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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/9404007 | null | David Brown | Reference Fluids as Standards of Space and Time | (plain TeX, 3 pages) | null | null | null | gr-qc hep-th | null | The idea that spacetime points are to be identified by a fleet of
clock--carrying particles can be traced to the earliest days of general
relativity. Such a fleet of clocks can be described phenomenologically as a
reference fluid. One approach to the problem of time consists in coupling the
metric to a reference fluid and solving the super--Hamiltonian constraint for
the momentum conjugate to the clock time variable. The resolved constraint
leads to a functional Schr\"{o}dinger equation and formally to a conserved
inner product. The reference fluid that is described phenomenologically as
incoherent dust has the extraordinary property that the true Hamiltonian
density for the coupled system depends only on the gravitational variables. The
dust particles also endow space with a privileged system of coordinates that
allows the supermomentum constraint to be solved explicitly. (Contribution to
the Proceedings of the Lanczos Centenary Conference.)
| [
{
"created": "Wed, 6 Apr 1994 15:53:14 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Brown",
"David",
""
]
] | The idea that spacetime points are to be identified by a fleet of clock--carrying particles can be traced to the earliest days of general relativity. Such a fleet of clocks can be described phenomenologically as a reference fluid. One approach to the problem of time consists in coupling the metric to a reference fluid and solving the super--Hamiltonian constraint for the momentum conjugate to the clock time variable. The resolved constraint leads to a functional Schr\"{o}dinger equation and formally to a conserved inner product. The reference fluid that is described phenomenologically as incoherent dust has the extraordinary property that the true Hamiltonian density for the coupled system depends only on the gravitational variables. The dust particles also endow space with a privileged system of coordinates that allows the supermomentum constraint to be solved explicitly. (Contribution to the Proceedings of the Lanczos Centenary Conference.) |
1211.1855 | Mayeul Arminjon | Mayeul Arminjon | Should there be a spin-rotation coupling for a Dirac particle? | 29 pages in standard 12pt. V2: Introduction reinforced. New Section 3
on the dependences of the Hamiltonian on the reference frame and on the
tetrad field. New references | Int. J. Theor. Phys., Vol. 53, No. 6, pp. 1993-2013 (2014) | 10.1007/s10773-014-2006-z | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It was argued by Mashhoon that a spin-rotation coupling term should add to
the Hamiltonian operator in a rotating frame, as compared with the one in an
inertial frame. For a Dirac particle, the Hamiltonian and energy operators H
and E were recently proved to depend on the tetrad field. We argue that this
non-uniqueness of H and E really is a physical problem. We compute the energy
operator in the inertial and the rotating frame, using three tetrad fields: one
for each of two frameworks proposed to select the tetrad field so as to solve
this non-uniqueness problem, and one proposed by Ryder. We find that Mashhoon's
term is there if the tetrad rotates as does the reference frame --- but then it
is also there in the energy operator for the inertial frame. In fact, the Dirac
Hamiltonian operators in two reference frames in relative rotation, but
corresponding to the same tetrad field, differ only by the angular momentum
term. If the Mashhoon effect is to exist for a Dirac particle, the tetrad field
must be selected in a specific way for each reference frame.
| [
{
"created": "Thu, 8 Nov 2012 14:08:09 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Sep 2013 14:03:19 GMT",
"version": "v2"
}
] | 2014-05-16 | [
[
"Arminjon",
"Mayeul",
""
]
] | It was argued by Mashhoon that a spin-rotation coupling term should add to the Hamiltonian operator in a rotating frame, as compared with the one in an inertial frame. For a Dirac particle, the Hamiltonian and energy operators H and E were recently proved to depend on the tetrad field. We argue that this non-uniqueness of H and E really is a physical problem. We compute the energy operator in the inertial and the rotating frame, using three tetrad fields: one for each of two frameworks proposed to select the tetrad field so as to solve this non-uniqueness problem, and one proposed by Ryder. We find that Mashhoon's term is there if the tetrad rotates as does the reference frame --- but then it is also there in the energy operator for the inertial frame. In fact, the Dirac Hamiltonian operators in two reference frames in relative rotation, but corresponding to the same tetrad field, differ only by the angular momentum term. If the Mashhoon effect is to exist for a Dirac particle, the tetrad field must be selected in a specific way for each reference frame. |
2107.03258 | Bei Sha | Bei Sha and Zhi-E Liu | Lorentz-breaking Theory and Tunneling Radiation Correction to
Vaidya-Banner de Sitter Black Hole | 13 pages,0 figure | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In Vaidya-Bonner de Sitter Black hole space-time, the tunneling radiation
characteristics of fermions and bosons are corrected by taking Lorentz symmetry
breaking theory into account. The corresponding gamma matrices and ether-like
field vectors of the black hole are constructed, then the new modified form of
Dirac equation for the fermion with spin 1/2 and the new modified form of
Klein-Gordon equation for boson in the curved space-time of the black hole are
obtained. Through solving the two equations, new and corrected expressions of
surface gravity, Hawking temperature and tunneling rate of the black hole are
obtained, and the results obtained are also discussed.
| [
{
"created": "Wed, 7 Jul 2021 14:45:20 GMT",
"version": "v1"
}
] | 2021-07-08 | [
[
"Sha",
"Bei",
""
],
[
"Liu",
"Zhi-E",
""
]
] | In Vaidya-Bonner de Sitter Black hole space-time, the tunneling radiation characteristics of fermions and bosons are corrected by taking Lorentz symmetry breaking theory into account. The corresponding gamma matrices and ether-like field vectors of the black hole are constructed, then the new modified form of Dirac equation for the fermion with spin 1/2 and the new modified form of Klein-Gordon equation for boson in the curved space-time of the black hole are obtained. Through solving the two equations, new and corrected expressions of surface gravity, Hawking temperature and tunneling rate of the black hole are obtained, and the results obtained are also discussed. |
2312.11358 | Harry Ho-Yin Ng | Harry Ho-Yin Ng, Jin-Liang Jiang, Carlo Musolino, Christian Ecker,
Samuel D.Tootle, Luciano Rezzolla | A hybrid approach to long-term binary neutron-star simulations | 25 pages, 13 figures | Phys. Rev. D (2024) 109, 064061 | 10.1103/PhysRevD.109.064061 | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | One of the main challenges in the numerical modeling of binary neutron-star
(BNS) mergers is long-term simulations of the post-merger remnant over
timescales of the order of seconds. When this modeling includes all the aspects
of complex physics, the computational costs can easily become enormous. To
address this challenge in part, we have developed a novel hybrid approach in
which the solution from a general-relativistic magnetohydrodynamics (GRMHD)
code solving the full set of the Einstein equations in Cartesian coordinates is
coupled with another GRMHD code in which the Einstein equations are solved
under the Conformally Flat Condition (CFC). The latter approximation has a long
history and has been shown to provide an accurate description of compact
objects in non-vacuum spacetimes. An important aspect of the CFC is that the
elliptic equations need to be solved only for a fraction of the steps needed
for the underlying HD/MHD evolution, thus allowing for a gain in computational
efficiency that can be up to a factor of $\sim 6~(230)$ in three-dimensional
(two-dimensional) simulations. We present the basic features of the new code,
the strategies necessary to interface it when importing both two- and
three-dimensional data, and a novel and robust approach to the recovery of the
primitive variables. To validate our new framework, we have carried out code
tests with various coordinate systems and different numbers of spatial
dimensions, involving a variety of astrophysical scenarios, including the
evolution of the post-merger remnant of a BNS merger over a timescale of one
second. \texttt{BHAC+}, can accurately reproduce the evolution of compact
objects in non-vacuum spacetimes and that, when compared with the evolution in
full general relativity, the CFC reproduces accurately both the gravitational
fields and the matter variables at a fraction of the computational costs.
| [
{
"created": "Mon, 18 Dec 2023 17:15:33 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Dec 2023 19:43:37 GMT",
"version": "v2"
},
{
"created": "Tue, 9 Apr 2024 13:08:35 GMT",
"version": "v3"
}
] | 2024-04-11 | [
[
"Ng",
"Harry Ho-Yin",
""
],
[
"Jiang",
"Jin-Liang",
""
],
[
"Musolino",
"Carlo",
""
],
[
"Ecker",
"Christian",
""
],
[
"Tootle",
"Samuel D.",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | One of the main challenges in the numerical modeling of binary neutron-star (BNS) mergers is long-term simulations of the post-merger remnant over timescales of the order of seconds. When this modeling includes all the aspects of complex physics, the computational costs can easily become enormous. To address this challenge in part, we have developed a novel hybrid approach in which the solution from a general-relativistic magnetohydrodynamics (GRMHD) code solving the full set of the Einstein equations in Cartesian coordinates is coupled with another GRMHD code in which the Einstein equations are solved under the Conformally Flat Condition (CFC). The latter approximation has a long history and has been shown to provide an accurate description of compact objects in non-vacuum spacetimes. An important aspect of the CFC is that the elliptic equations need to be solved only for a fraction of the steps needed for the underlying HD/MHD evolution, thus allowing for a gain in computational efficiency that can be up to a factor of $\sim 6~(230)$ in three-dimensional (two-dimensional) simulations. We present the basic features of the new code, the strategies necessary to interface it when importing both two- and three-dimensional data, and a novel and robust approach to the recovery of the primitive variables. To validate our new framework, we have carried out code tests with various coordinate systems and different numbers of spatial dimensions, involving a variety of astrophysical scenarios, including the evolution of the post-merger remnant of a BNS merger over a timescale of one second. \texttt{BHAC+}, can accurately reproduce the evolution of compact objects in non-vacuum spacetimes and that, when compared with the evolution in full general relativity, the CFC reproduces accurately both the gravitational fields and the matter variables at a fraction of the computational costs. |
1801.01420 | Paolo Pani | Vitor Cardoso, \'Oscar J. C. Dias, Gavin S. Hartnett, Matthew
Middleton, Paolo Pani, Jorge E. Santos | Constraining the mass of dark photons and axion-like particles through
black-hole superradiance | 24 pages, 12 pages. Includes supplemental datafile | null | 10.1088/1475-7516/2018/03/043 | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Ultralight bosons and axion-like particles appear naturally in different
scenarios and could solve some long-standing puzzles. Their detection is
challenging, and all direct methods hinge on unknown couplings to the Standard
Model of particle physics. However, the universal coupling to gravity provides
model-independent signatures for these fields. We explore here the superradiant
instability of spinning black holes triggered in the presence of such fields.
The instability taps angular momentum from and limits the maximum spin of
astrophysical black holes. We compute, for the first time, the spectrum of the
most unstable modes of a massive vector (Proca) field for generic black-hole
spin and Proca mass. The observed stability of the inner disk of stellar-mass
black holes can be used to derive \emph{direct} constraints on the mass of dark
photons in the mass range $ 10^{-13}\,{\rm eV}\lesssim m_V \lesssim 3\times
10^{-12}\,{\rm eV}$. By including also higher azimuthal modes, similar
constraints apply to axion-like particles in the mass range
$6\times10^{-13}\,{\rm eV}\lesssim m_{\rm ALP} \lesssim 10^{-11}\, {\rm eV}$.
Likewise, mass and spin distributions of supermassive BHs --~as measured
through continuum fitting, K$\alpha$ iron line, or with the future space-based
gravitational-wave detector LISA~-- imply indirect bounds in the mass range
approximately $10^{-19}\,{\rm eV}\lesssim m_V, m_{\rm ALP} \lesssim 10^{-13}\,
{\rm eV}$, for both axion-like particles and dark photons. Overall,
superradiance allows to explore a region of approximately $8$ orders of
magnitude in the mass of ultralight bosons.
| [
{
"created": "Thu, 4 Jan 2018 16:12:50 GMT",
"version": "v1"
}
] | 2018-04-11 | [
[
"Cardoso",
"Vitor",
""
],
[
"Dias",
"Óscar J. C.",
""
],
[
"Hartnett",
"Gavin S.",
""
],
[
"Middleton",
"Matthew",
""
],
[
"Pani",
"Paolo",
""
],
[
"Santos",
"Jorge E.",
""
]
] | Ultralight bosons and axion-like particles appear naturally in different scenarios and could solve some long-standing puzzles. Their detection is challenging, and all direct methods hinge on unknown couplings to the Standard Model of particle physics. However, the universal coupling to gravity provides model-independent signatures for these fields. We explore here the superradiant instability of spinning black holes triggered in the presence of such fields. The instability taps angular momentum from and limits the maximum spin of astrophysical black holes. We compute, for the first time, the spectrum of the most unstable modes of a massive vector (Proca) field for generic black-hole spin and Proca mass. The observed stability of the inner disk of stellar-mass black holes can be used to derive \emph{direct} constraints on the mass of dark photons in the mass range $ 10^{-13}\,{\rm eV}\lesssim m_V \lesssim 3\times 10^{-12}\,{\rm eV}$. By including also higher azimuthal modes, similar constraints apply to axion-like particles in the mass range $6\times10^{-13}\,{\rm eV}\lesssim m_{\rm ALP} \lesssim 10^{-11}\, {\rm eV}$. Likewise, mass and spin distributions of supermassive BHs --~as measured through continuum fitting, K$\alpha$ iron line, or with the future space-based gravitational-wave detector LISA~-- imply indirect bounds in the mass range approximately $10^{-19}\,{\rm eV}\lesssim m_V, m_{\rm ALP} \lesssim 10^{-13}\, {\rm eV}$, for both axion-like particles and dark photons. Overall, superradiance allows to explore a region of approximately $8$ orders of magnitude in the mass of ultralight bosons. |
1301.3508 | Ahmed Farag Ali | Ahmed Farag Ali (Benha U.) and A. Tawfik (Egyptian Ctr. Theor. Phys.,
Cairo and Freie U., Berlin) | Modified Newton's Law of Gravitation Due to Minimal Length in Quantum
Gravity | 12 pages, no figures, references added | Adv.High Energy Phys. 2013 (2013) 126528 | 10.1155/2013/126528 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A recent theory about the origin of the gravity suggests that the gravity is
originally an entropic force. In this work, we discuss the effects of
generalized uncertainty principle (GUP) which is proposed by some approaches to
quantum gravity such as string theory, black hole physics and doubly special
relativity theories (DSR), on the area law of the entropy. This leads to a
$\sqrt{Area}$-type correction to the area law of entropy which imply that the
number of bits $N$ is modified. Therefore, we obtain a modified Newton's law of
gravitation. Surprisingly, this modification agrees with different sign with
the prediction of Randall-Sundrum II model which contains one uncompactified
extra dimension. Furthermore, such modification may have observable
consequences at length scales much larger than the Planck scale.
| [
{
"created": "Tue, 15 Jan 2013 21:50:54 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Feb 2013 14:41:27 GMT",
"version": "v2"
}
] | 2013-02-25 | [
[
"Ali",
"Ahmed Farag",
"",
"Benha U."
],
[
"Tawfik",
"A.",
"",
"Egyptian Ctr. Theor. Phys.,\n Cairo and Freie U., Berlin"
]
] | A recent theory about the origin of the gravity suggests that the gravity is originally an entropic force. In this work, we discuss the effects of generalized uncertainty principle (GUP) which is proposed by some approaches to quantum gravity such as string theory, black hole physics and doubly special relativity theories (DSR), on the area law of the entropy. This leads to a $\sqrt{Area}$-type correction to the area law of entropy which imply that the number of bits $N$ is modified. Therefore, we obtain a modified Newton's law of gravitation. Surprisingly, this modification agrees with different sign with the prediction of Randall-Sundrum II model which contains one uncompactified extra dimension. Furthermore, such modification may have observable consequences at length scales much larger than the Planck scale. |
gr-qc/0009055 | Kazuhiro Tominaga | Kazuhiro Tominaga, Motoyuki Saijo, and Kei-ichi Maeda | Gravitational waves from a spinning particle scattered by a relativistic
star: Axial mode case | REVTeX, 17 pages with 13 figures. Submitted to Phys. Rev. D | Phys.Rev.D63:124012,2001 | 10.1103/PhysRevD.63.124012 | WU-AP/112/00 (Waseda Univ. Astrophysics) | gr-qc | null | We study gravitational waves from a spinning test particle scattered by a
relativistic star using a perturbation method. The present analysis is
restricted to axial modes. By calculating the energy spectrum, the waveforms
and the total energy and angular momentum of gravitational waves, we analyze
the dependence of the emitted gravitational waves on a particle spin. For a
normal neutron star, the energy spectrum has one broad peak whose
characteristic frequency corresponds to the angular velocity at the turning
point (a periastron). Since the turning point is determined by the orbital
parameter, there exists the dependence of the gravitational wave on a particle
spin. We find that the total energy of $l = 2$ gravitational waves gets larger
as the spin increases in the anti-parallel direction to the orbital angular
momentum. For an ultracompact star, in addition to such an orbital
contribution, we find the quasi-normal modes exited by a scattered particle,
whose excitation rate to gravitational waves depends on the particle spin. We
also discuss the ratio of the total angular momentum to the total energy of
gravitational waves and explain its spin dependence.
| [
{
"created": "Fri, 15 Sep 2000 15:31:35 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Tominaga",
"Kazuhiro",
""
],
[
"Saijo",
"Motoyuki",
""
],
[
"Maeda",
"Kei-ichi",
""
]
] | We study gravitational waves from a spinning test particle scattered by a relativistic star using a perturbation method. The present analysis is restricted to axial modes. By calculating the energy spectrum, the waveforms and the total energy and angular momentum of gravitational waves, we analyze the dependence of the emitted gravitational waves on a particle spin. For a normal neutron star, the energy spectrum has one broad peak whose characteristic frequency corresponds to the angular velocity at the turning point (a periastron). Since the turning point is determined by the orbital parameter, there exists the dependence of the gravitational wave on a particle spin. We find that the total energy of $l = 2$ gravitational waves gets larger as the spin increases in the anti-parallel direction to the orbital angular momentum. For an ultracompact star, in addition to such an orbital contribution, we find the quasi-normal modes exited by a scattered particle, whose excitation rate to gravitational waves depends on the particle spin. We also discuss the ratio of the total angular momentum to the total energy of gravitational waves and explain its spin dependence. |
gr-qc/9701038 | Paul Parsons | John D. Barrow (University of Sussex) | Cosmological Limits on Slightly Skew Stresses | Latex, requires sw20lart package. No figures | Phys.Rev. D55 (1997) 7451-7460 | 10.1103/PhysRevD.55.7451 | null | gr-qc astro-ph | null | We present an analysis of the cosmological evolution of matter sources with
small anisotropic pressures. This includes electric and magnetic fields,
collisionless relativistic particles, gravitons, antisymmetric axion fields in
low-energy string cosmologies, spatial curvature anisotropies, and stresses
arising from simple topological defects. We calculate their evolution during
the radiation and dust eras of an almost isotropic universe. In many
interesting cases the evolution displays a special critical behaviour created
by the non-linear evolution of the pressure and expansion anisotropies. The
isotropy of the microwave background is used to place strong limits of order
$\Omega _{a0}\leq 5\times 10^{-6}\Delta (1+z_{rec})^{-\Delta }$on the possible
contribution of these matter sources to the total density of the universe,
where $1\leq \Delta \leq 3$ characterises the anisotropic stress. The present
abundance of an anisotropic stress which becomes non-relativistic at a
characteristic low-energy scale is also calculated. We explain why the limits
obtained from primordial nucleosynthesis are generally weaker than those
imposed by the microwave background isotropy. The effect of inflation on these
stresses is also calculated.
| [
{
"created": "Thu, 16 Jan 1997 15:14:15 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Barrow",
"John D.",
"",
"University of Sussex"
]
] | We present an analysis of the cosmological evolution of matter sources with small anisotropic pressures. This includes electric and magnetic fields, collisionless relativistic particles, gravitons, antisymmetric axion fields in low-energy string cosmologies, spatial curvature anisotropies, and stresses arising from simple topological defects. We calculate their evolution during the radiation and dust eras of an almost isotropic universe. In many interesting cases the evolution displays a special critical behaviour created by the non-linear evolution of the pressure and expansion anisotropies. The isotropy of the microwave background is used to place strong limits of order $\Omega _{a0}\leq 5\times 10^{-6}\Delta (1+z_{rec})^{-\Delta }$on the possible contribution of these matter sources to the total density of the universe, where $1\leq \Delta \leq 3$ characterises the anisotropic stress. The present abundance of an anisotropic stress which becomes non-relativistic at a characteristic low-energy scale is also calculated. We explain why the limits obtained from primordial nucleosynthesis are generally weaker than those imposed by the microwave background isotropy. The effect of inflation on these stresses is also calculated. |
1804.10551 | Yusuf Sucu | Ganim Gecim and Yusuf Sucu | Quantum gravity effect on the Hawking radiation of charged rotating BTZ
black hole | Published version in General Relativity and Gravitation | Gen Relativ Gravit (2018) 50: 152 | 10.1007/s10714-018-2478-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this study, the quantum gravity effect on the tunnelling radiation of
charged massive spin-0 scalar particle from 2+1 dimensional charged rotating
Banados-Teitelboim-Zanelli (BTZ) black hole is looked into by using the
Hamilton-Jacobi approach. For this, we calculate the modified Hawking
temperature of the black hole by using the modified Klein-Gordon equation based
on the Generalized Uncertainty Principle (GUP), and we noticed that the
modified Hawking temperature of the black hole depends not only on the black
hole properties, but also on the angular momentum, energy, charge and mass of
the tunnelling scalar particle. Using the modified Hawking temperature, we
discussed the stability of the black hole in the context of the modified heat
capacity, and observed that it might undergo both first and second-type phase
transitions in the presence of the quantum gravity effect, but just a
first-type transition in the absence of the quantum gravity effect.
