null | The ADM approach to canonical general relativity combined with Dirac's method
of quantizing constrained systems leads to the Wheeler-DeWitt equation. A
number of mathematical as well as physical difficulties that arise in
connection with this equation may be circumvented if one employs a covariant
Hamiltonian method in conjunction with a recently developed, mathematically
rigorous technique to quantize constrained systems using Rieffel induction. The
classical constraints are cleanly separated into four components of a covariant
momentum map coming from the diffeomorphism group of spacetime, each of which
is linear in the canonical momenta, plus a single finite-dimensional quadratic
constraint that arises in any theory, parametrized or not. The new quantization
method is carried through in a minisuperspace example, and is found to produce
a ``wavefunction of the universe". This differs from the proposals of both
Vilenkin and Hartle-Hawking for a closed FRW universe, but happens to coincide
with the latter in the open case.
| [
{
"created": "Tue, 17 Oct 1995 11:12:15 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Nov 1995 13:33:10 GMT",
"version": "v2"
}
] | 2009-10-28 | [
[
"Landsman",
"N. P.",
"",
"DAMTP, Cambridge"
]
] | The ADM approach to canonical general relativity combined with Dirac's method of quantizing constrained systems leads to the Wheeler-DeWitt equation. A number of mathematical as well as physical difficulties that arise in connection with this equation may be circumvented if one employs a covariant Hamiltonian method in conjunction with a recently developed, mathematically rigorous technique to quantize constrained systems using Rieffel induction. The classical constraints are cleanly separated into four components of a covariant momentum map coming from the diffeomorphism group of spacetime, each of which is linear in the canonical momenta, plus a single finite-dimensional quadratic constraint that arises in any theory, parametrized or not. The new quantization method is carried through in a minisuperspace example, and is found to produce a ``wavefunction of the universe". This differs from the proposals of both Vilenkin and Hartle-Hawking for a closed FRW universe, but happens to coincide with the latter in the open case. |
1711.03199 | Jonas Mureika | Luciano Manfredi, Jonas Mureika, John Moffat | Quasinormal Modes of Modified Gravity (MOG) Black Holes | null | Phys. Lett. B779 (2018) 492-497 | 10.1016/j.physletb.2017.11.006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Quasinormal modes (QNMs) for gravitational and electromagnetic
perturbations are calculated in a Scalar-Tensor-Vector (Modified Gravity)
spacetime, which was initially proposed to obtain correct dynamics of galaxies
and galaxy clusters without the need for dark matter. It is found that for the
increasing model parameter $\alpha$, both the real and imaginary parts of the
QNMs decrease compared to those for a standard Schwarzschild black hole. On the
other hand, when taking into account the $1/(1+\alpha)$ mass re-scaling factor
present in MOG, Im($\omega$) matches almost identically that of GR, while
Re($\omega$) is higher. These results can be identified in the ringdown phase
of massive compact object mergers, and are thus timely in light of the recent
gravitational wave detections by LIGO.
| [
{
"created": "Wed, 8 Nov 2017 22:52:59 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Apr 2018 17:02:36 GMT",
"version": "v2"
}
] | 2018-04-18 | [
[
"Manfredi",
"Luciano",
""
],
[
"Mureika",
"Jonas",
""
],
[
"Moffat",
"John",
""
]
] | The Quasinormal modes (QNMs) for gravitational and electromagnetic perturbations are calculated in a Scalar-Tensor-Vector (Modified Gravity) spacetime, which was initially proposed to obtain correct dynamics of galaxies and galaxy clusters without the need for dark matter. It is found that for the increasing model parameter $\alpha$, both the real and imaginary parts of the QNMs decrease compared to those for a standard Schwarzschild black hole. On the other hand, when taking into account the $1/(1+\alpha)$ mass re-scaling factor present in MOG, Im($\omega$) matches almost identically that of GR, while Re($\omega$) is higher. These results can be identified in the ringdown phase of massive compact object mergers, and are thus timely in light of the recent gravitational wave detections by LIGO. |
1005.5397 | Valerio Faraoni | Valerio Faraoni (Bishop's University) | Horizons and singularity in Clifton's spherical solution of f(R) vacuum | 12 pages, LaTeX, 1 figure. Written for the proceedings of the
workshop "Cosmology, Quantum Vacuum and Zeta Functions" in honour of
Professor Emilio Elizalde's 60th birthday, Barcelona, March 8-10, 2010, | null | 10.1007/978-3-642-19760-4_16 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Due to the failure of Birkhoff's theorem, black holes in f(R) gravity
theories in which an effective time-varying cosmological "constant" is present
are, in general, dynamical. Clifton's exact spherical solution of R^(1+\delta)
gravity, which is dynamical and describes a central object embedded in a
spatially flat universe, is studied. It is shown that apparent black hole
horizons disappear and a naked singularity emerges at late times.
| [
{
"created": "Fri, 28 May 2010 20:35:56 GMT",
"version": "v1"
}
] | 2015-05-19 | [
[
"Faraoni",
"Valerio",
"",
"Bishop's University"
]
] | Due to the failure of Birkhoff's theorem, black holes in f(R) gravity theories in which an effective time-varying cosmological "constant" is present are, in general, dynamical. Clifton's exact spherical solution of R^(1+\delta) gravity, which is dynamical and describes a central object embedded in a spatially flat universe, is studied. It is shown that apparent black hole horizons disappear and a naked singularity emerges at late times. |
1711.11375 | Gonzalo Quiroga | C. N Kozameh, J. I. Nieva, and Gonzalo D Quiroga | Spin and Center of mass comparison between the PN approach and the
asymptotic formulation | null | Phys. Rev. D 98, 064005 (2018) | 10.1103/PhysRevD.98.064005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we analyse the similarities and differences between the
equations of motion for the center of mass and intrinsic angular momentum for
isolated sources of gravitational radiation obtained by two different
formulations. One approach is based on the asymptotic formulation of the GR
whereas the other relies on Post- Newtonian methods. Several conclusions are
obtained which could be useful for further developments in both approaches.
| [
{
"created": "Thu, 30 Nov 2017 13:20:36 GMT",
"version": "v1"
}
] | 2018-09-12 | [
[
"Kozameh",
"C. N",
""
],
[
"Nieva",
"J. I.",
""
],
[
"Quiroga",
"Gonzalo D",
""
]
] | In this work we analyse the similarities and differences between the equations of motion for the center of mass and intrinsic angular momentum for isolated sources of gravitational radiation obtained by two different formulations. One approach is based on the asymptotic formulation of the GR whereas the other relies on Post- Newtonian methods. Several conclusions are obtained which could be useful for further developments in both approaches. |
2405.08872 | Ra\'ul Carballo-Rubio | Ra\'ul Carballo-Rubio and Astrid Eichhorn | Black hole horizons must be veiled by photon spheres | 10 pages, 2 figures, Honorable Mention in the Gravity Research
Foundation 2024 Awards for Essays on Gravitation | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Horizons and bound photon orbits are defining features of black holes that
translate into key features of black hole images. We present a purely geometric
proof that spherically symmetric, isolated objects with horizons in gravity
theories with null-geodesic propagation of light must display bound photon
orbits forming a photon sphere. Identifying the key elements of the proof, we
articulate a simpler argument that carries over to more general situations with
modified light propagation and implies the existence of equatorial spherical
photon orbits in axisymmetric spacetimes with reflection symmetry. We conclude
that the \emph{non-}observation of photon rings with very-large-baseline
interferometry would be a very strong indication against a horizon,
irrespective of whether or not the image shows a central brightness depression.
| [
{
"created": "Tue, 14 May 2024 18:00:03 GMT",
"version": "v1"
}
] | 2024-05-16 | [
[
"Carballo-Rubio",
"Raúl",
""
],
[
"Eichhorn",
"Astrid",
""
]
] | Horizons and bound photon orbits are defining features of black holes that translate into key features of black hole images. We present a purely geometric proof that spherically symmetric, isolated objects with horizons in gravity theories with null-geodesic propagation of light must display bound photon orbits forming a photon sphere. Identifying the key elements of the proof, we articulate a simpler argument that carries over to more general situations with modified light propagation and implies the existence of equatorial spherical photon orbits in axisymmetric spacetimes with reflection symmetry. We conclude that the \emph{non-}observation of photon rings with very-large-baseline interferometry would be a very strong indication against a horizon, irrespective of whether or not the image shows a central brightness depression. |
1907.02334 | Yurii Ignat'ev | Yu. G. Ignat'ev and I. A. Kokh | Qualitative and Numerical Analysis of a Cosmological Model Based on an
Asymmetric Scalar Doublet with Minimal Couplings. I. Qualitative Analysis of
the Model | 12 pages, 2 figures, 3 references | Russian Physics Journal,Vol. 61, No. 6, 2018, pp. 1079-1092 | 10.1007/s11182-018-1500-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A qualitative analysis of a cosmological model based on the asymmetric scalar
doublet classical + phantom scalar field with minimal interaction is performed.
It is shown that depending on the parameters of the model, the corresponding
dynamical system can have 1, 3, or 9 stationary points corresponding to
attractive or repulsive centers (1--5) and saddle points (0--4). A physical
analysis of the model is performed.
| [
{
"created": "Thu, 4 Jul 2019 11:41:42 GMT",
"version": "v1"
}
] | 2019-07-05 | [
[
"Ignat'ev",
"Yu. G.",
""
],
[
"Kokh",
"I. A.",
""
]
] | A qualitative analysis of a cosmological model based on the asymmetric scalar doublet classical + phantom scalar field with minimal interaction is performed. It is shown that depending on the parameters of the model, the corresponding dynamical system can have 1, 3, or 9 stationary points corresponding to attractive or repulsive centers (1--5) and saddle points (0--4). A physical analysis of the model is performed. |
1101.5401 | Rahmede Christoph | Mark Hindmarsh, Daniel Litim, Christoph Rahmede | Asymptotically Safe Cosmology | 8 pages; v2: explanations and references added, accepted for
publication in JCAP | JCAP 1107:019,2011 | 10.1088/1475-7516/2011/07/019 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study quantum modifications to cosmology in a Friedmann-Robertson-Walker
universe with and without scalar fields by taking the renormalisation group
running of gravitational and matter couplings into account. We exploit the
Bianchi identity to relate the renormalisation group scale with scale factor
and derive the improved cosmological evolution equations. We find two types of
cosmological fixed points where the renormalisation group scale either freezes
in, or continues to evolve with scale factor. We discuss the implications of
each of these, and classify the different cosmological fixed points with and
without gravity displaying an asymptotically safe renormalisation group fixed
point. We state conditions of existence for an inflating ultraviolet
cosmological fixed point for Einstein gravity coupled to a scalar field. We
also discuss other fixed point solutions such as "scaling" solutions, or fixed
points with equipartition between kinetic and potential energies.
| [
{
"created": "Thu, 27 Jan 2011 21:37:50 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Jun 2011 13:54:33 GMT",
"version": "v2"
}
] | 2011-07-14 | [
[
"Hindmarsh",
"Mark",
""
],
[
"Litim",
"Daniel",
""
],
[
"Rahmede",
"Christoph",
""
]
] | We study quantum modifications to cosmology in a Friedmann-Robertson-Walker universe with and without scalar fields by taking the renormalisation group running of gravitational and matter couplings into account. We exploit the Bianchi identity to relate the renormalisation group scale with scale factor and derive the improved cosmological evolution equations. We find two types of cosmological fixed points where the renormalisation group scale either freezes in, or continues to evolve with scale factor. We discuss the implications of each of these, and classify the different cosmological fixed points with and without gravity displaying an asymptotically safe renormalisation group fixed point. We state conditions of existence for an inflating ultraviolet cosmological fixed point for Einstein gravity coupled to a scalar field. We also discuss other fixed point solutions such as "scaling" solutions, or fixed points with equipartition between kinetic and potential energies. |
0810.2161 | Chopin Soo | Chun-Yu Lin, Chopin Soo | Generalized Painlev\'e-Gullstrand metrics | Typos corrected, additional footnotes | Phys.Lett.B671:493-495,2009 | 10.1016/j.physletb.2008.12.051 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An obstruction to the implementation of spatially flat
Painleve-Gullstrand(PG) slicings is demonstrated, and explicitly discussed for
Reissner-Nordstrom and Schwarzschild-anti-deSitter spacetimes. Generalizations
of PG slicings which are not spatially flat but which remain regular at the
horizons are introduced. These metrics can be obtained from standard
spherically symmetric metrics by physical Lorentz boosts. With these
generalized PG metrics, problematic contributions to the imaginary part of the
action in the Parikh-Wilczek derivation of Hawking radiation due to the
obstruction can be avoided.
| [
{
"created": "Mon, 13 Oct 2008 13:30:16 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Jan 2009 05:12:23 GMT",
"version": "v2"
}
] | 2009-02-02 | [
[
"Lin",
"Chun-Yu",
""
],
[
"Soo",
"Chopin",
""
]
] | An obstruction to the implementation of spatially flat Painleve-Gullstrand(PG) slicings is demonstrated, and explicitly discussed for Reissner-Nordstrom and Schwarzschild-anti-deSitter spacetimes. Generalizations of PG slicings which are not spatially flat but which remain regular at the horizons are introduced. These metrics can be obtained from standard spherically symmetric metrics by physical Lorentz boosts. With these generalized PG metrics, problematic contributions to the imaginary part of the action in the Parikh-Wilczek derivation of Hawking radiation due to the obstruction can be avoided. |
1512.05860 | Rabin Banerjee | Rabin Banerjee, Pradip Mukherjee | Comment on "Thermal Hall Effect and Geometry with Torsion" | LaTeX, 2 pages, expanded with new input | null | null | null | gr-qc cond-mat.other hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is a comment on a paper by Gromov and Abanov [Phys. Rev. Lett. 114,
016802 (2015)]. We will show that there is an inconsistency which renders the
results untenable.
| [
{
"created": "Fri, 18 Dec 2015 06:34:24 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Jul 2016 07:51:04 GMT",
"version": "v2"
}
] | 2016-07-07 | [
[
"Banerjee",
"Rabin",
""
],
[
"Mukherjee",
"Pradip",
""
]
] | This is a comment on a paper by Gromov and Abanov [Phys. Rev. Lett. 114, 016802 (2015)]. We will show that there is an inconsistency which renders the results untenable. |
2304.09080 | Salim Shekh Dr. | S. H. Shekh, M. Muzammil, R. V. Mapari, G. U. Khapekar, A. Dixit | Holographic inflation in non-static plane symmetric space-time | 15-pages; 13-figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The current analysis uses the non-static plane symmetric space-time to
dynamically examine the holographic dark energy model as a candidates of IR
cut-offs (specifically Hubble's and Granda-Oliveros cut-off). Using the Markov
Chain Monte Carlo (MCMC) method, we estimate the best fit values for the model
parameters imposed from the combined datasets of $CC+SC+BAO$. Now, it has been
found that the characteristics of space-time that have been addressed and
formulated using both models are flat universe and observed that the model
appears to be in good agreement with the observations. In addition, we
investigate the behavior of equation of state parameters along with the energy
conditions. Finally, we found that in both the cut-offs the models predict that
the present and late universe are accelerating and the equation of state
parameter behaves like the quintessence model.
| [
{
"created": "Sun, 16 Apr 2023 09:11:37 GMT",
"version": "v1"
}
] | 2023-04-19 | [
[
"Shekh",
"S. H.",
""
],
[
"Muzammil",
"M.",
""
],
[
"Mapari",
"R. V.",
""
],
[
"Khapekar",
"G. U.",
""
],
[
"Dixit",
"A.",
""
]
] | The current analysis uses the non-static plane symmetric space-time to dynamically examine the holographic dark energy model as a candidates of IR cut-offs (specifically Hubble's and Granda-Oliveros cut-off). Using the Markov Chain Monte Carlo (MCMC) method, we estimate the best fit values for the model parameters imposed from the combined datasets of $CC+SC+BAO$. Now, it has been found that the characteristics of space-time that have been addressed and formulated using both models are flat universe and observed that the model appears to be in good agreement with the observations. In addition, we investigate the behavior of equation of state parameters along with the energy conditions. Finally, we found that in both the cut-offs the models predict that the present and late universe are accelerating and the equation of state parameter behaves like the quintessence model. |
gr-qc/0509007 | Andreas W. Aste | Andreas Aste, Dirk Trautmann | Radial fall of a test particle onto an evaporating black hole | 6 pages, 3 figures, LATEX | Can.J.Phys. 83 (2005) 1001-1006 | 10.1139/p05-058 | null | gr-qc | null | A test particle falling into a classical black hole crosses the event horizon
and ends up in the singularity within finite eigentime. In the `more realistic'
case of a `classical' evaporating black hole, an observer falling onto a black
hole observes a sudden evaporation of the hole. This illustrates the fact that
the discussion of the classical process commonly found in the literature may
become obsolete when the black hole has a finite lifetime. The situation is
basically the same for more complex cases, e.g. where a particle collides with
two merging black holes. It should be pointed out that the model used in this
paper is mainly of academic interest, since the description of the physics near
a black hole horizon still presents a difficult problem which is not yet fully
understood, but our model provides a valuable possibility for students to enter
the interesting field of black hole physics and to perform numerical
calculations of their own which are not very involved from the computational
point of view.
