id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1806.00601 | Mariusz P. Dabrowski | Mariusz P. Dabrowski and Konrad Marosek | Non-exotic conformal structure of weak exotic singularities | 12 pages, 6 figures, matches published GRG version | Gen. Rel. Grav. 50, 160 (2018) | 10.1007/s10714-018-2482-1 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the conformal structure of exotic (non-big-bang) singularity
universes using the hybrid big-bang/exotic singularity/big-bang and
big-rip/exotic singularity/big-rip models by investigating their appropriate
Penrose diagrams. We show that the diagrams have the standard structure for the
big-bang and big-rip and that exotic singularities appear just as the constant
time hypersurfaces for the time of a singularity and because of their geodesic
completeness are potentially transversable. We also comment on some
applications and extensions of the Penrose diagram method in studying exotic
singularities.
| [
{
"created": "Sat, 2 Jun 2018 08:00:48 GMT",
"version": "v1"
},
{
"created": "Sat, 26 Oct 2019 13:35:00 GMT",
"version": "v2"
}
] | 2019-11-06 | [
[
"Dabrowski",
"Mariusz P.",
""
],
[
"Marosek",
"Konrad",
""
]
] | We study the conformal structure of exotic (non-big-bang) singularity universes using the hybrid big-bang/exotic singularity/big-bang and big-rip/exotic singularity/big-rip models by investigating their appropriate Penrose diagrams. We show that the diagrams have the standard structure for the big-bang and big-rip and that exotic singularities appear just as the constant time hypersurfaces for the time of a singularity and because of their geodesic completeness are potentially transversable. We also comment on some applications and extensions of the Penrose diagram method in studying exotic singularities. |
1501.01205 | Claus Gerhardt | Claus Gerhardt | A unified field theory I: The quantization of gravity | This paper has been published in ATMP 22 (2018) under the title "The
quantization of gravity". The title of the arXiv version, however, will
remain unchanged since it had been referred to under the original title in a
number of other papers | Adv. Their. Math. Phys. 22, 709--757 (2018) | 10.4310/ATMP.2018.v22.n3.a4 | null | gr-qc hep-th math-ph math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a former paper we proposed a model for the quantization of gravity by
working in a bundle $E$ where we realized the Hamilton constraint as the
Wheeler-DeWitt equation. However, the corresponding operator only acts in the
fibers and not in the base space. Therefore, we now discard the Wheeler-DeWitt
equation and express the Hamilton constraint differently, either with the help
of the Hamilton equations or by employing a geometric evolution equation. There
are two modifications possible which both are equivalent to the Hamilton
constraint and which lead to two new models. In the first model we obtain a
hyperbolic operator that acts in the fibers as well as in the base space and we
can construct a symplectic vector space and a Weyl system.
\nd In the second model the resulting equation is a wave equation in $\so
\times (0,\infty)$ valid in points $(x,t,\xi)$ in $E$ and we look for solutions
for each fixed $\xi$. This set of equations contains as a special case the
equation of a quantized cosmological Friedmann universe without matter but with
a cosmological constant, when we look for solutions which only depend on $t$.
Moreover, in case $\so$ is compact we prove a spectral resolution of the
equation.
| [
{
"created": "Mon, 5 Jan 2015 19:55:09 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Sep 2015 12:44:49 GMT",
"version": "v2"
},
{
"created": "Thu, 14 Jan 2016 20:02:34 GMT",
"version": "v3"
},
{
"created": "Thu, 5 Apr 2018 19:20:23 GMT",
"version": "v4"
},
{
"crea... | 2018-10-23 | [
[
"Gerhardt",
"Claus",
""
]
] | In a former paper we proposed a model for the quantization of gravity by working in a bundle $E$ where we realized the Hamilton constraint as the Wheeler-DeWitt equation. However, the corresponding operator only acts in the fibers and not in the base space. Therefore, we now discard the Wheeler-DeWitt equation and express the Hamilton constraint differently, either with the help of the Hamilton equations or by employing a geometric evolution equation. There are two modifications possible which both are equivalent to the Hamilton constraint and which lead to two new models. In the first model we obtain a hyperbolic operator that acts in the fibers as well as in the base space and we can construct a symplectic vector space and a Weyl system. \nd In the second model the resulting equation is a wave equation in $\so \times (0,\infty)$ valid in points $(x,t,\xi)$ in $E$ and we look for solutions for each fixed $\xi$. This set of equations contains as a special case the equation of a quantized cosmological Friedmann universe without matter but with a cosmological constant, when we look for solutions which only depend on $t$. Moreover, in case $\so$ is compact we prove a spectral resolution of the equation. |
1603.09670 | Diego S\'aez-G\'omez | Diego Saez-Gomez, C. Sofia Carvalho, Francisco S. N. Lobo and Ismael
Tereno | Constraining $f(T, \mathcal{T})$ gravity models using type Ia supernovae | 10 pages, 3 figures. Version published in PRD | Phys. Rev. D 94, 024034 (2016) | 10.1103/PhysRevD.94.024034 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an analysis of an $f(T, \mathcal{T})$ extension of the
Teleparallel Equivalent of General Relativity, where $T$ denotes the torsion
and $\mathcal{T}$ the trace of the energy-momentum tensor. This extension
includes non--minimal couplings between torsion and matter. In particular, we
construct two specific models that recover the usual continuity equation,
namely, $f(T, \mathcal{T})=T+g(\mathcal{T})$ and $f(T, \mathcal{T})=T\times
g(\mathcal{T})$. We then constrain the parameters of each model by fitting the
predicted distance modulus to that measured from type Ia supernovae, and find
that both models can reproduce the late--time cosmic acceleration. We also
observe that one of the models satisfies well the observational constraints and
yields a goodness--of--fit similar to the $\Lambda$CDM model, thus
demonstrating that $f(T,\mathcal{T})$ gravity theory encompasses viable models
that can be an alternative to $\Lambda$CDM.