Furthermore, we investigated the modified Hawking temperature of the black hole
by using the tunnelling processes of the charged massive Dirac and vector boson
particles. We observed that scalar, Dirac and vector particles are tunnelled
from the black hole completely differently from each other in the presence of
the quantum gravity effect.
| [
{
"created": "Fri, 27 Apr 2018 15:12:55 GMT",
"version": "v1"
},
{
"created": "Sun, 10 Jun 2018 14:38:40 GMT",
"version": "v2"
},
{
"created": "Mon, 12 Nov 2018 10:02:02 GMT",
"version": "v3"
}
] | 2018-11-13 | [
[
"Gecim",
"Ganim",
""
],
[
"Sucu",
"Yusuf",
""
]
] | In this study, the quantum gravity effect on the tunnelling radiation of charged massive spin-0 scalar particle from 2+1 dimensional charged rotating Banados-Teitelboim-Zanelli (BTZ) black hole is looked into by using the Hamilton-Jacobi approach. For this, we calculate the modified Hawking temperature of the black hole by using the modified Klein-Gordon equation based on the Generalized Uncertainty Principle (GUP), and we noticed that the modified Hawking temperature of the black hole depends not only on the black hole properties, but also on the angular momentum, energy, charge and mass of the tunnelling scalar particle. Using the modified Hawking temperature, we discussed the stability of the black hole in the context of the modified heat capacity, and observed that it might undergo both first and second-type phase transitions in the presence of the quantum gravity effect, but just a first-type transition in the absence of the quantum gravity effect. Furthermore, we investigated the modified Hawking temperature of the black hole by using the tunnelling processes of the charged massive Dirac and vector boson particles. We observed that scalar, Dirac and vector particles are tunnelled from the black hole completely differently from each other in the presence of the quantum gravity effect. |
1212.6654 | Sunil Maharaj | M. C. Kweyama, K. S. Govinder, S. D. Maharaj | Noether and Lie symmetries for charged perfect fluids | 17 pages, To appear in Class. Quantum Grav | Class. Quantum Grav. 28: 105005, 2011 | 10.1088/0264-9381/28/10/105005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the underlying nonlinear partial differential equation that governs
the behaviour of spherically symmetric charged fluids in general relativity. We
investigate the conditions for the equation to admit a first integral or be
reduced to quadratures using symmetry methods for differential equations. A
general Noether first integral is found. We also undertake a comprehensive
group analysis of the underlying equation using Lie point symmetries. The
existence of a Lie symmetry is subject to solving an integro-differential
equation in general; we investigate the conditions under which it can be
reduced to quadratures. Earlier results for uncharged fluids and particular
first integrals for charged matter are regained as special cases of our
treatment.
| [
{
"created": "Sat, 29 Dec 2012 18:43:13 GMT",
"version": "v1"
}
] | 2015-06-12 | [
[
"Kweyama",
"M. C.",
""
],
[
"Govinder",
"K. S.",
""
],
[
"Maharaj",
"S. D.",
""
]
] | We study the underlying nonlinear partial differential equation that governs the behaviour of spherically symmetric charged fluids in general relativity. We investigate the conditions for the equation to admit a first integral or be reduced to quadratures using symmetry methods for differential equations. A general Noether first integral is found. We also undertake a comprehensive group analysis of the underlying equation using Lie point symmetries. The existence of a Lie symmetry is subject to solving an integro-differential equation in general; we investigate the conditions under which it can be reduced to quadratures. Earlier results for uncharged fluids and particular first integrals for charged matter are regained as special cases of our treatment. |
1409.6839 | Behrouz Mirza | Behrouz Mirza, Zeinab Sherkatghanad | Phase transitions of hairy black holes in massive gravity and
thermodynamic behavior of charged AdS black holes in an extended phase space | 7 pages, 6 figures | Phys. Rev. D 90, 084006 (2014) | 10.1103/PhysRevD.90.084006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the thermodynamic behavior of static and spherically symmetric hairy
black holes in massive gravity. In this case, the black hole is surrounded in a
spherical cavity with a fixed temperature on the surface. It is observed that
these black holes have a phase transition similar to the liquid-gas phase
transition of a Van der Waals fluid. Also, by treating the cosmological
constant $\Lambda$ as a thermodynamic pressure $P$, we study the thermodynamic
behavior of charged anti-de Sitter black holes in an ensemble with a pressure
of $P$ and an electric potential $\Phi$ as the natural variables. A second
order phase transition is observed to take place for all the values of the
electric potential $\Phi$.
| [
{
"created": "Wed, 24 Sep 2014 06:20:01 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Oct 2014 21:49:36 GMT",
"version": "v2"
}
] | 2015-06-23 | [
[
"Mirza",
"Behrouz",
""
],
[
"Sherkatghanad",
"Zeinab",
""
]
] | We study the thermodynamic behavior of static and spherically symmetric hairy black holes in massive gravity. In this case, the black hole is surrounded in a spherical cavity with a fixed temperature on the surface. It is observed that these black holes have a phase transition similar to the liquid-gas phase transition of a Van der Waals fluid. Also, by treating the cosmological constant $\Lambda$ as a thermodynamic pressure $P$, we study the thermodynamic behavior of charged anti-de Sitter black holes in an ensemble with a pressure of $P$ and an electric potential $\Phi$ as the natural variables. A second order phase transition is observed to take place for all the values of the electric potential $\Phi$. |
1605.04860 | Sharmanthie Fernando | Sharmanthie Fernando | Phase transitions of black holes in massive gravity | Accepted to be published in Modern Physics Letters A. Three more
references added | Modern Physics Lettets A, Vol.31, No. 16, 1650096 (2016) | 10.1142/S0217732316500966 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we have studied thermodynamics of a black hole in massive
gravity in the canonical ensemble. The massive gravity theory in consideration
here has a massive graviton due to Lorentz symmetry breaking. The black hole
studied here has a scalar charge due to the massive graviton and is
asymptotically anti-de Sitter. We have computed various thermodynamical
quantities such as temperature, specific heat and free energy. Both the local
and global stability of the black hole are studied by observing the behavior of
the specific heat and the free energy. We have observed that there is a first
order phase transition between small and large black hole for a certain range
of the scalar charge. This phase transition is similar to the liquid/gas phase
transition at constant temperature for a Van der Waals fluid. The coexistence
curves for the small and large black hole branches are also discussed in
detail.
| [
{
"created": "Mon, 16 May 2016 18:14:25 GMT",
"version": "v1"
},
{
"created": "Thu, 19 May 2016 18:02:48 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Dec 2016 15:10:44 GMT",
"version": "v3"
}
] | 2016-12-15 | [
[
"Fernando",
"Sharmanthie",
""
]
] | In this paper we have studied thermodynamics of a black hole in massive gravity in the canonical ensemble. The massive gravity theory in consideration here has a massive graviton due to Lorentz symmetry breaking. The black hole studied here has a scalar charge due to the massive graviton and is asymptotically anti-de Sitter. We have computed various thermodynamical quantities such as temperature, specific heat and free energy. Both the local and global stability of the black hole are studied by observing the behavior of the specific heat and the free energy. We have observed that there is a first order phase transition between small and large black hole for a certain range of the scalar charge. This phase transition is similar to the liquid/gas phase transition at constant temperature for a Van der Waals fluid. The coexistence curves for the small and large black hole branches are also discussed in detail. |
1405.5074 | Elena P. Savelova Dr. | A.A. Kirillov, E.P. Savelova | Effective action for a free scalar field in the presence of spacetime
foam | null | GRG 47, 97 (2015) | 10.1007/s10714-015-1941-1 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We model spacetime foam by a gas of virtual wormholes. For a free scalar
field we derive the effective Lagrangian which accounts for the interaction
with spacetime foam and contains two additional non-local terms. One term
describes the scattering of scalar particles on virtual wormholes and
explicitly reproduces the Pauli-Villars regularization procedure. The second
term describes the back reaction of particles on the number density of
wormholes and introduces a self-interaction between particles.
| [
{
"created": "Tue, 20 May 2014 13:13:09 GMT",
"version": "v1"
},
{
"created": "Sun, 8 Jun 2014 16:53:20 GMT",
"version": "v2"
},
{
"created": "Sat, 21 Jun 2014 17:25:00 GMT",
"version": "v3"
},
{
"created": "Sun, 9 Aug 2015 05:45:02 GMT",
"version": "v4"
}
] | 2015-08-11 | [
[
"Kirillov",
"A. A.",
""
],
[
"Savelova",
"E. P.",
""
]
] | We model spacetime foam by a gas of virtual wormholes. For a free scalar field we derive the effective Lagrangian which accounts for the interaction with spacetime foam and contains two additional non-local terms. One term describes the scattering of scalar particles on virtual wormholes and explicitly reproduces the Pauli-Villars regularization procedure. The second term describes the back reaction of particles on the number density of wormholes and introduces a self-interaction between particles. |
gr-qc/0611112 | Martin Bojowald | Martin Bojowald, Hector Hernandez, Mikhail Kagan and Aureliano
Skirzewski | Effective constraints of loop quantum gravity | 44 pages, 6 figures | Phys.Rev.D75:064022,2007 | 10.1103/PhysRevD.75.064022 | IGPG-06/11-4, AEI-2006-086 | gr-qc astro-ph hep-th | null | Within a perturbative cosmological regime of loop quantum gravity corrections
to effective constraints are computed. This takes into account all
inhomogeneous degrees of freedom relevant for scalar metric modes around flat
space and results in explicit expressions for modified coefficients and of
higher order terms. It also illustrates the role of different scales
determining the relative magnitude of corrections. Our results demonstrate that
loop quantum gravity has the correct classical limit, at least in its sector of
cosmological perturbations around flat space, in the sense of perturbative
effective theory.
| [
{
"created": "Tue, 21 Nov 2006 20:37:26 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Bojowald",
"Martin",
""
],
[
"Hernandez",
"Hector",
""
],
[
"Kagan",
"Mikhail",
""
],
[
"Skirzewski",
"Aureliano",
""
]
] | Within a perturbative cosmological regime of loop quantum gravity corrections to effective constraints are computed. This takes into account all inhomogeneous degrees of freedom relevant for scalar metric modes around flat space and results in explicit expressions for modified coefficients and of higher order terms. It also illustrates the role of different scales determining the relative magnitude of corrections. Our results demonstrate that loop quantum gravity has the correct classical limit, at least in its sector of cosmological perturbations around flat space, in the sense of perturbative effective theory. |
gr-qc/0307099 | Ozgur Delice | Ozgur Delice | Gravitational hedgehog, stringy hedgehog and stringy sphere | 11 pages | JHEP 0311 (2003) 058 | 10.1088/1126-6708/2003/11/058 | null | gr-qc | null | We investigate the solutions of Einstein equations such that a hedgehog
solution is matched to different exterior or interior solutions via a spherical
shell. In the case where both the exterior and the interior regions are
hedgehog solutions or one of them is flat, the resulting spherical shell
becomes a stringy shell. We also consider more general matchings and see that
in this case the shell deviates from its stringy character.
| [
{
"created": "Wed, 23 Jul 2003 11:53:52 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Oct 2003 17:39:44 GMT",
"version": "v2"
},
{
"created": "Wed, 3 Dec 2003 14:09:14 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Delice",
"Ozgur",
""
]
] | We investigate the solutions of Einstein equations such that a hedgehog solution is matched to different exterior or interior solutions via a spherical shell. In the case where both the exterior and the interior regions are hedgehog solutions or one of them is flat, the resulting spherical shell becomes a stringy shell. We also consider more general matchings and see that in this case the shell deviates from its stringy character. |
1608.00002 | Juan Antonio Nieto | J. A. Nieto | Alternative Self-dual Gravity in Eight Dimensions | 12 pages, Latex, accepted for publication in Modern Physics Letters A | null | 10.1142/S0217732316501479 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop an alternative Ashtekar formalism in eight dimensions. In fact,
using a MacDowell-Mansouri physical framework and a self-dual curvature
symmetry we propose an action in eight dimensions in which the Levi-Civita
tenor with eight indices plays a key role. We explicitly show that such an
action contains number of linear, quadratic and cubic terms in the Riemann
tensor, Ricci tensor and scalar curvature. In particular, the linear term is
reduced to the Einstein-Hilbert action with cosmological constant in eight
dimensions. We prove that such a reduced action is equivalent to the Lovelock
action in eight dimensions.
| [
{
"created": "Fri, 29 Jul 2016 16:47:04 GMT",
"version": "v1"
}
] | 2016-09-07 | [
[
"Nieto",
"J. A.",
""
]
] | We develop an alternative Ashtekar formalism in eight dimensions. In fact, using a MacDowell-Mansouri physical framework and a self-dual curvature symmetry we propose an action in eight dimensions in which the Levi-Civita tenor with eight indices plays a key role. We explicitly show that such an action contains number of linear, quadratic and cubic terms in the Riemann tensor, Ricci tensor and scalar curvature. In particular, the linear term is reduced to the Einstein-Hilbert action with cosmological constant in eight dimensions. We prove that such a reduced action is equivalent to the Lovelock action in eight dimensions. |
1201.2814 | Paolo Pani | Paolo Pani, Terence Delsate, Vitor Cardoso | Eddington-inspired Born-Infeld gravity. Phenomenology of non-linear
gravity-matter coupling | 16 pages, 13 figures. v2: improved section on the linear structure of
the theory, one reference added. Version accepted in PRD | null | 10.1103/PhysRevD.85.084020 | null | gr-qc astro-ph.SR hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Viable corrections to the matter sector of Poisson's equation may result in
qualitatively different astrophysical phenomenology, for example the
gravitational collapse and the properties of compact objects can change
drastically. We discuss a class of modified non-relativistic theories and focus
on a relativistic completion, Eddington-inspired Born-Infeld gravity. This
recently proposed theory is equivalent to General Relativity in vacuum, but its
non-trivial coupling to matter prevents singularities in early cosmology and in
the non-relativistic collapse of non-interacting particles. We extend our
previous analysis, discussing further developments. We present a full numerical
study of spherically symmetric non-relativistic gravitational collapse of dust.
For any positive coupling, the final state of the collapse is a regular
pressureless star rather than a singularity. We also argue that there is no
Chandrasekhar limit for the mass of non-relativistic white dwarf in this
theory. Finally, we extend our previous results in the fully relativistic
theory by constructing static and slowly rotating compact stars governed by
nuclear-physics inspired equations of state. In the relativistic theory, there
exists an upper bound on the mass of compact objects, suggesting that black
holes can still be formed in the relativistic collapse.
| [
{
"created": "Fri, 13 Jan 2012 12:08:02 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Mar 2012 18:00:06 GMT",
"version": "v2"
}
] | 2013-05-30 | [
[
"Pani",
"Paolo",
""
],
[
"Delsate",
"Terence",
""
],
[
"Cardoso",
"Vitor",
""
]
] | Viable corrections to the matter sector of Poisson's equation may result in qualitatively different astrophysical phenomenology, for example the gravitational collapse and the properties of compact objects can change drastically. We discuss a class of modified non-relativistic theories and focus on a relativistic completion, Eddington-inspired Born-Infeld gravity. This recently proposed theory is equivalent to General Relativity in vacuum, but its non-trivial coupling to matter prevents singularities in early cosmology and in the non-relativistic collapse of non-interacting particles. We extend our previous analysis, discussing further developments. We present a full numerical study of spherically symmetric non-relativistic gravitational collapse of dust. For any positive coupling, the final state of the collapse is a regular pressureless star rather than a singularity. We also argue that there is no Chandrasekhar limit for the mass of non-relativistic white dwarf in this theory. Finally, we extend our previous results in the fully relativistic theory by constructing static and slowly rotating compact stars governed by nuclear-physics inspired equations of state. In the relativistic theory, there exists an upper bound on the mass of compact objects, suggesting that black holes can still be formed in the relativistic collapse. |
2401.15965 | Qingyu Gan | Andrea Addazi, Salvatore Capozziello, Qingyu Gan | Resonant Graviton-Photon Conversion with Stochastic Magnetic Field in
the Expanding Universe | 29 pages, 5 figures | null | null | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate graviton-photon oscillations sourced by cosmological magnetic
fields from Gertsenshtein effect. We adopt a robust perturbative approach and
we find that the conversion probability from graviton to photon can be
resonantly enhanced in monochromatic, multi-chromatic and scale invariant
spectrum models of stochastic magnetic field fluctuations. In addition, the
expansion of the Universe acts as a decoherence factor, which demands a natural
discretization scheme along the line of sight. Including also decoherence from
cosmic acceleration, we find that conversion probabilities for stochastic
magnetic fields are completely different than results predicted from existing
magnetic domain-like models in a wide range of magnetic strengths and coherence
lengths. Resonances can be tested by radio telescopes as a probe of high
frequency gravitational wave sources and primordial magnetogenesis mechanisms.
| [
{
"created": "Mon, 29 Jan 2024 08:52:32 GMT",
"version": "v1"
}
] | 2024-01-30 | [
[
"Addazi",
"Andrea",
""
],
[
"Capozziello",
"Salvatore",
""
],
[
"Gan",
"Qingyu",
""
]
] | We investigate graviton-photon oscillations sourced by cosmological magnetic fields from Gertsenshtein effect. We adopt a robust perturbative approach and we find that the conversion probability from graviton to photon can be resonantly enhanced in monochromatic, multi-chromatic and scale invariant spectrum models of stochastic magnetic field fluctuations. In addition, the expansion of the Universe acts as a decoherence factor, which demands a natural discretization scheme along the line of sight. Including also decoherence from cosmic acceleration, we find that conversion probabilities for stochastic magnetic fields are completely different than results predicted from existing magnetic domain-like models in a wide range of magnetic strengths and coherence lengths. Resonances can be tested by radio telescopes as a probe of high frequency gravitational wave sources and primordial magnetogenesis mechanisms. |
gr-qc/0006062 | Fred C. Adams | Fred C. Adams (Physics Dept., University of Michigan) | The Life and Times of Extremal Black Holes | 9 pages, LaTeX, accepted to General Relativity and Gravitation | Gen.Rel.Grav. 32 (2000) 2229-2234 | 10.1023/A:1001907827388 | null | gr-qc | null | Charged extremal black holes cannot fully evaporate through the Hawking
effect and are thus long lived. Over their lifetimes, these black holes take
part in a variety of astrophysical processes, including many that lead to their
eventual destruction. This paper explores the various events that shape the
life of extremal black holes and calculates the corresponding time scales.
| [
{
"created": "Fri, 16 Jun 2000 15:53:41 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Adams",
"Fred C.",
"",
"Physics Dept., University of Michigan"
]
] | Charged extremal black holes cannot fully evaporate through the Hawking effect and are thus long lived. Over their lifetimes, these black holes take part in a variety of astrophysical processes, including many that lead to their eventual destruction. This paper explores the various events that shape the life of extremal black holes and calculates the corresponding time scales. |
1303.1687 | Jakub Mielczarek Ph.D. | Jean Pierre Gazeau, Jakub Mielczarek, Wlodzimierz Piechocki | Quantum states of the bouncing universe | 18 pages, 19 figures | null | 10.1103/PhysRevD.87.123508 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study quantum dynamics of the bouncing cosmological model.
We focus on the model of the flat Friedman-Robertson-Walker universe with a
free scalar field. The bouncing behavior, which replaces classical singularity,
appears due to the modification of general relativity along the methods of loop
quantum cosmology. We show that there exist a unitary transformation that
enables to describe the system as a free particle with Hamiltonian equal to
canonical momentum. We examine properties of the various quantum states of the
Universe: boxcar state, standard coherent state, and soliton-like state, as
well as Schr{\"o}dinger's cat states constructed from these states.
Characteristics of the states such as quantum moments and Wigner functions are
investigated. We show that each of these states have, for some range of
parameters, a proper semiclassical limit fulfilling the correspondence
principle. Decoherence of the superposition of two universes is described and
possible interpretations in terms of triad orientation and
Belinsky-Khalatnikov-Lifshitz conjecture are given. Some interesting features
regarding the area of the negative part of the Wigner function have emerged.
| [
{
"created": "Thu, 7 Mar 2013 13:34:40 GMT",
"version": "v1"
}
] | 2013-06-12 | [
[
"Gazeau",
"Jean Pierre",
""
],
[
"Mielczarek",
"Jakub",
""
],
[
"Piechocki",
"Wlodzimierz",
""
]
] | In this paper we study quantum dynamics of the bouncing cosmological model. We focus on the model of the flat Friedman-Robertson-Walker universe with a free scalar field. The bouncing behavior, which replaces classical singularity, appears due to the modification of general relativity along the methods of loop quantum cosmology. We show that there exist a unitary transformation that enables to describe the system as a free particle with Hamiltonian equal to canonical momentum. We examine properties of the various quantum states of the Universe: boxcar state, standard coherent state, and soliton-like state, as well as Schr{\"o}dinger's cat states constructed from these states. Characteristics of the states such as quantum moments and Wigner functions are investigated. We show that each of these states have, for some range of parameters, a proper semiclassical limit fulfilling the correspondence principle. Decoherence of the superposition of two universes is described and possible interpretations in terms of triad orientation and Belinsky-Khalatnikov-Lifshitz conjecture are given. Some interesting features regarding the area of the negative part of the Wigner function have emerged. |
gr-qc/9903061 | Kristin Schleich | Kristin Schleich and Donald M. Witt | Topological Censorship | Revtex 3, 6 epsf figures. This format differs slightly from that used
to produce the article as it originally appeared in the 1994 Proceedings of
the Lake Louise Winter Institute. However content is exactly the same | Published in Proceedings of the Lake Louise Winter Institute,
Particle Physics and Cosmology, Feb. 20-26, 1994, (World Scientific, 1994) | null | null | gr-qc | null | Classically, all topologies are allowed as solutions to the Einstein
equations. However, one does not observe any topological structures on medium
range distance scales, that is scales that are smaller than the size of the
observed universe but larger than the microscopic scales for which quantum
gravity becomes important. Recently, Friedman, Schleich and Witt have proven
that there is topological censorship on these medium range distance scales: the
Einstein equations, locally positive energy, and local predictability of
physics imply that any medium distance scale topological structures cannot be
seen. More precisely, we show that the topology of physically reasonable
isolated systems is shrouded from distant observers, or in other words there is
a topological censorship principle.
| [
{
"created": "Wed, 17 Mar 1999 00:04:32 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Schleich",
"Kristin",
""
],
[
"Witt",
"Donald M.",
""
]
] | Classically, all topologies are allowed as solutions to the Einstein equations. However, one does not observe any topological structures on medium range distance scales, that is scales that are smaller than the size of the observed universe but larger than the microscopic scales for which quantum gravity becomes important. Recently, Friedman, Schleich and Witt have proven that there is topological censorship on these medium range distance scales: the Einstein equations, locally positive energy, and local predictability of physics imply that any medium distance scale topological structures cannot be seen. More precisely, we show that the topology of physically reasonable isolated systems is shrouded from distant observers, or in other words there is a topological censorship principle. |
gr-qc/0207035 | Beverly K. Berger | Beverly K. Berger | Asymptotic Behavior of a Class of Expanding Gowdy Spacetimes | 21 pages, 14 figures, uses RevTeX 4, submitted to Phys. Rev. D | null | null | null | gr-qc | null | A systematic asymptotic expansion is developed for the gravitational wave
degrees of freedom of a class of expanding, vacuum Gowdy cosmological
spacetimes. In the wave map description of these models, the evolution of the
gravitational wave amplitudes defines an orbit in the target space. The
circumference of this orbit decays to zero indicating that the asymptotic
spacetime is spatially homogeneous. A prescription is given to identify the
asymptotic cosmological model for the gravitational wave degrees of freedom
using the asymptotic point in the target space. The remaining metric function
of the asymptotic cosmological model, found by solving the constraints, is
determined by an effective energy of the gravitational waves rather than from
the asymptotic point in the target space.
| [
{
"created": "Sun, 7 Jul 2002 23:35:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Berger",
"Beverly K.",
""
]
] | A systematic asymptotic expansion is developed for the gravitational wave degrees of freedom of a class of expanding, vacuum Gowdy cosmological spacetimes. In the wave map description of these models, the evolution of the gravitational wave amplitudes defines an orbit in the target space. The circumference of this orbit decays to zero indicating that the asymptotic spacetime is spatially homogeneous. A prescription is given to identify the asymptotic cosmological model for the gravitational wave degrees of freedom using the asymptotic point in the target space. The remaining metric function of the asymptotic cosmological model, found by solving the constraints, is determined by an effective energy of the gravitational waves rather than from the asymptotic point in the target space. |
1307.0745 | Joao Magueijo | Giovanni Amelino-Camelia, Michele Arzano, Giulia Gubitosi and Joao
Magueijo | Rainbow gravity and scale-invariant fluctuations | null | Phys. Rev. D 88, 041303, 2013 | 10.1103/PhysRevD.88.041303 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We re-examine a recently proposed scenario where the deformed dispersion
relations associated with a flow of the spectral dimension to a UV value of 2
leads to a scale-invariant spectrum of cosmological fluctuations, without the
need for inflation. In that scenario Einstein gravity was assumed. The theory
displays a wavelength-dependent speed of light but by transforming to a
suitable "rainbow frame" this feature can be removed, at the expense of
modifying gravity. We find that the ensuing rainbow gravity theory is such that
gravity switches off at high energy (or at least leads to a universal conformal
coupling). This explains why the fluctuations are scale-invariant on all
scales: there is no horizon scale as such. For dispersion relations that do not
lead to exact scale invariance we find instead esoteric inflation in the
rainbow frame. We argue that these results shed light on the behaviour of
gravity under the phenomenon of dimensional reduction.
| [
{
"created": "Tue, 2 Jul 2013 16:12:36 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Jul 2013 10:44:54 GMT",
"version": "v2"
}
] | 2015-06-16 | [
[
"Amelino-Camelia",
"Giovanni",
""
],
[
"Arzano",
"Michele",
""
],
[
"Gubitosi",
"Giulia",
""
],
[
"Magueijo",
"Joao",
""
]
] | We re-examine a recently proposed scenario where the deformed dispersion relations associated with a flow of the spectral dimension to a UV value of 2 leads to a scale-invariant spectrum of cosmological fluctuations, without the need for inflation. In that scenario Einstein gravity was assumed. The theory displays a wavelength-dependent speed of light but by transforming to a suitable "rainbow frame" this feature can be removed, at the expense of modifying gravity. We find that the ensuing rainbow gravity theory is such that gravity switches off at high energy (or at least leads to a universal conformal coupling). This explains why the fluctuations are scale-invariant on all scales: there is no horizon scale as such. For dispersion relations that do not lead to exact scale invariance we find instead esoteric inflation in the rainbow frame. We argue that these results shed light on the behaviour of gravity under the phenomenon of dimensional reduction. |
1611.08394 | Alejandro Perez | Alberto S. Cattaneo and Alejandro Perez | A note on the Poisson bracket of 2d smeared fluxes in loop quantum
gravity | 5 pages, no figures (journal version) | Class. Quant. Grav. 34, 107001 (2017) | 10.1088/1361-6382/aa69b4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the non-Abelian nature of geometric fluxes---the corner-stone in
the definition of quantum geometry in the framework of loop quantum gravity
(LQG)---follows directly form the continuum canonical commutations relations of
gravity in connection variables and the validity of the Gauss law. The present
treatment simplifies previous formulations and thus identifies more clearly the
root of the discreteness of geometric operators in LQG. Our statement
generalizes to arbitrary gauge theories and relies only on the validity of the
Gauss law.
| [
{
"created": "Fri, 25 Nov 2016 09:29:25 GMT",
"version": "v1"
},
{
"created": "Sat, 1 Apr 2017 22:53:36 GMT",
"version": "v2"
}
] | 2020-02-03 | [
[
"Cattaneo",
"Alberto S.",
""
],
[
"Perez",
"Alejandro",
""
]
] | We show that the non-Abelian nature of geometric fluxes---the corner-stone in the definition of quantum geometry in the framework of loop quantum gravity (LQG)---follows directly form the continuum canonical commutations relations of gravity in connection variables and the validity of the Gauss law. The present treatment simplifies previous formulations and thus identifies more clearly the root of the discreteness of geometric operators in LQG. Our statement generalizes to arbitrary gauge theories and relies only on the validity of the Gauss law. |
1801.05782 | Sean Gryb | Sean Gryb and Karim P. Y. Th\'ebault | Superpositions of the cosmological constant allow for singularity
resolution and unitary evolution in quantum cosmology | Version accepted to Physics Letters B. Minor revisions,
clarifications added. 7 pages, 3 figures | null | 10.1016/j.physletb.2018.08.013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A novel approach to quantization is shown to allow for superpositions of the
cosmological constant in isotropic and homogeneous mini-superspace models.