| [
{
"created": "Thu, 1 Sep 2005 12:36:36 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Aste",
"Andreas",
""
],
[
"Trautmann",
"Dirk",
""
]
] | A test particle falling into a classical black hole crosses the event horizon and ends up in the singularity within finite eigentime. In the `more realistic' case of a `classical' evaporating black hole, an observer falling onto a black hole observes a sudden evaporation of the hole. This illustrates the fact that the discussion of the classical process commonly found in the literature may become obsolete when the black hole has a finite lifetime. The situation is basically the same for more complex cases, e.g. where a particle collides with two merging black holes. It should be pointed out that the model used in this paper is mainly of academic interest, since the description of the physics near a black hole horizon still presents a difficult problem which is not yet fully understood, but our model provides a valuable possibility for students to enter the interesting field of black hole physics and to perform numerical calculations of their own which are not very involved from the computational point of view. |
1309.2670 | Grasiele Batista Dos Santos | N. Pinto-Neto, G. B. Santos and W. Struyve | Quantum-to-classical transition of primordial cosmological perturbations
in de Broglie-Bohm quantum theory: the bouncing scenario | 5 pages, no figures, revtex4 | Physical Review D 89, 023517 (2014) | 10.1103/PhysRevD.89.023517 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a previous work we have exhibited a clear description of the
quantum-to-classical transition of cosmological quantum fluctuations in the
inflationary scenario using the de Broglie-Bohm quantum theory. These
fluctuations are believed to seed the small inhomogeneities, which are then
responsible for the formation of large scale structures. In this work we show
that using the de Broglie-Bohm theory it is also possible to describe the
quantum-to-classical transition of primordial perturbations which takes place
around a bouncing phase, even if the latter is caused by quantum effects due to
the quantization of the background geometry.
| [
{
"created": "Tue, 10 Sep 2013 21:01:50 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Oct 2013 13:14:49 GMT",
"version": "v2"
}
] | 2014-01-21 | [
[
"Pinto-Neto",
"N.",
""
],
[
"Santos",
"G. B.",
""
],
[
"Struyve",
"W.",
""
]
] | In a previous work we have exhibited a clear description of the quantum-to-classical transition of cosmological quantum fluctuations in the inflationary scenario using the de Broglie-Bohm quantum theory. These fluctuations are believed to seed the small inhomogeneities, which are then responsible for the formation of large scale structures. In this work we show that using the de Broglie-Bohm theory it is also possible to describe the quantum-to-classical transition of primordial perturbations which takes place around a bouncing phase, even if the latter is caused by quantum effects due to the quantization of the background geometry. |
1609.06358 | Andrei Lebed G | Andrei G. Lebed | Breakdown of the equivalence between active gravitational mass and
energy for a quantum body | 4 pages | Journal of Physics: Conference Series, vol. 738, 012036 (2016) | 10.1088/1742-6596/738/1/012036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We determine active gravitational mass operator of the simplest composite
quantum body - a hydrogen atom - within the semiclassical approach to the
Einstein equation for a gravitational field. We show that the expectation value
of the mass is equivalent to energy for stationary quantum states. On the other
hand, it occurs that, for quantum superpositions of stationary states with
constant expectation values of energy, the expectation values of the
gravitational mass exhibit time-dependent oscillations. This breaks the
equivalence between active gravitational mass and energy and can be observed as
a macroscopic effect for a macroscopic ensemble of coherent quantum states of
the atoms. The corresponding experiment could be the first direct observation
of quantum effects in General Relativity.
| [
{
"created": "Tue, 20 Sep 2016 21:11:29 GMT",
"version": "v1"
}
] | 2016-09-28 | [
[
"Lebed",
"Andrei G.",
""
]
] | We determine active gravitational mass operator of the simplest composite quantum body - a hydrogen atom - within the semiclassical approach to the Einstein equation for a gravitational field. We show that the expectation value of the mass is equivalent to energy for stationary quantum states. On the other hand, it occurs that, for quantum superpositions of stationary states with constant expectation values of energy, the expectation values of the gravitational mass exhibit time-dependent oscillations. This breaks the equivalence between active gravitational mass and energy and can be observed as a macroscopic effect for a macroscopic ensemble of coherent quantum states of the atoms. The corresponding experiment could be the first direct observation of quantum effects in General Relativity. |
1901.06994 | Ion I. Cotaescu | Ion I. Cotaescu and Ion Cotaescu Jr | Integral representation of the scalar propagators on the de Sitter
expanding universe | 11 pages, 1 figure | Eur. Phys. J. C (2019) 79:671 | 10.1140/epjc/s10052-019-7180-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new type of integral representation is proposed for the propagators of the
massive Klein-Gordon field minimally coupled to the gravity of the de Sitter
expanding universe. This representation encapsulates the effects of the
Heaviside step functions of the Feynman propagators making possible for the
first time the calculation of Feynman diagrams involving scalar particles on
this background. In order to convince that, a simple example is given outlining
the amplitudes in the second order of perturbations of the Compton effect in
the de Sitter scalar quantum electrodynamics.
| [
{
"created": "Mon, 21 Jan 2019 16:32:59 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Jan 2019 08:26:20 GMT",
"version": "v2"
},
{
"created": "Thu, 31 Jan 2019 08:26:53 GMT",
"version": "v3"
},
{
"created": "Thu, 6 Jun 2019 13:31:08 GMT",
"version": "v4"
},
{
"created": "Mon, 15 Jul 2019 07:30:06 GMT",
"version": "v5"
},
{
"created": "Thu, 14 Jan 2021 18:23:49 GMT",
"version": "v6"
}
] | 2021-01-15 | [
[
"Cotaescu",
"Ion I.",
""
],
[
"Cotaescu",
"Ion",
"Jr"
]
] | A new type of integral representation is proposed for the propagators of the massive Klein-Gordon field minimally coupled to the gravity of the de Sitter expanding universe. This representation encapsulates the effects of the Heaviside step functions of the Feynman propagators making possible for the first time the calculation of Feynman diagrams involving scalar particles on this background. In order to convince that, a simple example is given outlining the amplitudes in the second order of perturbations of the Compton effect in the de Sitter scalar quantum electrodynamics. |
1709.06512 | Amir Hadi Ziaie | Hamid Shabani and Amir Hadi Ziaie | Static Vacuum Solutions on Curved Spacetimes with Torsion | 25 pages, 3 figures | Int. J. Mod. Phys. A 33 1850095 (2018) | 10.1142/S0217751X18500951 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Einstein-Cartan-Kibble-Sciama ({\sf ECKS}) theory of gravity naturally
extends Einstein\rq{}s general relativity ({\sf GR}) to include intrinsic
angular momentum (spin) of matter. The main feature of this theory consists of
an algebraic relation between spacetime torsion and spin of matter which indeed
deprives the torsion of its dynamical content. The Lagrangian of {\sf ECKS}
gravity is proportional to the Ricci curvature scalar constructed out of a
general affine connection so that owing to the influence of matter
energy-momentum and spin, curvature and torsion are produced and interact only
through the spacetime metric. In the absence of spin, the spacetime torsion
vanishes and the theory reduces to {\sf GR}. It is however possible to have
torsion propagation in vacuum by resorting to a model endowed with a
non-minimal coupling between curvature and torsion. In the present work we try
to investigate possible effects of the higher order terms that can be
constructed from spacetime curvature and torsion, as the two basic constituents
of Riemann-Cartan geometry. We consider Lagrangians that include fourth-order
scalar invariants from curvature and torsion and then investigate the resulted
field equations. The solutions that we find show that there could exist, even
in vacuum, nontrivial static spacetimes that admit both black holes and naked
singularities.
| [
{
"created": "Tue, 19 Sep 2017 16:27:44 GMT",
"version": "v1"
},
{
"created": "Thu, 31 May 2018 21:27:24 GMT",
"version": "v2"
}
] | 2018-06-04 | [
[
"Shabani",
"Hamid",
""
],
[
"Ziaie",
"Amir Hadi",
""
]
] | The Einstein-Cartan-Kibble-Sciama ({\sf ECKS}) theory of gravity naturally extends Einstein\rq{}s general relativity ({\sf GR}) to include intrinsic angular momentum (spin) of matter. The main feature of this theory consists of an algebraic relation between spacetime torsion and spin of matter which indeed deprives the torsion of its dynamical content. The Lagrangian of {\sf ECKS} gravity is proportional to the Ricci curvature scalar constructed out of a general affine connection so that owing to the influence of matter energy-momentum and spin, curvature and torsion are produced and interact only through the spacetime metric. In the absence of spin, the spacetime torsion vanishes and the theory reduces to {\sf GR}. It is however possible to have torsion propagation in vacuum by resorting to a model endowed with a non-minimal coupling between curvature and torsion. In the present work we try to investigate possible effects of the higher order terms that can be constructed from spacetime curvature and torsion, as the two basic constituents of Riemann-Cartan geometry. We consider Lagrangians that include fourth-order scalar invariants from curvature and torsion and then investigate the resulted field equations. The solutions that we find show that there could exist, even in vacuum, nontrivial static spacetimes that admit both black holes and naked singularities. |
2307.16161 | Kemal G\"ultekin | Kemal G\"ultekin | Bose-Einstein Condensation and Black Holes in Dark Matter and Dark
Energy | Ph.D thesis; 86 pages; 8 figures | null | null | null | gr-qc astro-ph.CO hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | The main aim of this study is to reveal curved space and particle physics
effects on the formation of Bose-Einstein condensate (BEC) scalar fields in
cosmology and around a black hole. Cosmological scalar fields for dark energy
and dark matter may be considered as a result of Bose-Einstein condensation. In
this regard, our main attention will be devoted to BECs in curved space. By
considering the dynamics of a BEC scalar field at a microscopic level, we first
study the initial phase of the formation of condensation in cosmology. To this
end, we initially introduce an effective Minkowski space formulation that
enables considering only the effect of particle physics processes, excluding
the effect of gravitational particle production and enabling us to see
cosmological evolution more easily. Then, by using this formulation, we study a
model with a trilinear coupling that induces the processes. After considering
the phase evolution of the produced particles, we find that they evolve towards
the formation of a BEC if some specific conditions are satisfied. In principle,
the effective Minkowski space formulation introduced in this study can be
applied to particle physics processes in any sufficiently smooth spacetime. In
this regard, we also analyse if a BEC scalar field is realized in the spacetime
around a Reissner - Nordstr\"om black hole. We find that the produced particles
of particle physics processes are localized in a region around the black hole
and have a tendency toward condensation if the emerged particles are much
heavier than ingoing particles. We also find that such a configuration is
phenomenologically viable only if the scalars and the black hole have dark
electric charges. Finally, we consider gravitational collapse around
Schwarzschild black holes and form a first step towards a study in future about
the effects of gravitational collapse on Bose-Einstein condensation.
| [
{
"created": "Sun, 30 Jul 2023 08:08:18 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Aug 2023 10:51:48 GMT",
"version": "v2"
}
] | 2023-08-11 | [
[
"Gültekin",
"Kemal",
""
]
] | The main aim of this study is to reveal curved space and particle physics effects on the formation of Bose-Einstein condensate (BEC) scalar fields in cosmology and around a black hole. Cosmological scalar fields for dark energy and dark matter may be considered as a result of Bose-Einstein condensation. In this regard, our main attention will be devoted to BECs in curved space. By considering the dynamics of a BEC scalar field at a microscopic level, we first study the initial phase of the formation of condensation in cosmology. To this end, we initially introduce an effective Minkowski space formulation that enables considering only the effect of particle physics processes, excluding the effect of gravitational particle production and enabling us to see cosmological evolution more easily. Then, by using this formulation, we study a model with a trilinear coupling that induces the processes. After considering the phase evolution of the produced particles, we find that they evolve towards the formation of a BEC if some specific conditions are satisfied. In principle, the effective Minkowski space formulation introduced in this study can be applied to particle physics processes in any sufficiently smooth spacetime. In this regard, we also analyse if a BEC scalar field is realized in the spacetime around a Reissner - Nordstr\"om black hole. We find that the produced particles of particle physics processes are localized in a region around the black hole and have a tendency toward condensation if the emerged particles are much heavier than ingoing particles. We also find that such a configuration is phenomenologically viable only if the scalars and the black hole have dark electric charges. Finally, we consider gravitational collapse around Schwarzschild black holes and form a first step towards a study in future about the effects of gravitational collapse on Bose-Einstein condensation. |
1707.00862 | Eduard Mychelkin G. | Eduard G. Mychelkin and Maxim A. Makukov | Unified geometrical basis for the generalized Ehlers identities and
Raychaudhuri equations | Accepted in Reports on Mathematical Physics | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that the timelike, spacelike and null versions of the Ehlers
identity, as well as ensuing Raychaudhuri equations, might be all derived
within a single geometrical approach based on the definition of the Riemann
curvature tensor specified with respect to the corresponding congruence. Still,
spacelike and null cases have a number of non-trivial peculiarities deserving
special attention.
| [
{
"created": "Tue, 4 Jul 2017 09:03:01 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jul 2017 06:32:25 GMT",
"version": "v2"
},
{
"created": "Sat, 28 Oct 2017 13:08:58 GMT",
"version": "v3"
}
] | 2017-10-31 | [
[
"Mychelkin",
"Eduard G.",
""
],
[
"Makukov",
"Maxim A.",
""
]
] | It is shown that the timelike, spacelike and null versions of the Ehlers identity, as well as ensuing Raychaudhuri equations, might be all derived within a single geometrical approach based on the definition of the Riemann curvature tensor specified with respect to the corresponding congruence. Still, spacelike and null cases have a number of non-trivial peculiarities deserving special attention. |
2408.03683 | Santosh Lohakare | Santosh V Lohakare, Soumyadip Niyogi, and B. Mishra | Cosmology in Modified $f(\mathcal{G})$ Gravity: A Late Time Cosmic
Phenomena | 15 pages, 8 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we have introduced a numerical method for solving the
Friedmann equations of modified $f(\mathcal{G})$ gravity in the presence of
pressureless matter, enabling us to predict the redshift behavior of the Hubble
expansion rate. To evaluate the credibility of the model, we applied a Bayesian
MCMC technique using late-time cosmic observations to impose limitations on the
free parameters of the theory. Our results suggest that the $f(\mathcal{G})$
model can reproduce the low-redshift behavior of the standard $\Lambda$CDM
model, but there are significant differences at high redshifts, leading to the
absence of a standard matter-dominated epoch. We also examined the profiles of
cosmographic parameters using the model parameter values from the standard
range to verify the intermediate epochs. Our analysis shows that the highly
promising $f(\mathcal{G})$ model is a feasible candidate for explaining the
current epochs. We presented a dynamical system analysis framework to examine
the stability of the model. Our study identified critical points depicting
various phases of the Universe and explained the evolutionary epochs. We
demonstrated that the model effectively captures the evolution of energy
components over cosmic time, supporting its validity as an alternate
explanation for the observed acceleration of the Universe.
| [
{
"created": "Wed, 7 Aug 2024 10:51:09 GMT",
"version": "v1"
}
] | 2024-08-08 | [
[
"Lohakare",
"Santosh V",
""
],
[
"Niyogi",
"Soumyadip",
""
],
[
"Mishra",
"B.",
""
]
] | In this paper, we have introduced a numerical method for solving the Friedmann equations of modified $f(\mathcal{G})$ gravity in the presence of pressureless matter, enabling us to predict the redshift behavior of the Hubble expansion rate. To evaluate the credibility of the model, we applied a Bayesian MCMC technique using late-time cosmic observations to impose limitations on the free parameters of the theory. Our results suggest that the $f(\mathcal{G})$ model can reproduce the low-redshift behavior of the standard $\Lambda$CDM model, but there are significant differences at high redshifts, leading to the absence of a standard matter-dominated epoch. We also examined the profiles of cosmographic parameters using the model parameter values from the standard range to verify the intermediate epochs. Our analysis shows that the highly promising $f(\mathcal{G})$ model is a feasible candidate for explaining the current epochs. We presented a dynamical system analysis framework to examine the stability of the model. Our study identified critical points depicting various phases of the Universe and explained the evolutionary epochs. We demonstrated that the model effectively captures the evolution of energy components over cosmic time, supporting its validity as an alternate explanation for the observed acceleration of the Universe. |
2106.12050 | Teodor Borislavov Vasilev | Teodor Borislavov Vasilev, Mariam Bouhmadi-L\'opez and Prado
Mart\'in-Moruno | Classical and quantum $f(R)$ cosmology: The big rip, the little rip and
the little sibling of the big rip | Invited review submitted to Universe for the Special Issue on
"Quantum Cosmology", ed. by Prof. Paulo Vargas Moniz, 32 pages, 3 tables. v2:
typos fixed, references added, matches published version | Universe 7 (2021) no.8, 288 | 10.3390/universe7080288 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | The big rip, the little rip and the little sibling of the big rip are
cosmological doomsdays predicted by some phantom dark energy models that could
describe the future evolution of our Universe. When the universe evolves
towards either of these future cosmic events all bounded structures and,
ultimately, space-time itself are ripped apart. Nevertheless, it is commonly
belief that quantum gravity effects may smooth or even avoid these classically
predicted singularities. In this review, we discuss the classical and quantum
occurrence of these riplike events in the scheme of metric $f(R)$ theories of
gravity. The quantum analysis is performed in the framework of $f(R)$ quantum
geometrodynamics. In this context, we analyse the fulfilment of the DeWitt
criterion for the avoidance of these singular fates.
| [
{
"created": "Tue, 22 Jun 2021 20:14:51 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Sep 2021 13:45:02 GMT",
"version": "v2"
}
] | 2021-09-27 | [
[
"Vasilev",
"Teodor Borislavov",
""
],
[
"Bouhmadi-López",
"Mariam",
""
],
[
"Martín-Moruno",
"Prado",
""
]
] | The big rip, the little rip and the little sibling of the big rip are cosmological doomsdays predicted by some phantom dark energy models that could describe the future evolution of our Universe. When the universe evolves towards either of these future cosmic events all bounded structures and, ultimately, space-time itself are ripped apart. Nevertheless, it is commonly belief that quantum gravity effects may smooth or even avoid these classically predicted singularities. In this review, we discuss the classical and quantum occurrence of these riplike events in the scheme of metric $f(R)$ theories of gravity. The quantum analysis is performed in the framework of $f(R)$ quantum geometrodynamics. In this context, we analyse the fulfilment of the DeWitt criterion for the avoidance of these singular fates. |
1004.1505 | Lorenzo Sebastiani | Olesya Gorbunova and Lorenzo Sebastiani | Viscous Fluids and Gauss-Bonnet Modified Gravity | 14 pages | Gen.Rel.Grav.42:2873-2890,2010 | 10.1007/s10714-010-1031-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study effects of cosmic fluids on finite-time future singularities in
modified $f(R,G)$-gravity, where $R$ and $G$ are the Ricci scalar and the
Gauss-Bonnet invariant, respectively. We consider the fluid equation of state
in the general form, $\omega=\omega(\rho)$, and we suppose the existence of a
bulk viscosity. We investigate quintessence region ($\omega>-1$) and phantom
region ($\omega<-1$) and the possibility to change or avoid the singularities
in $f(R,G)$-gravity. Finally, we study the inclusion of quantum effects in
large curvatures regime.