| [
{
"created": "Tue, 29 Mar 2016 10:51:27 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Jul 2016 15:39:08 GMT",
"version": "v2"
}
] | 2016-07-27 | [
[
"Saez-Gomez",
"Diego",
""
],
[
"Carvalho",
"C. Sofia",
""
],
[
"Lobo",
"Francisco S. N.",
""
],
[
"Tereno",
"Ismael",
""
]
] | We present an analysis of an $f(T, \mathcal{T})$ extension of the Teleparallel Equivalent of General Relativity, where $T$ denotes the torsion and $\mathcal{T}$ the trace of the energy-momentum tensor. This extension includes non--minimal couplings between torsion and matter. In particular, we construct two specific models that recover the usual continuity equation, namely, $f(T, \mathcal{T})=T+g(\mathcal{T})$ and $f(T, \mathcal{T})=T\times g(\mathcal{T})$. We then constrain the parameters of each model by fitting the predicted distance modulus to that measured from type Ia supernovae, and find that both models can reproduce the late--time cosmic acceleration. We also observe that one of the models satisfies well the observational constraints and yields a goodness--of--fit similar to the $\Lambda$CDM model, thus demonstrating that $f(T,\mathcal{T})$ gravity theory encompasses viable models that can be an alternative to $\Lambda$CDM. |
2301.10795 | Dishant Pandya M | Rinkal Patel and B. S. Ratanpal, D. M. Pandya | New charged anisotropic solution on paraboloidal spacetime | 29 Pages, 12 Figures, 3 Tables | null | 10.1007/s10509-023-04213-2 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | New exact solutions of Einstein's field equations for charged stellar models
by assuming linear equation of state $ P_r=A(\rho-\rho_{a}) $, where $ P_r $ is
the radial pressure and $ \rho_{a} $ is the surface density. By assuming $
e^{\lambda} = 1+\frac{r^2}{R^2} $ for metric potential. The physical
acceptability conditions of the model are investigated, and the model is
compatible with several compact star candidates like 4U 1820-30, PSR J1903+327,
EXO 1785-248, Vela X-1, PSR J1614-2230, Cen X-3. A noteworthy feature of the
model is that it satisfies all the conditions needed for a physically
acceptable model.
| [
{
"created": "Wed, 25 Jan 2023 19:23:35 GMT",
"version": "v1"
}
] | 2023-07-26 | [
[
"Patel",
"Rinkal",
""
],
[
"Ratanpal",
"B. S.",
""
],
[
"Pandya",
"D. M.",
""
]
] | New exact solutions of Einstein's field equations for charged stellar models by assuming linear equation of state $ P_r=A(\rho-\rho_{a}) $, where $ P_r $ is the radial pressure and $ \rho_{a} $ is the surface density. By assuming $ e^{\lambda} = 1+\frac{r^2}{R^2} $ for metric potential. The physical acceptability conditions of the model are investigated, and the model is compatible with several compact star candidates like 4U 1820-30, PSR J1903+327, EXO 1785-248, Vela X-1, PSR J1614-2230, Cen X-3. A noteworthy feature of the model is that it satisfies all the conditions needed for a physically acceptable model. |
2205.04777 | Minyong Guo | Hu Zhu and Minyong Guo | Polarized image of synchrotron radiations of hotspots in
Schwarzschilld-Melvin black hole spacetime | 20 pages, 10 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We revisit the innermost stable circular orbits (ISCOs) of charged particles
and study the polarized images of synchrotron radiations emitted from such
orbiting hotspots on the equatorial plane in Schwarzchild-Melvin black hole
spacetime. We obtain a constraint on the magnetic field to retain ISCOs for
charged particles. In particular, we identify a critical value for the strength
of the magnetic field $B_c$ that the circular orbits can have positive and
negative angular momentums above $B_c$ while only one branch survive below
$B_c$. Furthermore, we investigate and discuss the primary and secondary images
of circularly orbiting charged hotspots carrying the information of
polarization directions observed by distant observers.
| [
{
"created": "Tue, 10 May 2022 09:56:31 GMT",
"version": "v1"
}
] | 2022-05-11 | [
[
"Zhu",
"Hu",
""
],
[
"Guo",
"Minyong",
""
]
] | We revisit the innermost stable circular orbits (ISCOs) of charged particles and study the polarized images of synchrotron radiations emitted from such orbiting hotspots on the equatorial plane in Schwarzchild-Melvin black hole spacetime. We obtain a constraint on the magnetic field to retain ISCOs for charged particles. In particular, we identify a critical value for the strength of the magnetic field $B_c$ that the circular orbits can have positive and negative angular momentums above $B_c$ while only one branch survive below $B_c$. Furthermore, we investigate and discuss the primary and secondary images of circularly orbiting charged hotspots carrying the information of polarization directions observed by distant observers. |
1406.7636 | Farhad Darabi | F. Darabi, Y. Heydarzade and F. Hajkarim | Stability of Einstein Static Universe over Lyra Geometry | 11 pages | Can. J. Phys. 93, 1566 (2015) | 10.1139/cjp-2015-0312 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The existence and stability conditions of Einstein static universe against
homogeneous scalar perturbations in the context of Lyra geometry is
investigated. The stability condition is obtained in terms of the constant
equation of state parameter $\omega=p/\rho$ depending on energy density
$\rho_0$ and scale factor $a_0$ of the initial Einstein static universe. Also,
the stability against vector and tensor perturbations is studied. It is shown
that a stable Einstein static universe can be found in the context of Lyra
geometry against scalar, vector and tensor perturbations for suitable range and
values of physical parameters.