Generic solutions featuring such superpositions display unitary evolution and
resolution of the classical singularity. Physically well-motivated cosmological
solutions are constructed. These particular solutions exhibit characteristic
features of a cosmic bounce including universal phenomenology that can be
rendered insensitive to Planck-scale physics in a natural manner.
| [
{
"created": "Wed, 17 Jan 2018 18:14:40 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Aug 2018 13:21:44 GMT",
"version": "v2"
}
] | 2018-08-15 | [
[
"Gryb",
"Sean",
""
],
[
"Thébault",
"Karim P. Y.",
""
]
] | A novel approach to quantization is shown to allow for superpositions of the cosmological constant in isotropic and homogeneous mini-superspace models. Generic solutions featuring such superpositions display unitary evolution and resolution of the classical singularity. Physically well-motivated cosmological solutions are constructed. These particular solutions exhibit characteristic features of a cosmic bounce including universal phenomenology that can be rendered insensitive to Planck-scale physics in a natural manner. |
2304.03786 | Maria Charisi | Maria Charisi, Stephen R. Taylor, Caitlin A. Witt, Jessie Runnoe | Efficient large-scale, targeted gravitational-wave probes of
supermassive black-hole binaries | Comments welcome | null | null | null | gr-qc astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Supermassive black hole binaries are promising sources of low-frequency
gravitational waves (GWs) and bright electromagnetic emission. Pulsar timing
array searches for resolved binaries are complex and computationally expensive
and so far limited to only a few sources. We present an efficient approximation
that empowers large-scale targeted multi-messenger searches by neglecting GW
signal components from the pulsar term. This Earth-term approximation provides
similar constraints on the total mass and GW frequency of the binary, yet is
$>100$ times more efficient.
| [
{
"created": "Fri, 7 Apr 2023 18:00:00 GMT",
"version": "v1"
}
] | 2023-04-11 | [
[
"Charisi",
"Maria",
""
],
[
"Taylor",
"Stephen R.",
""
],
[
"Witt",
"Caitlin A.",
""
],
[
"Runnoe",
"Jessie",
""
]
] | Supermassive black hole binaries are promising sources of low-frequency gravitational waves (GWs) and bright electromagnetic emission. Pulsar timing array searches for resolved binaries are complex and computationally expensive and so far limited to only a few sources. We present an efficient approximation that empowers large-scale targeted multi-messenger searches by neglecting GW signal components from the pulsar term. This Earth-term approximation provides similar constraints on the total mass and GW frequency of the binary, yet is $>100$ times more efficient. |
1107.1181 | Bernard Kelly | Bernard J. Kelly, John G. Baker, William D. Boggs, Sean T. McWilliams,
Joan Centrella | Mergers of black-hole binaries with aligned spins: Waveform
characteristics | 19 pages, 17 figures; new version matches published article | Physical Review D 84:084009 (2011) | 10.1103/PhysRevD.84.084009 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We conduct a descriptive analysis of the multipolar structure of
gravitational-radiation waveforms from equal-mass aligned-spin mergers,
following an approach first presented in the complementary context of
nonspinning black holes of varying mass ratio [J.G. Baker et al. Phys. Rev. D
78 044046 (2008)]. We find that, as with the nonspinning mergers, the dominant
waveform mode phases evolve together in lock-step through inspiral and merger,
supporting the previous waveform description in terms of an adiabatically rigid
rotator driving gravitational-wave emission-an implicit rotating source. We
further apply the late-time merger-ringdown model for the rotational frequency
introduced in [J.G. Baker et al. Phys. Rev. D 78 044046 (2008)], along with an
improved amplitude model appropriate for the dominant (2, \pm2) modes. This
provides a quantitative description of the merger-ringdown waveforms, and
suggests that the major features of these waveforms can be described with
reference only to the intrinsic parameters associated with the state of the
final black hole formed in the merger. We provide an explicit model for the
merger-ringdown radiation, and demonstrate that this model agrees to fitting
factors better than 95% with the original numerical waveforms for system masses
above \sim150M\odot. This model may be directly applicable to
gravitational-wave detection of intermediate-mass black-hole mergers.
| [
{
"created": "Wed, 6 Jul 2011 16:46:41 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Oct 2011 17:13:37 GMT",
"version": "v2"
}
] | 2013-05-29 | [
[
"Kelly",
"Bernard J.",
""
],
[
"Baker",
"John G.",
""
],
[
"Boggs",
"William D.",
""
],
[
"McWilliams",
"Sean T.",
""
],
[
"Centrella",
"Joan",
""
]
] | We conduct a descriptive analysis of the multipolar structure of gravitational-radiation waveforms from equal-mass aligned-spin mergers, following an approach first presented in the complementary context of nonspinning black holes of varying mass ratio [J.G. Baker et al. Phys. Rev. D 78 044046 (2008)]. We find that, as with the nonspinning mergers, the dominant waveform mode phases evolve together in lock-step through inspiral and merger, supporting the previous waveform description in terms of an adiabatically rigid rotator driving gravitational-wave emission-an implicit rotating source. We further apply the late-time merger-ringdown model for the rotational frequency introduced in [J.G. Baker et al. Phys. Rev. D 78 044046 (2008)], along with an improved amplitude model appropriate for the dominant (2, \pm2) modes. This provides a quantitative description of the merger-ringdown waveforms, and suggests that the major features of these waveforms can be described with reference only to the intrinsic parameters associated with the state of the final black hole formed in the merger. We provide an explicit model for the merger-ringdown radiation, and demonstrate that this model agrees to fitting factors better than 95% with the original numerical waveforms for system masses above \sim150M\odot. This model may be directly applicable to gravitational-wave detection of intermediate-mass black-hole mergers. |
gr-qc/0611135 | Daniel R. Terno | Etera R. Livine and Daniel R. Terno | Quantum causal histories in the light of quantum information | 9 pages, 8 eps figures | Phys.Rev.D75:084001,2007 | 10.1103/PhysRevD.75.084001 | null | gr-qc astro-ph hep-th quant-ph | null | We use techniques of quantum information theory to analyze the quantum causal
histories approach to quantum gravity. We show that while it is consistent to
introduce closed timelike curves (CTCs), they cannot generically carry
independent degrees of freedom. Moreover, if the effective dynamics of the
chronology-respecting part of the system is linear, it should be completely
decoupled from the CTCs. In the absence of a CTC not all causal structures
admit the introduction of quantum mechanics. It is possible for those and only
for those causal structures that can be represented as quantum computational
networks. The dynamics of the subsystems should not be unitary or even
completely positive. However, we show that other commonly maid assumptions
ensure the complete positivity of the reduced dynamics.
| [
{
"created": "Sun, 26 Nov 2006 05:30:30 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Livine",
"Etera R.",
""
],
[
"Terno",
"Daniel R.",
""
]
] | We use techniques of quantum information theory to analyze the quantum causal histories approach to quantum gravity. We show that while it is consistent to introduce closed timelike curves (CTCs), they cannot generically carry independent degrees of freedom. Moreover, if the effective dynamics of the chronology-respecting part of the system is linear, it should be completely decoupled from the CTCs. In the absence of a CTC not all causal structures admit the introduction of quantum mechanics. It is possible for those and only for those causal structures that can be represented as quantum computational networks. The dynamics of the subsystems should not be unitary or even completely positive. However, we show that other commonly maid assumptions ensure the complete positivity of the reduced dynamics. |
1003.2105 | Mauro Cattani | M.Cattani | Gravitational Waves II: Emitting Systems | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use the basic equations that predict the emission of gravitational waves
according to the Einstein gravitation theory to calculate the luminosities and
the amplitudes of the waves generated by binary stars, pulsations of neutron
stars, wobbling of deformed neutron stars, oscillating quadrupoles, rotating
bars and collapsing and bouncing cores of supernovas. This paper was written to
graduate and postgraduate students of Physics.
| [
{
"created": "Wed, 10 Mar 2010 13:17:01 GMT",
"version": "v1"
}
] | 2010-03-11 | [
[
"Cattani",
"M.",
""
]
] | We use the basic equations that predict the emission of gravitational waves according to the Einstein gravitation theory to calculate the luminosities and the amplitudes of the waves generated by binary stars, pulsations of neutron stars, wobbling of deformed neutron stars, oscillating quadrupoles, rotating bars and collapsing and bouncing cores of supernovas. This paper was written to graduate and postgraduate students of Physics. |
0812.0533 | Valter Moretti | Romeo Brunetti, Lorenzo Franceschini, Valter Moretti (Dept. of
Mathematics, Trento U.) | Topological features of massive bosons on two dimensional Einstein
space-time | 41 pages, title changed, minor changes, typos corrected, references
added. Accepted for publication in Ann. Henri Poincare' | Annales Henri Poincare 10:1027-1073,2009 | 10.1007/s00023-009-0007-x | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we tackle the problem of constructing explicit examples of
topological cocycles of Roberts' net cohomology, as defined abstractly by
Brunetti and Ruzzi. We consider the simple case of massive bosonic quantum
field theory on the two dimensional Einstein cylinder. After deriving some
crucial results of the algebraic framework of quantization, we address the
problem of the construction of the topological cocycles. All constructed
cocycles lead to unitarily equivalent representations of the fundamental group
of the circle (seen as a diffeomorphic image of all possible Cauchy surfaces).
The construction is carried out using only Cauchy data and related net of local
algebras on the circle.
| [
{
"created": "Tue, 2 Dec 2008 16:07:47 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Jan 2009 20:34:11 GMT",
"version": "v2"
},
{
"created": "Fri, 10 Jul 2009 13:58:58 GMT",
"version": "v3"
}
] | 2009-12-15 | [
[
"Brunetti",
"Romeo",
"",
"Dept. of\n Mathematics, Trento U."
],
[
"Franceschini",
"Lorenzo",
"",
"Dept. of\n Mathematics, Trento U."
],
[
"Moretti",
"Valter",
"",
"Dept. of\n Mathematics, Trento U."
]
] | In this paper we tackle the problem of constructing explicit examples of topological cocycles of Roberts' net cohomology, as defined abstractly by Brunetti and Ruzzi. We consider the simple case of massive bosonic quantum field theory on the two dimensional Einstein cylinder. After deriving some crucial results of the algebraic framework of quantization, we address the problem of the construction of the topological cocycles. All constructed cocycles lead to unitarily equivalent representations of the fundamental group of the circle (seen as a diffeomorphic image of all possible Cauchy surfaces). The construction is carried out using only Cauchy data and related net of local algebras on the circle. |
1606.06545 | Saheb Soroushfar | Bahareh Hoseini, Reza Saffari, Saheb Soroushfar | Geodesic Motion in the Spacetime Of a SU(2)-Colored (A)dS Black Hole in
Conformal Gravity | 14 pages, 2 table, 18 figures | Eur. Phys. J. Plus 136, 489 (2021) | 10.1140/epjp/s13360-021-01511-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we study the geodesic motion in the spacetime of a
SU(2)-colored (A)dS black hole in conformal gravity, and also we investigate
spacetime features, such as light spheres and horizons. Moreover, we derive the
analytical solutions for the equation of motion of test particles and light
rays using Weierstrass elliptic and Kleinian sigma functions. Depending on the
particle energy levels and angular momentums, we classify the solutions of the
geodesic equations. Furthermore, several examples of possible types of orbits
illustrate the results
| [
{
"created": "Tue, 21 Jun 2016 12:44:15 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Aug 2016 19:49:37 GMT",
"version": "v2"
},
{
"created": "Sat, 15 Jul 2017 21:45:15 GMT",
"version": "v3"
},
{
"created": "Tue, 18 Jul 2017 12:49:38 GMT",
"version": "v4"
},
{
"created": "Tue, 17 Nov 2020 15:40:43 GMT",
"version": "v5"
},
{
"created": "Thu, 6 May 2021 20:31:02 GMT",
"version": "v6"
}
] | 2021-05-10 | [
[
"Hoseini",
"Bahareh",
""
],
[
"Saffari",
"Reza",
""
],
[
"Soroushfar",
"Saheb",
""
]
] | In this paper, we study the geodesic motion in the spacetime of a SU(2)-colored (A)dS black hole in conformal gravity, and also we investigate spacetime features, such as light spheres and horizons. Moreover, we derive the analytical solutions for the equation of motion of test particles and light rays using Weierstrass elliptic and Kleinian sigma functions. Depending on the particle energy levels and angular momentums, we classify the solutions of the geodesic equations. Furthermore, several examples of possible types of orbits illustrate the results |
1512.01667 | Sunil Maurya DR. | S.K. Maurya, Smitha T. T., Y.K.Gupta, Farook Rahaman | A new exact solution for anisotropic compact stars of embedding class
one | 16 pages, 12 figures and 3 tables in European physical Journal A -
2016 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have presented a new anisotropic solution of Einstein's field equations
for compact star models. The Einstein's field equations are solved by using the
class one condition \cite{1}. After that we constructed the physically valid
expression of anisotropy factor by the help of metric potentials and there
after we obtained the physical parameters like energy density, radial and
transverse pressure. These models parameters are well behaved inside the
compact star and satisfy all the required physical conditions. Also we observed
a very interesting result that all the physical parameters are depend on the
anisotropy factor. The present compact star models are quite compatible with
the observational astrophysical compact stellar objects like Her X-1, RXJ
1856-37, SAX J1808.4-3658(SS1), SAX J1808.4-3658(SS2)
| [
{
"created": "Sat, 5 Dec 2015 13:47:47 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Jul 2016 21:00:08 GMT",
"version": "v2"
}
] | 2016-08-01 | [
[
"Maurya",
"S. K.",
""
],
[
"T.",
"Smitha T.",
""
],
[
"Gupta",
"Y. K.",
""
],
[
"Rahaman",
"Farook",
""
]
] | We have presented a new anisotropic solution of Einstein's field equations for compact star models. The Einstein's field equations are solved by using the class one condition \cite{1}. After that we constructed the physically valid expression of anisotropy factor by the help of metric potentials and there after we obtained the physical parameters like energy density, radial and transverse pressure. These models parameters are well behaved inside the compact star and satisfy all the required physical conditions. Also we observed a very interesting result that all the physical parameters are depend on the anisotropy factor. The present compact star models are quite compatible with the observational astrophysical compact stellar objects like Her X-1, RXJ 1856-37, SAX J1808.4-3658(SS1), SAX J1808.4-3658(SS2) |
1310.2939 | Yi-Zen Chu | Yi-Zen Chu | A Line Source in Minkowski for the de Sitter Spacetime Scalar Green's
Function: Massive Case | 24 pages, 2 figures. v2: Causal structure figures added | null | 10.1088/0264-9381/32/13/135008 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | For certain classes of space(time)s embeddable in a higher dimensional flat
space(time), it appears possible to compute the minimally coupled massless
scalar Green's function in the former by convolving its cousin in the latter
with an appropriate scalar charge density. The physical interpretation is that
beings residing in the higher dimensional flat space(time) may set up sources
to fool the observer confined on the lower dimensional curved submanifold that
she is detecting the field generated by a space(time) point source in her own
world. In this paper we extend the general formula to include a non-zero mass.
We then employ it to derive the Green's function of the massive wave operator
in (d >= 2)-dimensional de Sitter spacetime and that of the Helmholtz
differential operator -- the Laplacian plus a "mass term" -- on the (d >=
2)-sphere. For both cases, the trajectories of the scalar sources are the same
as that of the massless case, while the required scalar charge densities are
determined by solving an eigenvalue equation. To source these massive Green's
functions, we show that the (d+1)-dimensional Minkowski/Euclidean
experimentalists may choose to use either massive or massless scalar line
charges. In de Sitter spacetime, the embedding method employed here leads
directly to a manifest separation between the null cone versus tail terms of
the Green's functions.
| [
{
"created": "Thu, 10 Oct 2013 20:00:01 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Sep 2014 17:36:44 GMT",
"version": "v2"
},
{
"created": "Wed, 27 May 2015 04:43:47 GMT",
"version": "v3"
}
] | 2015-07-15 | [
[
"Chu",
"Yi-Zen",
""
]
] | For certain classes of space(time)s embeddable in a higher dimensional flat space(time), it appears possible to compute the minimally coupled massless scalar Green's function in the former by convolving its cousin in the latter with an appropriate scalar charge density. The physical interpretation is that beings residing in the higher dimensional flat space(time) may set up sources to fool the observer confined on the lower dimensional curved submanifold that she is detecting the field generated by a space(time) point source in her own world. In this paper we extend the general formula to include a non-zero mass. We then employ it to derive the Green's function of the massive wave operator in (d >= 2)-dimensional de Sitter spacetime and that of the Helmholtz differential operator -- the Laplacian plus a "mass term" -- on the (d >= 2)-sphere. For both cases, the trajectories of the scalar sources are the same as that of the massless case, while the required scalar charge densities are determined by solving an eigenvalue equation. To source these massive Green's functions, we show that the (d+1)-dimensional Minkowski/Euclidean experimentalists may choose to use either massive or massless scalar line charges. In de Sitter spacetime, the embedding method employed here leads directly to a manifest separation between the null cone versus tail terms of the Green's functions. |
1907.12594 | Leandros Perivolaropoulos | F. Skara and L. Perivolaropoulos | Primordial Power Spectra of Cosmological Fluctuations with Generalized
Uncertainty Principle and Maximum Length Quantum Mechanics | 12 pages, 3 figures. Published version. Comments added, figure added,
improved statistical analysis. The Mathematica file that was used for the
production of the figures may be downloaded from
http://leandros.physics.uoi.gr/GUP-GFC/ | Phys. Rev. D 100, 123527 (2019) | 10.1103/PhysRevD.100.123527 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The existence of the cosmological particle horizon as the maximum measurable
length $l_{max}$ in the universe leads to a generalization of the quantum
uncertainty principle (GUP) to the form $\Delta x \Delta p \geq
\frac{\hbar}{2}\frac{1}{1-\alpha\Delta x^2} $, where $\alpha\equiv
l_{max}^{-2}$. The effects of this GUP on simple quantum mechanical systems has
been shown recently by one of the authors\cite{Perivolaropoulos:2017rgq} to be
extremely small (beyond current measurements) due to the extremely large scale
of the current particle horizon. This is not the case in the Early Universe
during the quantum generation of the inflationary primordial fluctuation
spectrum. We estimate the effects of such GUP on the primordial fluctuation
spectrum and on the corresponding spectral index. We generalize the field
commutation (GFC) relation to
$[\varphi(k),\pi_{\varphi}(k')]$=$i\delta(k-k')\frac{1}{1-\mu\varphi^2(k)}$,
where $\mu\sim \alpha^2\equiv l_{max}^{-4}$ is a GFC parameter, $\varphi$
denotes a scalar field and $\pi_{\varphi}$ denotes its canonical conjugate
momentum. We obtain the predicted primordial perturbation spectrum as
$P_S(k)=P_S^{(0)}(k)\left(1+\frac{\bar{\mu}}{k}\right)$ where
$\bar{\mu}\equiv\mu V_* \simeq \sqrt{\alpha}= l_{max}^{-1}$ (here $V_*\simeq
l_{max}^3$ is the volume corresponding to $l_{max}$) and $P_S^{(0)}(k)$ is the
standard primordial spectrum obtained in the context of the Heisenberg
uncertainty principle ($\mu=0$). We show that the predicted scalar spectral
index is $n_s=1-\lambda-\frac{\bar{\mu}}{k}$ where $\lambda$ is a slow-roll
parameter. Using observational constraints on the scale dependence of the
spectral index $n_s$ we show that the $2\sigma$ range of $\alpha$ corresponds
to $l_{max}\gtrsim 10^{26} m $ which is of the same order as the current
particle horizon.
| [
{
"created": "Mon, 29 Jul 2019 18:18:50 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Aug 2019 05:28:28 GMT",
"version": "v2"
},
{
"created": "Thu, 19 Dec 2019 20:19:53 GMT",
"version": "v3"
}
] | 2019-12-25 | [
[
"Skara",
"F.",
""
],
[
"Perivolaropoulos",
"L.",
""
]
] | The existence of the cosmological particle horizon as the maximum measurable length $l_{max}$ in the universe leads to a generalization of the quantum uncertainty principle (GUP) to the form $\Delta x \Delta p \geq \frac{\hbar}{2}\frac{1}{1-\alpha\Delta x^2} $, where $\alpha\equiv l_{max}^{-2}$. The effects of this GUP on simple quantum mechanical systems has been shown recently by one of the authors\cite{Perivolaropoulos:2017rgq} to be extremely small (beyond current measurements) due to the extremely large scale of the current particle horizon. This is not the case in the Early Universe during the quantum generation of the inflationary primordial fluctuation spectrum. We estimate the effects of such GUP on the primordial fluctuation spectrum and on the corresponding spectral index. We generalize the field commutation (GFC) relation to $[\varphi(k),\pi_{\varphi}(k')]$=$i\delta(k-k')\frac{1}{1-\mu\varphi^2(k)}$, where $\mu\sim \alpha^2\equiv l_{max}^{-4}$ is a GFC parameter, $\varphi$ denotes a scalar field and $\pi_{\varphi}$ denotes its canonical conjugate momentum. We obtain the predicted primordial perturbation spectrum as $P_S(k)=P_S^{(0)}(k)\left(1+\frac{\bar{\mu}}{k}\right)$ where $\bar{\mu}\equiv\mu V_* \simeq \sqrt{\alpha}= l_{max}^{-1}$ (here $V_*\simeq l_{max}^3$ is the volume corresponding to $l_{max}$) and $P_S^{(0)}(k)$ is the standard primordial spectrum obtained in the context of the Heisenberg uncertainty principle ($\mu=0$). We show that the predicted scalar spectral index is $n_s=1-\lambda-\frac{\bar{\mu}}{k}$ where $\lambda$ is a slow-roll parameter. Using observational constraints on the scale dependence of the spectral index $n_s$ we show that the $2\sigma$ range of $\alpha$ corresponds to $l_{max}\gtrsim 10^{26} m $ which is of the same order as the current particle horizon. |
0804.1084 | Jonathan R. Gair | Jonathan R Gair, Ilya Mandel, Linqing Wen | Improved time-frequency analysis of extreme-mass-ratio inspiral signals
in mock LISA data | 8 pages, 1 figure; submitted to proceedings of 12th Gravitational
Wave Data Analysis Workshop | Class.Quant.Grav.25:184031,2008 | 10.1088/0264-9381/25/18/184031 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The planned Laser Interferometer Space Antenna (LISA) is expected to detect
gravitational wave signals from ~100 extreme-mass-ratio inspirals (EMRIs) of
stellar-mass compact objects into massive black holes. The long duration and
large parameter space of EMRI signals makes data analysis for these signals a
challenging problem. One approach to EMRI data analysis is to use
time-frequency methods. This consists of two steps: (i) searching for tracks
from EMRI sources in a time-frequency spectrogram, and (ii) extracting
parameter estimates from the tracks. In this paper we discuss the results of
applying these techniques to the latest round of the Mock LISA Data Challenge,
Round 1B. This analysis included three new techniques not used in previous
analyses: (i) a new Chirp-based Algorithm for Track Search for track detection;
(ii) estimation of the inclination of the source to the line of sight; (iii) a
Metropolis-Hastings Monte Carlo over the parameter space in order to find the
best fit to the tracks.