| [
{
"created": "Fri, 9 Apr 2010 09:21:47 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Jun 2010 14:02:17 GMT",
"version": "v2"
},
{
"created": "Fri, 12 Nov 2010 16:13:42 GMT",
"version": "v3"
}
] | 2010-11-15 | [
[
"Gorbunova",
"Olesya",
""
],
[
"Sebastiani",
"Lorenzo",
""
]
] | We study effects of cosmic fluids on finite-time future singularities in modified $f(R,G)$-gravity, where $R$ and $G$ are the Ricci scalar and the Gauss-Bonnet invariant, respectively. We consider the fluid equation of state in the general form, $\omega=\omega(\rho)$, and we suppose the existence of a bulk viscosity. We investigate quintessence region ($\omega>-1$) and phantom region ($\omega<-1$) and the possibility to change or avoid the singularities in $f(R,G)$-gravity. Finally, we study the inclusion of quantum effects in large curvatures regime. |
1706.02354 | Marek Szydlowski | Marek Szydlowski and Aleksander Stachowski | Is a pole type singularity an alternative to inflation? | RevTeX 4.1; 33 pages, 9 figures; ver. 2: new title, new part on the
pole type singularities with inflation | Eur. Phys. J. C78, 552 (2018) | 10.1140/epjc/s10052-018-6036-1 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we apply a method of reducing the dynamics of FRW cosmological
models with the barotropic form of the equation of state to the dynamical
system of the Newtonian type to detect the finite scale factor singularities
and the finite-time singularities. In this approach all information concerning
the dynamics of the system is contained in a diagram of the potential function
$V(a)$ of the scale factor. Singularities of the finite scale factor manifest
by poles of the potential function. In our approach the different types of
singularities are represented by critical exponents in the power-law
approximation of the potential. The classification can be given in terms of
these exponents. We have found that the pole singularity can mimick an
inflation epoch. We demonstrate that the cosmological singularities can be
investigated in terms of the critical exponents of the potential function of
the cosmological dynamical systems. We assume the general form of the model
contains matter and some kind of dark energy which is parameterized by the
potential. We distinguish singularities (by ansatz about the Lagrangian) of the
pole type with the inflation and demonstrate that such a singularity can appear
in the past.
| [
{
"created": "Wed, 7 Jun 2017 19:29:26 GMT",
"version": "v1"
},
{
"created": "Mon, 21 May 2018 17:26:58 GMT",
"version": "v2"
}
] | 2019-09-27 | [
[
"Szydlowski",
"Marek",
""
],
[
"Stachowski",
"Aleksander",
""
]
] | In this paper, we apply a method of reducing the dynamics of FRW cosmological models with the barotropic form of the equation of state to the dynamical system of the Newtonian type to detect the finite scale factor singularities and the finite-time singularities. In this approach all information concerning the dynamics of the system is contained in a diagram of the potential function $V(a)$ of the scale factor. Singularities of the finite scale factor manifest by poles of the potential function. In our approach the different types of singularities are represented by critical exponents in the power-law approximation of the potential. The classification can be given in terms of these exponents. We have found that the pole singularity can mimick an inflation epoch. We demonstrate that the cosmological singularities can be investigated in terms of the critical exponents of the potential function of the cosmological dynamical systems. We assume the general form of the model contains matter and some kind of dark energy which is parameterized by the potential. We distinguish singularities (by ansatz about the Lagrangian) of the pole type with the inflation and demonstrate that such a singularity can appear in the past. |
1103.3092 | Kouji Nakamura | Kouji Nakamura | Alternative construction of gauge-invariant variables for linear metric
perturbation on general background spacetime | 8 pages, no figure | null | null | null | gr-qc astro-ph.CO hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Construction of the gauge-invariant variables for the linear metric
perturbation, which was proposed in the paper [K. Nakamura, arXiv:1101.1147],
is discussed through an alternative approach. Our starting point of the
construction of the gauge-invariant variables is an non-trivial non-local
decomposition of the linear metric perturbation. Assuming the existence of some
Green functions, we reproduce results in the above paper. This supports the
consistency of the result and implies that one can develop the
general-relativistic higher-order gauge-invariant perturbation theory on
general background spacetime.
| [
{
"created": "Wed, 16 Mar 2011 04:19:46 GMT",
"version": "v1"
}
] | 2011-03-17 | [
[
"Nakamura",
"Kouji",
""
]
] | Construction of the gauge-invariant variables for the linear metric perturbation, which was proposed in the paper [K. Nakamura, arXiv:1101.1147], is discussed through an alternative approach. Our starting point of the construction of the gauge-invariant variables is an non-trivial non-local decomposition of the linear metric perturbation. Assuming the existence of some Green functions, we reproduce results in the above paper. This supports the consistency of the result and implies that one can develop the general-relativistic higher-order gauge-invariant perturbation theory on general background spacetime. |
1705.01252 | James O'Brien | James G. O'Brien, Thomas L. Chiarelli, Jeremy Dentico, Modestas
Stulge, Brian Stefanski, Robert Moss and Spasen Chaykov | Alternative gravity rotation curves for the Little Things Survey | 13 Pages, 7 Figures, Accepted in Astrophysical Journal | null | 10.3847/1538-4357/aa99e1 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Galactic rotation curves have proven to be the testing ground for dark matter
bounds in spiral galaxies of all morphologies. Dwarf galaxies serve as an
increasingly interesting case of rotation curve dynamics due to their typically
rising rotation curve as opposed to the flattening curve of large spirals.
These galaxies usually vary in galactic structure and mostly terminate at small
radial distances. This, coupled with the fact that Cold Dark Matter theories
struggle with the universality of galactic rotation curves, allow for exclusive
features of alternative gravitational models to be analyzed. Recently, the
THINGS (The HI Nearby Galactic Survey) has been extended to include a sample of
25 dwarf galaxies now known as the LITTLE THINGS Survey. Here, we present a
thorough application of alternative gravitational models to the LITTLE THINGS
survey, specifically focusing on conformal gravity and Modified Newtonian
Dynamics. An analysis and discussion of the results of the fitting procedure of
the two alternative gravitational models are explored, as well as the resulting
rotation curve predictions of each. Further, we show how these two alternative
gravitational models account for the recently observed universal trends in
centripetal accelerations in spiral galaxies. We posit here that both conformal
gravity and MOND can provide an accurate description of the galactic dynamics
without the need for dark matter.
| [
{
"created": "Wed, 3 May 2017 04:44:36 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Dec 2017 15:11:57 GMT",
"version": "v2"
}
] | 2018-01-10 | [
[
"O'Brien",
"James G.",
""
],
[
"Chiarelli",
"Thomas L.",
""
],
[
"Dentico",
"Jeremy",
""
],
[
"Stulge",
"Modestas",
""
],
[
"Stefanski",
"Brian",
""
],
[
"Moss",
"Robert",
""
],
[
"Chaykov",
"Spasen",
""
]
] | Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral galaxies of all morphologies. Dwarf galaxies serve as an increasingly interesting case of rotation curve dynamics due to their typically rising rotation curve as opposed to the flattening curve of large spirals. These galaxies usually vary in galactic structure and mostly terminate at small radial distances. This, coupled with the fact that Cold Dark Matter theories struggle with the universality of galactic rotation curves, allow for exclusive features of alternative gravitational models to be analyzed. Recently, the THINGS (The HI Nearby Galactic Survey) has been extended to include a sample of 25 dwarf galaxies now known as the LITTLE THINGS Survey. Here, we present a thorough application of alternative gravitational models to the LITTLE THINGS survey, specifically focusing on conformal gravity and Modified Newtonian Dynamics. An analysis and discussion of the results of the fitting procedure of the two alternative gravitational models are explored, as well as the resulting rotation curve predictions of each. Further, we show how these two alternative gravitational models account for the recently observed universal trends in centripetal accelerations in spiral galaxies. We posit here that both conformal gravity and MOND can provide an accurate description of the galactic dynamics without the need for dark matter. |
gr-qc/9801011 | Leonid Grishchuk | L P Grishchuk | Comment on the "Influence of Cosmological Transitions on the Evolution
of Density Perturbations" | 15 pages, revised in connection with remarks of a neutral referee | null | null | null | gr-qc astro-ph hep-ph | null | A recent paper by Martin and Schwarz [1] argues that the ``standard
inflationary result" has been finally proven. The result itself is formulated
as: ``the closer the inflationary epoch is to the de Sitter space-time, the
less important are large-scale gravitational waves in the CMBR today".
Beginning from the basic equations of Grishchuk [2, 3] the authors say [1] that
Grishchuk's conclusion about approximate equality of metric amplitudes for
gravitational waves and density perturbations ``is wrong because the time
evolution of the scalar metric perturbation through the (smooth) reheating
transition was not calculated correctly". They reiterate a claim about ``big
amplification" of scalar perturbations (in contrast to gravitational waves)
during reheating. The authors say [1] that after appropriate correction they
have recovered the "standard result" within Grishchuk's approach. It is shown
in this Comment that the "big amplification" is a misinterpretation. There is
no difference in the evolution of long-wavelength metric perturbations for
gravitational waves and density perturbations: they both stay approximately
constant. The influence of cosmological transitions on the evolution is none at
all, as long as the wavelength of the perturbation is much larger than the
Hubble radius. It is shown that from the approach of [2, 3] follow the
conclusions of [2, 3] without change. Finally, it is argued that the ``standard
inflationary result" does not follow from the correct evolution and quantum
normalization of density perturbations.
| [
{
"created": "Tue, 6 Jan 1998 14:58:48 GMT",
"version": "v1"
},
{
"created": "Sat, 17 Jan 1998 17:37:53 GMT",
"version": "v2"
},
{
"created": "Fri, 17 Sep 1999 11:27:37 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Grishchuk",
"L P",
""
]
] | A recent paper by Martin and Schwarz [1] argues that the ``standard inflationary result" has been finally proven. The result itself is formulated as: ``the closer the inflationary epoch is to the de Sitter space-time, the less important are large-scale gravitational waves in the CMBR today". Beginning from the basic equations of Grishchuk [2, 3] the authors say [1] that Grishchuk's conclusion about approximate equality of metric amplitudes for gravitational waves and density perturbations ``is wrong because the time evolution of the scalar metric perturbation through the (smooth) reheating transition was not calculated correctly". They reiterate a claim about ``big amplification" of scalar perturbations (in contrast to gravitational waves) during reheating. The authors say [1] that after appropriate correction they have recovered the "standard result" within Grishchuk's approach. It is shown in this Comment that the "big amplification" is a misinterpretation. There is no difference in the evolution of long-wavelength metric perturbations for gravitational waves and density perturbations: they both stay approximately constant. The influence of cosmological transitions on the evolution is none at all, as long as the wavelength of the perturbation is much larger than the Hubble radius. It is shown that from the approach of [2, 3] follow the conclusions of [2, 3] without change. Finally, it is argued that the ``standard inflationary result" does not follow from the correct evolution and quantum normalization of density perturbations. |
2309.02678 | Muhammad Sharif | M. Sharif and K. Hassan | Analysis of Complexity Factor for Charged Dissipative Configuration in
Modified Gravity | 28 pages, no figure | Eur. Phys. J. Plus 138(2023)787 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we determine the electromagnetic effects on the complexity
factor of radiating anisotropic cylindrical geometry in the background of
$f(G,\mathcal{T})$ theory. The self-gravitating objects possessing
inhomogeneous energy density, pressure anisotropy, heat flux, charge and
correction terms appear to encounter the complexity producing phase. Herrera's
orthogonal splitting method is used to identify the scalar functions in which
the factor that incorporates all of the fundamental aspects of the system is
assumed to be the complexity factor. We also look at the evolution of charged
cylindrical matter source by selecting homologous pattern as the most basic
evolutionary mode. In addition to this, homologous and complexity free
conditions are utilized to address dissipative as well as non-dissipative
scenarios. The complexity producing parameters throughout the evolutionary
process are assessed at the end. It is concluded that the complexity of the
astrophysical entities is elevated due to the contribution of charge and
modified terms of this theory.
| [
{
"created": "Wed, 6 Sep 2023 03:12:13 GMT",
"version": "v1"
}
] | 2023-09-07 | [
[
"Sharif",
"M.",
""
],
[
"Hassan",
"K.",
""
]
] | In this paper, we determine the electromagnetic effects on the complexity factor of radiating anisotropic cylindrical geometry in the background of $f(G,\mathcal{T})$ theory. The self-gravitating objects possessing inhomogeneous energy density, pressure anisotropy, heat flux, charge and correction terms appear to encounter the complexity producing phase. Herrera's orthogonal splitting method is used to identify the scalar functions in which the factor that incorporates all of the fundamental aspects of the system is assumed to be the complexity factor. We also look at the evolution of charged cylindrical matter source by selecting homologous pattern as the most basic evolutionary mode. In addition to this, homologous and complexity free conditions are utilized to address dissipative as well as non-dissipative scenarios. The complexity producing parameters throughout the evolutionary process are assessed at the end. It is concluded that the complexity of the astrophysical entities is elevated due to the contribution of charge and modified terms of this theory. |
2108.07069 | Daniela Pugliese Dr | D. Pugliese, Z. Stuchlik | General relativistic rotational energy extraction from black
holes-accretion disk systems | Published in: Class.Quant.Grav. 38 (2021) 14, 145014 | Class.Quant.Grav. 38 (2021) 14, 145014 | 10.1088/1361-6382/abff97 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We constrain the BHs spin with the evaluation of the dimensionless parameter
\xi, the total rotational energy extracted versus the BH mass. The energy
extraction can power an outflow which can be then observed. We relate the
energy extraction to the accreting configurations and the accretion processes
occurring in a cluster of corotating and counter-rotating tori orbiting one
central Kerr SMBH, associating \xi to the accretion processes characteristics.
We relate the regions of tori parameters to the energy extraction processes,
binding \xi to properties of light surfaces by using the bundles, relating
measures in different regions of the spacetimes. We evaluate properties of the
BH accretions disks, and correlate spacetimes prior and after their transition
due to the energy extraction. Light surfaces are related to the generators of
Killing horizons, proving limiting frequency of the stationary observers of the
geometries. We consider the photon limiting curves of the stationary observers
as constraints for various processes regulated by these frequencies, to relate
different BH states, prior and after the energy extraction, investigating
regions close to the BH horizons and rotational axis. From methodological
view-point we used a naked singularity -BH correspondence defined with metric
bundles to predict the BH--accretion disk system observational characteristics.
The analysis points relevant BH spins a\approx0.94M, a\approx 0.7M and
a\approx0.3M. We show the relation between the rotational law of the tori, the
bundle characteristic frequency and the relativistic velocity defining the von
Zeipel surfaces. The inferior limit on the formation of corotating is
\ell/a\geq2, for counter-rotating tori \ell/a\leq -22/5 (\ell is the fluids
specific angular momentum).
| [
{
"created": "Mon, 16 Aug 2021 13:03:51 GMT",
"version": "v1"
}
] | 2021-08-17 | [
[
"Pugliese",
"D.",
""
],
[
"Stuchlik",
"Z.",
""
]
] | We constrain the BHs spin with the evaluation of the dimensionless parameter \xi, the total rotational energy extracted versus the BH mass. The energy extraction can power an outflow which can be then observed. We relate the energy extraction to the accreting configurations and the accretion processes occurring in a cluster of corotating and counter-rotating tori orbiting one central Kerr SMBH, associating \xi to the accretion processes characteristics. We relate the regions of tori parameters to the energy extraction processes, binding \xi to properties of light surfaces by using the bundles, relating measures in different regions of the spacetimes. We evaluate properties of the BH accretions disks, and correlate spacetimes prior and after their transition due to the energy extraction. Light surfaces are related to the generators of Killing horizons, proving limiting frequency of the stationary observers of the geometries. We consider the photon limiting curves of the stationary observers as constraints for various processes regulated by these frequencies, to relate different BH states, prior and after the energy extraction, investigating regions close to the BH horizons and rotational axis. From methodological view-point we used a naked singularity -BH correspondence defined with metric bundles to predict the BH--accretion disk system observational characteristics. The analysis points relevant BH spins a\approx0.94M, a\approx 0.7M and a\approx0.3M. We show the relation between the rotational law of the tori, the bundle characteristic frequency and the relativistic velocity defining the von Zeipel surfaces. The inferior limit on the formation of corotating is \ell/a\geq2, for counter-rotating tori \ell/a\leq -22/5 (\ell is the fluids specific angular momentum). |
0810.4515 | James Lindesay | James Lindesay | Quantum Behaviors on an Excreting Black Hole | 33 pages, 14 figures | Class.Quant.Grav.26:125014,2009 | 10.1088/0264-9381/26/12/125014 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Often, geometries with horizons offer insights into the intricate
relationships between general relativity and quantum physics. However, some
subtle aspects of gravitating quantum systems might be difficult to ascertain
using static backgrounds, since quantum mechanics incorporates dynamic
measurability constraints (such as the uncertainty principle, etc.).