| [
{
"created": "Mon, 30 Jun 2014 08:52:36 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Dec 2015 14:40:33 GMT",
"version": "v2"
}
] | 2023-07-19 | [
[
"Darabi",
"F.",
""
],
[
"Heydarzade",
"Y.",
""
],
[
"Hajkarim",
"F.",
""
]
] | The existence and stability conditions of Einstein static universe against homogeneous scalar perturbations in the context of Lyra geometry is investigated. The stability condition is obtained in terms of the constant equation of state parameter $\omega=p/\rho$ depending on energy density $\rho_0$ and scale factor $a_0$ of the initial Einstein static universe. Also, the stability against vector and tensor perturbations is studied. It is shown that a stable Einstein static universe can be found in the context of Lyra geometry against scalar, vector and tensor perturbations for suitable range and values of physical parameters. |
2401.07512 | Davide Batic | Davide Batic and Marek Nowakowski | Gravitational Collapse via Wheeler-DeWitt Equation | 14 pages, 2 figures | Ann. Phys. 2024, 461, 169579 | 10.1016/j.aop.2023.169579 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We analyze the Wheeler-DeWitt (WDW) equation in the context of a
gravitational collapse. The physics of an expanding/collapsing universe and
many details of a collapsing star can classically be described by the
Roberston-Walker metric in which the WDW equation takes the form of a
times-less Schr\"odinger equation. We set up the corresponding WDW potential
for the collapse and study the solutions of the wave function. The results show
that the central singularity appearing in classical general relativity is
avoided, the density is quantized in terms of the Planck density and the
expectation value of the scale factor exhibits a discrete behavior.
| [
{
"created": "Mon, 15 Jan 2024 07:27:35 GMT",
"version": "v1"
}
] | 2024-01-17 | [
[
"Batic",
"Davide",
""
],
[
"Nowakowski",
"Marek",
""
]
] | We analyze the Wheeler-DeWitt (WDW) equation in the context of a gravitational collapse. The physics of an expanding/collapsing universe and many details of a collapsing star can classically be described by the Roberston-Walker metric in which the WDW equation takes the form of a times-less Schr\"odinger equation. We set up the corresponding WDW potential for the collapse and study the solutions of the wave function. The results show that the central singularity appearing in classical general relativity is avoided, the density is quantized in terms of the Planck density and the expectation value of the scale factor exhibits a discrete behavior. |
2104.07533 | Alessandro Nagar | Gunnar Riemenschneider, Piero Rettegno, Matteo Breschi, Angelica
Albertini, Rossella Gamba, Sebastiano Bernuzzi and Alessandro Nagar | TEOBResumS: assessment of consistent next-to-quasicircular corrections
and post-adiabatic approximation in multipolar binary black holes waveforms | 13 pages, 11 figures, submitted to Phys. Rev. D | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The use of effective-one-body (EOB) waveforms for black hole binaries
analysis in gravitational-wave astronomy requires faithful models and fast
generation times. A key aspect to achieve faithfulness is the inclusion of
numerical-relativity (NR) informed next-to-quasicircular corrections(NQC),
dependent on the radial momentum, to the waveform and radiation reaction. A
robust method to speed up the waveform generation is the post-adiabatic
iteration to approximate the solution of the EOB Hamiltonian equations. In this
work, we assess the performances of a fast NQC prescription in combination to
the post-adiabatic method for generating multipolar gravitational waves. The
outlined approach allows a consistent treatment of NQC in both the waveform and
the radiation-reaction, does not require iterative procedures to achieve high
faithfulness, and can be efficiently employed for parameter estimation.
Comparing to 611 NR simulations, for total mass $10M_\odot\leq M \leq
200M_\odot$ and using the Advanded LIGO noise, the model has EOB/NR
unfaithfulness well below $0.01$, with 78.5\% of the cases below $0.001$. We
apply the model to the parameter estimation of GW150914 exploring the impact of
the new NQC and of the higher modes up to $\ell=m=8$.