| [
{
"created": "Mon, 7 Apr 2008 17:12:00 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Gair",
"Jonathan R",
""
],
[
"Mandel",
"Ilya",
""
],
[
"Wen",
"Linqing",
""
]
] | The planned Laser Interferometer Space Antenna (LISA) is expected to detect gravitational wave signals from ~100 extreme-mass-ratio inspirals (EMRIs) of stellar-mass compact objects into massive black holes. The long duration and large parameter space of EMRI signals makes data analysis for these signals a challenging problem. One approach to EMRI data analysis is to use time-frequency methods. This consists of two steps: (i) searching for tracks from EMRI sources in a time-frequency spectrogram, and (ii) extracting parameter estimates from the tracks. In this paper we discuss the results of applying these techniques to the latest round of the Mock LISA Data Challenge, Round 1B. This analysis included three new techniques not used in previous analyses: (i) a new Chirp-based Algorithm for Track Search for track detection; (ii) estimation of the inclination of the source to the line of sight; (iii) a Metropolis-Hastings Monte Carlo over the parameter space in order to find the best fit to the tracks. |
1605.05975 | Klaus Liegener | Klaus Liegener and Thomas Thiemann | Towards the fundamental spectrum of the Quantum Yang-Mills Theory | 51 pages | Phys. Rev. D 94, 024042 (2016) | 10.1103/PhysRevD.94.024042 | null | gr-qc hep-lat hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we focus on the quantum Einstein-Yang-Mills sector quantised by
the methods of Loop Quantum Gravity (LQG). We point out the improved UV
behaviour of the coupled system as compared to pure quantum Yang-Mills theory
on a fixed, classical background spacetime as was considered in a seminal work
by Kogut and Susskind. Furthermore, we develop a calculational scheme by which
the fundamental spectrum of the quantum Yang-Mills Hamiltonian can be computed
in principle and by which one can make contact to the Wilsonian renormalization
group, possibly purely within the Hamiltonian framework. Finally, we comment on
the relation of the fundamental spectrum to that of pure Yang-Mills theory on a
(flat) classical spacetime.
| [
{
"created": "Thu, 19 May 2016 14:36:12 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Jul 2016 18:00:46 GMT",
"version": "v2"
}
] | 2016-07-29 | [
[
"Liegener",
"Klaus",
""
],
[
"Thiemann",
"Thomas",
""
]
] | In this work we focus on the quantum Einstein-Yang-Mills sector quantised by the methods of Loop Quantum Gravity (LQG). We point out the improved UV behaviour of the coupled system as compared to pure quantum Yang-Mills theory on a fixed, classical background spacetime as was considered in a seminal work by Kogut and Susskind. Furthermore, we develop a calculational scheme by which the fundamental spectrum of the quantum Yang-Mills Hamiltonian can be computed in principle and by which one can make contact to the Wilsonian renormalization group, possibly purely within the Hamiltonian framework. Finally, we comment on the relation of the fundamental spectrum to that of pure Yang-Mills theory on a (flat) classical spacetime. |
gr-qc/0601139 | Gregor Leiler | Gregor Leiler and Luciano Rezzolla | On the iterated Crank-Nicolson for hyperbolic and parabolic equations in
numerical relativity | 7 pages, 3 figures | Phys.Rev. D73 (2006) 044001 | 10.1103/PhysRevD.73.044001 | null | gr-qc | null | The iterated Crank-Nicolson is a predictor-corrector algorithm commonly used
in numerical relativity for the solution of both hyperbolic and parabolic
partial differential equations. We here extend the recent work on the stability
of this scheme for hyperbolic equations by investigating the properties when
the average between the predicted and corrected values is made with unequal
weights and when the scheme is applied to a parabolic equation. We also propose
a variant of the scheme in which the coefficients in the averages are swapped
between two corrections leading to systematically larger amplification factors
and to a smaller numerical dispersion.
| [
{
"created": "Tue, 31 Jan 2006 10:46:45 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Leiler",
"Gregor",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | The iterated Crank-Nicolson is a predictor-corrector algorithm commonly used in numerical relativity for the solution of both hyperbolic and parabolic partial differential equations. We here extend the recent work on the stability of this scheme for hyperbolic equations by investigating the properties when the average between the predicted and corrected values is made with unequal weights and when the scheme is applied to a parabolic equation. We also propose a variant of the scheme in which the coefficients in the averages are swapped between two corrections leading to systematically larger amplification factors and to a smaller numerical dispersion. |
1807.11330 | Neo Namane | Neo Namane, Heba Sami and Amare Abebe | Oscillating cosmological correlations in f(R) gravity | 6 pages, 4 figures, SAIP2018 conference proceedings | null | null | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | The purpose of this paper is to investigate the oscillatory behavior of the
universe through a Schr\"odinger-like Friedmann equation and a modified
gravitational background described by the theory of f (R) gravity. The
motivation for this stems from the observed periodic behaviour of large-scale
cosmological structures when described within the scope of the general theory
of relativity. The analysis of the modified Friedmann equation for the dust
epoch in power-law f (R) models results in different behaviors for the
wave-function of the universe.
| [
{
"created": "Mon, 30 Jul 2018 13:05:23 GMT",
"version": "v1"
}
] | 2018-07-31 | [
[
"Namane",
"Neo",
""
],
[
"Sami",
"Heba",
""
],
[
"Abebe",
"Amare",
""
]
] | The purpose of this paper is to investigate the oscillatory behavior of the universe through a Schr\"odinger-like Friedmann equation and a modified gravitational background described by the theory of f (R) gravity. The motivation for this stems from the observed periodic behaviour of large-scale cosmological structures when described within the scope of the general theory of relativity. The analysis of the modified Friedmann equation for the dust epoch in power-law f (R) models results in different behaviors for the wave-function of the universe. |
1808.03472 | Alessia Platania | Ademola Adeifeoba, Astrid Eichhorn, Alessia Platania | Towards conditions for black-hole singularity-resolution in
asymptotically safe quantum gravity | 12 pages, 1 figure | null | 10.1088/1361-6382/aae6ef | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explore the fate of the curvature singularity of Schwarzschild (deSitter)
black holes in asymptotically safe quantum gravity. Specifically, we upgrade
the classical spacetime by including the running of the Newton coupling and
cosmological constant. In this setting, the antiscreening character of the
gravitational interaction can remove the singularity, yet a nonzero value of
the cosmological constant in the ultraviolet appears to reintroduce it. We find
hints that a finite value of the cosmological constant in the infrared is
compatible with singularity resolution provided that the cosmological constant
is driven to zero fast enough in the ultraviolet. We compare the corresponding
bounds on the critical exponents to the literature.
| [
{
"created": "Fri, 10 Aug 2018 10:07:20 GMT",
"version": "v1"
}
] | 2018-11-14 | [
[
"Adeifeoba",
"Ademola",
""
],
[
"Eichhorn",
"Astrid",
""
],
[
"Platania",
"Alessia",
""
]
] | We explore the fate of the curvature singularity of Schwarzschild (deSitter) black holes in asymptotically safe quantum gravity. Specifically, we upgrade the classical spacetime by including the running of the Newton coupling and cosmological constant. In this setting, the antiscreening character of the gravitational interaction can remove the singularity, yet a nonzero value of the cosmological constant in the ultraviolet appears to reintroduce it. We find hints that a finite value of the cosmological constant in the infrared is compatible with singularity resolution provided that the cosmological constant is driven to zero fast enough in the ultraviolet. We compare the corresponding bounds on the critical exponents to the literature. |
gr-qc/9905037 | Andrew P. Billyard | A. G. Agnese and A. P. Billyard and H. Liu and P. S. Wesson | Possible Wormhole Solutions in (4+1) Gravity | 3 pages, latex, 1 figures | Gen.Rel.Grav. 31 (1999) 527-535 | 10.1023/A:1026646223189 | Dal-99-05 | gr-qc | null | We extend previous analyses of soliton solutions in (4+1) gravity to new
ranges of their defining parameters. The geometry, as studied using invariants,
has the topology of wormholes found in (3+1) gravity. In the induced-matter
picture, the fluid does not satisfy the strong energy conditions, but its
gravitational mass is positive. We infer the possible existance of (4+1)
wormholes which, compared to their (3+1) counterparts, are less exotic.
| [
{
"created": "Wed, 12 May 1999 14:14:03 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Agnese",
"A. G.",
""
],
[
"Billyard",
"A. P.",
""
],
[
"Liu",
"H.",
""
],
[
"Wesson",
"P. S.",
""
]
] | We extend previous analyses of soliton solutions in (4+1) gravity to new ranges of their defining parameters. The geometry, as studied using invariants, has the topology of wormholes found in (3+1) gravity. In the induced-matter picture, the fluid does not satisfy the strong energy conditions, but its gravitational mass is positive. We infer the possible existance of (4+1) wormholes which, compared to their (3+1) counterparts, are less exotic. |
0905.0765 | Cornelia Feiler | E. Kajari, M. Buser, C. Feiler and W. P. Schleich | Rotation in relativity and the propagation of light | 102 pages, 35 figures, The original publication is available at
http://www.sif.it/SIF/en/portal/journals.html, to appear in "Atom Optics and
Space Physics", Proceedings of the International School of Physics "Enrico
Fermi", Course CLXVIII, edited by E. Arimondo, W. Ertmer, E. M. Rasel and W.
P. Schleich, (IOS Press, Amsterdam) 2009 | Proceedings of the International School of Physics "Enrico Fermi",
Course CLXVIII, pp. 45-148 (2009) | 10.3254/978-1-58603-990-5-45 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compare and contrast the different points of view of rotation in general
relativity, put forward by Mach, Thirring and Lense, and Goedel. Our analysis
relies on two tools: (i) the Sagnac effect which allows us to measure rotations
of a coordinate system or induced by the curvature of spacetime, and (ii)
computer visualizations which bring out the alien features of the Goedel
Universe. In order to keep the paper self-contained, we summarize in several
appendices crucial ingredients of the mathematical tools used in general
relativity. In this way, our lecture notes should be accessible to researchers
familiar with the basic elements of tensor calculus and general relativity.
| [
{
"created": "Wed, 6 May 2009 08:18:57 GMT",
"version": "v1"
}
] | 2011-08-02 | [
[
"Kajari",
"E.",
""
],
[
"Buser",
"M.",
""
],
[
"Feiler",
"C.",
""
],
[
"Schleich",
"W. P.",
""
]
] | We compare and contrast the different points of view of rotation in general relativity, put forward by Mach, Thirring and Lense, and Goedel. Our analysis relies on two tools: (i) the Sagnac effect which allows us to measure rotations of a coordinate system or induced by the curvature of spacetime, and (ii) computer visualizations which bring out the alien features of the Goedel Universe. In order to keep the paper self-contained, we summarize in several appendices crucial ingredients of the mathematical tools used in general relativity. In this way, our lecture notes should be accessible to researchers familiar with the basic elements of tensor calculus and general relativity. |
gr-qc/0203096 | Friedrich W. Hehl | Friedrich W. Hehl (Cologne), Yuri N. Obukhov (Cologne/Moscow),
Guillermo F. Rubilar (Cologne) | On a possible new type of a T odd skewon field linked to
electromagnetism | 17 pages, LaTeX2e. Invited paper, Proceedings 1st Mexican Meeting on
Math. and Exp. Physics, Mexico City, Sept.2001, corrected and slightly
updated | null | null | null | gr-qc hep-th | null | In the framework of generally covariant (pre-metric) electrodynamics
(``charge & flux electrodynamics''), the Maxwell equations can be formulated in
terms of the electromagnetic excitation $H=({\cal D}, {\cal H})$ and the field
strength $F=(E,B)$. If the spacetime relation linking $H$ and $F$ is assumed to
be {\em linear}, the electromagnetic properties of (vacuum) spacetime are
encoded into 36 components of the vacuum constitutive tensor density $\chi$. We
study the propagation of electromagnetic waves and find that the metric of
spacetime emerges eventually from the principal part $^{(1)}\chi$ of $\chi$ (20
independent components). In this article, we concentrate on the remaining
skewon part $^{(2)}\chi$ (15 components) and the axion part $^{(3)}\chi$ (1
component). The skewon part, as we'll show for the first time, can be
represented by a 2nd rank traceless tensor $\not S_i{}^j$. By means of the
Fresnel equation, we discuss how this tensor disturbs the light cones.
Accordingly, this is a mechanism for violating Lorentz invariance and time
symmetry. In contrast, the (abelian) axion part $^{(3)}\chi$ does {\em not}
interfere with the light cones.
| [
{
"created": "Tue, 26 Mar 2002 23:50:03 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Hehl",
"Friedrich W.",
"",
"Cologne"
],
[
"Obukhov",
"Yuri N.",
"",
"Cologne/Moscow"
],
[
"Rubilar",
"Guillermo F.",
"",
"Cologne"
]
] | In the framework of generally covariant (pre-metric) electrodynamics (``charge & flux electrodynamics''), the Maxwell equations can be formulated in terms of the electromagnetic excitation $H=({\cal D}, {\cal H})$ and the field strength $F=(E,B)$. If the spacetime relation linking $H$ and $F$ is assumed to be {\em linear}, the electromagnetic properties of (vacuum) spacetime are encoded into 36 components of the vacuum constitutive tensor density $\chi$. We study the propagation of electromagnetic waves and find that the metric of spacetime emerges eventually from the principal part $^{(1)}\chi$ of $\chi$ (20 independent components). In this article, we concentrate on the remaining skewon part $^{(2)}\chi$ (15 components) and the axion part $^{(3)}\chi$ (1 component). The skewon part, as we'll show for the first time, can be represented by a 2nd rank traceless tensor $\not S_i{}^j$. By means of the Fresnel equation, we discuss how this tensor disturbs the light cones. Accordingly, this is a mechanism for violating Lorentz invariance and time symmetry. In contrast, the (abelian) axion part $^{(3)}\chi$ does {\em not} interfere with the light cones. |
1312.3956 | Alexander Vilenkin | Alexander Vilenkin and Aron C. Wall | Cosmological singularity theorems and black holes | References added | Phys. Rev. D 89, 064035 (2014) | 10.1103/PhysRevD.89.064035 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An extension of Penrose's singularity theorem is proved for spacetimes where
black holes are allowed to form from non-singular initial data. With standard
assumptions about the spacetime, and assuming the existence of a trapped
surface which lies outside of black hole horizons and is not completely
surrounded by horizons, we show that the spacetime region outside (or on) the
horizons must contain singularities. If the trapped surface is surrounded by
horizons, we show that the horizons divide spacetime into causally disconnected
pieces. Unlike the original Penrose's theorem, our theorems provide some
information about the location of singularities. We illustrate how they can be
used to rule out some cosmological scenarios.
| [
{
"created": "Fri, 13 Dec 2013 21:15:48 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Jan 2014 15:46:20 GMT",
"version": "v2"
}
] | 2014-03-26 | [
[
"Vilenkin",
"Alexander",
""
],
[
"Wall",
"Aron C.",
""
]
] | An extension of Penrose's singularity theorem is proved for spacetimes where black holes are allowed to form from non-singular initial data. With standard assumptions about the spacetime, and assuming the existence of a trapped surface which lies outside of black hole horizons and is not completely surrounded by horizons, we show that the spacetime region outside (or on) the horizons must contain singularities. If the trapped surface is surrounded by horizons, we show that the horizons divide spacetime into causally disconnected pieces. Unlike the original Penrose's theorem, our theorems provide some information about the location of singularities. We illustrate how they can be used to rule out some cosmological scenarios. |
2101.07527 | Xiangdong Zhang | Xiangdong Zhang, Gaoping Long and Yongge Ma | Loop quantum gravity and cosmological constant | 6 pages, 1 figure; v2, accepted by PLB | Physics Letters B 823, (2021) 136770 | 10.1016/j.physletb.2021.136770 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | An one-parameter regularization freedom of the Hamiltonian constraint for
loop quantum gravity is analyzed. The corresponding spatially flat, homogenous
and isotropic model includes the two well-known models of loop quantum
cosmology as special cases. The quantum bounce nature is tenable in the
generalized cases. For positive value of the regularization parameter, the
effective Hamiltonian leads to an asymptotic de-Sitter branch of the Universe
connecting to the standard Friedmann branch by the quantum bounce. Remarkably,
by suitably choosing the value of the regularization parameter, the
observational cosmological constant can emerge at large volume limit from the
effect of quantum gravity, and the effective Newtonian constant satisfies the
experimental restrictions in the meantime.
| [
{
"created": "Tue, 19 Jan 2021 09:28:23 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Nov 2021 11:44:02 GMT",
"version": "v2"
}
] | 2021-11-12 | [
[
"Zhang",
"Xiangdong",
""
],
[
"Long",
"Gaoping",
""
],
[
"Ma",
"Yongge",
""
]
] | An one-parameter regularization freedom of the Hamiltonian constraint for loop quantum gravity is analyzed. The corresponding spatially flat, homogenous and isotropic model includes the two well-known models of loop quantum cosmology as special cases. The quantum bounce nature is tenable in the generalized cases. For positive value of the regularization parameter, the effective Hamiltonian leads to an asymptotic de-Sitter branch of the Universe connecting to the standard Friedmann branch by the quantum bounce. Remarkably, by suitably choosing the value of the regularization parameter, the observational cosmological constant can emerge at large volume limit from the effect of quantum gravity, and the effective Newtonian constant satisfies the experimental restrictions in the meantime. |
1901.11236 | Sayan Kar | Indranil Chakraborty and Sayan Kar (IIT Kharagpur, India) | Geodesic congruences in exact plane wave spacetimes and the memory
effect | 27 pages, 13 figures, major changes (including title and abstract),
rewritten with a different focus, new results added | Phys. Rev. D 101, 064022 (2020) | 10.1103/PhysRevD.101.064022 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Displacement and velocity memory effects in the exact, vacuum, plane
gravitational wave line element have been studied recently by looking at the
behaviour of pairs of geodesics or via geodesic deviation. Instead, one may
investigate the evolution of geodesic congruences. In our work here, we obtain
the evolution of the kinematic variables which characterise timelike geodesic
congruences, using chosen pulse profiles (square and sech-squared) in the
exact, plane gravitational wave line element. We also analyse the behaviour of
geodesic congruences in possible physical scenarios describable using
derivatives (first, second and third) of one of the chosen pulses. Beginning
with a discussion on the generic behaviour of such congruences and consequences
thereof, we find exact analytical expressions for shear and expansion with the
two chosen pulse profiles. Qualitatively similar numerical results are noted
when various derivatives of the sech-squared pulse are used. We conclude that
for geodesic congruences, a growth (or decay) of shear causes focusing of an
initially parallel congruence, after the departure of the pulse. A correlation
between the `focusing time (or $u$ value, $u$ being the affine parameter)' and
the amplitude of the pulse (or its derivatives) is found. Such features
distinctly suggest a memory effect, named in recent literature as ${\cal B}$
memory.
| [
{
"created": "Thu, 31 Jan 2019 07:02:02 GMT",
"version": "v1"
},
{
"created": "Wed, 29 May 2019 10:46:26 GMT",
"version": "v2"
},
{
"created": "Mon, 25 Nov 2019 09:57:23 GMT",
"version": "v3"
},
{
"created": "Sat, 14 Mar 2020 04:59:34 GMT",
"version": "v4"
}
] | 2020-03-18 | [
[
"Chakraborty",
"Indranil",
"",
"IIT Kharagpur, India"
],
[
"Kar",
"Sayan",
"",
"IIT Kharagpur, India"
]
] | Displacement and velocity memory effects in the exact, vacuum, plane gravitational wave line element have been studied recently by looking at the behaviour of pairs of geodesics or via geodesic deviation. Instead, one may investigate the evolution of geodesic congruences. In our work here, we obtain the evolution of the kinematic variables which characterise timelike geodesic congruences, using chosen pulse profiles (square and sech-squared) in the exact, plane gravitational wave line element. We also analyse the behaviour of geodesic congruences in possible physical scenarios describable using derivatives (first, second and third) of one of the chosen pulses. Beginning with a discussion on the generic behaviour of such congruences and consequences thereof, we find exact analytical expressions for shear and expansion with the two chosen pulse profiles. Qualitatively similar numerical results are noted when various derivatives of the sech-squared pulse are used. We conclude that for geodesic congruences, a growth (or decay) of shear causes focusing of an initially parallel congruence, after the departure of the pulse. A correlation between the `focusing time (or $u$ value, $u$ being the affine parameter)' and the amplitude of the pulse (or its derivatives) is found. Such features distinctly suggest a memory effect, named in recent literature as ${\cal B}$ memory. |
2010.06386 | Rustam Gainutdinov | Rustam Gainutdinov and Yurij Baryshev | Relativistic effects in orbital motion of the S-stars at the Galactic
Center | Accepted for publication in the journal Universe, 08.10.2020 | Universe 2020, 6(10), 177 | 10.3390/universe6100177 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Galactic Center star cluster, known as S-stars, is a perfect source of
relativistic phenomena observations. The stars are located in the strong field
of relativistic compact object Sgr A* and are moving with very high velocities
at pericenters of their orbits. In this work we consider motion of several
S-stars by using the Parameterized Post-Newtonian (PPN) formalism of General
Relativity (GR) and Post-Newtonian (PN) equations of motion of the Feynman's
quantum-field gravity theory, where the positive energy density of the gravity
field can be measured via the relativistic pericenter shift. The PPN parameters
$\beta$ and $\gamma$ are constrained using the S-stars data. The positive value
of the $T_g^{00}$ component of the gravity energy-momentum tensor is confirmed
for condition of S-stars motion.
| [
{
"created": "Sat, 10 Oct 2020 04:41:56 GMT",
"version": "v1"
}
] | 2020-10-15 | [
[
"Gainutdinov",
"Rustam",
""
],
[
"Baryshev",
"Yurij",
""
]
] | The Galactic Center star cluster, known as S-stars, is a perfect source of relativistic phenomena observations. The stars are located in the strong field of relativistic compact object Sgr A* and are moving with very high velocities at pericenters of their orbits. In this work we consider motion of several S-stars by using the Parameterized Post-Newtonian (PPN) formalism of General Relativity (GR) and Post-Newtonian (PN) equations of motion of the Feynman's quantum-field gravity theory, where the positive energy density of the gravity field can be measured via the relativistic pericenter shift. The PPN parameters $\beta$ and $\gamma$ are constrained using the S-stars data. The positive value of the $T_g^{00}$ component of the gravity energy-momentum tensor is confirmed for condition of S-stars motion. |
1512.07017 | Nilanjana Mahata | Nilanjana Mahata and Subenoy Chakraborty | A Dynamical System Analysis of Three Fluid cosmological Model | 10 pages, 7 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In Friedman-Robertson-Walker flat spacetime, we consider a three fluid
cosmological model which contains dark matter, dark energy and baryonic matter
in the form of perfect fluid with a barotropic equation of state. Dark matter
is taken in form of dust and dark energy is described by a scalar field with a
potential $V(\phi)$. Einstein's field equations are reduced to an autonomous
dynamical system by suitable redefinition of basic variables. Considering
exponential potential for the scalar field, critical points are obtained for
the autonomous system. Finally stability of the critical points and
cosmological implications are analyzed.
| [
{
"created": "Tue, 22 Dec 2015 10:21:11 GMT",
"version": "v1"
}
] | 2015-12-23 | [
[
"Mahata",
"Nilanjana",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | In Friedman-Robertson-Walker flat spacetime, we consider a three fluid cosmological model which contains dark matter, dark energy and baryonic matter in the form of perfect fluid with a barotropic equation of state. Dark matter is taken in form of dust and dark energy is described by a scalar field with a potential $V(\phi)$. Einstein's field equations are reduced to an autonomous dynamical system by suitable redefinition of basic variables. Considering exponential potential for the scalar field, critical points are obtained for the autonomous system. Finally stability of the critical points and cosmological implications are analyzed. |
1311.4443 | Sebastiano Bernuzzi | Sebastiano Bernuzzi, Tim Dietrich, Wolfgang Tichy, and Bernd Bruegmann | Mergers of binary neutron stars with realistic spin | null | Phys. Rev. D 89, 104021 (2014) | 10.1103/PhysRevD.89.104021 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Simulations of binary neutron stars have seen great advances in terms of
physical detail and numerical quality. However, the spin of the neutron stars,
one of the simplest global parameters of binaries, remains mostly unstudied. We
present the first, fully nonlinear general relativistic dynamical evolutions of
the last three orbits for constraint satisfying initial data of spinning
neutron star binaries, with astrophysically realistic spins aligned and
anti-aligned to the orbital angular momentum. The initial data is computed with
the constant rotational velocity approach. The dynamics of the systems is
analyzed in terms of gauge-invariant binding energy vs. orbital angular
momentum curves. By comparing to a binary black hole configuration we can
estimate the different tidal and spin contributions to the binding energy for
the first time. First results on the gravitational wave forms are presented.