For this reason, the behaviors of quantum systems on a dynamic black hole
background are explored in this paper. The velocities and trajectories of
representative outgoing, ingoing, and stationary classical particles are
calculated and contrasted, and the dynamics of simple quantum fields (both
massless and massive) on the space-time are examined. Invariant densities
associated with the quantum fields are exhibited on the Penrose diagram that
represents the excreting black hole.
Furthermore, a generic approach for the consistent mutual gravitation of
quanta in a manner that reproduces the given geometry is developed. The
dynamics of the mutually gravitating quantum fields are expressed in terms of
the affine parameter that describes local motions of a given quantum type on
the space-time. Algebraic equations that relate the energy-momentum densities
of the quantum fields to Einstein's tensor can then be developed. An example
mutually gravitating system of macroscopically coherent quanta along with a
core gravitating field is demonstrated. Since the approach is generic and
algebraic, it can be used to represent a variety of systems with specified
boundary conditions.
| [
{
"created": "Fri, 24 Oct 2008 17:39:35 GMT",
"version": "v1"
}
] | 2009-11-19 | [
[
"Lindesay",
"James",
""
]
] | Often, geometries with horizons offer insights into the intricate relationships between general relativity and quantum physics. However, some subtle aspects of gravitating quantum systems might be difficult to ascertain using static backgrounds, since quantum mechanics incorporates dynamic measurability constraints (such as the uncertainty principle, etc.). For this reason, the behaviors of quantum systems on a dynamic black hole background are explored in this paper. The velocities and trajectories of representative outgoing, ingoing, and stationary classical particles are calculated and contrasted, and the dynamics of simple quantum fields (both massless and massive) on the space-time are examined. Invariant densities associated with the quantum fields are exhibited on the Penrose diagram that represents the excreting black hole. Furthermore, a generic approach for the consistent mutual gravitation of quanta in a manner that reproduces the given geometry is developed. The dynamics of the mutually gravitating quantum fields are expressed in terms of the affine parameter that describes local motions of a given quantum type on the space-time. Algebraic equations that relate the energy-momentum densities of the quantum fields to Einstein's tensor can then be developed. An example mutually gravitating system of macroscopically coherent quanta along with a core gravitating field is demonstrated. Since the approach is generic and algebraic, it can be used to represent a variety of systems with specified boundary conditions. |
2309.16107 | Daniel Mata-Pacheco | H. Garcia-Compean, D. Mata-Pacheco | Scalar field inflation driven by a modification of the Heisenberg
algebra | 36 pages, 1 figure. All sections were improved. References added | null | 10.1142/S0218271824500378 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the modifications induced on scalar field inflation produced by
considering a general modification of the Heisenberg algebra. We proceed by
modifying the Poisson brackets on the classical theory whenever the
corresponding quantum commutator is modified. We do not restrict ourselves to a
specific form for such modification, instead we constrain the functions
involved by the cosmological behaviour of interest. We present whenever
possible the way in which inflation can be realized approximately via three
slow roll Hubble parameters that depend on the standard slow roll parameters in
a very different form than in the usual case and that can be less restrictive.
Furthermore we find a general analytical solution describing an expanding
universe with constant Hubble parameter that generalizes the standard
cosmological constant case by restricting the form of the modification of the
Heisenberg algebra. It is found that even if such modification can be neglected
in some limit and the cosmological constant is set to zero in that limit, the
exponential expansion is present when the modification is important. Thus an
appropriate modification of the Heisenberg algebra is sufficient to produce an
exponentially expanding universe without the need of any other source.
| [
{
"created": "Thu, 28 Sep 2023 02:18:16 GMT",
"version": "v1"
},
{
"created": "Sun, 11 Aug 2024 16:49:45 GMT",
"version": "v2"
}
] | 2024-08-13 | [
[
"Garcia-Compean",
"H.",
""
],
[
"Mata-Pacheco",
"D.",
""
]
] | We study the modifications induced on scalar field inflation produced by considering a general modification of the Heisenberg algebra. We proceed by modifying the Poisson brackets on the classical theory whenever the corresponding quantum commutator is modified. We do not restrict ourselves to a specific form for such modification, instead we constrain the functions involved by the cosmological behaviour of interest. We present whenever possible the way in which inflation can be realized approximately via three slow roll Hubble parameters that depend on the standard slow roll parameters in a very different form than in the usual case and that can be less restrictive. Furthermore we find a general analytical solution describing an expanding universe with constant Hubble parameter that generalizes the standard cosmological constant case by restricting the form of the modification of the Heisenberg algebra. It is found that even if such modification can be neglected in some limit and the cosmological constant is set to zero in that limit, the exponential expansion is present when the modification is important. Thus an appropriate modification of the Heisenberg algebra is sufficient to produce an exponentially expanding universe without the need of any other source. |
2103.01182 | Sotirios Karamitsos | Alexandros Karam, Sotirios Karamitsos, Margus Saal | $\beta$-function reconstruction of Palatini inflationary attractors | 26 pages, 2 figures | null | 10.1088/1475-7516/2021/10/068 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Attractor inflation is a particularly robust framework for developing
inflationary models that are insensitive to the details of the potential. Such
models are most often considered in the metric formulation of gravity. However,
non-minimal models may not necessarily maintain their attractor nature in the
Palatini formalism where the connection is independent of the metric. In this
work, we employ the $\beta$-function formalism to classify the strong coupling
limit of inflationary models in both the metric and the Palatini approaches.
Furthermore, we determine the range of values for the non-minimal coupling that
lead to theories being observationally indistinguishable in metric and Palatini
within current accuracy. Finally, we reconstruct the Jordan frame potential for
$\xi$-attractors by imposing an explicit form for the $\beta$-function,
demonstrating the effect that the choice of metric or Palatini has on the
inflationary observables of the theory.
| [
{
"created": "Mon, 1 Mar 2021 18:27:41 GMT",
"version": "v1"
}
] | 2021-11-03 | [
[
"Karam",
"Alexandros",
""
],
[
"Karamitsos",
"Sotirios",
""
],
[
"Saal",
"Margus",
""
]
] | Attractor inflation is a particularly robust framework for developing inflationary models that are insensitive to the details of the potential. Such models are most often considered in the metric formulation of gravity. However, non-minimal models may not necessarily maintain their attractor nature in the Palatini formalism where the connection is independent of the metric. In this work, we employ the $\beta$-function formalism to classify the strong coupling limit of inflationary models in both the metric and the Palatini approaches. Furthermore, we determine the range of values for the non-minimal coupling that lead to theories being observationally indistinguishable in metric and Palatini within current accuracy. Finally, we reconstruct the Jordan frame potential for $\xi$-attractors by imposing an explicit form for the $\beta$-function, demonstrating the effect that the choice of metric or Palatini has on the inflationary observables of the theory. |
2011.06932 | M. Farasat Shamir | M. Farasat Shamir | Massive Compact Bardeen Stars with Conformal Motion | 12 pages, 6 figures | Phys. Lett. B811(2020)135927 | 10.1016/j.physletb.2020.135927 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The main focus of this paper is to discuss the solutions of
Einstein-Maxwell's field equations for compact stars study. We have chosen the
MIT bag model equation of state for the pressure-energy density relationship
and conformal Killing vectors are used to investigate the appropriate forms for
metric coefficients. We impose the boundary conditions, by choosing the Bardeen
model to describe as an exterior spacetime. The Bardeen model may provide the
analysis with some interesting results. For example, the extra terms involved
in the asymptotic representations as compared to the usual Reissner-Nordstrom
case may influence the mass of a stellar structure. Both energy density and
pressure profiles behave realistically except a central singularity. It is
shown that the energy conditions are satisfied in our study. The equilibrium
conditions through TOV equation and stability criteria through Adiabatic index
for the charged stellar structure study are investigated. Lastly, we have also
provided a little review of the case with Reissner-Nordstrom spacetime as an
exterior geometry for the matching condition. In both cases, the masses obey
the Andreasson's limit $\sqrt{M} \leq \sqrt{R}/3+\sqrt{R/9+q^2/3R}$ requirement
for a charged star. Conclusively, the results show that Bardeen model geometry
provides more massive stellar objects as compared to usual Reissner-Nordstrom
spacetime. In particular, the current study supports the existence of realistic
massive structures like PSR J $1614-2230$.
| [
{
"created": "Thu, 12 Nov 2020 09:16:21 GMT",
"version": "v1"
}
] | 2020-11-16 | [
[
"Shamir",
"M. Farasat",
""
]
] | The main focus of this paper is to discuss the solutions of Einstein-Maxwell's field equations for compact stars study. We have chosen the MIT bag model equation of state for the pressure-energy density relationship and conformal Killing vectors are used to investigate the appropriate forms for metric coefficients. We impose the boundary conditions, by choosing the Bardeen model to describe as an exterior spacetime. The Bardeen model may provide the analysis with some interesting results. For example, the extra terms involved in the asymptotic representations as compared to the usual Reissner-Nordstrom case may influence the mass of a stellar structure. Both energy density and pressure profiles behave realistically except a central singularity. It is shown that the energy conditions are satisfied in our study. The equilibrium conditions through TOV equation and stability criteria through Adiabatic index for the charged stellar structure study are investigated. Lastly, we have also provided a little review of the case with Reissner-Nordstrom spacetime as an exterior geometry for the matching condition. In both cases, the masses obey the Andreasson's limit $\sqrt{M} \leq \sqrt{R}/3+\sqrt{R/9+q^2/3R}$ requirement for a charged star. Conclusively, the results show that Bardeen model geometry provides more massive stellar objects as compared to usual Reissner-Nordstrom spacetime. In particular, the current study supports the existence of realistic massive structures like PSR J $1614-2230$. |
2106.08572 | Heba Sami | Heba Sami and Amare Abebe | Cosmic hierarchy in $f(R)$ gravity | 15 pages and 20 figures | null | 10.1142/S0219887822501675 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this contribution, we investigate hierarchical nature of large-scale
structure clustering through the oscillatory nature of the solutions of the
Schr\"{o}dinger-like Friedmann equation in a modified gravitational background
described by the $f(R)$ gravity theory. We find the cosmological solutions to
the Schr\"{o}dinger equation for different ranges of $n$ of the $R^{n}$ toy
model for both radiation and matter-dominated epochs of the expansion history
for open, flat, and closed spacetimes. Our results show that, for certain
choices of the model parameters and initial conditions, the formation and
distribution of cosmic structures might indeed be hierarchical, leading to a
natural explanation for the breakdown of the cosmological principle on small
scales.
| [
{
"created": "Wed, 16 Jun 2021 06:41:43 GMT",
"version": "v1"
}
] | 2022-10-05 | [
[
"Sami",
"Heba",
""
],
[
"Abebe",
"Amare",
""
]
] | In this contribution, we investigate hierarchical nature of large-scale structure clustering through the oscillatory nature of the solutions of the Schr\"{o}dinger-like Friedmann equation in a modified gravitational background described by the $f(R)$ gravity theory. We find the cosmological solutions to the Schr\"{o}dinger equation for different ranges of $n$ of the $R^{n}$ toy model for both radiation and matter-dominated epochs of the expansion history for open, flat, and closed spacetimes. Our results show that, for certain choices of the model parameters and initial conditions, the formation and distribution of cosmic structures might indeed be hierarchical, leading to a natural explanation for the breakdown of the cosmological principle on small scales. |
1105.4724 | Carlo Ligi | M. Bassan, B. Buonomo, G. Cavallari, E. Coccia, S. D'Antonio, V.
Fafone, L.G. Foggetta, C. Ligi, A. Marini, G. Mazzitelli, G. Modestino, G.
Pizzella, L. Quintieri, F. Ronga, P. Valente, S. M. Vinko | Vibrational excitation induced by electron beam and cosmic rays in
normal and superconductive aluminum bars | 28 pages, 13 figures | null | 10.1016/j.nima.2011.08.028 | null | gr-qc astro-ph.IM physics.ins-det | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We report new measurements of the acoustic excitation of an Al5056
superconductive bar when hit by an electron beam, in a previously unexplored
temperature range, down to 0.35 K. These data, analyzed together with previous
results of the RAP experiment obtained for T > 0.54 K, show a vibrational
response enhanced by a factor 4.9 with respect to that measured in the normal
state. This enhancement explains the anomalous large signals due to cosmic rays
previously detected in the NAUTILUS gravitational wave detector.
| [
{
"created": "Tue, 24 May 2011 10:25:04 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Aug 2011 09:27:08 GMT",
"version": "v2"
}
] | 2015-05-28 | [
[
"Bassan",
"M.",
""
],
[
"Buonomo",
"B.",
""
],
[
"Cavallari",
"G.",
""
],
[
"Coccia",
"E.",
""
],
[
"D'Antonio",
"S.",
""
],
[
"Fafone",
"V.",
""
],
[
"Foggetta",
"L. G.",
""
],
[
"Ligi",
"C.",
""
],
[
"Marini",
"A.",
""
],
[
"Mazzitelli",
"G.",
""
],
[
"Modestino",
"G.",
""
],
[
"Pizzella",
"G.",
""
],
[
"Quintieri",
"L.",
""
],
[
"Ronga",
"F.",
""
],
[
"Valente",
"P.",
""
],
[
"Vinko",
"S. M.",
""
]
] | We report new measurements of the acoustic excitation of an Al5056 superconductive bar when hit by an electron beam, in a previously unexplored temperature range, down to 0.35 K. These data, analyzed together with previous results of the RAP experiment obtained for T > 0.54 K, show a vibrational response enhanced by a factor 4.9 with respect to that measured in the normal state. This enhancement explains the anomalous large signals due to cosmic rays previously detected in the NAUTILUS gravitational wave detector. |
2306.07411 | D\'avid Szepessy | P. Hrask\'o, D. Szepessy | On the Absoluteness of Rotation | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We argue that in the general relativistic calculation of planetary orbits,
the choice of a reference frame which is an obligatory condition in the
Newtonian approach is replaced by an appropriate boundary condition on the
solution of Einstein equation. Implications of this observation on the nature
of rotation and the physical interpretation of the metric tensor are discussed.
| [
{
"created": "Mon, 12 Jun 2023 20:38:41 GMT",
"version": "v1"
}
] | 2023-06-14 | [
[
"Hraskó",
"P.",
""
],
[
"Szepessy",
"D.",
""
]
] | We argue that in the general relativistic calculation of planetary orbits, the choice of a reference frame which is an obligatory condition in the Newtonian approach is replaced by an appropriate boundary condition on the solution of Einstein equation. Implications of this observation on the nature of rotation and the physical interpretation of the metric tensor are discussed. |
2303.08153 | Charalampos Markakis | Charalampos Markakis, Sean Bray, An{\i}l Zengino\u{g}lu | Symmetric integration of the 1+1 Teukolsky equation on hyperboloidal
foliations of Kerr spacetimes | 28 pages, 9 figures | null | null | null | gr-qc astro-ph.HE cs.NA math.NA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work outlines a fast, high-precision time-domain solver for scalar,
electromagnetic and gravitational perturbations on hyperboloidal foliations of
Kerr space-times. Time-domain Teukolsky equation solvers have typically used
explicit methods, which numerically violate Noether symmetries and are
Courant-limited. These restrictions can limit the performance of explicit
schemes when simulating long-time extreme mass ratio inspirals, expected to
appear in LISA band for 2-5 years. We thus explore symmetric (exponential,
Pad\'e or Hermite) integrators, which are unconditionally stable and known to
preserve certain Noether symmetries and phase-space volume. For linear
hyperbolic equations, these implicit integrators can be cast in explicit form,
making them well-suited for long-time evolution of black hole perturbations.
The 1+1 modal Teukolsky equation is discretized in space using polynomial
collocation methods and reduced to a linear system of ordinary differential
equations, coupled via mode-coupling arrays and discretized (matrix)
differential operators. We use a matricization technique to cast the
mode-coupled system in a form amenable to a method-of-lines framework, which
simplifies numerical implementation and enables efficient parallelization on
CPU and GPU architectures. We test our numerical code by studying late-time
tails of Kerr spacetime perturbations in the sub-extremal and extremal cases.
| [
{
"created": "Tue, 14 Mar 2023 18:00:28 GMT",
"version": "v1"
}
] | 2023-03-16 | [
[
"Markakis",
"Charalampos",
""
],
[
"Bray",
"Sean",
""
],
[
"Zenginoğlu",
"Anıl",
""
]
] | This work outlines a fast, high-precision time-domain solver for scalar, electromagnetic and gravitational perturbations on hyperboloidal foliations of Kerr space-times. Time-domain Teukolsky equation solvers have typically used explicit methods, which numerically violate Noether symmetries and are Courant-limited. These restrictions can limit the performance of explicit schemes when simulating long-time extreme mass ratio inspirals, expected to appear in LISA band for 2-5 years. We thus explore symmetric (exponential, Pad\'e or Hermite) integrators, which are unconditionally stable and known to preserve certain Noether symmetries and phase-space volume. For linear hyperbolic equations, these implicit integrators can be cast in explicit form, making them well-suited for long-time evolution of black hole perturbations. The 1+1 modal Teukolsky equation is discretized in space using polynomial collocation methods and reduced to a linear system of ordinary differential equations, coupled via mode-coupling arrays and discretized (matrix) differential operators. We use a matricization technique to cast the mode-coupled system in a form amenable to a method-of-lines framework, which simplifies numerical implementation and enables efficient parallelization on CPU and GPU architectures. We test our numerical code by studying late-time tails of Kerr spacetime perturbations in the sub-extremal and extremal cases. |
1102.0016 | Doron Ludwin | Doron ludwin | A Quantum Twin Paradox | 9 pages, 2 figures | null | null | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Classical Twin Paradox is widely dealt in literature and neatly resolved.