| [
{
"created": "Thu, 15 Apr 2021 15:38:24 GMT",
"version": "v1"
},
{
"created": "Sat, 17 Apr 2021 05:12:19 GMT",
"version": "v2"
}
] | 2021-04-20 | [
[
"Riemenschneider",
"Gunnar",
""
],
[
"Rettegno",
"Piero",
""
],
[
"Breschi",
"Matteo",
""
],
[
"Albertini",
"Angelica",
""
],
[
"Gamba",
"Rossella",
""
],
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Nagar",
"Alessandr... | The use of effective-one-body (EOB) waveforms for black hole binaries analysis in gravitational-wave astronomy requires faithful models and fast generation times. A key aspect to achieve faithfulness is the inclusion of numerical-relativity (NR) informed next-to-quasicircular corrections(NQC), dependent on the radial momentum, to the waveform and radiation reaction. A robust method to speed up the waveform generation is the post-adiabatic iteration to approximate the solution of the EOB Hamiltonian equations. In this work, we assess the performances of a fast NQC prescription in combination to the post-adiabatic method for generating multipolar gravitational waves. The outlined approach allows a consistent treatment of NQC in both the waveform and the radiation-reaction, does not require iterative procedures to achieve high faithfulness, and can be efficiently employed for parameter estimation. Comparing to 611 NR simulations, for total mass $10M_\odot\leq M \leq 200M_\odot$ and using the Advanded LIGO noise, the model has EOB/NR unfaithfulness well below $0.01$, with 78.5\% of the cases below $0.001$. We apply the model to the parameter estimation of GW150914 exploring the impact of the new NQC and of the higher modes up to $\ell=m=8$. |
2112.07455 | Yunqi Liu | Cheng-Yong Zhang, Qian Chen, Yunqi Liu, Wen-Kun Luo, Yu Tian, Bin Wang | Critical phenomena in dynamical scalarization of charged black hole | Phys. Rev. Lett. 128, 161105 | null | 10.1103/PhysRevLett.128.161105 | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | We report a new black hole scalarization mechanism and disclose novel
dynamical critical phenomena in the process of the nonlinear accretion of the
scalar field into black holes. The accretion process can transform a seed black
hole into a final scalarized or bald black hole, depending on the initial
parameter of the scalar field $p$. There is a critical parameter $p_{\ast}$ and
near it all intermediate solutions are attracted to a critical solution and
stay there for a time scaling as $T\propto-\gamma\ln|p-p_{\ast}|$. At late
times, the solutions evolve into scalarized black holes if $p>p_{\ast}$, or
bald black holes if $p<p_{\ast}$. The final masses of the resulting
scalarized/bald black holes satisfy power-laws
$M_{p}-M_{\pm}\propto|p-p_{\ast}|^{\gamma_{\pm}}$ where $M_{\pm}$ are the
masses of the scalarized/bald black holes when $p\to p_\ast$ from above/below,
and $\gamma_{\pm}$ the corresponding exponents.
| [
{
"created": "Tue, 14 Dec 2021 15:12:46 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Jan 2022 01:48:54 GMT",
"version": "v2"
},
{
"created": "Mon, 4 Apr 2022 15:37:00 GMT",
"version": "v3"
},
{
"created": "Fri, 22 Apr 2022 14:30:59 GMT",
"version": "v4"
}
] | 2022-04-25 | [
[
"Zhang",
"Cheng-Yong",
""
],
[
"Chen",
"Qian",
""
],
[
"Liu",
"Yunqi",
""
],
[
"Luo",
"Wen-Kun",
""
],
[
"Tian",
"Yu",
""
],
[
"Wang",
"Bin",
""
]
] | We report a new black hole scalarization mechanism and disclose novel dynamical critical phenomena in the process of the nonlinear accretion of the scalar field into black holes. The accretion process can transform a seed black hole into a final scalarized or bald black hole, depending on the initial parameter of the scalar field $p$. There is a critical parameter $p_{\ast}$ and near it all intermediate solutions are attracted to a critical solution and stay there for a time scaling as $T\propto-\gamma\ln|p-p_{\ast}|$. At late times, the solutions evolve into scalarized black holes if $p>p_{\ast}$, or bald black holes if $p<p_{\ast}$. The final masses of the resulting scalarized/bald black holes satisfy power-laws $M_{p}-M_{\pm}\propto|p-p_{\ast}|^{\gamma_{\pm}}$ where $M_{\pm}$ are the masses of the scalarized/bald black holes when $p\to p_\ast$ from above/below, and $\gamma_{\pm}$ the corresponding exponents. |
2210.07971 | Laxmipriya Pati Miss | Laxmipriya Pati, Daniel Blixt and Maria-Jose Guzman | Hamilton's equations in the covariant teleparallel equivalent of general
relativity | 22 Pages, No figures | Physical Review D 107, 044071 (2023) | 10.1103/PhysRevD.107.044071 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We present Hamilton's equations for the teleparallel equivalent of general
relativity (TEGR), which is a reformulation of general relativity based on a
curvatureless, metric compatible, and torsionful connection. For this, we
consider the Hamiltonian for TEGR obtained through the vector, antisymmetric,
symmetric and trace-free, and trace irreducible decomposition of the phase
space variables. We present the Hamiltonian for TEGR in the covariant formalism
for the first time in the literature, by considering a spin connection
depending on Lorentz matrices. We introduce the mathematical formalism
necessary to compute Hamilton's equations in both Weitzenbock gauge and
covariant formulation, where for the latter we must introduce new fields:
Lorentz matrices and their associated momenta. We also derive explicit
relations between the conjugate momenta of the tetrad and the conjugate momenta
for the metric that are traditionally defined in GR, which are important to
compare both formalisms.