The phase evolution during the orbital motion is significantly affected by
spin-orbit interactions, leading to delayed or early mergers. Furthermore, a
frequency shift in the main emission mode of the hyper massive neutron star is
observed. Our results suggest that a detailed modeling of merger waveforms
requires the inclusion of spin, even for the moderate magnitudes observed in
binary neutron star systems.
| [
{
"created": "Mon, 18 Nov 2013 16:35:30 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Jun 2014 14:10:27 GMT",
"version": "v2"
}
] | 2015-04-15 | [
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Dietrich",
"Tim",
""
],
[
"Tichy",
"Wolfgang",
""
],
[
"Bruegmann",
"Bernd",
""
]
] | Simulations of binary neutron stars have seen great advances in terms of physical detail and numerical quality. However, the spin of the neutron stars, one of the simplest global parameters of binaries, remains mostly unstudied. We present the first, fully nonlinear general relativistic dynamical evolutions of the last three orbits for constraint satisfying initial data of spinning neutron star binaries, with astrophysically realistic spins aligned and anti-aligned to the orbital angular momentum. The initial data is computed with the constant rotational velocity approach. The dynamics of the systems is analyzed in terms of gauge-invariant binding energy vs. orbital angular momentum curves. By comparing to a binary black hole configuration we can estimate the different tidal and spin contributions to the binding energy for the first time. First results on the gravitational wave forms are presented. The phase evolution during the orbital motion is significantly affected by spin-orbit interactions, leading to delayed or early mergers. Furthermore, a frequency shift in the main emission mode of the hyper massive neutron star is observed. Our results suggest that a detailed modeling of merger waveforms requires the inclusion of spin, even for the moderate magnitudes observed in binary neutron star systems. |
gr-qc/0005079 | Bahram Mashhoon | Hongya Liu (Dalian University of Technology, China), and Bahram
Mashhoon (University of Missouri-Columbia, USA) | Spacetime Measurements in Kaluza-Klein Gravity | LaTeX, 12 pages, no figures, 2 references added, to appear in Phys.
Lett. A | Phys.Lett. A272 (2000) 26-31 | 10.1016/S0375-9601(00)00407-2 | null | gr-qc | null | We extend the classical general relativistic theory of measurement to include
the possibility of existence of higher dimensions. The intrusion of these
dimensions in the spacetime interval implies that the inertial mass of a
particle in general varies along its worldline if the observations are analyzed
assuming the existence of only the four spacetime dimensions. The variations of
mass and spin are explored in a simple 5D Kaluza-Klein model.
| [
{
"created": "Thu, 18 May 2000 00:44:39 GMT",
"version": "v1"
},
{
"created": "Thu, 25 May 2000 21:34:15 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Liu",
"Hongya",
"",
"Dalian University of Technology, China"
],
[
"Mashhoon",
"Bahram",
"",
"University of Missouri-Columbia, USA"
]
] | We extend the classical general relativistic theory of measurement to include the possibility of existence of higher dimensions. The intrusion of these dimensions in the spacetime interval implies that the inertial mass of a particle in general varies along its worldline if the observations are analyzed assuming the existence of only the four spacetime dimensions. The variations of mass and spin are explored in a simple 5D Kaluza-Klein model. |
gr-qc/9712089 | Yuri N. Obukhov | Friedrich W. Hehl and Yuri N. Obukhov | Is a `hadronic' shear current one of the sources in metric-affine
gravity? | Latex, mprocl.sty, 3 pages. Contribution to 8th Marcel Grossmann
meeting, Jerusalem 1997 | null | null | null | gr-qc | null | The Minkowski space of special relativity can be understood as a flat
4-dimensional affine space enriched by a constant Minkowski metric. If we gauge
the general affine group and `superimpose' the metric, then we arrive at the
metric-affine theory of gravity (MAG). The gravitational potentials are the
spacetime coframe, the metric, and the linear connection. The material
energy-momentum is coupled to the coframe (and the metric), a hypothetical
hypermomentum current to the connection. The hypermomentum splits in a spin, a
dilation, and a shear piece. We collect some evidence in favor of the existence
of a material shear current in the context of Regge type trajectories of
`hadronic' matter, thus supporting the link between particle physics and MAG.
| [
{
"created": "Tue, 23 Dec 1997 16:38:57 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Hehl",
"Friedrich W.",
""
],
[
"Obukhov",
"Yuri N.",
""
]
] | The Minkowski space of special relativity can be understood as a flat 4-dimensional affine space enriched by a constant Minkowski metric. If we gauge the general affine group and `superimpose' the metric, then we arrive at the metric-affine theory of gravity (MAG). The gravitational potentials are the spacetime coframe, the metric, and the linear connection. The material energy-momentum is coupled to the coframe (and the metric), a hypothetical hypermomentum current to the connection. The hypermomentum splits in a spin, a dilation, and a shear piece. We collect some evidence in favor of the existence of a material shear current in the context of Regge type trajectories of `hadronic' matter, thus supporting the link between particle physics and MAG. |
gr-qc/0311056 | Mariano Cadoni | Mariano Cadoni | Black Hole fragmentation and holography | 7 pages, no figures | Phys.Rev. D69 (2004) 084021 | 10.1103/PhysRevD.69.084021 | INFNCA-TH0304 | gr-qc hep-th | null | We discuss the entropy change due to fragmentation for black hole solutions
in various dimensions. We find three different types of behavior. The entropy
may decrease, increase or have a mixed behavior, characterized by the presence
of a threshold mass. For two-dimensional (2D) black holes we give a complete
characterization of the entropy behavior under fragmentation, in the form of
sufficient conditions imposed on the function J, which defines the 2D
gravitational model. We compare the behavior of the gravitational solutions
with that of free field theories in d dimensions. This excludes the possibility
of finding a gravity/field theory realization of the holographic principle for
a broad class of solutions, including asymptotically flat black holes. We find
that the most natural candidates for holographic duals of the black hole
solutions with mixed behavior are field theories with a mass gap. We also
discuss the possibility of formulating entropy bounds that make reference only
to the energy of a system.
| [
{
"created": "Tue, 18 Nov 2003 13:33:00 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Cadoni",
"Mariano",
""
]
] | We discuss the entropy change due to fragmentation for black hole solutions in various dimensions. We find three different types of behavior. The entropy may decrease, increase or have a mixed behavior, characterized by the presence of a threshold mass. For two-dimensional (2D) black holes we give a complete characterization of the entropy behavior under fragmentation, in the form of sufficient conditions imposed on the function J, which defines the 2D gravitational model. We compare the behavior of the gravitational solutions with that of free field theories in d dimensions. This excludes the possibility of finding a gravity/field theory realization of the holographic principle for a broad class of solutions, including asymptotically flat black holes. We find that the most natural candidates for holographic duals of the black hole solutions with mixed behavior are field theories with a mass gap. We also discuss the possibility of formulating entropy bounds that make reference only to the energy of a system. |
1909.05811 | Philip Tee | Philip Tee | Dynamics and the Emergence of Geometry in an Information Mesh | null | null | 10.1140/epjc/s10052-020-8282-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The idea of a graph theoretical approach to modeling the emergence of a
quantized geometry and consequently spacetime, has been proposed previously,
but not well studied. In most approaches the focus has been upon how to
generate a spacetime that possesses properties that would be desirable at the
continuum limit, and the question of how to model matter and its dynamics has
not been directly addressed. Recent advances in network science have yielded
new approaches to the mechanism by which spacetime can emerge as the ground
state of a simple Hamiltonian, based upon a multi-dimensional Ising model with
one dimensionless coupling constant. Extensions to this model have been
proposed that improve the ground state geometry, but they require additional
coupling constants. In this paper we conduct an extensive exploration of the
graph properties of the ground states of these models, and a simplification
requiring only one coupling constant. We demonstrate that the simplification is
effective at producing an acceptable ground state. Moreover we propose a scheme
for the inclusion of matter and dynamics as excitations above the ground state
of the simplified Hamiltonian. Intriguingly, enforcing locality has the
consequence of reproducing the free non-relativistic dynamics of a quantum
particle.
| [
{
"created": "Thu, 12 Sep 2019 17:13:04 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Apr 2020 22:24:14 GMT",
"version": "v2"
},
{
"created": "Mon, 27 Jul 2020 14:50:10 GMT",
"version": "v3"
},
{
"created": "Sun, 25 Apr 2021 23:06:09 GMT",
"version": "v4"
}
] | 2021-04-27 | [
[
"Tee",
"Philip",
""
]
] | The idea of a graph theoretical approach to modeling the emergence of a quantized geometry and consequently spacetime, has been proposed previously, but not well studied. In most approaches the focus has been upon how to generate a spacetime that possesses properties that would be desirable at the continuum limit, and the question of how to model matter and its dynamics has not been directly addressed. Recent advances in network science have yielded new approaches to the mechanism by which spacetime can emerge as the ground state of a simple Hamiltonian, based upon a multi-dimensional Ising model with one dimensionless coupling constant. Extensions to this model have been proposed that improve the ground state geometry, but they require additional coupling constants. In this paper we conduct an extensive exploration of the graph properties of the ground states of these models, and a simplification requiring only one coupling constant. We demonstrate that the simplification is effective at producing an acceptable ground state. Moreover we propose a scheme for the inclusion of matter and dynamics as excitations above the ground state of the simplified Hamiltonian. Intriguingly, enforcing locality has the consequence of reproducing the free non-relativistic dynamics of a quantum particle. |
1005.5670 | Yousef Bisabr | Yousef Bisabr | Local Gravity Constraints and Power Law f(R) Theories | 11 Pages, no figure. To appear in Gravitation and Cosmology | Grav.Cosmol.16:239-244,2010 | 10.1134/S0202289310030084 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There is a conformal equivalence between power law $f(R)$ theories and scalar
field theories in which the scalar degree of freedom evolves under the action
of an exponential potential function. In the scalar field representation there
is a strong coupling of the scalar field with the matter sector due to the
conformal transformation. We use chameleon mechanism to implement constraints
on the potential function of the scalar field in order that the resulting model
be in accord with Solar System experiments. Investigation of these constraints
reveals that there may be no possibility to distinguish between a power law
$f(R)$ function and the usual Einstein-Hilbert Lagrangian density.
| [
{
"created": "Mon, 31 May 2010 12:25:17 GMT",
"version": "v1"
}
] | 2014-11-21 | [
[
"Bisabr",
"Yousef",
""
]
] | There is a conformal equivalence between power law $f(R)$ theories and scalar field theories in which the scalar degree of freedom evolves under the action of an exponential potential function. In the scalar field representation there is a strong coupling of the scalar field with the matter sector due to the conformal transformation. We use chameleon mechanism to implement constraints on the potential function of the scalar field in order that the resulting model be in accord with Solar System experiments. Investigation of these constraints reveals that there may be no possibility to distinguish between a power law $f(R)$ function and the usual Einstein-Hilbert Lagrangian density. |
gr-qc/9409014 | null | D. Giulini and C. Kiefer | Consistency of Semiclassical Gravity | 12 pages, LATEX, Report Freiburg THEP-94/20 | Class.Quant.Grav.12:403-412,1995 | 10.1088/0264-9381/12/2/009 | null | gr-qc | null | We discuss some subtleties which arise in the semiclassical approximation to
quantum gravity. We show that integrability conditions prevent the existence of
Tomonaga-Schwinger time functions on the space of three-metrics but admit them
on superspace. The concept of semiclassical time is carefully examined. We
point out that central charges in the matter sector spoil the consistency of
the semiclassical approximation unless the full quantum theory of gravity and
matter is anomaly-free. We finally discuss consequences of these considerations
for quantum field theory in flat spacetime, but with arbitrary foliations.
| [
{
"created": "Thu, 8 Sep 1994 08:00:42 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Giulini",
"D.",
""
],
[
"Kiefer",
"C.",
""
]
] | We discuss some subtleties which arise in the semiclassical approximation to quantum gravity. We show that integrability conditions prevent the existence of Tomonaga-Schwinger time functions on the space of three-metrics but admit them on superspace. The concept of semiclassical time is carefully examined. We point out that central charges in the matter sector spoil the consistency of the semiclassical approximation unless the full quantum theory of gravity and matter is anomaly-free. We finally discuss consequences of these considerations for quantum field theory in flat spacetime, but with arbitrary foliations. |
1307.1603 | Stefan Hollands | Stefan Hollands, Alexander Thorne | Bondi mass cannot become negative in higher dimensions | 19 pages, Latex, no figures, v2: Introduction partly reorganized,
minor corrections | null | 10.1007/s00220-014-2096-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We prove that the Bondi mass of an asymptotically flat, vacuum, spacetime
cannot become negative in any even dimension $d \ge 4$. The notion of Bondi
mass is more subtle in $d > 4$ dimensions because radiating metrics have a
slower decay than stationary ones, and those subtleties are reflected by a
considerably more difficult proof of positivity. Our proof holds for the
standard spherical infinities, but also extends to infinities of more general
type which are $(d-2)$-dimensional manifolds admitting a real Killing spinor.
Such manifolds typically have special holonomy and Sasakian structures. The
main technical advance of the paper is an expansion technique based on
"conformal Gaussian null coordinates". This expansion helps us to understand
the consequences imposed by Einstein's equations on the asymptotic tail of the
metric field. As a by-product, we derive a coordinate expression for the
geometrically invariant formula for the Bondi mass originally given by Hollands
and Ishibashi.
| [
{
"created": "Fri, 5 Jul 2013 13:05:32 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Jan 2014 11:40:39 GMT",
"version": "v2"
}
] | 2015-06-16 | [
[
"Hollands",
"Stefan",
""
],
[
"Thorne",
"Alexander",
""
]
] | We prove that the Bondi mass of an asymptotically flat, vacuum, spacetime cannot become negative in any even dimension $d \ge 4$. The notion of Bondi mass is more subtle in $d > 4$ dimensions because radiating metrics have a slower decay than stationary ones, and those subtleties are reflected by a considerably more difficult proof of positivity. Our proof holds for the standard spherical infinities, but also extends to infinities of more general type which are $(d-2)$-dimensional manifolds admitting a real Killing spinor. Such manifolds typically have special holonomy and Sasakian structures. The main technical advance of the paper is an expansion technique based on "conformal Gaussian null coordinates". This expansion helps us to understand the consequences imposed by Einstein's equations on the asymptotic tail of the metric field. As a by-product, we derive a coordinate expression for the geometrically invariant formula for the Bondi mass originally given by Hollands and Ishibashi. |
2309.15853 | Salim Shekh Dr. | S. H. Shekh, Hira Sohail, Irfan Mahmood, Allah Ditta, Anil Kumar Yadav | Models of f(Q) gravity with electromagnetic field | pages-16, Figures-0, | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There are so many ideas that potentially explain the dark energy phenomenon,
current research is focusing on a more in-depth analysis of the potential
effects of modified gravity on both local and cosmic scales. In this paper we
have investigated some cosmic reconstructions in $f (Q)$ cosmology where $Q$ is
the non-metricity corresponding to the evolution background in the
Friedmann-Lamatre-Robertson-Walker $(FLRW)$ universe. This allows us to
determine how any $FLRW$ cosmology can emerge from a particular $f (Q)$ theory.
We employ the reconstruction technique to generate explicit formulations of the
$f (Q)$ Lagrangian for several types of matter sources like perfect fluid, dust
like fluid, stiff fluid and the binary mixture of two fluids. Furthermore, we
computed the field equations and equation of state (EoS) parameter $\omega$ for
two different reconstructed $f(Q)$ models with the variation of the involved
constants, which gives the scenario of accelerating universe, quintessence
region and cosmological constant. We also observed that the time dependence of
$\omega$ admits cosmic acceleration. These new $f(Q)$ gravity inspired models
may have an impact on gravitational phenomena at other cosmological scales.
| [
{
"created": "Thu, 31 Aug 2023 16:16:45 GMT",
"version": "v1"
}
] | 2023-09-29 | [
[
"Shekh",
"S. H.",
""
],
[
"Sohail",
"Hira",
""
],
[
"Mahmood",
"Irfan",
""
],
[
"Ditta",
"Allah",
""
],
[
"Yadav",
"Anil Kumar",
""
]
] | There are so many ideas that potentially explain the dark energy phenomenon, current research is focusing on a more in-depth analysis of the potential effects of modified gravity on both local and cosmic scales. In this paper we have investigated some cosmic reconstructions in $f (Q)$ cosmology where $Q$ is the non-metricity corresponding to the evolution background in the Friedmann-Lamatre-Robertson-Walker $(FLRW)$ universe. This allows us to determine how any $FLRW$ cosmology can emerge from a particular $f (Q)$ theory. We employ the reconstruction technique to generate explicit formulations of the $f (Q)$ Lagrangian for several types of matter sources like perfect fluid, dust like fluid, stiff fluid and the binary mixture of two fluids. Furthermore, we computed the field equations and equation of state (EoS) parameter $\omega$ for two different reconstructed $f(Q)$ models with the variation of the involved constants, which gives the scenario of accelerating universe, quintessence region and cosmological constant. We also observed that the time dependence of $\omega$ admits cosmic acceleration. These new $f(Q)$ gravity inspired models may have an impact on gravitational phenomena at other cosmological scales. |
2211.07469 | Alejandro C\'ardenas-Avenda\~no | Alejandro C\'ardenas-Avenda\~no, Alexandru Lupsasca, Hengrui Zhu | Adaptive Analytical Ray Tracing of Black Hole Photon Rings | 39 pages, 16 figures. Updated to match published version. V4:
corrected two very minor typos (in Eqs. 50 and 70) | Phys. Rev. D 107, 043030, 2023 | 10.1103/PhysRevD.107.043030 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | Recent interferometric observations by the Event Horizon Telescope have
resolved the horizon-scale emission from sources in the vicinity of nearby
supermassive black holes. Future space-based interferometers promise to measure
the "photon ring"--a narrow, ring-shaped, lensed feature predicted by general
relativity, but not yet observed--and thereby open a new window into strong
gravity. Here we present AART: an Adaptive Analytical Ray-Tracing code that
exploits the integrability of light propagation in the Kerr spacetime to
rapidly compute high-resolution simulated black hole images, together with the
corresponding radio visibility accessible on very long space-ground baselines.
The code samples images on a nonuniform adaptive grid that is specially
tailored to the lensing behavior of the Kerr geometry and is therefore
particularly well-suited to studying photon rings. This numerical approach
guarantees that interferometric signatures are correctly computed on long
baselines, and the modularity of the code allows for detailed studies of
equatorial sources with complex emission profiles and time variability. To
demonstrate its capabilities, we use AART to simulate a black hole movie of a
stochastic, non-stationary, non-axisymmetric equatorial source; by
time-averaging the visibility amplitude of each snapshot, we are able to
extract the projected diameter of the photon ring and recover the shape
predicted by general relativity.
| [
{
"created": "Mon, 14 Nov 2022 15:51:50 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Feb 2023 17:26:29 GMT",
"version": "v2"
},
{
"created": "Wed, 22 Feb 2023 16:11:17 GMT",
"version": "v3"
},
{
"created": "Tue, 4 Jun 2024 23:14:52 GMT",
"version": "v4"
}
] | 2024-06-06 | [
[
"Cárdenas-Avendaño",
"Alejandro",
""
],
[
"Lupsasca",
"Alexandru",
""
],
[
"Zhu",
"Hengrui",
""
]
] | Recent interferometric observations by the Event Horizon Telescope have resolved the horizon-scale emission from sources in the vicinity of nearby supermassive black holes. Future space-based interferometers promise to measure the "photon ring"--a narrow, ring-shaped, lensed feature predicted by general relativity, but not yet observed--and thereby open a new window into strong gravity. Here we present AART: an Adaptive Analytical Ray-Tracing code that exploits the integrability of light propagation in the Kerr spacetime to rapidly compute high-resolution simulated black hole images, together with the corresponding radio visibility accessible on very long space-ground baselines. The code samples images on a nonuniform adaptive grid that is specially tailored to the lensing behavior of the Kerr geometry and is therefore particularly well-suited to studying photon rings. This numerical approach guarantees that interferometric signatures are correctly computed on long baselines, and the modularity of the code allows for detailed studies of equatorial sources with complex emission profiles and time variability. To demonstrate its capabilities, we use AART to simulate a black hole movie of a stochastic, non-stationary, non-axisymmetric equatorial source; by time-averaging the visibility amplitude of each snapshot, we are able to extract the projected diameter of the photon ring and recover the shape predicted by general relativity. |
gr-qc/0307090 | Enrique Alvarez | Enrique \'Alvarez (IFT UAM/CSIC, Madrid) | Loops versus strings | 19 pages. Talk given in the meeting "What comes beyond the standard
model?", Portoroz, Eslovenia, 12-17 July 2003 | null | null | IFT-UAM/CSIC-03-23 | gr-qc hep-th | null | Two popular attempts to understand the quantum physics of gravitation are
critically assessed. The talk on which this paper is based was intended for a
general particle-physics audience.
| [
{
"created": "Mon, 21 Jul 2003 09:22:07 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Jul 2003 11:25:48 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Álvarez",
"Enrique",
"",
"IFT UAM/CSIC, Madrid"
]
] | Two popular attempts to understand the quantum physics of gravitation are critically assessed. The talk on which this paper is based was intended for a general particle-physics audience. |
gr-qc/0406076 | Alessandro D. A. M. Spallicci | Alessandro D.A.M. Spallicci, Sofiane Aoudia, Jose De Freitas Pacheco,
Giorgio Frossati, Tania Regimbau | Advanced VIRGO: detector optimization for gravitational waves by
inspiralling binaries | Change of title (Virgo detector optimization for gravitational waves
by coalescing binaries) and partially of text. 6 figures | Class.Quant.Grav. 22 (2005) S461-S469 | 10.1088/0264-9381/22/10/044 | null | gr-qc | null | For future configurations, we study the relation between the abatement of the
noise sources and the Signal to Noise Ratio (SNR) for coalescing binaries. Our
aim is not the proposition of a new design, but an indication of where in the
bandwidth or for which noise source, a noise reduction would be most efficient.
We take VIRGO as the reference for our considerations, solely applicable to the
inspiralling phase of a coalescing binary. Thus, only neutron stars and small
black holes of few solar masses are encompassed by our analysis. The
contributions to the SNR given by final merge and quasi-normal ringing are
neglected. It is identified that i) the reduction in the mirror thermal noise
band provides the highest gain for the SNR, when the VIRGO bandwidth is divided
according to the dominant noises; ii) it exists a specific frequency at which
lies the potential largest increment in the SNR, and that the enlargement of
the bandwidth, where the noise is reduced, produces a shift of such optimal
frequency to higher values; iii) the abatement of the pendulum thermal noise
provides the largest, but modest, gain, when noise sources are considered
separately. Our recent astrophysical analysis on event rates for neutron stars
leads to a detection rate of one every 148 or 125 years for VIRGO and LIGO,
respectively, while a recently proposed and improved, but still conservative,
VIRGO configuration would provide an increase to 1.5 events per year. Instead,
a bi-monthly event rate, similar to advanced LIGO, requires a 16 times gain. We
analyse the 3D (pendulum, mirror, shot noises) parameter space showing how such
gain could be achieved.
| [
{
"created": "Sun, 20 Jun 2004 09:53:21 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Dec 2004 21:59:05 GMT",
"version": "v2"
},
{
"created": "Tue, 14 Jun 2005 23:36:45 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Spallicci",
"Alessandro D. A. M.",
""
],
[
"Aoudia",
"Sofiane",
""
],
[
"Pacheco",
"Jose De Freitas",
""
],
[
"Frossati",
"Giorgio",
""
],
[
"Regimbau",
"Tania",
""
]
] | For future configurations, we study the relation between the abatement of the noise sources and the Signal to Noise Ratio (SNR) for coalescing binaries. Our aim is not the proposition of a new design, but an indication of where in the bandwidth or for which noise source, a noise reduction would be most efficient. We take VIRGO as the reference for our considerations, solely applicable to the inspiralling phase of a coalescing binary. Thus, only neutron stars and small black holes of few solar masses are encompassed by our analysis. The contributions to the SNR given by final merge and quasi-normal ringing are neglected. It is identified that i) the reduction in the mirror thermal noise band provides the highest gain for the SNR, when the VIRGO bandwidth is divided according to the dominant noises; ii) it exists a specific frequency at which lies the potential largest increment in the SNR, and that the enlargement of the bandwidth, where the noise is reduced, produces a shift of such optimal frequency to higher values; iii) the abatement of the pendulum thermal noise provides the largest, but modest, gain, when noise sources are considered separately. Our recent astrophysical analysis on event rates for neutron stars leads to a detection rate of one every 148 or 125 years for VIRGO and LIGO, respectively, while a recently proposed and improved, but still conservative, VIRGO configuration would provide an increase to 1.5 events per year. Instead, a bi-monthly event rate, similar to advanced LIGO, requires a 16 times gain. We analyse the 3D (pendulum, mirror, shot noises) parameter space showing how such gain could be achieved. |
1306.6299 | Alessandro Nagar | Alessandro Nagar | Gravitational recoil in nonspinning black hole binaries: the span of
test-mass results | 5 pages, 3 figures. Matches published version | Physical Review D 88, 121501 (R), 2013 | 10.1103/PhysRevD.88.121501 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider binary systems of coalescing, nonspinning, black holes of masses
$m_{1}$ and $m_{2}$ and show that the gravitational recoil velocity for any
mass ratio can be obtained accurately by extrapolating the waveform of the
test-mass limit case. The waveform obtained in the limit $m_1/m_2\ll 1$ via a
perturbative approach is extrapolated in $\nu= m_{1} m_{2}/(m_{1}+m_{2})^{2} $
multipole by multipole using the corresponding, analytically known,
leading-in-$\nu$ behavior. The final kick velocity computed from this
$\nu$-flexed waveform is written as $v(\nu)/c = 0.04457
\nu^2\sqrt{1-4\nu}\,(1-2.07106\nu + 3.93472\nu^2 -4.78404\nu^3+2.52040\nu^{4})$
and is compatible with the outcome of numerical relativity simulations
| [
{
"created": "Wed, 26 Jun 2013 17:45:26 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Dec 2013 22:27:26 GMT",
"version": "v2"
}
] | 2015-06-16 | [
[
"Nagar",
"Alessandro",
""
]
] | We consider binary systems of coalescing, nonspinning, black holes of masses $m_{1}$ and $m_{2}$ and show that the gravitational recoil velocity for any mass ratio can be obtained accurately by extrapolating the waveform of the test-mass limit case. The waveform obtained in the limit $m_1/m_2\ll 1$ via a perturbative approach is extrapolated in $\nu= m_{1} m_{2}/(m_{1}+m_{2})^{2} $ multipole by multipole using the corresponding, analytically known, leading-in-$\nu$ behavior. The final kick velocity computed from this $\nu$-flexed waveform is written as $v(\nu)/c = 0.04457 \nu^2\sqrt{1-4\nu}\,(1-2.07106\nu + 3.93472\nu^2 -4.78404\nu^3+2.52040\nu^{4})$ and is compatible with the outcome of numerical relativity simulations |
0704.2508 | Paul Tod | Paul Tod | Analyticity of strictly static and strictly stationary, inheriting and
non-inheriting Einstein-Maxwell solutions | 11 pages; to appear in Gen.Rel.Grav | Gen.Rel.Grav.39:1031-1042,2007 | 10.1007/s10714-007-0436-0 | null | gr-qc | null | Following the technique of M\"uller-zum-Hagen, refs [1,2], we show that
strictly static and strictly stationary solutions of the Einstein-Maxwell
equations are analytic in harmonic coordinates. This holds whether or not the
Maxwell field inherits the symmetry.
| [
{
"created": "Thu, 19 Apr 2007 11:23:29 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Tod",
"Paul",
""
]
] | Following the technique of M\"uller-zum-Hagen, refs [1,2], we show that strictly static and strictly stationary solutions of the Einstein-Maxwell equations are analytic in harmonic coordinates. This holds whether or not the Maxwell field inherits the symmetry. |
2310.13405 | Federico Stachurski Mr. | Federico Stachurski, Christopher Messenger, Martin Hendry | Cosmological Inference using Gravitational Waves and Normalising Flows | 5 pages, 2 figures, to be submitted to Physics Review Letters (PRL) | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We present a machine learning approach using normalising flows for inferring
cosmological parameters from gravitational wave events. Our methodology is
general to any type of compact binary coalescence event and cosmological model
and relies on the generation of training data representing distributions of
gravitational wave event parameters. These parameters are conditional on the
underlying cosmology and incorporate prior information from galaxy catalogues.