In addition, it is also well known that, when looking at two systems which are
boosted relative to each other, the concept of the simultaneous effect of a
quantum measurement in space-time causes some discrepancies in the cause-effect
behavior. However, these discrepancies have been thought not to cause any
apparent paradox except for violating the Free-Will postulate. In this paper we
suggest that using the local t axis, all over space, as the axis in which the
quantum measurement is thought to be simultaneous, we do reach a kind of true
"Twin Paradox". The resolution of this paradox requires the introduction of a
global proper time into a covariant quantum theory.
| [
{
"created": "Mon, 31 Jan 2011 21:25:48 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Feb 2011 10:10:43 GMT",
"version": "v2"
}
] | 2011-02-10 | [
[
"ludwin",
"Doron",
""
]
] | The Classical Twin Paradox is widely dealt in literature and neatly resolved. In addition, it is also well known that, when looking at two systems which are boosted relative to each other, the concept of the simultaneous effect of a quantum measurement in space-time causes some discrepancies in the cause-effect behavior. However, these discrepancies have been thought not to cause any apparent paradox except for violating the Free-Will postulate. In this paper we suggest that using the local t axis, all over space, as the axis in which the quantum measurement is thought to be simultaneous, we do reach a kind of true "Twin Paradox". The resolution of this paradox requires the introduction of a global proper time into a covariant quantum theory. |
1001.0575 | Steven L. Liebling | Steven L. Liebling, Luis Lehner, David Neilsen, Carlos Palenzuela | Evolutions of Magnetized and Rotating Neutron Stars | 12 pages, 8 figures | Phys.Rev.D81:124023,2010 | 10.1103/PhysRevD.81.124023 | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the evolution of magnetized and rigidly rotating neutron stars
within a fully general relativistic implementation of ideal
magnetohydrodynamics with no assumed symmetries in three spatial dimensions.
The stars are modeled as rotating, magnetized polytropic stars and we examine
diverse scenarios to study their dynamics and stability properties. In
particular we concentrate on the stability of the stars and possible critical
behavior. In addition to their intrinsic physical significance, we use these
evolutions as further tests of our implementation which incorporates new
developments to handle magnetized systems.
| [
{
"created": "Mon, 4 Jan 2010 21:04:58 GMT",
"version": "v1"
},
{
"created": "Mon, 24 May 2010 20:08:42 GMT",
"version": "v2"
}
] | 2010-08-24 | [
[
"Liebling",
"Steven L.",
""
],
[
"Lehner",
"Luis",
""
],
[
"Neilsen",
"David",
""
],
[
"Palenzuela",
"Carlos",
""
]
] | We study the evolution of magnetized and rigidly rotating neutron stars within a fully general relativistic implementation of ideal magnetohydrodynamics with no assumed symmetries in three spatial dimensions. The stars are modeled as rotating, magnetized polytropic stars and we examine diverse scenarios to study their dynamics and stability properties. In particular we concentrate on the stability of the stars and possible critical behavior. In addition to their intrinsic physical significance, we use these evolutions as further tests of our implementation which incorporates new developments to handle magnetized systems. |
gr-qc/9510036 | Dario Nunez | Dar\'io N\'u\~nez, Hernando Quevedo, and Daniel Sudarsky | How short can the hair of a black hole be? | 8 pages in Latex | null | null | null | gr-qc | null | We show that in all theories in which black hole hair has been discovered,
the region with non-trivial structure of the non-linear matter fields must
extend beyond $3/ 2$ the horizon radius, independently of all other parameters
present in the theory. We argue that this is a universal lower bound that
applies in every theory where hair is present. This {\it no short hair
conjecture} is then put forward as a more modest alternative to the now
debunked {\it no hair conjecture}.
| [
{
"created": "Tue, 17 Oct 1995 18:27:25 GMT",
"version": "v1"
}
] | 2016-08-15 | [
[
"Núñez",
"Darío",
""
],
[
"Quevedo",
"Hernando",
""
],
[
"Sudarsky",
"Daniel",
""
]
] | We show that in all theories in which black hole hair has been discovered, the region with non-trivial structure of the non-linear matter fields must extend beyond $3/ 2$ the horizon radius, independently of all other parameters present in the theory. We argue that this is a universal lower bound that applies in every theory where hair is present. This {\it no short hair conjecture} is then put forward as a more modest alternative to the now debunked {\it no hair conjecture}. |
2005.14481 | Hiroaki Tahara | Hiroaki W. H. Tahara, Tsutomu Kobayashi and Jun'ichi Yokoyama | A new mechanism for freezing extra dimensions with higher-order
curvature terms | 6 pages | null | 10.1016/j.physletb.2020.135857 | RUP-20-17, RESCEU-9/20 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct a model of higher dimensional cosmology in which extra
dimensions are frozen by virtue of the cubic-order Lovelock gravity throughout
the cosmic history from inflation to the present with radiation and
matter-dominated regimes in between.
| [
{
"created": "Fri, 29 May 2020 09:57:30 GMT",
"version": "v1"
}
] | 2020-10-21 | [
[
"Tahara",
"Hiroaki W. H.",
""
],
[
"Kobayashi",
"Tsutomu",
""
],
[
"Yokoyama",
"Jun'ichi",
""
]
] | We construct a model of higher dimensional cosmology in which extra dimensions are frozen by virtue of the cubic-order Lovelock gravity throughout the cosmic history from inflation to the present with radiation and matter-dominated regimes in between. |
1506.08073 | Garrett Lisi | A. Garrett Lisi | Lie Group Cosmology | 42 pages, 1 figure; v2: minor corrections | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Our universe is a deforming Lie group.
| [
{
"created": "Wed, 24 Jun 2015 20:01:11 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Sep 2015 18:08:39 GMT",
"version": "v2"
}
] | 2015-09-25 | [
[
"Lisi",
"A. Garrett",
""
]
] | Our universe is a deforming Lie group. |
2207.08235 | David Benisty | David Benisty | Testing modified gravity via Yukawa potential in two body problem:
Analytical solution and observational constraints | Accepted for Phys Rev D | Phys Rev D 106, 043001 (2022) | 10.1103/PhysRevD.106.043001 | null | gr-qc astro-ph.EP hep-th | http://creativecommons.org/licenses/by/4.0/ | Many alternative theories of gravity screens a Yukawa-type potential. This
article shows Keplerian-type parametrization as a solution of Yukawa type
potential accurate equations of motion for two non-spinning compact objects
moving in an eccentric orbit. A bound from the solar system is presented.
| [
{
"created": "Sun, 17 Jul 2022 17:23:27 GMT",
"version": "v1"
}
] | 2022-08-02 | [
[
"Benisty",
"David",
""
]
] | Many alternative theories of gravity screens a Yukawa-type potential. This article shows Keplerian-type parametrization as a solution of Yukawa type potential accurate equations of motion for two non-spinning compact objects moving in an eccentric orbit. A bound from the solar system is presented. |
gr-qc/9702048 | Pablo Laguna | W. Krivan, P. Laguna, P. Papadopoulos (Penn State) and N. Andersson
(Wash U) | Dynamics of perturbations of rotating black holes | 15 pages, 3 Postscript figures, LaTex | Phys.Rev. D56 (1997) 3395-3404 | 10.1103/PhysRevD.56.3395 | null | gr-qc | null | We present a numerical study of the time evolution of perturbations of
rotating black holes. The solutions are obtained by integrating the Teukolsky
equation written as a first-order in time, coupled system of equations, in a
form that explicitly captures its hyperbolic structure. We address the
numerical difficulties of solving the equation in its original form. We follow
the propagation of generic initial data through the burst, quasinormal ringing
and power-law tail phases. In particular, we calculate the effects due to the
rotation of the black hole on the scattering of incident gravitational wave
pulses. These results may help explain how the angular momentum of the black
hole affects the gravitational waves that are generated during the final stages
of black hole coalescence.
| [
{
"created": "Mon, 24 Feb 1997 21:41:17 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Krivan",
"W.",
"",
"Penn State"
],
[
"Laguna",
"P.",
"",
"Penn State"
],
[
"Papadopoulos",
"P.",
"",
"Penn State"
],
[
"Andersson",
"N.",
"",
"Wash U"
]
] | We present a numerical study of the time evolution of perturbations of rotating black holes. The solutions are obtained by integrating the Teukolsky equation written as a first-order in time, coupled system of equations, in a form that explicitly captures its hyperbolic structure. We address the numerical difficulties of solving the equation in its original form. We follow the propagation of generic initial data through the burst, quasinormal ringing and power-law tail phases. In particular, we calculate the effects due to the rotation of the black hole on the scattering of incident gravitational wave pulses. These results may help explain how the angular momentum of the black hole affects the gravitational waves that are generated during the final stages of black hole coalescence. |
1204.1773 | Gergely Sz\'ekely | P\'eter N\'emeti and Gergely Sz\'ekely | Existence of Faster Than Light Signals Implies Hypercomputation Already
in Special Relativity | 14 pages, 2 figures | Lecture Notes in Computer Science Volume 7318, 2012, pp 528-538 | 10.1007/978-3-642-30870-3_53 | null | gr-qc math.LO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Within an axiomatic framework, we investigate the possibility of
hypercomputation in special relativity via faster than light signals. We
formally show that hypercomputation is theoretically possible in special
relativity if and only if there are faster than light signals.
| [
{
"created": "Mon, 9 Apr 2012 00:21:25 GMT",
"version": "v1"
}
] | 2012-11-27 | [
[
"Németi",
"Péter",
""
],
[
"Székely",
"Gergely",
""
]
] | Within an axiomatic framework, we investigate the possibility of hypercomputation in special relativity via faster than light signals. We formally show that hypercomputation is theoretically possible in special relativity if and only if there are faster than light signals. |
1406.0438 | Artur Alho | Artur Alho and Claes Uggla | Global dynamics and inflationary center manifold and slow-roll
approximants | 32 pages, 24 figures. Appendices incorporated into main text. Matches
final published version | null | 10.1063/1.4906081 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the familiar problem of a minimally coupled scalar field with
quadratic potential in flat Friedmann-Lema\^itre-Robertson-Walker cosmology to
illustrate a number of techniques and tools, which can be applied to a wide
range of scalar field potentials and problems in e.g. modified gravity. We
present a global and regular dynamical systems description that yields a global
understanding of the solution space, including asymptotic features. We
introduce dynamical systems techniques such as center manifold expansions and
use Pad\'e approximants to obtain improved approximations for the `attractor
solution' at early times. We also show that future asymptotic behavior is
associated with a limit cycle, which shows that manifest self-similarity is
asymptotically broken toward the future, and give approximate expressions for
this behavior. We then combine these results to obtain global approximations
for the attractor solution, which, e.g., might be used in the context of global
measures. In addition we elucidate the connection between slow-roll based
approximations and the attractor solution, and compare these approximations
with the center manifold based approximants.
| [
{
"created": "Mon, 2 Jun 2014 16:36:09 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Sep 2014 18:09:04 GMT",
"version": "v2"
},
{
"created": "Thu, 15 Jan 2015 00:08:17 GMT",
"version": "v3"
}
] | 2015-06-19 | [
[
"Alho",
"Artur",
""
],
[
"Uggla",
"Claes",
""
]
] | We consider the familiar problem of a minimally coupled scalar field with quadratic potential in flat Friedmann-Lema\^itre-Robertson-Walker cosmology to illustrate a number of techniques and tools, which can be applied to a wide range of scalar field potentials and problems in e.g. modified gravity. We present a global and regular dynamical systems description that yields a global understanding of the solution space, including asymptotic features. We introduce dynamical systems techniques such as center manifold expansions and use Pad\'e approximants to obtain improved approximations for the `attractor solution' at early times. We also show that future asymptotic behavior is associated with a limit cycle, which shows that manifest self-similarity is asymptotically broken toward the future, and give approximate expressions for this behavior. We then combine these results to obtain global approximations for the attractor solution, which, e.g., might be used in the context of global measures. In addition we elucidate the connection between slow-roll based approximations and the attractor solution, and compare these approximations with the center manifold based approximants. |
1308.0229 | Victor Shchigolev Konstantinovich | V.K. Shchigolev | Cosmological Sigma Model with Non-Minimal Coupling to the Target Space | 12 pages, no figures | Cent. Eur. J. Phys., 12(1), 2014, 32-41 | 10.2478/s11534-014-0504-5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A homogeneous and isotropic Universe in the framework of nonlinear sigma
model with non-minimal coupling to the target space is considered. A
two-component model of such a sort is preliminary investigated. Some solutions
for this model are given. Perspectives and directions of development of such a
sort of models are designated.
| [
{
"created": "Thu, 1 Aug 2013 14:44:41 GMT",
"version": "v1"
}
] | 2018-02-14 | [
[
"Shchigolev",
"V. K.",
""
]
] | A homogeneous and isotropic Universe in the framework of nonlinear sigma model with non-minimal coupling to the target space is considered. A two-component model of such a sort is preliminary investigated. Some solutions for this model are given. Perspectives and directions of development of such a sort of models are designated. |
2303.16566 | Felix Finster | Felix Finster, Eduardo Guendelman, Claudio F. Paganini | Modified Measures as an Effective Theory for Causal Fermion Systems | 25 pages, LaTeX, 3 figures (published version) | Class. Quantum Grav. 41 (2024) 035007 | 10.1088/1361-6382/ad1711 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compare the structures of the theory of causal fermion systems (CFS), an
approach to unify quantum theory with general relativity (GR), with those of
modified measure theories (MMT), which are a set of modified gravity theories.
Classical spacetimes with MMT can be obtained as the continuum limit of a CFS.
This suggests that MMT could serve as effective descriptions of modifications
to GR implied by CFS. The goal is to lay the foundation for future research on
exploring which MMTs are consistent with the causal action principle of CFS.
| [
{
"created": "Wed, 29 Mar 2023 09:49:52 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Sep 2023 11:24:53 GMT",
"version": "v2"
},
{
"created": "Tue, 19 Dec 2023 18:10:07 GMT",
"version": "v3"
}
] | 2024-01-19 | [
[
"Finster",
"Felix",
""
],
[
"Guendelman",
"Eduardo",
""
],
[
"Paganini",
"Claudio F.",
""
]
] | We compare the structures of the theory of causal fermion systems (CFS), an approach to unify quantum theory with general relativity (GR), with those of modified measure theories (MMT), which are a set of modified gravity theories. Classical spacetimes with MMT can be obtained as the continuum limit of a CFS. This suggests that MMT could serve as effective descriptions of modifications to GR implied by CFS. The goal is to lay the foundation for future research on exploring which MMTs are consistent with the causal action principle of CFS. |
1503.01956 | Wen-Biao Liu | Jie-Xiong Mo, Wen-Biao Liu | Non-extended phase space thermodynamics of Lovelock AdS black holes in
grand canonical ensemble | null | Eur. Phys. J. C75 (2015) 5, 211 | 10.1140/epjc/s10052-015-3434-5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, extended phase space thermodynamics of Lovelock AdS black holes has
been of great interest. To provide insight from a different perspective and
gain a unified phase transition picture, non-extended phase space
thermodynamics of $(n+1)$-dimensional charged topological Lovelock AdS black
holes is investigated detailedly in the grand canonical ensemble. Specifically,
the specific heat at constant electric potential is calculated and phase
transition in the grand canonical ensemble is discussed. To probe the impact of
the various parameters, we utilize the control variate method and solve the
phase transition condition equation numerically for the case $k=1,-1$. There
are two critical points for the case $n=6,k=1$ while there is only one for
other cases. For $k=0$, there exists no phase transition point. To figure out
the nature of phase transition in the grand canonical ensemble, we carry out an
analytic check of the analog form of Ehrenfest equations proposed by Banerjee
et al. It is shown that Lovelock AdS black holes in the grand canonical
ensemble undergo a second order phase transition. To examine the phase
structure in the grand canonical ensemble, we utilize the thermodynamic
geometry method and calculate both the Weinhold metric and Ruppeiner metric. It
is shown that for both analytic and graphical results that the divergence
structure of the Ruppeiner scalar curvature coincides with that of the specific
heat. Our research provides one more example that Ruppeiner metric serves as a
wonderful tool to probe the phase structures of black holes.
| [
{
"created": "Fri, 6 Mar 2015 13:57:42 GMT",
"version": "v1"
}
] | 2015-05-25 | [
[
"Mo",
"Jie-Xiong",
""
],
[
"Liu",
"Wen-Biao",
""
]
] | Recently, extended phase space thermodynamics of Lovelock AdS black holes has been of great interest. To provide insight from a different perspective and gain a unified phase transition picture, non-extended phase space thermodynamics of $(n+1)$-dimensional charged topological Lovelock AdS black holes is investigated detailedly in the grand canonical ensemble. Specifically, the specific heat at constant electric potential is calculated and phase transition in the grand canonical ensemble is discussed. To probe the impact of the various parameters, we utilize the control variate method and solve the phase transition condition equation numerically for the case $k=1,-1$. There are two critical points for the case $n=6,k=1$ while there is only one for other cases. For $k=0$, there exists no phase transition point. To figure out the nature of phase transition in the grand canonical ensemble, we carry out an analytic check of the analog form of Ehrenfest equations proposed by Banerjee et al. It is shown that Lovelock AdS black holes in the grand canonical ensemble undergo a second order phase transition. To examine the phase structure in the grand canonical ensemble, we utilize the thermodynamic geometry method and calculate both the Weinhold metric and Ruppeiner metric. It is shown that for both analytic and graphical results that the divergence structure of the Ruppeiner scalar curvature coincides with that of the specific heat. Our research provides one more example that Ruppeiner metric serves as a wonderful tool to probe the phase structures of black holes. |
1312.2250 | Mirjam Cvetic | M. Cvetic, G.W. Gibbons | Exact quasi-normal modes for the near horizon Kerr metric | 4 pages | Phys. Rev. D 89, 064057 (2014) | 10.1103/PhysRevD.89.064057 | UPR-1257-T | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the quasi-normal modes of a massless scalar field in a general
sub-extreme Kerr back- ground by exploiting the hidden SL(2, R) x SL(2, R) x
SO(3) symmetry of the subtracted geometry approximation. This faithfully models
the near horizon geometry but locates the black hole in a confining
asymptotically conical box analogous to the anti-de-Sitter backgrounds used in
string the- ory. There are just two series of modes, given in terms of
hypergeometric functions and spherical harmonics, reminiscent of the
left-moving and right-moving degrees in string theory: one is over- damped, the
other is underdamped and exhibits rotational splitting. The remarkably simple
exact formulae for the complex frequencies would in principle allow the
determination of the mass and angular momentum from observations of a black
hole. No black hole bomb is possible because the Killing field which co-rotates
with the horizon is everywhere timelike outside the black hole.