| [
{
"created": "Fri, 14 Oct 2022 17:10:07 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Mar 2023 08:44:31 GMT",
"version": "v2"
}
] | 2023-03-08 | [
[
"Pati",
"Laxmipriya",
""
],
[
"Blixt",
"Daniel",
""
],
[
"Guzman",
"Maria-Jose",
""
]
] | We present Hamilton's equations for the teleparallel equivalent of general relativity (TEGR), which is a reformulation of general relativity based on a curvatureless, metric compatible, and torsionful connection. For this, we consider the Hamiltonian for TEGR obtained through the vector, antisymmetric, symmetric and trace-free, and trace irreducible decomposition of the phase space variables. We present the Hamiltonian for TEGR in the covariant formalism for the first time in the literature, by considering a spin connection depending on Lorentz matrices. We introduce the mathematical formalism necessary to compute Hamilton's equations in both Weitzenbock gauge and covariant formulation, where for the latter we must introduce new fields: Lorentz matrices and their associated momenta. We also derive explicit relations between the conjugate momenta of the tetrad and the conjugate momenta for the metric that are traditionally defined in GR, which are important to compare both formalisms. |
2403.01436 | Shoichiro Miyashita | Shoichiro Miyashita | Thermodynamics of the 3-dimensional Einstein-Maxwell system | 18pages, 9 figures; v3: typos corrected; v2: the introduction
expanded, references and footnotes added, the implication of the result for
the thermodynamics of 3-dimensional gravity added to the abstract and the
conclusion | JHEP 06 (2024) 134 | 10.1007/JHEP06(2024)134 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Recently, I studied the thermodynamical properties of the Einstein-Maxwell
system with a box boundary in 4-dimensions [1](JHEP 04 (2024) 083). In this
paper, I investigate those in 3-dimensions using the zero-loop saddle-point
approximation and focusing only on a simple topology sector as usual. Similar
to the 4-dimensional case, the system is thermodynamically well-behaved when
$\Lambda<0$ (due to the contribution of the "bag of gold" saddles). However,
when $\Lambda=0$, a crucial difference to the 4-dimensional case appears, i.e.
the 3-dimensional system turns out to be thermodynamically unstable, while the
4-dimensional one is thermodynamically stable. This may offer two options for
how we think about the thermodynamics of 3-dimensional gravity with
$\Lambda=0$. One is that the zero-loop approximation or restricting the simple
topology sector is not sufficient for 3-dimensions with $\Lambda=0$. The other
is that 3-dimensional gravity is really thermodynamically unstable when
$\Lambda=0$.
| [
{
"created": "Sun, 3 Mar 2024 08:14:51 GMT",
"version": "v1"
},
{
"created": "Fri, 10 May 2024 02:57:03 GMT",
"version": "v2"
},
{
"created": "Thu, 20 Jun 2024 15:36:26 GMT",
"version": "v3"
}
] | 2024-06-21 | [
[
"Miyashita",
"Shoichiro",
""
]
] | Recently, I studied the thermodynamical properties of the Einstein-Maxwell system with a box boundary in 4-dimensions [1](JHEP 04 (2024) 083). In this paper, I investigate those in 3-dimensions using the zero-loop saddle-point approximation and focusing only on a simple topology sector as usual. Similar to the 4-dimensional case, the system is thermodynamically well-behaved when $\Lambda<0$ (due to the contribution of the "bag of gold" saddles). However, when $\Lambda=0$, a crucial difference to the 4-dimensional case appears, i.e. the 3-dimensional system turns out to be thermodynamically unstable, while the 4-dimensional one is thermodynamically stable. This may offer two options for how we think about the thermodynamics of 3-dimensional gravity with $\Lambda=0$. One is that the zero-loop approximation or restricting the simple topology sector is not sufficient for 3-dimensions with $\Lambda=0$. The other is that 3-dimensional gravity is really thermodynamically unstable when $\Lambda=0$. |
1508.06859 | Adam Solomon | Adam R. Solomon | Cosmology Beyond Einstein | PhD thesis, University of Cambridge, April 2015. 301 pages, 20
figures | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The accelerating expansion of the Universe poses a major challenge to our
understanding of fundamental physics. One promising avenue is to modify general
relativity and obtain a new description of the gravitational force. Because
gravitation dominates the other forces mostly on large scales, cosmological
probes provide an ideal testing ground for theories of gravity. In this thesis,
we describe two complementary approaches to the problem of testing gravity
using cosmology.
In the first part, we discuss the cosmological solutions of massive gravity
and its generalisation to a bimetric theory. These theories describe a graviton
with a small mass, and can potentially explain the late-time acceleration in a
technically-natural way. We describe these self-accelerating solutions and
investigate the cosmological perturbations in depth, beginning with an
investigation of their linear stability, followed by the construction of a
method for solving these perturbations in the quasistatic limit. This allows
the predictions of stable bimetric models to be compared to observations of
structure formation. Next, we discuss prospects for theories in which matter
"doubly couples" to both metrics, and examine the cosmological expansion
history in both massive gravity and bigravity with a specific double coupling
which is ghost-free at low energies.
In the second and final part, we study the consequences of Lorentz violation
during inflation. We consider Einstein-aether theory, in which a vector field
spontaneously breaks Lorentz symmetry and couples nonminimally to the metric,
and allow the vector to couple in a general way to a scalar field. Specialising
to inflation, we discuss the slow-roll solutions in background and at the
perturbative level. The system exhibits a severe instability which places
constraints on such a vector-scalar coupling to be at least five orders of
magnitude stronger [...]