We provide an example analysis inferring the Hubble constant using binary black
holes detected during the O1, O2, and O3 observational runs conducted by the
advanced LIGO/VIRGO gravitational wave detectors. We obtain a Bayesian
posterior on the Hubble constant from which we derive an estimate and 1$\sigma$
confidence bounds of $H_{0} = 74.51^{+14.80}_{-13.63} \: \text{km}
\:\text{s}^{-1} \text{Mpc}^{-1}$. We are able to compute this result in
$\mathcal{O}(1)$ s using our trained Normalising Flow model.
| [
{
"created": "Fri, 20 Oct 2023 10:23:41 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Oct 2023 16:46:10 GMT",
"version": "v2"
}
] | 2023-10-26 | [
[
"Stachurski",
"Federico",
""
],
[
"Messenger",
"Christopher",
""
],
[
"Hendry",
"Martin",
""
]
] | We present a machine learning approach using normalising flows for inferring cosmological parameters from gravitational wave events. Our methodology is general to any type of compact binary coalescence event and cosmological model and relies on the generation of training data representing distributions of gravitational wave event parameters. These parameters are conditional on the underlying cosmology and incorporate prior information from galaxy catalogues. We provide an example analysis inferring the Hubble constant using binary black holes detected during the O1, O2, and O3 observational runs conducted by the advanced LIGO/VIRGO gravitational wave detectors. We obtain a Bayesian posterior on the Hubble constant from which we derive an estimate and 1$\sigma$ confidence bounds of $H_{0} = 74.51^{+14.80}_{-13.63} \: \text{km} \:\text{s}^{-1} \text{Mpc}^{-1}$. We are able to compute this result in $\mathcal{O}(1)$ s using our trained Normalising Flow model. |
2011.13499 | Daniel Flores | D. Flores-Alfonso, C. S. Lopez-Monsalvo, M. Maceda | Contact Geometry in Superconductors and New Massive Gravity | null | Phys. Lett. B 815 (2021) 136143 | 10.1016/j.physletb.2021.136143 | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | The defining property of every three-dimensional $\varepsilon$-contact
manifold is shown to be equivalent to requiring the fulfillment of London's
equation in 2+1 electromagnetism. To illustrate this point, we show that every
such manifold that is also K-contact and $\eta$-Einstein is a vacuum solution
to the most general quadratic-curvature gravity action, in particular of New
Massive Gravity. As an example we analyse $S^3$ equipped with a contact
structure together with an associated metric tensor such that the canonical
generators of the contact distribution are null. The resulting Lorentzian
metric is shown to be a vacuum solution of three-dimensional massive gravity.
Moreover, by coupling the New Massive Gravity action to Maxwell-Chern-Simons we
obtain a class of charged solutions stemming directly from the para-contact
metric structure. Finally, we repeat the exercise for the Abelian Higgs theory.
| [
{
"created": "Thu, 26 Nov 2020 23:52:03 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Dec 2020 23:33:58 GMT",
"version": "v2"
},
{
"created": "Mon, 22 Feb 2021 15:29:08 GMT",
"version": "v3"
}
] | 2021-02-23 | [
[
"Flores-Alfonso",
"D.",
""
],
[
"Lopez-Monsalvo",
"C. S.",
""
],
[
"Maceda",
"M.",
""
]
] | The defining property of every three-dimensional $\varepsilon$-contact manifold is shown to be equivalent to requiring the fulfillment of London's equation in 2+1 electromagnetism. To illustrate this point, we show that every such manifold that is also K-contact and $\eta$-Einstein is a vacuum solution to the most general quadratic-curvature gravity action, in particular of New Massive Gravity. As an example we analyse $S^3$ equipped with a contact structure together with an associated metric tensor such that the canonical generators of the contact distribution are null. The resulting Lorentzian metric is shown to be a vacuum solution of three-dimensional massive gravity. Moreover, by coupling the New Massive Gravity action to Maxwell-Chern-Simons we obtain a class of charged solutions stemming directly from the para-contact metric structure. Finally, we repeat the exercise for the Abelian Higgs theory. |
1904.11089 | Huan Yang | Huan Yang | Inspiralling eccentric binary neutron stars: orbital motion and tidal
resonance | 18 pages, 1 figure | Phys. Rev. D 100, 064023 (2019) | 10.1103/PhysRevD.100.064023 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the orbital evolution of eccentric binary neutron stars. The orbit
is described as a Quasi-Keplarian orbit with perturbations due to tidal
couplings. We find that the tidal interaction between stars contributes to
orbital precession, in addition to the Post-Newtonian procession. The coupling
between the angular and radial motion of the binary also excites a series of
harmonics in the stars' oscillation. In the small eccentricity limit, this
coupling mainly gives rise to an additional orbital resonance, with the orbital
frequency being one third of the f-mode frequency. For a binary with initial
eccentricity $\sim 0.2$ at $50$Hz orbital frequency, the presence of this tidal
resonance introduces $\sim 0.5$ phase shift in the gravitational waveform till
merger, subject to uncertainties in neutron star equation of state and the
distribution of binary component masses. Such phase shift in the late-inspiral
stage is likely detectable with third-generation gravitational-wave detectors.
| [
{
"created": "Wed, 24 Apr 2019 22:39:01 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Sep 2019 13:37:14 GMT",
"version": "v2"
}
] | 2019-09-25 | [
[
"Yang",
"Huan",
""
]
] | We study the orbital evolution of eccentric binary neutron stars. The orbit is described as a Quasi-Keplarian orbit with perturbations due to tidal couplings. We find that the tidal interaction between stars contributes to orbital precession, in addition to the Post-Newtonian procession. The coupling between the angular and radial motion of the binary also excites a series of harmonics in the stars' oscillation. In the small eccentricity limit, this coupling mainly gives rise to an additional orbital resonance, with the orbital frequency being one third of the f-mode frequency. For a binary with initial eccentricity $\sim 0.2$ at $50$Hz orbital frequency, the presence of this tidal resonance introduces $\sim 0.5$ phase shift in the gravitational waveform till merger, subject to uncertainties in neutron star equation of state and the distribution of binary component masses. Such phase shift in the late-inspiral stage is likely detectable with third-generation gravitational-wave detectors. |
2307.15384 | Xiangdong Zhang | Wenxi Zhai and Xiangdong Zhang | Gauss-Bonnet solution with a cloud of strings in de Sitter and anti-de
Sitter space | 16 pages, 7 figures | Chinese Physics C Vol. 48, No. 1 (2024) 015101 | 10.1088/1674-1137/ad010d | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, we present exact spherically symmetric Gauss-Bonnet black hole
solutions surrounded by a cloud of strings fluid with cosmological constant in
$D>4$ dimensions. Both charged and uncharged cases are considered. We focus on
the de Sitter solutions in the main text and leave the Anti-de Sitter solutions
in the appendix. We analyze the features of thermodynamic properties of the
black hole solutions. The mass, Hawking temperature as well as thermal
stability and the phase transitions are discussed. Moreover, the equation of
state and critical phenomena associated with these solutions are also explored.
| [
{
"created": "Fri, 28 Jul 2023 08:14:24 GMT",
"version": "v1"
}
] | 2023-12-27 | [
[
"Zhai",
"Wenxi",
""
],
[
"Zhang",
"Xiangdong",
""
]
] | In this paper, we present exact spherically symmetric Gauss-Bonnet black hole solutions surrounded by a cloud of strings fluid with cosmological constant in $D>4$ dimensions. Both charged and uncharged cases are considered. We focus on the de Sitter solutions in the main text and leave the Anti-de Sitter solutions in the appendix. We analyze the features of thermodynamic properties of the black hole solutions. The mass, Hawking temperature as well as thermal stability and the phase transitions are discussed. Moreover, the equation of state and critical phenomena associated with these solutions are also explored. |
1711.07730 | Qiang Wang | Jianfeng Su and Qiang Wang and Qinghua Wang and Philippe Jetzer | Low-frequency Gravitational Wave Detection via Double Optical Clocks in
Space | 18 pages, 2 figures | null | 10.1088/1361-6382/aab2eb | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a Doppler tracking system for gravitational wave detection via
Double Optical Clocks in Space (DOCS). In this configuration two spacecrafts
(each containing an optical clock) are launched to space for Doppler shift
observations. Compared to the similar attempt of gravitational wave detection
in the Cassini mission, the radio signal of DOCS that contains the relative
frequency changes avoids completely noise effects due for instance to
troposphere, ionosphere, ground-based antenna and transponder. Given the high
stabilities of the two optical clocks (Allan deviation $\sim 4.1\times
10^{-17}$ @ 1000 s), an overall estimated sensitivity of $5 \times 10^{-19}$
could be achieved with an observation time of 2 years, and would allow to
detect gravitational waves in the frequency range from $\sim 10^{-4}$ Hz to
$\sim 10^{-2}$ Hz.
| [
{
"created": "Tue, 21 Nov 2017 11:43:14 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Feb 2018 11:33:48 GMT",
"version": "v2"
}
] | 2018-04-18 | [
[
"Su",
"Jianfeng",
""
],
[
"Wang",
"Qiang",
""
],
[
"Wang",
"Qinghua",
""
],
[
"Jetzer",
"Philippe",
""
]
] | We propose a Doppler tracking system for gravitational wave detection via Double Optical Clocks in Space (DOCS). In this configuration two spacecrafts (each containing an optical clock) are launched to space for Doppler shift observations. Compared to the similar attempt of gravitational wave detection in the Cassini mission, the radio signal of DOCS that contains the relative frequency changes avoids completely noise effects due for instance to troposphere, ionosphere, ground-based antenna and transponder. Given the high stabilities of the two optical clocks (Allan deviation $\sim 4.1\times 10^{-17}$ @ 1000 s), an overall estimated sensitivity of $5 \times 10^{-19}$ could be achieved with an observation time of 2 years, and would allow to detect gravitational waves in the frequency range from $\sim 10^{-4}$ Hz to $\sim 10^{-2}$ Hz. |
gr-qc/0312019 | Stoytcho Yazadjiev | Stoytcho S. Yazadjiev (Sofia University) | Interior perfect fluid scalar-tensor solution | 8 pages, 3 figures, LaTex | Phys.Rev. D69 (2004) 127501 | 10.1103/PhysRevD.69.127501 | null | gr-qc | null | We present a new exact perfect fluid interior solution for a particular
scalar-tensor theory. The solution is regular everywhere and has a well defined
boundary where the fluid pressure vanishes. The metric and the dilaton field
match continuously the external solution.
| [
{
"created": "Wed, 3 Dec 2003 08:25:17 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Yazadjiev",
"Stoytcho S.",
"",
"Sofia University"
]
] | We present a new exact perfect fluid interior solution for a particular scalar-tensor theory. The solution is regular everywhere and has a well defined boundary where the fluid pressure vanishes. The metric and the dilaton field match continuously the external solution. |
gr-qc/9307014 | Gary Horowitz | Dieter Brill, Gary Horowitz, David Kastor, and Jennie Traschen | Testing Cosmic Censorship with Black Hole Collisions | 30 pages, 8 figs., phyzzx | Phys.Rev. D49 (1994) 840-852 | 10.1103/PhysRevD.49.840 | null | gr-qc hep-th | null | There exists an upper limit on the mass of black holes when the cosmological
constant $\Lambda$ is positive. We study the collision of two black holes whose
total mass exceeds this limit. Our investigation is based on a recently
discovered exact solution describing the collision of $Q=M$ black holes with
$\Lambda > 0$. The global structure of this solution is analyzed. We find that
if the total mass is less than the extremal limit, then the black holes
coalesce. If it is greater, then a naked singularity forms to the future of a
Cauchy horizon. However, the horizon is not smooth. Generically, there is a
mild curvature singularity, which still allows geodesics to be extended. The
implications of these results for cosmic censorship are discussed.
| [
{
"created": "Mon, 12 Jul 1993 20:32:44 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Brill",
"Dieter",
""
],
[
"Horowitz",
"Gary",
""
],
[
"Kastor",
"David",
""
],
[
"Traschen",
"Jennie",
""
]
] | There exists an upper limit on the mass of black holes when the cosmological constant $\Lambda$ is positive. We study the collision of two black holes whose total mass exceeds this limit. Our investigation is based on a recently discovered exact solution describing the collision of $Q=M$ black holes with $\Lambda > 0$. The global structure of this solution is analyzed. We find that if the total mass is less than the extremal limit, then the black holes coalesce. If it is greater, then a naked singularity forms to the future of a Cauchy horizon. However, the horizon is not smooth. Generically, there is a mild curvature singularity, which still allows geodesics to be extended. The implications of these results for cosmic censorship are discussed. |
gr-qc/9512047 | Sergey Solodukhin | A.O. Barvinsky and S.N. Solodukhin | Non-minimal coupling, boundary terms and renormalization of the
Einstein-Hilbert action | 14 pages, latex. More discussion added, the case of 2D Maxwell field
considered in more details | Nucl.Phys. B479 (1996) 305-318 | 10.1016/0550-3213(96)00438-5 | WATPHYS-TH-95-11 | gr-qc hep-th | null | A consistent variational procedure applied to the gravitational action
requires according to Gibbons and Hawking a certain balance between the volume
and boundary parts of the action. We consider the problem of preserving this
balance in the quantum effective action for the matter non-minimally coupled to
metric. It is shown that one has to add a special boundary term to the matter
action analogous to the Gibbons-Hawking one. This boundary term modifies the
one-loop quantum corrections to give a correct balance for the effective action
as well. This means that the boundary UV divergences do not require independent
renormalization and are automatically renormalized simultaneously with their
volume part. This result is derived for arbitrary non-minimally coupled matter.
The example of 2D Maxwell field is considered in much detail. The relevance of
the results obtained to the problem of the renormalization of the black hole
entropy is discussed.
| [
{
"created": "Thu, 28 Dec 1995 23:36:18 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Jul 1996 19:59:32 GMT",
"version": "v2"
}
] | 2009-10-28 | [
[
"Barvinsky",
"A. O.",
""
],
[
"Solodukhin",
"S. N.",
""
]
] | A consistent variational procedure applied to the gravitational action requires according to Gibbons and Hawking a certain balance between the volume and boundary parts of the action. We consider the problem of preserving this balance in the quantum effective action for the matter non-minimally coupled to metric. It is shown that one has to add a special boundary term to the matter action analogous to the Gibbons-Hawking one. This boundary term modifies the one-loop quantum corrections to give a correct balance for the effective action as well. This means that the boundary UV divergences do not require independent renormalization and are automatically renormalized simultaneously with their volume part. This result is derived for arbitrary non-minimally coupled matter. The example of 2D Maxwell field is considered in much detail. The relevance of the results obtained to the problem of the renormalization of the black hole entropy is discussed. |
1901.05449 | S Habib Mazharimousavi | S. Habib Mazharimousavi and M. Halilsoy | Einstein-non-linear Maxwell-Yukawa black hole | 8 pages, 6 figures | null | 10.1142/S0218271819501207 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Within the context of nonlinear electromagnetism we consider the Yukawa
extension of a Reissner-Nordstr\"{o}m black hole. Exact solution is given which
modifies certain characteristics of the latter. Some thermodynamical aspects
are given for comparison. The model may be considered as a useful agent to
describe a short-ranged, charged, massive interaction.
| [
{
"created": "Wed, 16 Jan 2019 12:22:11 GMT",
"version": "v1"
}
] | 2019-07-24 | [
[
"Mazharimousavi",
"S. Habib",
""
],
[
"Halilsoy",
"M.",
""
]
] | Within the context of nonlinear electromagnetism we consider the Yukawa extension of a Reissner-Nordstr\"{o}m black hole. Exact solution is given which modifies certain characteristics of the latter. Some thermodynamical aspects are given for comparison. The model may be considered as a useful agent to describe a short-ranged, charged, massive interaction. |
2405.10604 | Nandan Roy | Chonticha Kritpetch, Nandan Roy and Narayan Banerjee | Interacting dark sector: a dynamical system perspective | 19 pages, 8 figures | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | We investigate the interaction between the dark sectors from a dynamical
systems perspective. A general setup for interacting dark energy models that
incorporates both quintessence and phantom fields through a switch parameter,
allowing an interaction in the dark sectors has been considered. In the first
part of our analysis, we have not assumed any specific form of the interaction
and in the second part, we invoked examples in general framework of the
interaction. The potentials of the scalar field are classified into two broad
classes of potentials: exponential and non-exponential. We identify the
potential late-time attractors of the system which have a complete dark energy
domination. From our analysis, it is evident there could be an interaction
between the dark sector. The interaction, if any, weakens over time. We find
for the quintessence field the transfer of energy from dark matter to dark
energy can flip the direction and on the contrary, for the phantom field, it is
only from dark matter to dark energy.
| [
{
"created": "Fri, 17 May 2024 07:59:11 GMT",
"version": "v1"
}
] | 2024-05-20 | [
[
"Kritpetch",
"Chonticha",
""
],
[
"Roy",
"Nandan",
""
],
[
"Banerjee",
"Narayan",
""
]
] | We investigate the interaction between the dark sectors from a dynamical systems perspective. A general setup for interacting dark energy models that incorporates both quintessence and phantom fields through a switch parameter, allowing an interaction in the dark sectors has been considered. In the first part of our analysis, we have not assumed any specific form of the interaction and in the second part, we invoked examples in general framework of the interaction. The potentials of the scalar field are classified into two broad classes of potentials: exponential and non-exponential. We identify the potential late-time attractors of the system which have a complete dark energy domination. From our analysis, it is evident there could be an interaction between the dark sector. The interaction, if any, weakens over time. We find for the quintessence field the transfer of energy from dark matter to dark energy can flip the direction and on the contrary, for the phantom field, it is only from dark matter to dark energy. |
2206.03828 | Rituparno Goswami | Sayuri Singh, Dharmanand Baboolal, Rituparno Goswami, Sunil D. Maharaj | Gaussian curvature of spherical shells: A geometric measure of
complexity | 8 pages, 1 figure, Revtex 4 | null | 10.1088/1361-6382/ac9efe | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we consider a semitetrad covariant decomposition of spherically
symmetric spacetimes and find a governing hyperbolic equation of the Gaussian
curvature of two dimensional spherical shells, that emerges due to the
decomposition. The restoration factor of this hyperbolic travelling wave
equation allows us to construct a geometric measure of complexity. This measure
depends critically on the Gaussian curvature, and we demonstrate this geometric
connection to complexity for the first time. We illustrate the utility of this
measure by classifying well known spherically symmetric metrics with different
matter distributions. We also define an order structure on the set of all
spherically symmetric spacetimes, according to their complexity and physical
properties.
| [
{
"created": "Wed, 8 Jun 2022 11:58:05 GMT",
"version": "v1"
}
] | 2022-11-23 | [
[
"Singh",
"Sayuri",
""
],
[
"Baboolal",
"Dharmanand",
""
],
[
"Goswami",
"Rituparno",
""
],
[
"Maharaj",
"Sunil D.",
""
]
] | In this paper we consider a semitetrad covariant decomposition of spherically symmetric spacetimes and find a governing hyperbolic equation of the Gaussian curvature of two dimensional spherical shells, that emerges due to the decomposition. The restoration factor of this hyperbolic travelling wave equation allows us to construct a geometric measure of complexity. This measure depends critically on the Gaussian curvature, and we demonstrate this geometric connection to complexity for the first time. We illustrate the utility of this measure by classifying well known spherically symmetric metrics with different matter distributions. We also define an order structure on the set of all spherically symmetric spacetimes, according to their complexity and physical properties. |
gr-qc/0703115 | Jose M. M. Senovilla | Jos\'e M M Senovilla | Classification of spacelike surfaces in spacetime | 42 pages, 10 tables, many diagrams | Class.Quant.Grav.24:3091-3124,2007 | 10.1088/0264-9381/24/11/020 | null | gr-qc math.DG | null | A classification of 2-dimensional surfaces imbedded in spacetime is
presented, according to the algebraic properties of their shape tensor. The
classification has five levels, and provides among other things a refinement of
the concepts of trapped, umbilical and extremal surfaces, which split into
several different classes. The classification raises new important questions
and opens many possible new lines of research. These, together with some
applications and examples, are briefly considered.
| [
{
"created": "Thu, 22 Mar 2007 17:48:48 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Senovilla",
"José M M",
""
]
] | A classification of 2-dimensional surfaces imbedded in spacetime is presented, according to the algebraic properties of their shape tensor. The classification has five levels, and provides among other things a refinement of the concepts of trapped, umbilical and extremal surfaces, which split into several different classes. The classification raises new important questions and opens many possible new lines of research. These, together with some applications and examples, are briefly considered. |
gr-qc/0612078 | Ari Peltola | Jarmo Makela and Ari Peltola | Gravitation and Thermodynamics: The Einstein Equation of State Revisited | 17 pages, 2 figures. Final version, accepted for publication in
IJMPD. The paper has been re-organized, and significantly re-written,
although the conclusions remain essentially the same | Int.J.Mod.Phys.D18:669-689,2009 | 10.1142/S0218271809014698 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform an analysis where Einstein's field equation is derived by means of
very simple thermodynamical arguments. Our derivation is based on a
consideration of the properties of a very small, spacelike two-plane in a
uniformly accelerating motion.