| [
{
"created": "Sun, 8 Dec 2013 19:45:14 GMT",
"version": "v1"
}
] | 2014-04-02 | [
[
"Cvetic",
"M.",
""
],
[
"Gibbons",
"G. W.",
""
]
] | We study the quasi-normal modes of a massless scalar field in a general sub-extreme Kerr back- ground by exploiting the hidden SL(2, R) x SL(2, R) x SO(3) symmetry of the subtracted geometry approximation. This faithfully models the near horizon geometry but locates the black hole in a confining asymptotically conical box analogous to the anti-de-Sitter backgrounds used in string the- ory. There are just two series of modes, given in terms of hypergeometric functions and spherical harmonics, reminiscent of the left-moving and right-moving degrees in string theory: one is over- damped, the other is underdamped and exhibits rotational splitting. The remarkably simple exact formulae for the complex frequencies would in principle allow the determination of the mass and angular momentum from observations of a black hole. No black hole bomb is possible because the Killing field which co-rotates with the horizon is everywhere timelike outside the black hole. |
1906.06691 | David Benisty | David Benisty, Eduardo Guendelman, Emil Nissimov, Svetlana Pacheva | Dynamically Generated Inflation from Non-Riemannian Volume Forms | 9 pages, to appear in European Physical Journal C | Eur. Phys. J. C (2019) 79: 806 | 10.1140/epjc/s10052-019-7310-6 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a simple modified gravity model without any initial matter fields
in terms of several alternative non-Riemannian spacetime volume elements within
the metric (second order) formalism. We show how the non-Riemannian
volume-elements, when passing to the physical Einstein frame, create a
canonical scalar field and produce dynamically a non-trivial inflationary-type
potential for the latter with a large flat region and a stable low-lying
minimum. We study the evolution of the cosmological solutions from the point of
view of theory of dynamical systems. The theory predicts the spectral index
$n_s \approx 0.96$ and the tensor-to-scalar ratio $r \approx 0.002$ for 60
e-folds, which is in accordance with the observational data. In the future
Euclid and SPHEREx missions or the BICEP3 experiment are expected to provide
experimental evidence to test those predictions.
| [
{
"created": "Sun, 16 Jun 2019 14:02:01 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Sep 2019 18:46:40 GMT",
"version": "v2"
}
] | 2019-10-02 | [
[
"Benisty",
"David",
""
],
[
"Guendelman",
"Eduardo",
""
],
[
"Nissimov",
"Emil",
""
],
[
"Pacheva",
"Svetlana",
""
]
] | We propose a simple modified gravity model without any initial matter fields in terms of several alternative non-Riemannian spacetime volume elements within the metric (second order) formalism. We show how the non-Riemannian volume-elements, when passing to the physical Einstein frame, create a canonical scalar field and produce dynamically a non-trivial inflationary-type potential for the latter with a large flat region and a stable low-lying minimum. We study the evolution of the cosmological solutions from the point of view of theory of dynamical systems. The theory predicts the spectral index $n_s \approx 0.96$ and the tensor-to-scalar ratio $r \approx 0.002$ for 60 e-folds, which is in accordance with the observational data. In the future Euclid and SPHEREx missions or the BICEP3 experiment are expected to provide experimental evidence to test those predictions. |
1902.04988 | Reginald Christian Bernardo | Reginald Christian Bernardo and Ian Vega | Hair-dressing Horndeski: an approach to hairy solutions in cubic
Horndeski gravity | 15 pages, 12 figures | Phys. Rev. D 99, 124049 (2019) | 10.1103/PhysRevD.99.124049 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In obtaining exact solutions in gravitational theories containing arbitrary
model functions, such as Horndeski gravity, one usually starts by prescribing
the model functions of the theory and then goes on to solving their
corresponding field equations. In this paper, we explore the extent to which
the reverse procedure can be useful, whereby one starts with desired solutions
and then determines the models that support them. Working within the
phenomenologically interesting cubic and shift-symmetric sector of Horndeski
gravity, we develop a method for obtaining exact static and
spherically-symmetric solutions, one of which happens to be a new hairy black
hole. We study this black hole and its properties. We also discuss the
limitations of the method and its possible extension to other Horndeski
sectors.
| [
{
"created": "Wed, 13 Feb 2019 16:26:49 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Apr 2019 00:59:07 GMT",
"version": "v2"
}
] | 2019-07-02 | [
[
"Bernardo",
"Reginald Christian",
""
],
[
"Vega",
"Ian",
""
]
] | In obtaining exact solutions in gravitational theories containing arbitrary model functions, such as Horndeski gravity, one usually starts by prescribing the model functions of the theory and then goes on to solving their corresponding field equations. In this paper, we explore the extent to which the reverse procedure can be useful, whereby one starts with desired solutions and then determines the models that support them. Working within the phenomenologically interesting cubic and shift-symmetric sector of Horndeski gravity, we develop a method for obtaining exact static and spherically-symmetric solutions, one of which happens to be a new hairy black hole. We study this black hole and its properties. We also discuss the limitations of the method and its possible extension to other Horndeski sectors. |
gr-qc/9805026 | Thomas Baumgarte | M. Shibata, T. W. Baumgarte, and S. L. Shapiro | Stability of coalescing binary stars against gravitational collapse:
hydrodynamical simulations | 13 pages, 10 figures, RevTex, to appear in Phys. Rev. D | Phys.Rev.D58:023002,1998 | 10.1103/PhysRevD.58.023002 | null | gr-qc astro-ph | null | We perform simulations of relativistic binary stars in post-Newtonian gravity
to investigate their dynamical stability prior to merger against gravitational
collapse in a tidal field. In general, our equations are only strictly accurate
to first post-Newtonian order, but they recover full general relativity for
spherical, static stars. We study both corotational and irrotational binary
configurations of identical stars in circular orbits. We adopt a soft,
adiabatic equation of state with $\Gamma = 1.4$, for which the onset of
instability occurs at a sufficiently small value of the compaction $M/R$ that a
post-Newtonian approximation is quite accurate. For such a soft equation of
state there is no innermost stable circular orbit, so that we can study
arbitrarily close binaries. This choice still allows us to study all the
qualitative features exhibited by any adiabatic equation of state regarding
stability against gravitational collapse. We demonstrate that, independent of
the internal stellar velocity profile, the tidal field from a binary companion
stabilizes a star against gravitational collapse.
| [
{
"created": "Fri, 8 May 1998 14:43:21 GMT",
"version": "v1"
}
] | 2009-12-30 | [
[
"Shibata",
"M.",
""
],
[
"Baumgarte",
"T. W.",
""
],
[
"Shapiro",
"S. L.",
""
]
] | We perform simulations of relativistic binary stars in post-Newtonian gravity to investigate their dynamical stability prior to merger against gravitational collapse in a tidal field. In general, our equations are only strictly accurate to first post-Newtonian order, but they recover full general relativity for spherical, static stars. We study both corotational and irrotational binary configurations of identical stars in circular orbits. We adopt a soft, adiabatic equation of state with $\Gamma = 1.4$, for which the onset of instability occurs at a sufficiently small value of the compaction $M/R$ that a post-Newtonian approximation is quite accurate. For such a soft equation of state there is no innermost stable circular orbit, so that we can study arbitrarily close binaries. This choice still allows us to study all the qualitative features exhibited by any adiabatic equation of state regarding stability against gravitational collapse. We demonstrate that, independent of the internal stellar velocity profile, the tidal field from a binary companion stabilizes a star against gravitational collapse. |
2011.04313 | Vladimir S. Manko | V. S. Manko, E. Ruiz | Equatorially symmetric configurations of two Kerr-Newman black holes | 20 pages, 2 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we employ the general equatorially symmetric two-soliton
solution of the Einstein-Maxwell equations for elaborating two physically
meaningful configurations describing a pair of equal Kerr-Newman corotating
black holes separated by a massless strut. The first configuration is
characterized by opposite magnetic charges of its constituents, while in the
second configuration the black holes carry equal electric and opposite magnetic
charges, thus providing a nontrivial example of a binary dyonic black-hole
system. The thermodynamic properties of these binary configurations are studied
and the first law of thermodynamics taking correctly into account the magnetic
field contribution is formulated for each case.
| [
{
"created": "Mon, 9 Nov 2020 10:38:30 GMT",
"version": "v1"
}
] | 2020-11-10 | [
[
"Manko",
"V. S.",
""
],
[
"Ruiz",
"E.",
""
]
] | In this paper, we employ the general equatorially symmetric two-soliton solution of the Einstein-Maxwell equations for elaborating two physically meaningful configurations describing a pair of equal Kerr-Newman corotating black holes separated by a massless strut. The first configuration is characterized by opposite magnetic charges of its constituents, while in the second configuration the black holes carry equal electric and opposite magnetic charges, thus providing a nontrivial example of a binary dyonic black-hole system. The thermodynamic properties of these binary configurations are studied and the first law of thermodynamics taking correctly into account the magnetic field contribution is formulated for each case. |
0907.0934 | Carlo Cafaro | S. A. Ali, C. Cafaro, S. Capozziello, Ch. Corda | On the Poincare Gauge Theory of Gravitation | v2: minor changes, references added; 18 pages, no figures | Int.J.Theor.Phys.48:3426-3448,2009 | 10.1007/s10773-009-0149-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a compact, self-contained review of the conventional gauge
theoretical approach to gravitation based on the local Poincare group of
symmetry transformations. The covariant field equations, Bianchi identities and
conservation laws for angular momentum and energy-momentum are obtained.
| [
{
"created": "Mon, 6 Jul 2009 08:33:46 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Dec 2009 08:52:57 GMT",
"version": "v2"
}
] | 2010-03-25 | [
[
"Ali",
"S. A.",
""
],
[
"Cafaro",
"C.",
""
],
[
"Capozziello",
"S.",
""
],
[
"Corda",
"Ch.",
""
]
] | We present a compact, self-contained review of the conventional gauge theoretical approach to gravitation based on the local Poincare group of symmetry transformations. The covariant field equations, Bianchi identities and conservation laws for angular momentum and energy-momentum are obtained. |
1705.11008 | Rajibul Shaikh | Rajibul Shaikh, Sayan Kar | Gravitational lensing by scalar-tensor wormholes and the energy
conditions | 29 pages, 11 figures, revised version with a new section, published
in PRD | Phys. Rev. D 96, 044037 (2017) | 10.1103/PhysRevD.96.044037 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study gravitational lensing by a class of zero Ricci scalar wormholes
which arise as solutions in a scalar-tensor theory of gravity. An attempt is
made to find a possible link between lensing features, stable/unstable photon
orbits and the energy conditions on the matter required to support these
spacetimes. Our analysis shows (for this class of wormholes) that light rays
always exhibit a positive deflection if the energy conditions are satisfied
(nonexotic matter content). In contrast, if the energy conditions are violated
(exotic matter), the net deflection of a light ray may be positive, negative or
even zero, depending on values of the metric and impact parameters. This
prompts us to introduce a surface defined by a turning point value at which the
net deflection of a light ray is equal to zero, even though we have a curved
spacetime geometry. We argue that the existence of such a surface may be linked
to exotic/energy condition violating matter. Wormholes in modified gravity with
matter satisfying the energy conditions do not seem to have such a zero
deflection surface. Finally, we study strong gravitational lensing briefly and
also look into the formation of Einstein and relativistic Einstein rings. We
conclude with some estimates on the wormhole mass, throat-radius and the
detectability of the Einstein rings.
| [
{
"created": "Wed, 31 May 2017 10:00:15 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Aug 2017 15:19:48 GMT",
"version": "v2"
}
] | 2017-08-29 | [
[
"Shaikh",
"Rajibul",
""
],
[
"Kar",
"Sayan",
""
]
] | We study gravitational lensing by a class of zero Ricci scalar wormholes which arise as solutions in a scalar-tensor theory of gravity. An attempt is made to find a possible link between lensing features, stable/unstable photon orbits and the energy conditions on the matter required to support these spacetimes. Our analysis shows (for this class of wormholes) that light rays always exhibit a positive deflection if the energy conditions are satisfied (nonexotic matter content). In contrast, if the energy conditions are violated (exotic matter), the net deflection of a light ray may be positive, negative or even zero, depending on values of the metric and impact parameters. This prompts us to introduce a surface defined by a turning point value at which the net deflection of a light ray is equal to zero, even though we have a curved spacetime geometry. We argue that the existence of such a surface may be linked to exotic/energy condition violating matter. Wormholes in modified gravity with matter satisfying the energy conditions do not seem to have such a zero deflection surface. Finally, we study strong gravitational lensing briefly and also look into the formation of Einstein and relativistic Einstein rings. We conclude with some estimates on the wormhole mass, throat-radius and the detectability of the Einstein rings. |
1107.2458 | Jonathan McDonald | Paul M. Alsing, Jonathan R. McDonald, Warner A. Miller | The Simplicial Ricci Tensor | 19 pages, 2 figures | Class.Quant.Grav.28:155007,2011 | 10.1088/0264-9381/28/15/155007 | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Ricci tensor (Ric) is fundamental to Einstein's geometric theory of
gravitation. The 3-dimensional Ric of a spacelike surface vanishes at the
moment of time symmetry for vacuum spacetimes. The 4-dimensional Ric is the
Einstein tensor for such spacetimes. More recently the Ric was used by Hamilton
to define a non-linear, diffusive Ricci flow (RF) that was fundamental to
Perelman's proof of the Poincare conjecture. Analytic applications of RF can be
found in many fields including general relativity and mathematics. Numerically
it has been applied broadly to communication networks, medical physics,
computer design and more. In this paper, we use Regge calculus (RC) to provide
the first geometric discretization of the Ric. This result is fundamental for
higher-dimensional generalizations of discrete RF. We construct this tensor on
both the simplicial lattice and its dual and prove their equivalence. We show
that the Ric is an edge-based weighted average of deficit divided by an
edge-based weighted average of dual area -- an expression similar to the
vertex-based weighted average of the scalar curvature reported recently. We use
this Ric in a third and independent geometric derivation of the RC Einstein
tensor in arbitrary dimension.
| [
{
"created": "Wed, 13 Jul 2011 03:42:51 GMT",
"version": "v1"
}
] | 2011-11-10 | [
[
"Alsing",
"Paul M.",
""
],
[
"McDonald",
"Jonathan R.",
""
],
[
"Miller",
"Warner A.",
""
]
] | The Ricci tensor (Ric) is fundamental to Einstein's geometric theory of gravitation. The 3-dimensional Ric of a spacelike surface vanishes at the moment of time symmetry for vacuum spacetimes. The 4-dimensional Ric is the Einstein tensor for such spacetimes. More recently the Ric was used by Hamilton to define a non-linear, diffusive Ricci flow (RF) that was fundamental to Perelman's proof of the Poincare conjecture. Analytic applications of RF can be found in many fields including general relativity and mathematics. Numerically it has been applied broadly to communication networks, medical physics, computer design and more. In this paper, we use Regge calculus (RC) to provide the first geometric discretization of the Ric. This result is fundamental for higher-dimensional generalizations of discrete RF. We construct this tensor on both the simplicial lattice and its dual and prove their equivalence. We show that the Ric is an edge-based weighted average of deficit divided by an edge-based weighted average of dual area -- an expression similar to the vertex-based weighted average of the scalar curvature reported recently. We use this Ric in a third and independent geometric derivation of the RC Einstein tensor in arbitrary dimension. |
gr-qc/0408007 | Victor Tapia | Victor Tapia | Differential Invariants for Higher-Rank Tensors. A Progress Report | null | null | null | null | gr-qc | null | We outline the construction of differential invariants for higher--rank
tensors.
| [
{
"created": "Tue, 3 Aug 2004 08:06:57 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Tapia",
"Victor",
""
]
] | We outline the construction of differential invariants for higher--rank tensors. |
2104.14258 | Laur J\"arv | Laur J\"arv and Joosep Lember | Global portraits of nonminimal teleparallel inflation | 22 pages, 14 plots; v2: minor typos corrected, references added,
version accepted by "Universe" | Universe 2021, 7(6), 179 | 10.3390/universe7060179 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct the global phase portraits of inflationary dynamics in
teleparallel gravity models with a scalar field nonminimally coupled to torsion
scalar. The adopted set of variables can clearly distinguish between different
asymptotic states as fixed points, including the kinetic and inflationary
regimes. The key role in the description of inflation is played by the
heteroclinic orbits which run from the asymptotic saddle points to the late
time attractor point and are approximated by nonminimal slow roll conditions.