| [
{
"created": "Tue, 25 Aug 2015 20:06:31 GMT",
"version": "v1"
}
] | 2015-08-28 | [
[
"Solomon",
"Adam R.",
""
]
] | The accelerating expansion of the Universe poses a major challenge to our understanding of fundamental physics. One promising avenue is to modify general relativity and obtain a new description of the gravitational force. Because gravitation dominates the other forces mostly on large scales, cosmological probes provide an ideal testing ground for theories of gravity. In this thesis, we describe two complementary approaches to the problem of testing gravity using cosmology. In the first part, we discuss the cosmological solutions of massive gravity and its generalisation to a bimetric theory. These theories describe a graviton with a small mass, and can potentially explain the late-time acceleration in a technically-natural way. We describe these self-accelerating solutions and investigate the cosmological perturbations in depth, beginning with an investigation of their linear stability, followed by the construction of a method for solving these perturbations in the quasistatic limit. This allows the predictions of stable bimetric models to be compared to observations of structure formation. Next, we discuss prospects for theories in which matter "doubly couples" to both metrics, and examine the cosmological expansion history in both massive gravity and bigravity with a specific double coupling which is ghost-free at low energies. In the second and final part, we study the consequences of Lorentz violation during inflation. We consider Einstein-aether theory, in which a vector field spontaneously breaks Lorentz symmetry and couples nonminimally to the metric, and allow the vector to couple in a general way to a scalar field. Specialising to inflation, we discuss the slow-roll solutions in background and at the perturbative level. The system exhibits a severe instability which places constraints on such a vector-scalar coupling to be at least five orders of magnitude stronger [...] |
gr-qc/0306018 | Gilles Esposito-Farese | Gilles Esposito-Farese | Scalar-tensor theories and cosmology | 8 pages, 2 figures, uses "moriond.sty", contribution to the XXXVIIIth
Rencontres de Moriond on Gravitational Waves and Experimental Gravity, Les
Arcs (France), March 23-29 2003 | Proceedings The Gioi Publishers (Vietnam, 2003) p. 427 | null | null | gr-qc astro-ph | null | Scalar-tensor theories are the best motivated alternatives to general
relativity and provide a mathematically consistent framework to test the
various observable predictions. They can involve three functions of the scalar
field: (i) a potential (as in "quintessence" models), (ii) a matter-scalar
coupling function (as in "extended quintessence", where it may also be
rewritten as a nonminimal coupling of the scalar field to the scalar
curvature), and (iii) a coupling function of the scalar field to the
Gauss-Bonnet topological invariant. We recall the main experimental constraints
on this class of theories, and underline that solar-system, binary-pulsar, and
cosmological observations give qualitatively different tests. We finally show
that the combination of these data is necessary to constrain the existence of a
scalar-Gauss-Bonnet coupling.
| [
{
"created": "Wed, 4 Jun 2003 14:04:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Esposito-Farese",
"Gilles",
""
]
] | Scalar-tensor theories are the best motivated alternatives to general relativity and provide a mathematically consistent framework to test the various observable predictions. They can involve three functions of the scalar field: (i) a potential (as in "quintessence" models), (ii) a matter-scalar coupling function (as in "extended quintessence", where it may also be rewritten as a nonminimal coupling of the scalar field to the scalar curvature), and (iii) a coupling function of the scalar field to the Gauss-Bonnet topological invariant. We recall the main experimental constraints on this class of theories, and underline that solar-system, binary-pulsar, and cosmological observations give qualitatively different tests. We finally show that the combination of these data is necessary to constrain the existence of a scalar-Gauss-Bonnet coupling. |
1803.03246 | Clement Delcamp | Clement Delcamp, Laurent Freidel, Florian Girelli | Dual loop quantizations of 3d gravity | 33 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The loop quantization of 3d gravity consists in defining the Hilbert space of
states satisfying the Gau{\ss} constraint and the flatness constraint. The
Gau{\ss} constraint is enforced at the kinematical level by introducing spin
networks which form a basis for the Hilbert space of gauge invariant
functionals. The flatness constraint is implemented at the dynamical level via
the Ponzano-Regge state-sum model. We propose in this work a dual loop
quantization scheme where the role of the constraints is exchanged. The
flatness constraint is imposed first via the introduction of a new basis
labeled by group variables, while the Gau{\ss} constraint is implemented
dynamically using a projector which is related to the Dijkgraaf-Witten model.
We discuss how this alternative quantization program is related to 3d
teleparallel gravity.
| [
{
"created": "Thu, 8 Mar 2018 18:40:41 GMT",
"version": "v1"
}
] | 2018-03-09 | [
[
"Delcamp",
"Clement",
""
],
[
"Freidel",
"Laurent",
""
],
[
"Girelli",
"Florian",
""
]
] | The loop quantization of 3d gravity consists in defining the Hilbert space of states satisfying the Gau{\ss} constraint and the flatness constraint. The Gau{\ss} constraint is enforced at the kinematical level by introducing spin networks which form a basis for the Hilbert space of gauge invariant functionals. The flatness constraint is implemented at the dynamical level via the Ponzano-Regge state-sum model. We propose in this work a dual loop quantization scheme where the role of the constraints is exchanged. The flatness constraint is imposed first via the introduction of a new basis labeled by group variables, while the Gau{\ss} constraint is implemented dynamically using a projector which is related to the Dijkgraaf-Witten model. We discuss how this alternative quantization program is related to 3d teleparallel gravity. |
1009.6064 | Azad Akhter Siddiqui Professor | Azad A. Siddiqui | Foliation of the Kottler-Schwarzschild-De Sitter Spacetime by Flat
Spacelike Hypersurfaces | 12 pages, 4 figures | Gen.Rel.Grav.43:1189-1196,2011 | 10.1007/s10714-010-1064-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There exist Kruskal like coordinates for the Reissner-Nordstrom (RN) black
hole spacetime which are regular at coordinate singularities. Non existence of
such coordinates for the extreme RN black hole spacetime has already been
shown. Also the Carter coordinates available for the extreme case are not
manifestly regular at the coordinate singularity, therefore, a numerical
procedure was developed to obtain free fall geodesics and flat foliation for
the extreme RN black hole spacetime. The Kottler-Schwarzschild-de Sitter
(KSSdS) spacetime geometry is similar to the RN geometry in the sense that,
like the RN case, there exist non-singular coordinates when there are two
distinct coordinate singularities. There are no manifestly regular coordinates
for the extreme KSSdS case. In this paper foliation of all the cases of the
KSSdS spacetime by flat spacelike hypersurfaces is obtained by introducing a
non-singular time coordinate.