| [
{
"created": "Wed, 13 Dec 2006 10:28:38 GMT",
"version": "v1"
},
{
"created": "Thu, 10 May 2007 13:57:20 GMT",
"version": "v2"
},
{
"created": "Tue, 19 Aug 2008 16:11:38 GMT",
"version": "v3"
}
] | 2010-11-11 | [
[
"Makela",
"Jarmo",
""
],
[
"Peltola",
"Ari",
""
]
] | We perform an analysis where Einstein's field equation is derived by means of very simple thermodynamical arguments. Our derivation is based on a consideration of the properties of a very small, spacelike two-plane in a uniformly accelerating motion. |
gr-qc/9710035 | Jai-chan Hwang | J. Hwang and H. Noh | Cosmological Vorticity in a Gravity with Quadratic Order Curvature
Couplings | 5 pages, revtex, no figures | Phys.Rev.D57:2617-2620,1998 | 10.1103/PhysRevD.57.2617 | null | gr-qc | null | We analyse the evolution of the rotational type cosmological perturbation in
a gravity with general quadratic order gravitational coupling terms. The result
is expressed independently of the generalized nature of the gravity theory, and
is simply interpreted as a conservation of the angular momentum.
| [
{
"created": "Tue, 7 Oct 1997 04:44:04 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Hwang",
"J.",
""
],
[
"Noh",
"H.",
""
]
] | We analyse the evolution of the rotational type cosmological perturbation in a gravity with general quadratic order gravitational coupling terms. The result is expressed independently of the generalized nature of the gravity theory, and is simply interpreted as a conservation of the angular momentum. |
gr-qc/9902009 | Amir H. Abbassi | Amir H. Abbassi | Non-Static Spherically Symmetric solution of Einstein vacuum Field
Equations with $Lambda$ | 9pages,no figures, Latex | JHEP 9904 (1999) 011 | 10.1088/1126-6708/1999/04/011 | null | gr-qc | null | The Schwarzschild-deSitter metric is the known solution of Einstein field
equations with cosmological constant term for vacuum spherically symmetric
space around a point mass M. Recently it has been reported that in a
$Lamda$-dominant world the Schwarzschild type coordinate systems are
disqualified by redshift-magnitude test as a proper frame of
reference(gr-qc/9812092). We derive the solution in a FRW type coordinate
system which is qualified according to the mentioned test. Asymptotically it
approachs to the non-static form of deSitter metric. The obtained metric is
transformable to Schwarzschild-deSitter metric. It is an analytic function of
$r$ for all values except $r=0$which is singular. This is carried out with no
making use of Eddington-Finkelstein coordinates and without entering any cross
term in the metric.
| [
{
"created": "Tue, 2 Feb 1999 17:50:30 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Abbassi",
"Amir H.",
""
]
] | The Schwarzschild-deSitter metric is the known solution of Einstein field equations with cosmological constant term for vacuum spherically symmetric space around a point mass M. Recently it has been reported that in a $Lamda$-dominant world the Schwarzschild type coordinate systems are disqualified by redshift-magnitude test as a proper frame of reference(gr-qc/9812092). We derive the solution in a FRW type coordinate system which is qualified according to the mentioned test. Asymptotically it approachs to the non-static form of deSitter metric. The obtained metric is transformable to Schwarzschild-deSitter metric. It is an analytic function of $r$ for all values except $r=0$which is singular. This is carried out with no making use of Eddington-Finkelstein coordinates and without entering any cross term in the metric. |
1702.04720 | Mohd Shahalam | M. Shahalam, S. D. Pathak, Shiyuan Li, R. Myrzakulov, Anzhong Wang | Dynamics of coupled phantom and tachyon fields | 16 pages, 6 caption figures, 3 Tables, text, figure are added,
matches with the published version | Eur. Phys. J. C (2017) 77:686 | 10.1140/epjc/s10052-017-5255-1 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we apply the dynamical analysis to a coupled phantom field
with scaling potential taking particular forms of the coupling (linear and
combination of linear), and present phase space analysis. We investigate if
there exist late time accelerated scaling attractor that has the ratio of dark
energy and dark matter densities of the order one. We observe that the
scrutinized couplings cannot alleviate the coincidence problem, however acquire
stable late time accelerated solutions. We also discuss coupled tachyon field
with inverse square potential assuming linear coupling.
| [
{
"created": "Wed, 15 Feb 2017 17:17:13 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Feb 2017 07:16:46 GMT",
"version": "v2"
},
{
"created": "Mon, 23 Oct 2017 09:40:15 GMT",
"version": "v3"
}
] | 2017-10-24 | [
[
"Shahalam",
"M.",
""
],
[
"Pathak",
"S. D.",
""
],
[
"Li",
"Shiyuan",
""
],
[
"Myrzakulov",
"R.",
""
],
[
"Wang",
"Anzhong",
""
]
] | In this paper, we apply the dynamical analysis to a coupled phantom field with scaling potential taking particular forms of the coupling (linear and combination of linear), and present phase space analysis. We investigate if there exist late time accelerated scaling attractor that has the ratio of dark energy and dark matter densities of the order one. We observe that the scrutinized couplings cannot alleviate the coincidence problem, however acquire stable late time accelerated solutions. We also discuss coupled tachyon field with inverse square potential assuming linear coupling. |
2211.03497 | Breno Giacchini | Luca Buoninfante, Breno L. Giacchini and Tib\'erio de Paula Netto | Black holes in non-local gravity | Invited chapter for the Section "Nonlocal Quantum Gravity" of the
"Handbook of Quantum Gravity" (Eds. C. Bambi, L. Modesto and I.L. Shapiro,
Springer Singapore, expected in 2023). 29 pages | null | null | NORDITA 2022-076 | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this chapter we present a status report of black hole-like solutions in
non-local theories of gravity in which the Lagrangians are at least quadratic
in curvature and contain specific non-polynomial (i.e., non-local) operators.
In the absence of exact black hole solutions valid in the whole spacetime, most
of the literature on this topic focus on approximate and simplified equations
of motion, which could provide insights on the full non-linear solutions.
Therefore, the largest part of this chapter is devoted to the linear
approximation. We present results on stationary metric solutions (including
both static and rotating cases) and dynamical spacetimes describing the
formation of non-rotating mini black holes by the collapse of null shells.
Non-local effects can regularize the curvature singularities in both scenarios
and, in the dynamical case, there exists a mass gap below which the formation
of an apparent horizon can be avoided. In the final part we discuss interesting
attempts towards finding non-linear black hole solutions in non-local gravity.
Throughout this chapter, instead of focusing on a particular non-local model,
we present results valid for large classes of theories (to a feasible extent).
This more general approach allows the comparison of similarities and
differences of the various types of non-local gravity models.
| [
{
"created": "Mon, 7 Nov 2022 12:39:25 GMT",
"version": "v1"
}
] | 2022-11-08 | [
[
"Buoninfante",
"Luca",
""
],
[
"Giacchini",
"Breno L.",
""
],
[
"Netto",
"Tibério de Paula",
""
]
] | In this chapter we present a status report of black hole-like solutions in non-local theories of gravity in which the Lagrangians are at least quadratic in curvature and contain specific non-polynomial (i.e., non-local) operators. In the absence of exact black hole solutions valid in the whole spacetime, most of the literature on this topic focus on approximate and simplified equations of motion, which could provide insights on the full non-linear solutions. Therefore, the largest part of this chapter is devoted to the linear approximation. We present results on stationary metric solutions (including both static and rotating cases) and dynamical spacetimes describing the formation of non-rotating mini black holes by the collapse of null shells. Non-local effects can regularize the curvature singularities in both scenarios and, in the dynamical case, there exists a mass gap below which the formation of an apparent horizon can be avoided. In the final part we discuss interesting attempts towards finding non-linear black hole solutions in non-local gravity. Throughout this chapter, instead of focusing on a particular non-local model, we present results valid for large classes of theories (to a feasible extent). This more general approach allows the comparison of similarities and differences of the various types of non-local gravity models. |
1512.02836 | Carlos Eduardo Cede\~no Monta\~na | C. E. Cede\~no M. and J. C. N. de Araujo | Master equation solutions in the linear regime of characteristic
formulation of general relativity | 19 pages | Phys. Rev. D 92, 124015 (2015) | 10.1103/PhysRevD.92.124015 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | From the field equations in the linear regime of the characteristic
formulation of general relativity, Bishop, for a Schwarzschild's background,
and M\"adler, for a Minkowski's background, were able to show that it is
possible to derive a fourth order ordinary differential equation, called master
equation, for the $J$ metric variable of the Bondi-Sachs metric. Once $\beta$,
another Bondi-Sachs potential, is obtained from the field equations, and $J$ is
obtained from the master equation, the other metric variables are solved
integrating directly the rest of the field equations. In the past, the master
equation was solved for the first multipolar terms, for both the Minkowski's
and Schwarzschild's backgrounds. Also, M\"adler recently reported a
generalisation of the exact solutions to the linearised field equations when a
Minkowski's background is considered, expressing the master equation family of
solutions for the vacuum in terms of Bessel's functions of the first and the
second kind. Here, we report new solutions to the master equation for any
multipolar moment $l$, with and without matter sources in terms only of the
first kind Bessel's functions for the Minkowski, and in terms of the Confluent
Heun's functions (Generalised Hypergeometric) for radiative (nonradiative) case
in the Schwarzschild's background. We particularize our families of solutions
for the known cases for $l=2$ reported previously in the literature and find
complete agreement, showing the robustness of our results.
| [
{
"created": "Wed, 9 Dec 2015 12:36:56 GMT",
"version": "v1"
}
] | 2015-12-10 | [
[
"M.",
"C. E. Cedeño",
""
],
[
"de Araujo",
"J. C. N.",
""
]
] | From the field equations in the linear regime of the characteristic formulation of general relativity, Bishop, for a Schwarzschild's background, and M\"adler, for a Minkowski's background, were able to show that it is possible to derive a fourth order ordinary differential equation, called master equation, for the $J$ metric variable of the Bondi-Sachs metric. Once $\beta$, another Bondi-Sachs potential, is obtained from the field equations, and $J$ is obtained from the master equation, the other metric variables are solved integrating directly the rest of the field equations. In the past, the master equation was solved for the first multipolar terms, for both the Minkowski's and Schwarzschild's backgrounds. Also, M\"adler recently reported a generalisation of the exact solutions to the linearised field equations when a Minkowski's background is considered, expressing the master equation family of solutions for the vacuum in terms of Bessel's functions of the first and the second kind. Here, we report new solutions to the master equation for any multipolar moment $l$, with and without matter sources in terms only of the first kind Bessel's functions for the Minkowski, and in terms of the Confluent Heun's functions (Generalised Hypergeometric) for radiative (nonradiative) case in the Schwarzschild's background. We particularize our families of solutions for the known cases for $l=2$ reported previously in the literature and find complete agreement, showing the robustness of our results. |
2104.11996 | Cristian Quinzacara | Fernando G\'omez, Samuel Lepe, Cristian Quinzacara and Patricio
Salgado | Five-dimensional Einstein-Chern-Simons cosmology | 14 pages, 2 figures | Phys. Rev. D 103, 104058 (2021) | 10.1103/PhysRevD.103.104058 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We consider a five-dimensional Einstein-Chern-Simons action which is composed
of a gravitational sector and a sector of matter, where the gravitational
sector is given by a Chern-Simons gravity action instead of the
Einstein-Hilbert action, and where the matter sector is given by a perfect
fluid. The gravitational lagrangian is obtained gauging some Lie-algebras,
which in turn, were obtained by S-expansion procedure of Anti-de Sitter and de
Sitter algebras. On the cosmological plane, we discuss the field equations
resulting from the Anti-de Sitter and de Sitter frameworks and we show
analogies with four-dimensional cosmological schemes.
| [
{
"created": "Sat, 24 Apr 2021 18:31:53 GMT",
"version": "v1"
}
] | 2021-05-28 | [
[
"Gómez",
"Fernando",
""
],
[
"Lepe",
"Samuel",
""
],
[
"Quinzacara",
"Cristian",
""
],
[
"Salgado",
"Patricio",
""
]
] | We consider a five-dimensional Einstein-Chern-Simons action which is composed of a gravitational sector and a sector of matter, where the gravitational sector is given by a Chern-Simons gravity action instead of the Einstein-Hilbert action, and where the matter sector is given by a perfect fluid. The gravitational lagrangian is obtained gauging some Lie-algebras, which in turn, were obtained by S-expansion procedure of Anti-de Sitter and de Sitter algebras. On the cosmological plane, we discuss the field equations resulting from the Anti-de Sitter and de Sitter frameworks and we show analogies with four-dimensional cosmological schemes. |
gr-qc/0608002 | Larry Ford | Chun-Hsien Wu, Kin-Wang Ng, and L.H. Ford | Possible Constraints on the Duration of Inflationary Expansion from
Quantum Stress Tensor Fluctuations | 21 pages, no figures; Sect. IV rewritten and expanded, several
comments and references added | Phys.Rev.D75:103502,2007 | 10.1103/PhysRevD.75.103502 | null | gr-qc astro-ph hep-th | null | We discuss the effect of quantum stress tensor fluctuations in deSitter
spacetime upon the expansion of a congruence of timelike geodesics. We treat a
model in which the expansion fluctuations begin on a given hypersurface in
deSitter spacetime, and find that this effect tends to grow, in contrast to the
situation in flat spacetime. This growth potentially leads to observable
consequences in inflationary cosmology in the form of density perturbations
which depend upon the duration of the inflationary period. In the context of
our model, the effect may be used to place upper bounds on this duration.
| [
{
"created": "Mon, 31 Jul 2006 21:57:00 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Apr 2007 00:59:30 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Wu",
"Chun-Hsien",
""
],
[
"Ng",
"Kin-Wang",
""
],
[
"Ford",
"L. H.",
""
]
] | We discuss the effect of quantum stress tensor fluctuations in deSitter spacetime upon the expansion of a congruence of timelike geodesics. We treat a model in which the expansion fluctuations begin on a given hypersurface in deSitter spacetime, and find that this effect tends to grow, in contrast to the situation in flat spacetime. This growth potentially leads to observable consequences in inflationary cosmology in the form of density perturbations which depend upon the duration of the inflationary period. In the context of our model, the effect may be used to place upper bounds on this duration. |
1601.05932 | Ettore Minguzzi | E. Minguzzi | On the existence of smooth Cauchy steep time functions | Latex2e, 4 pages | Classical and Quantum Gravity 33 (2016) 115001 | 10.1088/0264-9381/33/11/115001 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A simple proof is given that every globally hyperbolic spacetime admits a
smooth Cauchy steep time function. This result is useful in order to show that
globally hyperbolic spacetimes can be isometrically embedded in Minkowski
spacetimes and that they spit as a product. The proof is based on a recent
result on the differentiability of Geroch's volume functions.
| [
{
"created": "Fri, 22 Jan 2016 09:57:16 GMT",
"version": "v1"
}
] | 2016-04-28 | [
[
"Minguzzi",
"E.",
""
]
] | A simple proof is given that every globally hyperbolic spacetime admits a smooth Cauchy steep time function. This result is useful in order to show that globally hyperbolic spacetimes can be isometrically embedded in Minkowski spacetimes and that they spit as a product. The proof is based on a recent result on the differentiability of Geroch's volume functions. |
1408.1896 | Pierre-Andr\'e Mandrin Ph.D. | Pierre-Andr\'e Mandrin | Spin-compatible construction of a consistent quantum gravity model from
minimum information | 9 pages, detailed information in relation to the poster presented at
the Symposium "Frontiers of Fundamental Physic" in July 2014. v2: "Tetrad
bath" instead of "stress bath"; cleaner notation of boundary integrals; use
of Gauss' law and S properly decomposed into generalised Palatini + torsion
terms | null | null | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This article shows in detail the computations made for the poster presented
at the Symposium "Frontiers of Fundamental Physics" in July 2014. As was shown
in a previous publication, a quantum gravity formulation exists on the basis of
abstract quantum number conservation, the laws of thermodynamics, unspecific
interactions, and locally maximising the ratio of resulting degrees of freedom
per imposed degree of freedom of the theory. The first law of thermodynamics
was evaluated by imposing boundary conditions on small volumes of optimised
dimension (3+1). As a consequence, no explicit microscopic quantum structure
was required in order to recover all well established physics as special cases
(Quantum Field Theory, QFT, and General Relativity, GR) and compute all
measurable quantities. This article presents the generalised action in terms of
tetrads and shows how this action may be related to the spin of generalised
matter fields, especially for fermionic matter.
| [
{
"created": "Fri, 8 Aug 2014 16:03:09 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Dec 2014 21:37:40 GMT",
"version": "v2"
}
] | 2015-01-05 | [
[
"Mandrin",
"Pierre-André",
""
]
] | This article shows in detail the computations made for the poster presented at the Symposium "Frontiers of Fundamental Physics" in July 2014. As was shown in a previous publication, a quantum gravity formulation exists on the basis of abstract quantum number conservation, the laws of thermodynamics, unspecific interactions, and locally maximising the ratio of resulting degrees of freedom per imposed degree of freedom of the theory. The first law of thermodynamics was evaluated by imposing boundary conditions on small volumes of optimised dimension (3+1). As a consequence, no explicit microscopic quantum structure was required in order to recover all well established physics as special cases (Quantum Field Theory, QFT, and General Relativity, GR) and compute all measurable quantities. This article presents the generalised action in terms of tetrads and shows how this action may be related to the spin of generalised matter fields, especially for fermionic matter. |
gr-qc/0303092 | Alicia Herrero | A. Herrero and M. Portilla | Effect of a non null pressure on the evolution of perturbations in the
matter dominated epoch | 6 figures, you will need some Mathematica fonts to see them correctly | null | null | null | gr-qc | null | We analyze the effect of pressure on the evolution of perturbations of an
Einstein-de Sitter Universe in the matter dominated epoch assuming an ideal gas
equation of state. For the sake of simplicity the temperature is considered
uniform. The goal of the paper is to examine the validity of the linear
approximation. With this purpose the evolution equations are developed
including quadratic terms in the derivatives of the metric perturbations and
using coordinate conditions that, in the linear case, reduce to the
longitudinal gauge. We obtain the general solution, in the coordinate space, of
the evolution equation for the scalar mode, and, in the case of spherical
symmetry, we express this solution in terms of unidimensional integrals of the
initial conditions: the initial values of the Newtonian potential and its first
time derivative. We find that the contribution of the initial first time
derivative, which has been systematically forgotten, allows to form
inhomogeneities similar to a cluster of galaxies starting with very small
density contrast. Finally, we obtain the first non linear correction to the
linearized solution due to the quadratic terms in the evolution equations. Here
we find that a non null pressure plays a crucial role in constraining the non
linear corrections. It is shown, by means of examples, that reasonable thermal
velocities at the present epoch (non bigger than $10^{-6}$) make the ratio
between the first non linear correction and the linear solution of the order of
$10^{-2}$ for a galaxy cluster inhomogeneity.
| [
{
"created": "Mon, 24 Mar 2003 12:49:53 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Sep 2003 14:06:44 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Herrero",
"A.",
""
],
[
"Portilla",
"M.",
""
]
] | We analyze the effect of pressure on the evolution of perturbations of an Einstein-de Sitter Universe in the matter dominated epoch assuming an ideal gas equation of state. For the sake of simplicity the temperature is considered uniform. The goal of the paper is to examine the validity of the linear approximation. With this purpose the evolution equations are developed including quadratic terms in the derivatives of the metric perturbations and using coordinate conditions that, in the linear case, reduce to the longitudinal gauge. We obtain the general solution, in the coordinate space, of the evolution equation for the scalar mode, and, in the case of spherical symmetry, we express this solution in terms of unidimensional integrals of the initial conditions: the initial values of the Newtonian potential and its first time derivative. We find that the contribution of the initial first time derivative, which has been systematically forgotten, allows to form inhomogeneities similar to a cluster of galaxies starting with very small density contrast. Finally, we obtain the first non linear correction to the linearized solution due to the quadratic terms in the evolution equations. Here we find that a non null pressure plays a crucial role in constraining the non linear corrections. It is shown, by means of examples, that reasonable thermal velocities at the present epoch (non bigger than $10^{-6}$) make the ratio between the first non linear correction and the linear solution of the order of $10^{-2}$ for a galaxy cluster inhomogeneity. |
1111.5266 | Ivana Bochicchio Dr | Ivana Bochicchio and Valerio Faraoni | Cosmological expansion and local systems: a Lema\^{i}tre-Tolman-Bondi
model | null | General Relativity and Gravitation, Vol. 44 (2012) pp. 1479-1487 | 10.1007/s10714-012-1350-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a Lema\^{i}tre-Tolman-Bondi system mimicking a two-body system to
address the problem of the cosmological expansion versus local dynamics. This
system is strongly bound but participates in the cosmic expansion and is
exactly comoving with the cosmic substratum.
| [
{
"created": "Tue, 22 Nov 2011 17:59:27 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Mar 2012 11:00:12 GMT",
"version": "v2"
},
{
"created": "Tue, 8 Jan 2013 13:48:52 GMT",
"version": "v3"
}
] | 2013-01-09 | [
[
"Bochicchio",
"Ivana",
""
],
[
"Faraoni",
"Valerio",
""
]
] | We propose a Lema\^{i}tre-Tolman-Bondi system mimicking a two-body system to address the problem of the cosmological expansion versus local dynamics. This system is strongly bound but participates in the cosmic expansion and is exactly comoving with the cosmic substratum. |
gr-qc/0204059 | Peter Dunsby | Naureen Goheer and Peter Dunsby | Braneworld Dynamics of Inflationary Cosmologies with Exponential
Potentials | 15 pages, 9 figures, RevTex 4. Submitted to Physical Review D | Phys.Rev. D66 (2002) 043527 | 10.1103/PhysRevD.66.043527 | null | gr-qc | null | In this work we consider Randall-Sundrum braneworld type scenarios, in which
the spacetime is described by a five-dimensional manifold with matter fields
confined in a domain wall or three-brane. We present the results of a
systematic analysis, using dynamical systems techniques, of the qualitative
behaviour of Friedmann-Lemaitre-Robertson-Walker type models, whose matter is
described by a scalar field with an exponential potential. We construct the
state spaces for these models and discuss how their structure changes with
respect to the general-relativistic case, in particular, what new critical
points appear and their nature and the occurrence of bifurcation.
| [
{
"created": "Thu, 18 Apr 2002 05:29:35 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Goheer",
"Naureen",
""
],
[
"Dunsby",
"Peter",
""
]
] | In this work we consider Randall-Sundrum braneworld type scenarios, in which the spacetime is described by a five-dimensional manifold with matter fields confined in a domain wall or three-brane. We present the results of a systematic analysis, using dynamical systems techniques, of the qualitative behaviour of Friedmann-Lemaitre-Robertson-Walker type models, whose matter is described by a scalar field with an exponential potential. We construct the state spaces for these models and discuss how their structure changes with respect to the general-relativistic case, in particular, what new critical points appear and their nature and the occurrence of bifurcation. |
gr-qc/0606053 | Oliver Rinne | Oliver Rinne | Stable radiation-controlling boundary conditions for the generalized
harmonic Einstein equations | 27 pages, 4 figures; more numerical results and references added,
several minor amendments; version accepted for publication in Class. Quantum
Grav | Class. Quantum Grav. 23, 6275-6300 (2006) | 10.1088/0264-9381/23/22/013 | null | gr-qc | null | This paper is concerned with the initial-boundary value problem for the
Einstein equations in a first-order generalized harmonic formulation. We impose
boundary conditions that preserve the constraints and control the incoming
gravitational radiation by prescribing data for the incoming fields of the Weyl
tensor. High-frequency perturbations about any given spacetime (including a
shift vector with subluminal normal component) are analyzed using the
Fourier-Laplace technique. We show that the system is boundary-stable. In
addition, we develop a criterion that can be used to detect weak instabilities
with polynomial time dependence, and we show that our system does not suffer
from such instabilities. A numerical robust stability test supports our claim
that the initial-boundary value problem is most likely to be well-posed even if
nonzero initial and source data are included.
| [
{
"created": "Mon, 12 Jun 2006 19:01:56 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Sep 2006 20:13:32 GMT",
"version": "v2"
}
] | 2008-11-22 | [
[
"Rinne",
"Oliver",
""
]
] | This paper is concerned with the initial-boundary value problem for the Einstein equations in a first-order generalized harmonic formulation. We impose boundary conditions that preserve the constraints and control the incoming gravitational radiation by prescribing data for the incoming fields of the Weyl tensor. High-frequency perturbations about any given spacetime (including a shift vector with subluminal normal component) are analyzed using the Fourier-Laplace technique. We show that the system is boundary-stable. In addition, we develop a criterion that can be used to detect weak instabilities with polynomial time dependence, and we show that our system does not suffer from such instabilities. A numerical robust stability test supports our claim that the initial-boundary value problem is most likely to be well-posed even if nonzero initial and source data are included. |
2402.18750 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Wormholes supported by small extra dimensions | 7 pages, no figures | Adv. Studies Theor. Phys., vol. 18, no.1, pp. 41-48, 2024 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Holding a Morris-Thorne wormhole open requires a violation of the null energy
condition, calling for the need for so-called exotic matter near the throat.