To seek the asymptotic fixed points we outline a heuristic method in terms of
the "effective potential" and "effective mass", which can be applied for any
nonminimally coupled theories. As particular examples we study positive
quadratic nonminimal couplings with quadratic and quartic potentials, and note
how the portraits differ qualitatively from the known scalar-curvature
counterparts. For quadratic models inflation can only occur at small nonminimal
coupling to torsion, as for larger coupling the asymptotic de Sitter saddle
point disappears from the physical phase space. Teleparallel models with
quartic potentials are not viable for inflation at all, since for small
nonminimal coupling the asymptotic saddle point exhibits weaker than
exponential expansion, and for larger coupling disappears too.
| [
{
"created": "Thu, 29 Apr 2021 11:04:48 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Mar 2022 14:15:02 GMT",
"version": "v2"
}
] | 2022-03-03 | [
[
"Järv",
"Laur",
""
],
[
"Lember",
"Joosep",
""
]
] | We construct the global phase portraits of inflationary dynamics in teleparallel gravity models with a scalar field nonminimally coupled to torsion scalar. The adopted set of variables can clearly distinguish between different asymptotic states as fixed points, including the kinetic and inflationary regimes. The key role in the description of inflation is played by the heteroclinic orbits which run from the asymptotic saddle points to the late time attractor point and are approximated by nonminimal slow roll conditions. To seek the asymptotic fixed points we outline a heuristic method in terms of the "effective potential" and "effective mass", which can be applied for any nonminimally coupled theories. As particular examples we study positive quadratic nonminimal couplings with quadratic and quartic potentials, and note how the portraits differ qualitatively from the known scalar-curvature counterparts. For quadratic models inflation can only occur at small nonminimal coupling to torsion, as for larger coupling the asymptotic de Sitter saddle point disappears from the physical phase space. Teleparallel models with quartic potentials are not viable for inflation at all, since for small nonminimal coupling the asymptotic saddle point exhibits weaker than exponential expansion, and for larger coupling disappears too. |
0810.1328 | Andreas Ross | James B. Gilmore, Andreas Ross | Effective field theory calculation of second post-Newtonian binary
dynamics | Replaced with published version | Phys.Rev.D78:124021,2008 | 10.1103/PhysRevD.78.124021 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use the effective field theory for gravitational bound states, proposed by
Goldberger and Rothstein, to compute the interaction Lagrangian of a binary
system at the second Post-Newtonian order. Throughout the calculation, we use a
metric parametrization based on a temporal Kaluza-Klein decomposition and test
the claim by Kol and Smolkin that this parametrization provides important
calculational advantages. We demonstrate how to use the effective field theory
method efficiently in precision calculations, and we reproduce known results
for the second Post-Newtonian order equations of motion in harmonic gauge in a
straightforward manner.
| [
{
"created": "Wed, 8 Oct 2008 19:35:20 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Feb 2009 23:57:04 GMT",
"version": "v2"
}
] | 2009-02-11 | [
[
"Gilmore",
"James B.",
""
],
[
"Ross",
"Andreas",
""
]
] | We use the effective field theory for gravitational bound states, proposed by Goldberger and Rothstein, to compute the interaction Lagrangian of a binary system at the second Post-Newtonian order. Throughout the calculation, we use a metric parametrization based on a temporal Kaluza-Klein decomposition and test the claim by Kol and Smolkin that this parametrization provides important calculational advantages. We demonstrate how to use the effective field theory method efficiently in precision calculations, and we reproduce known results for the second Post-Newtonian order equations of motion in harmonic gauge in a straightforward manner. |
1511.03933 | Laur J\~Arv | Laur Jarv, Alexey Toporensky | General relativity as an attractor for scalar-torsion cosmology | 8 pages, typos corrected | Phys. Rev. D 93, 024051 (2016) | 10.1103/PhysRevD.93.024051 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study flat Friedmann-Lemaitre-Robertson-Walker cosmological models for a
scalar field coupled nonminimally to teleparallel gravity with generic coupling
and potential functions. The goal of this paper is to determine the conditions
under which the cosmological evolution tends to the limit where the variation
of the gravitational "constant" ceases and the system evolves close to general
relativity. These conditions can be read off from the approximate analytical
solutions describing the process in matter and potential domination eras. Only
those models where the GR limit exists and is an attractor can be considered
viable. We expect the results to hold in the original "pure tetrad" formulation
as well as in the recently suggested covariant formulation of the teleparallel
theory. In the former case the GR attractor simultaneously provides a mechanism
how cosmological evolution suppresses the problematic degrees of freedom
stemming from the lack of local Lorentz invariance.
| [
{
"created": "Thu, 12 Nov 2015 15:48:08 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Jan 2016 18:31:07 GMT",
"version": "v2"
}
] | 2016-08-08 | [
[
"Jarv",
"Laur",
""
],
[
"Toporensky",
"Alexey",
""
]
] | We study flat Friedmann-Lemaitre-Robertson-Walker cosmological models for a scalar field coupled nonminimally to teleparallel gravity with generic coupling and potential functions. The goal of this paper is to determine the conditions under which the cosmological evolution tends to the limit where the variation of the gravitational "constant" ceases and the system evolves close to general relativity. These conditions can be read off from the approximate analytical solutions describing the process in matter and potential domination eras. Only those models where the GR limit exists and is an attractor can be considered viable. We expect the results to hold in the original "pure tetrad" formulation as well as in the recently suggested covariant formulation of the teleparallel theory. In the former case the GR attractor simultaneously provides a mechanism how cosmological evolution suppresses the problematic degrees of freedom stemming from the lack of local Lorentz invariance. |
1201.2882 | John Barrow | John D. Barrow | Some Inflationary Einstein-Aether Cosmologies | 10 pages, no figures | Phys. Rev. D 85, 047503 (2012) | 10.1103/PhysRevD.85.047503 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show how to derive several families of accelerating universe solutions to
an Einstein-Aether gravity theory. These solutions provide possible
descriptions of inflationary behaviour in the early universe and late-time
cosmological acceleration.
| [
{
"created": "Fri, 13 Jan 2012 16:13:51 GMT",
"version": "v1"
}
] | 2015-06-03 | [
[
"Barrow",
"John D.",
""
]
] | We show how to derive several families of accelerating universe solutions to an Einstein-Aether gravity theory. These solutions provide possible descriptions of inflationary behaviour in the early universe and late-time cosmological acceleration. |
0804.1899 | Branislav Cvetkovi\'c | M. Blagojevi\'c and B. Cvetkovi\'c | Electric field in 3D gravity with torsion | LATEX, 15 pages, v2: minor corrections | Phys.Rev.D78:044036,2008 | 10.1103/PhysRevD.78.044036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that in static and spherically symmetric configurations of the
system of Maxwell field coupled to 3D gravity with torsion, at least one of the
Maxwell field components has to vanish. Restricting our attention to the
electric sector of the theory, we find an interesting exact solution,
corresponding to the azimuthal electric field. Its geometric structure is to a
large extent influenced by the values of two different central charges,
associated to the asymptotic AdS structure of spacetime.
| [
{
"created": "Fri, 11 Apr 2008 13:51:08 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Sep 2008 11:04:40 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Blagojević",
"M.",
""
],
[
"Cvetković",
"B.",
""
]
] | It is shown that in static and spherically symmetric configurations of the system of Maxwell field coupled to 3D gravity with torsion, at least one of the Maxwell field components has to vanish. Restricting our attention to the electric sector of the theory, we find an interesting exact solution, corresponding to the azimuthal electric field. Its geometric structure is to a large extent influenced by the values of two different central charges, associated to the asymptotic AdS structure of spacetime. |
gr-qc/9708035 | Bernd Bruegmann | Bernd Bruegmann | Binary Black Hole Mergers in 3d Numerical Relativity | 8 pages, 9 figures, REVTeX; expanded discussion, results unchanged | Int.J.Mod.Phys.D8:85,1999 | 10.1142/S0218271899000080 | null | gr-qc astro-ph | null | The standard approach to the numerical evolution of black hole data using the
ADM formulation with maximal slicing and vanishing shift is extended to
non-symmetric black hole data containing black holes with linear momentum and
spin by using a time-independent conformal rescaling based on the puncture
representation of the black holes. We give an example for a concrete three
dimensional numerical implementation. The main result of the simulations is
that this approach allows for the first time to evolve through a brief period
of the merger phase of the black hole inspiral.
| [
{
"created": "Mon, 18 Aug 1997 19:47:22 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Aug 1997 15:07:57 GMT",
"version": "v2"
},
{
"created": "Thu, 11 Mar 1999 08:27:40 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Bruegmann",
"Bernd",
""
]
] | The standard approach to the numerical evolution of black hole data using the ADM formulation with maximal slicing and vanishing shift is extended to non-symmetric black hole data containing black holes with linear momentum and spin by using a time-independent conformal rescaling based on the puncture representation of the black holes. We give an example for a concrete three dimensional numerical implementation. The main result of the simulations is that this approach allows for the first time to evolve through a brief period of the merger phase of the black hole inspiral. |
1601.03940 | Massimo Tessarotto | Massimo Tessarotto (Department of Mathematics and Geosciences,
University of Trieste, Italy and Institute of Physics, Faculty of Philosophy
and Science, Silesian University in Opava, Bezru\v{c}ovo n\'am.13, CZ-74601
Opava, Czech Republic) and Claudio Cremaschini (Institute of Physics, Faculty
of Philosophy and Science, Silesian University in Opava, Bezru\v{c}ovo
n\'am.13, CZ-74601 Opava, Czech Republic) | Theory of non-local point transformations - Part 1: Representation of
Teleparallel Gravity | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper the extension of the functional setting customarily adopted in
General Relativity (GR) is considered. For this purpose, an explicit solution
of the so-called Einstein's\ Teleparallel problem is sought. This is achieved
by a suitable extension of the traditional concept of GR reference frame and is
based on the notion of non-local point transformation (NLPT). In particular, it
is shown that a solution to the said problem can be reached by introducing a
suitable subset of transformations denoted here as \textit{special}
\textit{NLPT}. These are found to realize a phase-space transformation
connecting\emph{\}the flat Minkowski space-time with, in principle, an
arbitrary curved space-time. The functional setting and basic properties of the
new transformations are investigated.
| [
{
"created": "Wed, 13 Jan 2016 07:54:01 GMT",
"version": "v1"
}
] | 2016-01-18 | [
[
"Tessarotto",
"Massimo",
"",
"Department of Mathematics and Geosciences,\n University of Trieste, Italy and Institute of Physics, Faculty of Philosophy\n and Science, Silesian University in Opava, Bezručovo nám.13, CZ-74601\n Opava, Czech Republic"
],
[
"Cremaschini",
"Claudio",
"",
"Institute of Physics, Faculty\n of Philosophy and Science, Silesian University in Opava, Bezručovo\n nám.13, CZ-74601 Opava, Czech Republic"
]
] | In this paper the extension of the functional setting customarily adopted in General Relativity (GR) is considered. For this purpose, an explicit solution of the so-called Einstein's\ Teleparallel problem is sought. This is achieved by a suitable extension of the traditional concept of GR reference frame and is based on the notion of non-local point transformation (NLPT). In particular, it is shown that a solution to the said problem can be reached by introducing a suitable subset of transformations denoted here as \textit{special} \textit{NLPT}. These are found to realize a phase-space transformation connecting\emph{\}the flat Minkowski space-time with, in principle, an arbitrary curved space-time. The functional setting and basic properties of the new transformations are investigated. |
1706.05470 | David Figueiredo | David Figueiredo, Fernando Moraes, S\'ebastien Fumeron and Bertrand
Berche | Cosmology in the laboratory: an analogy between hyperbolic metamaterials
and the Milne universe | 12 pages, 9 figures | Phys. Rev. D 96, 105012 (2017) | 10.1103/PhysRevD.96.105012 | null | gr-qc cond-mat.soft | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This article shows that the compactified Milne universe geometry, a toy model
for the big crunch/big bang transition, can be realized in hyperbolic
metamaterials, a new class of nanoengineered systems which have recently found
its way as an experimental playground for cosmological ideas. On one side,
Klein-Gordon particles, as well as tachyons, are used as probes of the Milne
geometry. On the other side, the propagation of light in two versions of a
liquid crystal-based metamaterial provides the analogy. It is shown that ray
and wave optics in the metamaterial mimic, respectively, the classical
trajectories and wave function propagation, of the Milne probes, leading to the
exciting perspective of realizing experimental tests of particle tunneling
through the cosmic singularity, for instance.
| [
{
"created": "Sat, 17 Jun 2017 02:28:46 GMT",
"version": "v1"
},
{
"created": "Sun, 19 Nov 2017 18:05:59 GMT",
"version": "v2"
}
] | 2017-11-22 | [
[
"Figueiredo",
"David",
""
],
[
"Moraes",
"Fernando",
""
],
[
"Fumeron",
"Sébastien",
""
],
[
"Berche",
"Bertrand",
""
]
] | This article shows that the compactified Milne universe geometry, a toy model for the big crunch/big bang transition, can be realized in hyperbolic metamaterials, a new class of nanoengineered systems which have recently found its way as an experimental playground for cosmological ideas. On one side, Klein-Gordon particles, as well as tachyons, are used as probes of the Milne geometry. On the other side, the propagation of light in two versions of a liquid crystal-based metamaterial provides the analogy. It is shown that ray and wave optics in the metamaterial mimic, respectively, the classical trajectories and wave function propagation, of the Milne probes, leading to the exciting perspective of realizing experimental tests of particle tunneling through the cosmic singularity, for instance. |
2104.08851 | Jacques Smulevici | Grigorios Fournodavlos, Jacques Smulevici | The initial boundary value problem in General Relativity: the umbilic
case | null | null | null | null | gr-qc math.AP math.DG | http://creativecommons.org/licenses/by/4.0/ | We give a short proof of local well-posedness for the initial boundary value
problem in general relativity with sole boundary condition the requirement that
the boundary is umbilic. This includes as a special case the totally geodesic
boundary condition that we had previously addressed in [8]. The proof is based
on wave coordinates and the key observation that the momentum constraint is
always valid for umbilic boundaries. This allows for a greater freedom in the
choice of boundary conditions, since imposing the umbilic condition also
provides Neumann boundary conditions for three of the four wave coordinates
conditions. Moreover, the umbilic condition, being geometric, implies that
geometric uniqueness in the sense of Friedrich holds in this specific case.
| [
{
"created": "Sun, 18 Apr 2021 13:25:57 GMT",
"version": "v1"
}
] | 2021-04-20 | [
[
"Fournodavlos",
"Grigorios",
""
],
[
"Smulevici",
"Jacques",
""
]
] | We give a short proof of local well-posedness for the initial boundary value problem in general relativity with sole boundary condition the requirement that the boundary is umbilic. This includes as a special case the totally geodesic boundary condition that we had previously addressed in [8]. The proof is based on wave coordinates and the key observation that the momentum constraint is always valid for umbilic boundaries. This allows for a greater freedom in the choice of boundary conditions, since imposing the umbilic condition also provides Neumann boundary conditions for three of the four wave coordinates conditions. Moreover, the umbilic condition, being geometric, implies that geometric uniqueness in the sense of Friedrich holds in this specific case. |
1010.0227 | J. Brian Pitts | J. Brian Pitts | Massive Nordstr\"om Scalar (Density) Gravities from Universal Coupling | Forthcoming in General Relativity and Gravitation | Gen.Rel.Grav.43:871-895,2011 | 10.1007/s10714-010-1100-7 | null | gr-qc hep-th physics.hist-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Both particle physics and the 1890s Seeliger-Neumann modification of
Newtonian gravity suggest considering a "mass term" for gravity, yielding a
finite range due to an exponentially decaying Yukawa potential. Unlike
Nordstr\"{o}m's "massless" theory, massive scalar gravities are strictly
Special Relativistic, being invariant under the Poincar\'{e} group but not the
conformal group. Geometry is a poor guide to understanding massive scalar
gravities: matter sees a conformally flat metric, but gravity also sees the
rest of the flat metric, barely, in the mass term. Infinitely many theories
exhibit this bimetric 'geometry,' all with the total stress-energy's trace as
source. All are new except the Freund-Nambu theory. The smooth massless limit
indicates underdetermination of theories by data between massless and massive
scalar gravities. The ease of accommodating electrons, protons and other
fermions using density-weighted Ogievetsky-Polubarinov spinors in scalar
gravity is noted.
| [
{
"created": "Fri, 1 Oct 2010 18:08:01 GMT",
"version": "v1"
}
] | 2011-02-23 | [
[
"Pitts",
"J. Brian",
""
]
] | Both particle physics and the 1890s Seeliger-Neumann modification of Newtonian gravity suggest considering a "mass term" for gravity, yielding a finite range due to an exponentially decaying Yukawa potential. Unlike Nordstr\"{o}m's "massless" theory, massive scalar gravities are strictly Special Relativistic, being invariant under the Poincar\'{e} group but not the conformal group. Geometry is a poor guide to understanding massive scalar gravities: matter sees a conformally flat metric, but gravity also sees the rest of the flat metric, barely, in the mass term. Infinitely many theories exhibit this bimetric 'geometry,' all with the total stress-energy's trace as source. All are new except the Freund-Nambu theory. The smooth massless limit indicates underdetermination of theories by data between massless and massive scalar gravities. The ease of accommodating electrons, protons and other fermions using density-weighted Ogievetsky-Polubarinov spinors in scalar gravity is noted. |
2107.07370 | Rajes Ghosh | Rajes Ghosh and Sudipta Sarkar | Light rings of stationary spacetimes | 5 pages, no figure | Phys. Rev. D 104, 044019 (2021) | 10.1103/PhysRevD.104.044019 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a novel theorem regarding light rings in a stationary spacetime
with an ergoregion. We prove that any stationary, axisymmetric, and
asymptotically flat spacetime in 1 + 3 dimensions with an ergoregion must have
at least one light ring outside the ergoregion. A possible extension of the
proof for asymptotically de-Sitter and anti-de-Sitter spherically symmetric
black holes is also discussed.