| [
{
"created": "Thu, 30 Sep 2010 08:31:00 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Nov 2011 07:23:57 GMT",
"version": "v2"
}
] | 2011-12-01 | [
[
"Siddiqui",
"Azad A.",
""
]
] | There exist Kruskal like coordinates for the Reissner-Nordstrom (RN) black hole spacetime which are regular at coordinate singularities. Non existence of such coordinates for the extreme RN black hole spacetime has already been shown. Also the Carter coordinates available for the extreme case are not manifestly regular at the coordinate singularity, therefore, a numerical procedure was developed to obtain free fall geodesics and flat foliation for the extreme RN black hole spacetime. The Kottler-Schwarzschild-de Sitter (KSSdS) spacetime geometry is similar to the RN geometry in the sense that, like the RN case, there exist non-singular coordinates when there are two distinct coordinate singularities. There are no manifestly regular coordinates for the extreme KSSdS case. In this paper foliation of all the cases of the KSSdS spacetime by flat spacelike hypersurfaces is obtained by introducing a non-singular time coordinate. |
gr-qc/0305040 | Bahram Mashhoon | Bahram Mashhoon | Nonlocality of Accelerated Systems | LaTeX file, no figures, 9 pages, to appear in: "Black Holes,
Gravitational Waves and Cosmology" (World Scientific, Singapore, 2003) | Int.J.Mod.Phys. D14 (2005) 171-179 | 10.1142/S0218271805005864 | null | gr-qc astro-ph | null | The conceptual basis for the nonlocality of accelerated systems is presented.
The nonlocal theory of accelerated observers and its consequences are briefly
described. Nonlocal field equations are developed for the case of the
electrodynamics of linearly accelerated systems.
| [
{
"created": "Sun, 11 May 2003 20:18:50 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Mashhoon",
"Bahram",
""
]
] | The conceptual basis for the nonlocality of accelerated systems is presented. The nonlocal theory of accelerated observers and its consequences are briefly described. Nonlocal field equations are developed for the case of the electrodynamics of linearly accelerated systems. |
1004.1989 | Stefan Liebscher | Stefan Liebscher, J\"org H\"arterich, Kevin Webster, Marc Georgi | Ancient Dynamics in Bianchi Models: Approach to Periodic Cycles | Minor corrections and clarifications throughout the text, according
to referee's suggestions | Commun.Math.Phys.305:59-83,2011 | 10.1007/s00220-011-1248-3 | null | gr-qc math.DS | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider cosmological models of Bianchi type. In particular, we are
interested in the alpha-limit dynamics near the Kasner circle of equilibria for
Bianchi classes VIII and IX. They correspond to cosmological models close to
the big-bang singularity.
We prove the existence of a codimension-one family of solutions that limit,
for t to negative infinity, onto a heteroclinic 3-cycle to the Kasner circle of
equilibria. The theory extends to arbitrary heteroclinic chains that are
uniformly bounded away from the three critical Taub points on the Kasner
circle, in particular to all closed heteroclinic cycles of the Kasner map.
| [
{
"created": "Mon, 12 Apr 2010 15:32:05 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Apr 2010 09:15:15 GMT",
"version": "v2"
},
{
"created": "Wed, 20 Oct 2010 16:43:47 GMT",
"version": "v3"
}
] | 2011-05-18 | [
[
"Liebscher",
"Stefan",
""
],
[
"Härterich",
"Jörg",
""
],
[
"Webster",
"Kevin",
""
],
[
"Georgi",
"Marc",
""
]
] | We consider cosmological models of Bianchi type. In particular, we are interested in the alpha-limit dynamics near the Kasner circle of equilibria for Bianchi classes VIII and IX. They correspond to cosmological models close to the big-bang singularity. We prove the existence of a codimension-one family of solutions that limit, for t to negative infinity, onto a heteroclinic 3-cycle to the Kasner circle of equilibria. The theory extends to arbitrary heteroclinic chains that are uniformly bounded away from the three critical Taub points on the Kasner circle, in particular to all closed heteroclinic cycles of the Kasner map. |
1503.01417 | Gabriel Leon | Gabriel Leon and Daniel Sudarsky | Origin of structure: Statistical characterization of the primordial
density fluctuations and the collapse of the wave function | 24 pages, 3 figures. Minor corrections, accepted for publication in
JCAP. arXiv admin note: substantial text overlap with arXiv:1312.7590 | JCAP 06(2015)020 | 10.1088/1475-7516/2015/06/020 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The statistical properties of the primordial density perturbations has been
considered in the past decade as a powerful probe of the physical processes
taking place in the early universe. Within the inflationary paradigm, the
properties of the bispectrum are one of the keys that serves to discriminate
among competing scenarios concerning the details of the origin of cosmological
perturbations. However, all of the scenarios, based on the conventional
approach to the so-called "quantum-to-classical transition" during inflation,
lack the ability to point out the precise physical mechanism responsible for
generating the inhomogeneity and anisotropy of our universe starting from and
exactly homogeneous and isotropic vacuum state associated with the early
inflationary regime. In past works, we have shown that the proposals involving
a spontaneous dynamical reduction of the quantum state provide plausible
explanations for the birth of said primordial inhomogeneities and anisotropies.