Many researchers consider exotic matter to be completely unphysical in
classical general relativity. It has been shown, however, that the existence of
an extra macroscopic dimension can resolve this issue: the throat could be
lined with ordinary matter, while the extra dimension is then responsible for
the unavoidable energy violation. The purpose of this paper is to show that the
extra dimension can be microscopic, a result that is consistent with string
theory.
| [
{
"created": "Wed, 28 Feb 2024 23:11:22 GMT",
"version": "v1"
}
] | 2024-03-01 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | Holding a Morris-Thorne wormhole open requires a violation of the null energy condition, calling for the need for so-called exotic matter near the throat. Many researchers consider exotic matter to be completely unphysical in classical general relativity. It has been shown, however, that the existence of an extra macroscopic dimension can resolve this issue: the throat could be lined with ordinary matter, while the extra dimension is then responsible for the unavoidable energy violation. The purpose of this paper is to show that the extra dimension can be microscopic, a result that is consistent with string theory. |
2102.08339 | Massimiliano Maria Riva | Stavros Mougiakakos, Massimiliano Maria Riva and Filippo Vernizzi | Gravitational Bremsstrahlung in the Post-Minkowskian Effective Field
Theory | 11 pages, 1 figure | Phys. Rev. D 104, 024041 (2021) | 10.1103/PhysRevD.104.024041 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the gravitational radiation emitted during the scattering of two
spinless bodies in the post-Minkowskian Effective Field Theory approach. We
derive the conserved stress-energy tensor linearly coupled to gravity and the
classical probability amplitude of graviton emission at leading and
next-to-leading order in the Newton's constant $G$. The amplitude can be
expressed in compact form as one-dimensional integrals over a Feynman parameter
involving Bessel functions. We use it to recover the leading-order radiated
angular momentum expression. Upon expanding it in the relative velocity between
the two bodies $v$, we compute the total four-momentum radiated into
gravitational waves at leading-order in $G$ and up to an order $v^8$, finding
agreement with what was recently computed using scattering amplitude methods.
Our results also allow us to investigate the zero frequency limit of the
emitted energy spectrum.
| [
{
"created": "Tue, 16 Feb 2021 18:24:44 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Jun 2021 15:58:36 GMT",
"version": "v2"
}
] | 2021-07-21 | [
[
"Mougiakakos",
"Stavros",
""
],
[
"Riva",
"Massimiliano Maria",
""
],
[
"Vernizzi",
"Filippo",
""
]
] | We study the gravitational radiation emitted during the scattering of two spinless bodies in the post-Minkowskian Effective Field Theory approach. We derive the conserved stress-energy tensor linearly coupled to gravity and the classical probability amplitude of graviton emission at leading and next-to-leading order in the Newton's constant $G$. The amplitude can be expressed in compact form as one-dimensional integrals over a Feynman parameter involving Bessel functions. We use it to recover the leading-order radiated angular momentum expression. Upon expanding it in the relative velocity between the two bodies $v$, we compute the total four-momentum radiated into gravitational waves at leading-order in $G$ and up to an order $v^8$, finding agreement with what was recently computed using scattering amplitude methods. Our results also allow us to investigate the zero frequency limit of the emitted energy spectrum. |
0803.3399 | Tomi Koivisto | Tomi Koivisto | Dynamics of Nonlocal Cosmology | 14 pages, 3 figures. V2: minor corrections | Phys.Rev.D77:123513,2008 | 10.1103/PhysRevD.77.123513 | null | gr-qc astro-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Nonlocal quantum corrections to gravity have been recently proposed as a
possible solution to the cosmological fine tuning problems. We study the
dynamics of a class of nonlocal actions defined by a function of the inverse
d'Alembertian of the Ricci scalar. Power-law and expnential functions are
considered in detail, but we also show a method to reconstruct a nonlocal
correction that generates a given background expansion. We find that even the
simplest terms can, while involving only Planck scale constants, drive the late
time acceleration without changing early cosmology. This leads to a sudden
future singularity, which however may be avoided by regularizing the
d'Alembertian. We also consider the Einstein frame versions of these models.
| [
{
"created": "Mon, 24 Mar 2008 12:50:16 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Jun 2008 09:33:08 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Koivisto",
"Tomi",
""
]
] | Nonlocal quantum corrections to gravity have been recently proposed as a possible solution to the cosmological fine tuning problems. We study the dynamics of a class of nonlocal actions defined by a function of the inverse d'Alembertian of the Ricci scalar. Power-law and expnential functions are considered in detail, but we also show a method to reconstruct a nonlocal correction that generates a given background expansion. We find that even the simplest terms can, while involving only Planck scale constants, drive the late time acceleration without changing early cosmology. This leads to a sudden future singularity, which however may be avoided by regularizing the d'Alembertian. We also consider the Einstein frame versions of these models. |
1705.09633 | Yen Chin Ong | Zi-Yu Tang, Yen Chin Ong, Bin Wang | Lux in obscuro II: Photon Orbits of Extremal AdS Black Holes Revisited | 23 pages, 8 figures. Fixed some typos. Version accepted by CQG | null | 10.1088/1361-6382/aa95ff | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A large class of spherically symmetric static extremal black hole spacetimes
possesses a stable null photon sphere on their horizons. For the extremal
Kerr-Newman family, the photon sphere only really coincides with the horizon in
the sense clarified by Doran. The condition under which photon orbit is stable
on an asymptotically flat extremal Kerr-Newman black hole horizon has recently
been clarified; it is found that a sufficiently large angular momentum
destabilizes the photon orbit, whereas electrical charge tends to stabilize it.
We investigated the effect of a negative cosmological constant on this
observation, and found the same behavior in the case of an extremal
asymptotically Kerr-Newman-AdS black holes in (3+1)-dimensions. In
(2+1)-dimensions, in the presence of electrical charge, the angular momentum
never becomes large enough to destabilize the photon orbit. We comment on the
instabilities of black hole spacetimes with a stable photon orbit.
| [
{
"created": "Fri, 26 May 2017 16:09:24 GMT",
"version": "v1"
},
{
"created": "Mon, 14 Aug 2017 16:52:04 GMT",
"version": "v2"
},
{
"created": "Fri, 3 Nov 2017 09:51:22 GMT",
"version": "v3"
}
] | 2017-11-06 | [
[
"Tang",
"Zi-Yu",
""
],
[
"Ong",
"Yen Chin",
""
],
[
"Wang",
"Bin",
""
]
] | A large class of spherically symmetric static extremal black hole spacetimes possesses a stable null photon sphere on their horizons. For the extremal Kerr-Newman family, the photon sphere only really coincides with the horizon in the sense clarified by Doran. The condition under which photon orbit is stable on an asymptotically flat extremal Kerr-Newman black hole horizon has recently been clarified; it is found that a sufficiently large angular momentum destabilizes the photon orbit, whereas electrical charge tends to stabilize it. We investigated the effect of a negative cosmological constant on this observation, and found the same behavior in the case of an extremal asymptotically Kerr-Newman-AdS black holes in (3+1)-dimensions. In (2+1)-dimensions, in the presence of electrical charge, the angular momentum never becomes large enough to destabilize the photon orbit. We comment on the instabilities of black hole spacetimes with a stable photon orbit. |
2401.14643 | Qiaoyin Pan | Muxin Han, Qiaoyin Pan | Deficit Angles in 4D Spinfoam with Cosmological Constant: (Anti) de
Sitter-ness and More | a figure corrected | null | null | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by-nc-sa/4.0/ | This paper investigates the critical behaviors of the 4-dimensional spinfoam
model with cosmological constant for a general 4-dimensional simplicial complex
as the discretization of spacetime. We find that, at the semi-classical regime,
the spinfoam amplitude is peaked at the real critical points that correspond to
zero deficit angles (modulo $4\pi\mathbb{Z}/\gamma$) hinged by internal
triangles of the 4-complex. Since the 4-simplices from the model are of
constant curvature, the discrete geometry with zero deficit angle manifests a
de Sitter (dS) spacetime or an anti de Sitter (AdS) spacetime depending on the
sign of the cosmological constant fixed by the boundary condition. The
non-(A)dS spacetimes emerge from the complex critical points by an analytic
continuation to complex configurations.
| [
{
"created": "Fri, 26 Jan 2024 04:22:45 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Feb 2024 03:35:19 GMT",
"version": "v2"
}
] | 2024-02-15 | [
[
"Han",
"Muxin",
""
],
[
"Pan",
"Qiaoyin",
""
]
] | This paper investigates the critical behaviors of the 4-dimensional spinfoam model with cosmological constant for a general 4-dimensional simplicial complex as the discretization of spacetime. We find that, at the semi-classical regime, the spinfoam amplitude is peaked at the real critical points that correspond to zero deficit angles (modulo $4\pi\mathbb{Z}/\gamma$) hinged by internal triangles of the 4-complex. Since the 4-simplices from the model are of constant curvature, the discrete geometry with zero deficit angle manifests a de Sitter (dS) spacetime or an anti de Sitter (AdS) spacetime depending on the sign of the cosmological constant fixed by the boundary condition. The non-(A)dS spacetimes emerge from the complex critical points by an analytic continuation to complex configurations. |
1311.4661 | Titus K Mathew | Titus K Mathew and P. Praseetha | Holographic Ricci dark energy and generalized second law | null | Mod.Phys.Lett. A29 (2014) no.06, 1450023 | 10.1142/S0217732314500230 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explore the validity of the generalized second law (GSL) of thermodynamics
in flat FRW universe with apparent horizon and event horizon as the boundary.
We found that in a universe with holographic Ricci dark energy and dark matter,
interacting with each other, the GSL is satisfied at the apparent horizon and
partially satisfied at the event horizon under thermal equilibrium conditions.
We also analyses the GSL under non-equilibrium conditions and shows that the
fulfillment of GSL at the apparent horizon implies that the temperature of the
dark energy is greater than that of the horizon. Thus there occurs a flow of
dark energy towards the apparent horizon. As a result the entropy of the dark
energy decreases and that of horizon increases. This is verified by finding the
evolution of the dark energy entropy and horizon entropy in a dark energy
dominated universe under non-equilibrium conditions.
| [
{
"created": "Tue, 19 Nov 2013 09:12:14 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Nov 2013 09:02:24 GMT",
"version": "v2"
}
] | 2019-05-13 | [
[
"Mathew",
"Titus K",
""
],
[
"Praseetha",
"P.",
""
]
] | We explore the validity of the generalized second law (GSL) of thermodynamics in flat FRW universe with apparent horizon and event horizon as the boundary. We found that in a universe with holographic Ricci dark energy and dark matter, interacting with each other, the GSL is satisfied at the apparent horizon and partially satisfied at the event horizon under thermal equilibrium conditions. We also analyses the GSL under non-equilibrium conditions and shows that the fulfillment of GSL at the apparent horizon implies that the temperature of the dark energy is greater than that of the horizon. Thus there occurs a flow of dark energy towards the apparent horizon. As a result the entropy of the dark energy decreases and that of horizon increases. This is verified by finding the evolution of the dark energy entropy and horizon entropy in a dark energy dominated universe under non-equilibrium conditions. |
2304.03261 | Ahmad Sheykhi | A. Sheykhi and S. Ghaffari | Note on agegraphic dark energy inspired by modified Barrow entropy | 11 pages | Physics of the Dark Universe 41 (2023) 101241 | 10.1016/j.dark.2023.101241 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We revisit agegraphic dark energy (ADE) model when the entropy associated
with the apparent horizon is in the form of Barrow entropy, $S\sim
A^{1+\delta/2}$, where $0\leq\delta\leq1$ indicates the amount of the
quantum-gravitational deformation effects of the horizon. The modification to
the entropy expression, not only change the energy density of ADE, but also
modifies the Friedmann equations due to thermodynamics-gravity conjecture.
Based on this, we investigate the cosmological consequences of ADE through
modified Barrow cosmology and disclose the effects of Barrow exponent $\delta$
on the evolutions of the cosmological parameters. We observe that, depending on
the values of $\delta$, the transition from early decelerated phase to the late
time accelerated phase occurs, and the equation of state (EoS) parameter $
w_{de} $ varies from quintessence $ -1<w_{de}<-1/3 $ to the phantom regime $
(w_{de}<-1)$. When $\delta=0$, all results of ADE in standard cosmology are
restored.
| [
{
"created": "Thu, 6 Apr 2023 17:47:12 GMT",
"version": "v1"
}
] | 2023-05-18 | [
[
"Sheykhi",
"A.",
""
],
[
"Ghaffari",
"S.",
""
]
] | We revisit agegraphic dark energy (ADE) model when the entropy associated with the apparent horizon is in the form of Barrow entropy, $S\sim A^{1+\delta/2}$, where $0\leq\delta\leq1$ indicates the amount of the quantum-gravitational deformation effects of the horizon. The modification to the entropy expression, not only change the energy density of ADE, but also modifies the Friedmann equations due to thermodynamics-gravity conjecture. Based on this, we investigate the cosmological consequences of ADE through modified Barrow cosmology and disclose the effects of Barrow exponent $\delta$ on the evolutions of the cosmological parameters. We observe that, depending on the values of $\delta$, the transition from early decelerated phase to the late time accelerated phase occurs, and the equation of state (EoS) parameter $ w_{de} $ varies from quintessence $ -1<w_{de}<-1/3 $ to the phantom regime $ (w_{de}<-1)$. When $\delta=0$, all results of ADE in standard cosmology are restored. |
1906.08583 | Abbas Sherif | Abbas Sherif, Rituparno Goswami, Sunil D. Maharaj | On Properties of Expansion-free Dynamical Stars | 6 pages | Phys. Rev. D 100, 044039 (2019) | 10.1103/PhysRevD.100.044039 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the geometrical and dynamical features of expansion-free dynamical
stars in general relativity. Such stars can exist only if particular physical
and geometric conditions are satisfied. Firstly, for trapping to exist in an
expansion-free dynamical star, the star must accelerate and radiate
simultaneously. If either are zero, then the shear \(Sigma\) must be zero
through out the star, in which case the star is static (\(\Theta=\Sigma=0\)).
Secondly, we prove that with nonzero acceleration and radiation expansion-free
dynamical stars must be conformally flat.
| [
{
"created": "Thu, 20 Jun 2019 12:49:16 GMT",
"version": "v1"
},
{
"created": "Sun, 25 Aug 2019 23:22:44 GMT",
"version": "v2"
}
] | 2019-08-28 | [
[
"Sherif",
"Abbas",
""
],
[
"Goswami",
"Rituparno",
""
],
[
"Maharaj",
"Sunil D.",
""
]
] | We study the geometrical and dynamical features of expansion-free dynamical stars in general relativity. Such stars can exist only if particular physical and geometric conditions are satisfied. Firstly, for trapping to exist in an expansion-free dynamical star, the star must accelerate and radiate simultaneously. If either are zero, then the shear \(Sigma\) must be zero through out the star, in which case the star is static (\(\Theta=\Sigma=0\)). Secondly, we prove that with nonzero acceleration and radiation expansion-free dynamical stars must be conformally flat. |
gr-qc/9503060 | Bernard Linet | B. Linet | Vacuum polarization induced by a uniformly accelerated charge | 13 pages, latex, no figures, to appear in Int. J. Theor. Phys. | Int.J.Theor.Phys. 34 (1995) 1055-1064 | 10.1007/BF00671366 | GCR-941003 | gr-qc | null | We consider a point charge fixed in the Rindler coordinates which describe a
uniformly accelerated frame. We determine an integral expression of the induced
charge density due to the vacuum polarization at the first order in the fine
structure constant. In the case where the acceleration is weak, we give
explicitly the induced electrostatic potential.
| [
{
"created": "Thu, 30 Mar 1995 12:55:07 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Linet",
"B.",
""
]
] | We consider a point charge fixed in the Rindler coordinates which describe a uniformly accelerated frame. We determine an integral expression of the induced charge density due to the vacuum polarization at the first order in the fine structure constant. In the case where the acceleration is weak, we give explicitly the induced electrostatic potential. |
gr-qc/0610059 | John W. Moffat | J. W. Moffat | Non-Singular Cosmology in Modified Gravity | 10 pages, no figures, Latex file. Revised version of paper | null | null | null | gr-qc | null | A non-singular cosmology is derived in modified gravity (MOG) with a varying
gravitational coupling strength $G(t)=G_N\xi(t)$. Assuming that the curvature
$k$, the cosmological constant $\Lambda$ and $\rho$ vanish at $t=0$, we obtain
a non-singular universe with a negative pressure, $p_G < 0$. Quantum
fluctuations at $t\sim 0$ produce creation of pairs of particles from the
vacuum explaining the origin of matter. The universe expands for $t\to \infty$
according to the standard radiation and matter dominated solutions. The arrow
of time reverses at $t=0$ always pointing in the direction of increasing
entropy ${\cal S}$ and the entropy is at a minimum value at $t=0$, solving the
conundrum of the Second Law of Thermodynamics. The Hubble radius $H^{-1}(t)$ is
infinite at $t=0$ removing the curvature and particle horizons. The negative
pressure $p_G$ generated by the scalar field $\xi$ at $t\sim 0$ can produce
quantum spontaneous creation of particles explaining the origin of matter and
radiation.
| [
{
"created": "Wed, 11 Oct 2006 22:09:19 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Feb 2007 19:11:00 GMT",
"version": "v2"
},
{
"created": "Wed, 24 Oct 2007 18:38:49 GMT",
"version": "v3"
}
] | 2007-10-24 | [
[
"Moffat",
"J. W.",
""
]
] | A non-singular cosmology is derived in modified gravity (MOG) with a varying gravitational coupling strength $G(t)=G_N\xi(t)$. Assuming that the curvature $k$, the cosmological constant $\Lambda$ and $\rho$ vanish at $t=0$, we obtain a non-singular universe with a negative pressure, $p_G < 0$. Quantum fluctuations at $t\sim 0$ produce creation of pairs of particles from the vacuum explaining the origin of matter. The universe expands for $t\to \infty$ according to the standard radiation and matter dominated solutions. The arrow of time reverses at $t=0$ always pointing in the direction of increasing entropy ${\cal S}$ and the entropy is at a minimum value at $t=0$, solving the conundrum of the Second Law of Thermodynamics. The Hubble radius $H^{-1}(t)$ is infinite at $t=0$ removing the curvature and particle horizons. The negative pressure $p_G$ generated by the scalar field $\xi$ at $t\sim 0$ can produce quantum spontaneous creation of particles explaining the origin of matter and radiation. |
1206.3689 | Lorenzo Fatibene | L. Fatibene, M. Francaviglia, S.Garruto | Do Barbero-Immirzi connections exist in different dimensions and
signatures? | 8 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We shall show that no reductive splitting of the spin group exists in
dimension 3 \leq m \leq 20 other than in dimension m = 4. In dimension 4 there
are reductive splittings in any signature. Euclidean and Lorentzian signatures
are reviewed in particular and signature (2, 2) is investigated explicitly in
detail. Reductive splittings allow to define a global SU(2)-connection over
spacetime which encodes in an weird way the holonomy of the standard spin
connection. The standard Barbero-Immirzi (BI) connection used in LQG is then
obtained by restriction to a spacelike slice. This mechanism provides a good
control on globality and covariance of BI connection showing that in dimension
other than 4 one needs to provide some other mechanism to define the analogous
of BI connection and control its globality.
| [
{
"created": "Sat, 16 Jun 2012 18:44:21 GMT",
"version": "v1"
}
] | 2012-06-19 | [
[
"Fatibene",
"L.",
""
],
[
"Francaviglia",
"M.",
""
],
[
"Garruto",
"S.",
""
]
] | We shall show that no reductive splitting of the spin group exists in dimension 3 \leq m \leq 20 other than in dimension m = 4. In dimension 4 there are reductive splittings in any signature. Euclidean and Lorentzian signatures are reviewed in particular and signature (2, 2) is investigated explicitly in detail. Reductive splittings allow to define a global SU(2)-connection over spacetime which encodes in an weird way the holonomy of the standard spin connection. The standard Barbero-Immirzi (BI) connection used in LQG is then obtained by restriction to a spacelike slice. This mechanism provides a good control on globality and covariance of BI connection showing that in dimension other than 4 one needs to provide some other mechanism to define the analogous of BI connection and control its globality. |
gr-qc/9901081 | N. K. Dadhich | Naresh Dadhich and A.K. Raychaudhuri | Oscillating non-singular relativistic spherical model | 6 pages, REVTEX version | Mod.Phys.Lett. A14 (1999) 2135-2138 | 10.1142/S0217732399002194 | IUCAA-5/99 | gr-qc | null | A particular choice of the time function in the recently presented spherical
solution by Dadhich [1] leads to a singularity free cosmological model which
oscillates between two regular states. The energy-stress tensor involves
anisotropic pressure and a heat flux term but is consistent with the usual
energy conditions (strong, weak and dominant). By choosing the parameters
suitably one can make the model consistent with observational data. An
interesting feature of the model is that it involves blue shifts as in the
quasi steady state model [2] but without violating general relativity.
| [
{
"created": "Thu, 28 Jan 1999 09:11:16 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Dadhich",
"Naresh",
""
],
[
"Raychaudhuri",
"A. K.",
""
]
] | A particular choice of the time function in the recently presented spherical solution by Dadhich [1] leads to a singularity free cosmological model which oscillates between two regular states. The energy-stress tensor involves anisotropic pressure and a heat flux term but is consistent with the usual energy conditions (strong, weak and dominant). By choosing the parameters suitably one can make the model consistent with observational data. An interesting feature of the model is that it involves blue shifts as in the quasi steady state model [2] but without violating general relativity. |
2308.01812 | Daniela Cors | Daniela Cors, Sarah Renkhoff, Hannes R. R\"uter, David Hilditch and
Bernd Br\"ugmann | Formulation Improvements for Critical Collapse Simulations | 19 pages, 10 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The precise tuning required to observe critical phenomena in gravitational
collapse poses a challenge for most numerical codes. First, threshold
estimation searches may be obstructed by the appearance of coordinate
singularities, indicating the need for a better gauge choice. Second, the
constraint violations to which simulations are susceptible may be too large and
force searches to terminate prematurely. This is a particularly serious issue
for first order formulations. We want our adaptive pseudospectral code bamps to
be a robust tool for the study of critical phenomena so, having encountered
both of these difficulties in work on the vacuum setting, we turn here to
investigate these issues in the classic context of a spherically symmetric
massless scalar field. We suggest two general improvements. We propose a
necessary condition for a gauge choice to respect discrete self-similarity
(DSS). The condition is not restricted to spherical symmetry and could be
verified with any 3+1 formulation. After evaluating common gauge choices
against this condition, we suggest a DSS-compatible gauge source function in
generalized harmonic gauge (GHG). To control constraint violations, we modify
the constraint damping parameters of GHG, adapting them to collapse spacetimes.
This allows us to improve our tuning of the critical amplitude for several
families of initial data, even going from 6 up to 11 digits. This is the most
precise tuning achieved with the first order GHG formulation to date.
Consequently, we are able to reproduce the well known critical phenomena as
well as competing formulations and methods, clearly observing up to 3 echoes.
| [
{
"created": "Thu, 3 Aug 2023 15:17:42 GMT",
"version": "v1"
}
] | 2023-08-04 | [
[
"Cors",
"Daniela",
""
],
[
"Renkhoff",
"Sarah",
""
],
[
"Rüter",
"Hannes R.",
""
],
[
"Hilditch",
"David",
""
],
[
"Brügmann",
"Bernd",
""
]
] | The precise tuning required to observe critical phenomena in gravitational collapse poses a challenge for most numerical codes. First, threshold estimation searches may be obstructed by the appearance of coordinate singularities, indicating the need for a better gauge choice. Second, the constraint violations to which simulations are susceptible may be too large and force searches to terminate prematurely. This is a particularly serious issue for first order formulations. We want our adaptive pseudospectral code bamps to be a robust tool for the study of critical phenomena so, having encountered both of these difficulties in work on the vacuum setting, we turn here to investigate these issues in the classic context of a spherically symmetric massless scalar field. We suggest two general improvements. We propose a necessary condition for a gauge choice to respect discrete self-similarity (DSS). The condition is not restricted to spherical symmetry and could be verified with any 3+1 formulation. After evaluating common gauge choices against this condition, we suggest a DSS-compatible gauge source function in generalized harmonic gauge (GHG). To control constraint violations, we modify the constraint damping parameters of GHG, adapting them to collapse spacetimes. This allows us to improve our tuning of the critical amplitude for several families of initial data, even going from 6 up to 11 digits. This is the most precise tuning achieved with the first order GHG formulation to date. Consequently, we are able to reproduce the well known critical phenomena as well as competing formulations and methods, clearly observing up to 3 echoes. |
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