| [
{
"created": "Thu, 15 Jul 2021 14:50:06 GMT",
"version": "v1"
}
] | 2021-08-11 | [
[
"Ghosh",
"Rajes",
""
],
[
"Sarkar",
"Sudipta",
""
]
] | We present a novel theorem regarding light rings in a stationary spacetime with an ergoregion. We prove that any stationary, axisymmetric, and asymptotically flat spacetime in 1 + 3 dimensions with an ergoregion must have at least one light ring outside the ergoregion. A possible extension of the proof for asymptotically de-Sitter and anti-de-Sitter spherically symmetric black holes is also discussed. |
1209.4085 | Roman Gold | Roman Gold, Bernd Bruegmann | Eccentric black hole mergers and zoom-whirl behavior from elliptic
inspirals to hyperbolic encounters | 19 pages, 23 figures | null | 10.1103/PhysRevD.88.064051 | null | gr-qc astro-ph.CO astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform a parameter study of non-spinning, equal and unequal mass black
hole binaries on generic, eccentric orbits in numerical relativity. The linear
momentum considered ranges from that of a circular orbit to ten times that
value. We discuss the different manifestations of zoom-whirl behavior in the
hyperbolic and the elliptic regime. The hyperbolic data set applies to
dynamical capture scenarios (e.g. in globular clusters). Evolutions in the
elliptic regime correspond to possible end states of supermassive black hole
binaries. We spot zoom-whirl behavior for eccentricities as low as $e\sim0.5$,
i.e. within the expected range of eccentricities in massive black hole binaries
from galaxy mergers and binaries near galactic centers. The resulting
gravitational waveforms reveal a rich structure, which will effectively break
degeneracies in parameter space improving parameter estimation.
| [
{
"created": "Tue, 18 Sep 2012 20:00:07 GMT",
"version": "v1"
}
] | 2013-10-02 | [
[
"Gold",
"Roman",
""
],
[
"Bruegmann",
"Bernd",
""
]
] | We perform a parameter study of non-spinning, equal and unequal mass black hole binaries on generic, eccentric orbits in numerical relativity. The linear momentum considered ranges from that of a circular orbit to ten times that value. We discuss the different manifestations of zoom-whirl behavior in the hyperbolic and the elliptic regime. The hyperbolic data set applies to dynamical capture scenarios (e.g. in globular clusters). Evolutions in the elliptic regime correspond to possible end states of supermassive black hole binaries. We spot zoom-whirl behavior for eccentricities as low as $e\sim0.5$, i.e. within the expected range of eccentricities in massive black hole binaries from galaxy mergers and binaries near galactic centers. The resulting gravitational waveforms reveal a rich structure, which will effectively break degeneracies in parameter space improving parameter estimation. |
2306.03999 | Himanshu Chaudhary | Himanshu Chaudhary, Amine Bouali, Niyaz Uddin Molla, Ujjal Debnath,
G.Mustafa | Cosmological Tests of $f(R,G,\mathcal{T})$ Dark Energy Model in FRW
Universe | 19 pages, 10 figures; accepted for publication in EPJC | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This research article presents a new cosmological model formulated within the
$f(R,G,\mathcal{T})$ framework, focusing on the observational signatures and
parameter constraints of the model. The Markov Chain Monte Carlo (MCMC)
technique is employed to effectively explore the parameter space using data
from 36 Cosmic Chronometers and 1701 Pantheon Plus data points. A comparative
analysis is conducted between the proposed $f(R,G,\mathcal{T})$ model and the
widely accepted $\Lambda$CDM model, considering various cosmological
parameters, such as Deceleration, Snap, and Jerk. By evaluating these
parameters, valuable insights into the dynamics and evolution of the universe
within the context of the new model are obtained. Diagnostic tests including
Statefinder and Om Diagnostic are performed to further investigate the behavior
and consistency of the $f(R,G,\mathcal{T})$ model. These tests provide deeper
insights into the properties of the model and its compatibility with
observational data. The model is subjected to statistical analysis using
Information Criteria to rigorously assess its goodness of fit to the data. This
analysis helps determine the level of agreement between the
$f(R,G,\mathcal{T})$ model and the observational data, establishing the
viability and reliability of the proposed cosmological framework. The results
highlight the potential of the $f(R,G,\mathcal{T})$ framework in understanding
the fundamental aspects of the universe's evolution and dynamics. The
comparative analysis with the $\Lambda$CDM model, along with the comprehensive
diagnostic tests performed, demonstrates the efficacy and validity of the
$f(R,G,\mathcal{T})$ model in explaining observed cosmological phenomena. These
findings contribute to the ongoing pursuit of accurate and comprehensive models
that provide a deeper understanding of the nature of our universe.
| [
{
"created": "Tue, 6 Jun 2023 20:21:19 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Sep 2023 08:26:49 GMT",
"version": "v2"
}
] | 2023-09-29 | [
[
"Chaudhary",
"Himanshu",
""
],
[
"Bouali",
"Amine",
""
],
[
"Molla",
"Niyaz Uddin",
""
],
[
"Debnath",
"Ujjal",
""
],
[
"Mustafa",
"G.",
""
]
] | This research article presents a new cosmological model formulated within the $f(R,G,\mathcal{T})$ framework, focusing on the observational signatures and parameter constraints of the model. The Markov Chain Monte Carlo (MCMC) technique is employed to effectively explore the parameter space using data from 36 Cosmic Chronometers and 1701 Pantheon Plus data points. A comparative analysis is conducted between the proposed $f(R,G,\mathcal{T})$ model and the widely accepted $\Lambda$CDM model, considering various cosmological parameters, such as Deceleration, Snap, and Jerk. By evaluating these parameters, valuable insights into the dynamics and evolution of the universe within the context of the new model are obtained. Diagnostic tests including Statefinder and Om Diagnostic are performed to further investigate the behavior and consistency of the $f(R,G,\mathcal{T})$ model. These tests provide deeper insights into the properties of the model and its compatibility with observational data. The model is subjected to statistical analysis using Information Criteria to rigorously assess its goodness of fit to the data. This analysis helps determine the level of agreement between the $f(R,G,\mathcal{T})$ model and the observational data, establishing the viability and reliability of the proposed cosmological framework. The results highlight the potential of the $f(R,G,\mathcal{T})$ framework in understanding the fundamental aspects of the universe's evolution and dynamics. The comparative analysis with the $\Lambda$CDM model, along with the comprehensive diagnostic tests performed, demonstrates the efficacy and validity of the $f(R,G,\mathcal{T})$ model in explaining observed cosmological phenomena. These findings contribute to the ongoing pursuit of accurate and comprehensive models that provide a deeper understanding of the nature of our universe. |
gr-qc/9304035 | Henri Waelbrock | Michael P. Ryan and Sergio Hojman | Non-standard phase space variables, quantization, and path integrals, or
little ado about much | ICN-UNAM-93-07, 12 pages | null | null | null | gr-qc | null | Contribution to the Misner Festshrift, no abstract.
| [
{
"created": "Thu, 22 Apr 1993 19:39:05 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Ryan",
"Michael P.",
""
],
[
"Hojman",
"Sergio",
""
]
] | Contribution to the Misner Festshrift, no abstract. |
1510.03701 | Clare Burrage | Philippe Brax, Clare Burrage, Anne-Christine Davis | The Speed of Galileon Gravity | 17 pages, 3 figures | JCAP 1603 (2016) no.03, 004 | 10.1088/1475-7516/2016/03/004 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyse the speed of gravitational waves in coupled Galileon models with
an equation of state $\omega_\phi=-1$ now and a ghost-free Minkowski limit. We
find that the gravitational waves propagate much faster than the speed of light
unless these models are small perturbations of cubic Galileons and the Galileon
energy density is sub-dominant to a dominant cosmological constant. In this
case, the binary pulsar bounds on the speed of gravitational waves can be
satisfied and the equation of state can be close to -1 when the coupling to
matter and the coefficient of the cubic term of the Galileon Lagrangian are
related. This severely restricts the allowed cosmological behaviour of Galileon
models and we are forced to conclude that Galileons with a stable Minkowski
limit cannot account for the observed acceleration of the expansion of the
universe on their own. Moreover any sub-dominant Galileon component of our
universe must be dominated by the cubic term. For such models with gravitons
propagating faster than the speed of light, the gravitons become potentially
unstable and could decay into photon pairs. They could also emit photons by
Cerenkov radiation. We show that the decay rate of such speedy gravitons into
photons and the Cerenkov radiation are in fact negligible. Moreover the time
delay between the gravitational signal and light emitted by explosive
astrophysical events could serve as a confirmation that a modification of
gravity acts on the largest scales of the Universe.
| [
{
"created": "Fri, 9 Oct 2015 17:14:52 GMT",
"version": "v1"
}
] | 2016-06-21 | [
[
"Brax",
"Philippe",
""
],
[
"Burrage",
"Clare",
""
],
[
"Davis",
"Anne-Christine",
""
]
] | We analyse the speed of gravitational waves in coupled Galileon models with an equation of state $\omega_\phi=-1$ now and a ghost-free Minkowski limit. We find that the gravitational waves propagate much faster than the speed of light unless these models are small perturbations of cubic Galileons and the Galileon energy density is sub-dominant to a dominant cosmological constant. In this case, the binary pulsar bounds on the speed of gravitational waves can be satisfied and the equation of state can be close to -1 when the coupling to matter and the coefficient of the cubic term of the Galileon Lagrangian are related. This severely restricts the allowed cosmological behaviour of Galileon models and we are forced to conclude that Galileons with a stable Minkowski limit cannot account for the observed acceleration of the expansion of the universe on their own. Moreover any sub-dominant Galileon component of our universe must be dominated by the cubic term. For such models with gravitons propagating faster than the speed of light, the gravitons become potentially unstable and could decay into photon pairs. They could also emit photons by Cerenkov radiation. We show that the decay rate of such speedy gravitons into photons and the Cerenkov radiation are in fact negligible. Moreover the time delay between the gravitational signal and light emitted by explosive astrophysical events could serve as a confirmation that a modification of gravity acts on the largest scales of the Universe. |
1310.7849 | George E. A. Matsas | George E. A. Matsas, Raissa F. P. Mendes, and Daniel A. T. Vanzella | Reply to "Comment on `Quantum versus classical instability of scalar
fields in curved backgrounds'" | 2 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the reasoning which led the author of arXiv:1310.6252 to reach
his conclusions relies on an incorrect criterion for the existence of
normalizable bound solutions. We reinforce that the general result derived in
the Appendix of our paper (arXiv:1310.2185), namely, that "there are no
tachyonic (i.e., unstable) modes for minimally coupled scalar fields in
asymptotically flat spherically symmetric static spacetimes containing no
horizons" is indeed correct.
| [
{
"created": "Tue, 29 Oct 2013 15:44:46 GMT",
"version": "v1"
}
] | 2013-10-30 | [
[
"Matsas",
"George E. A.",
""
],
[
"Mendes",
"Raissa F. P.",
""
],
[
"Vanzella",
"Daniel A. T.",
""
]
] | We show that the reasoning which led the author of arXiv:1310.6252 to reach his conclusions relies on an incorrect criterion for the existence of normalizable bound solutions. We reinforce that the general result derived in the Appendix of our paper (arXiv:1310.2185), namely, that "there are no tachyonic (i.e., unstable) modes for minimally coupled scalar fields in asymptotically flat spherically symmetric static spacetimes containing no horizons" is indeed correct. |
1510.04957 | Ra\'ul Carballo-Rubio | Carlos Barcel\'o, Ra\'ul Carballo-Rubio and Luis J. Garay | Where does the physics of extreme gravitational collapse reside? | 43 pages, 1 figure. Review article with new results on the black to
white hole transition. Prepared for the special issue "Open Questions in
Black Hole Physics" edited by Gonzalo J. Olmo | Universe 2 (2016) no.2, 7 | 10.3390/universe2020007 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The gravitational collapse of massive stars serves to manifest the most
severe deviations of general relativity with respect to Newtonian gravity: the
formation of horizons and spacetime singularities. Both features have proven to
be catalysts of deep physical developments, especially when combined with the
principles of quantum mechanics. Nonetheless, it is seldom remarked that it is
hardly possible to combine all these developments into a unified theoretical
model, while maintaining reasonable prospects for the independent experimental
corroboration of its different parts. In this paper we review the current
theoretical understanding of the physics of gravitational collapse in order to
highlight this tension, stating the position that the standard view on
evaporating black holes stands for. This serves as the motivation for the
discussion of a recent proposal that offers the opposite perspective,
represented by a set of geometries that regularize the classical singular
behavior and present modifications of the near-horizon Schwarzschild geometry
as the result of the propagation of non-perturbative ultraviolet effects
originated in regions of high curvature. We present an extensive exploration of
the necessary steps on the explicit construction of these geometries, and
discuss how this proposal could change our present understanding of
astrophysical black holes and even offer the possibility of detecting genuine
ultraviolet effects on future gravitational wave experiments.
| [
{
"created": "Fri, 16 Oct 2015 17:24:14 GMT",
"version": "v1"
}
] | 2016-08-15 | [
[
"Barceló",
"Carlos",
""
],
[
"Carballo-Rubio",
"Raúl",
""
],
[
"Garay",
"Luis J.",
""
]
] | The gravitational collapse of massive stars serves to manifest the most severe deviations of general relativity with respect to Newtonian gravity: the formation of horizons and spacetime singularities. Both features have proven to be catalysts of deep physical developments, especially when combined with the principles of quantum mechanics. Nonetheless, it is seldom remarked that it is hardly possible to combine all these developments into a unified theoretical model, while maintaining reasonable prospects for the independent experimental corroboration of its different parts. In this paper we review the current theoretical understanding of the physics of gravitational collapse in order to highlight this tension, stating the position that the standard view on evaporating black holes stands for. This serves as the motivation for the discussion of a recent proposal that offers the opposite perspective, represented by a set of geometries that regularize the classical singular behavior and present modifications of the near-horizon Schwarzschild geometry as the result of the propagation of non-perturbative ultraviolet effects originated in regions of high curvature. We present an extensive exploration of the necessary steps on the explicit construction of these geometries, and discuss how this proposal could change our present understanding of astrophysical black holes and even offer the possibility of detecting genuine ultraviolet effects on future gravitational wave experiments. |
2112.01308 | Subhajit Barman | Subhajit Barman, Dipankar Barman, Bibhas Ranjan Majhi | Entanglement harvesting from conformal vacuums between two Unruh-DeWitt
detectors moving along null paths | Comments added, published in JHEP | null | 10.1007/JHEP09(2022)106 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well-known that the $(1+1)$ dimensional Schwarzschild and spatially
flat FLRW spacetimes are conformally flat. This work examines entanglement
harvesting from the conformal field vacuums in these spacetimes between two
Unruh-DeWitt detectors, moving along outgoing null trajectories. In $(1+1)$
dimensional Schwarzschild spacetime, we considered the Boulware and Unruh
vacuums for our investigations. In this analysis, one observes that while
entanglement harvesting is possible in $(1+1)$ dimensional Schwarzschild and
$(1+3)$ dimensional de Sitter spacetimes, it is not possible in the $(1+1)$
dimensional de Sitter background for the same set of parameters when the
detectors move along the same outgoing null trajectory. The qualitative results
from the Boulware and the Unruh vacuums are alike. Furthermore, we observed
that the concurrence depends on the distance $d$ between the two null paths of
the detectors periodically, and depending on the parameter values, there could
be entanglement harvesting shadow points or regions. We also observe that the
mutual information does not depend on $d$ in $(1+1)$ dimensional Schwarzschild
and de Sitter spacetimes but periodically depends on it in $(1+3)$ dimensional
de Sitter background. We also provide elucidation on the origin of the
harvested entanglement.
| [
{
"created": "Thu, 2 Dec 2021 15:05:18 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Sep 2022 16:50:53 GMT",
"version": "v2"
}
] | 2022-09-28 | [
[
"Barman",
"Subhajit",
""
],
[
"Barman",
"Dipankar",
""
],
[
"Majhi",
"Bibhas Ranjan",
""
]
] | It is well-known that the $(1+1)$ dimensional Schwarzschild and spatially flat FLRW spacetimes are conformally flat. This work examines entanglement harvesting from the conformal field vacuums in these spacetimes between two Unruh-DeWitt detectors, moving along outgoing null trajectories. In $(1+1)$ dimensional Schwarzschild spacetime, we considered the Boulware and Unruh vacuums for our investigations. In this analysis, one observes that while entanglement harvesting is possible in $(1+1)$ dimensional Schwarzschild and $(1+3)$ dimensional de Sitter spacetimes, it is not possible in the $(1+1)$ dimensional de Sitter background for the same set of parameters when the detectors move along the same outgoing null trajectory. The qualitative results from the Boulware and the Unruh vacuums are alike. Furthermore, we observed that the concurrence depends on the distance $d$ between the two null paths of the detectors periodically, and depending on the parameter values, there could be entanglement harvesting shadow points or regions. We also observe that the mutual information does not depend on $d$ in $(1+1)$ dimensional Schwarzschild and de Sitter spacetimes but periodically depends on it in $(1+3)$ dimensional de Sitter background. We also provide elucidation on the origin of the harvested entanglement. |
2307.16626 | Yasuyuki Hatsuda | Yasuyuki Hatsuda, Masashi Kimura | Perturbative quasinormal mode frequencies | 48 pages | null | null | RUP-23-13 | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We often encounter a situation that black hole solutions can be regarded as
continuous deformations of simpler ones, or modify general relativity by
continuous parameters. We develop a general framework to compute high-order
perturbative corrections to quasinormal mode frequencies in such deformed
problems. Our method has many applications, and allows to compute numerical
values of the high-order corrections very accurately. For several examples, we
perform this computation explicitly, and discuss analytic properties of the
quasinormal mode frequencies for deformation parameters.
| [
{
"created": "Mon, 31 Jul 2023 13:04:04 GMT",
"version": "v1"
},
{
"created": "Sat, 3 Feb 2024 02:05:31 GMT",
"version": "v2"
}
] | 2024-02-06 | [
[
"Hatsuda",
"Yasuyuki",
""
],
[
"Kimura",
"Masashi",
""
]
] | We often encounter a situation that black hole solutions can be regarded as continuous deformations of simpler ones, or modify general relativity by continuous parameters. We develop a general framework to compute high-order perturbative corrections to quasinormal mode frequencies in such deformed problems. Our method has many applications, and allows to compute numerical values of the high-order corrections very accurately. For several examples, we perform this computation explicitly, and discuss analytic properties of the quasinormal mode frequencies for deformation parameters. |
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