In the present manuscript we show that, when considering within the context of
such proposals, the characterization of the spectrum and bispectrum turn out to
be quite different from those found in the traditional approach, and in
particular, some of the statistical features, must be treated in a different
way leading to some rather different conclusions.
| [
{
"created": "Wed, 4 Mar 2015 18:59:34 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Jun 2015 22:31:17 GMT",
"version": "v2"
}
] | 2015-06-15 | [
[
"Leon",
"Gabriel",
""
],
[
"Sudarsky",
"Daniel",
""
]
] | The statistical properties of the primordial density perturbations has been considered in the past decade as a powerful probe of the physical processes taking place in the early universe. Within the inflationary paradigm, the properties of the bispectrum are one of the keys that serves to discriminate among competing scenarios concerning the details of the origin of cosmological perturbations. However, all of the scenarios, based on the conventional approach to the so-called "quantum-to-classical transition" during inflation, lack the ability to point out the precise physical mechanism responsible for generating the inhomogeneity and anisotropy of our universe starting from and exactly homogeneous and isotropic vacuum state associated with the early inflationary regime. In past works, we have shown that the proposals involving a spontaneous dynamical reduction of the quantum state provide plausible explanations for the birth of said primordial inhomogeneities and anisotropies. In the present manuscript we show that, when considering within the context of such proposals, the characterization of the spectrum and bispectrum turn out to be quite different from those found in the traditional approach, and in particular, some of the statistical features, must be treated in a different way leading to some rather different conclusions. |
2208.11615 | En-Kun Li | Jun Cheng, En-Kun Li, Yi-Ming Hu, Zheng-Cheng Liang, Jian-dong Zhang,
Jianwei Mei | Detecting the stochastic gravitational wave background with the TianQin
detector | 28 pages, 8 figures | null | 10.1103/PhysRevD.106.124027 | null | gr-qc astro-ph.CO astro-ph.IM | http://creativecommons.org/licenses/by/4.0/ | The detection of stochastic gravitational wave background (SGWB) is among the
leading scientific goals of the space-borne gravitational wave observatory,
which would have significant impact on astrophysics and fundamental physics. In
this work, we developed a data analysis software, \texttt{TQSGWB}, which can
extract isotropic SGWB using the Bayes analysis method based on the TianQin
detector. We find that for the noise cross spectrum, there are imaginary
components and they play an important role in breaking the degeneracy of the
position noise in the common laser link. When the imaginary corrections are
considered, the credible regions of the position noise parameters are reduced
by two orders of magnitude. We demonstrate that the parameters of various
signals and instrumental noise could be estimated directly in the absence of a
Galactic confusion foreground through Markov chain Monte Carlo sampling. With
only a three-month observation, we find that TianQin could be able to
confidently detect SGWBs with energy density as low as $\Omega_{\rm PL} = 1.3
\times 10^{-12}$, $\Omega_{\rm Flat} = 6.0 \times 10^{-12}$, and $\Omega_{\rm
SP} = 9.0 \times 10^{-12}$, for power-law, flat, and single-peak models
respectively.
| [
{
"created": "Wed, 24 Aug 2022 15:36:02 GMT",
"version": "v1"
},
{
"created": "Sun, 4 Dec 2022 15:32:12 GMT",
"version": "v2"
}
] | 2023-01-04 | [
[
"Cheng",
"Jun",
""
],
[
"Li",
"En-Kun",
""
],
[
"Hu",
"Yi-Ming",
""
],
[
"Liang",
"Zheng-Cheng",
""
],
[
"Zhang",
"Jian-dong",
""
],
[
"Mei",
"Jianwei",
""
]
] | The detection of stochastic gravitational wave background (SGWB) is among the leading scientific goals of the space-borne gravitational wave observatory, which would have significant impact on astrophysics and fundamental physics. In this work, we developed a data analysis software, \texttt{TQSGWB}, which can extract isotropic SGWB using the Bayes analysis method based on the TianQin detector. We find that for the noise cross spectrum, there are imaginary components and they play an important role in breaking the degeneracy of the position noise in the common laser link. When the imaginary corrections are considered, the credible regions of the position noise parameters are reduced by two orders of magnitude. We demonstrate that the parameters of various signals and instrumental noise could be estimated directly in the absence of a Galactic confusion foreground through Markov chain Monte Carlo sampling. With only a three-month observation, we find that TianQin could be able to confidently detect SGWBs with energy density as low as $\Omega_{\rm PL} = 1.3 \times 10^{-12}$, $\Omega_{\rm Flat} = 6.0 \times 10^{-12}$, and $\Omega_{\rm SP} = 9.0 \times 10^{-12}$, for power-law, flat, and single-peak models respectively. |
1601.01072 | Atsushi Nishizawa | Atsushi Nishizawa | Constraining the propagation speed of gravitational waves with compact
binaries at cosmological distances | 9 pages, 9 figures | Phys. Rev. D 93, 124036 (2016) | 10.1103/PhysRevD.93.124036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In testing gravity a model-independent way, one of crucial tests is measuring
the propagation speed of a gravitational wave (GW). In general relativity, a GW
propagates with the speed of light, while in the alternative theories of
gravity the propagation speed could deviate from the speed of light due to the
modification of gravity or spacetime structure at a quantum level. Previously
we proposed the method measuring the GW speed by directly comparing the arrival
times between a GW and a photon from the binary merger of neutron stars or
neutron star and black hole, assuming that it is associated with a short
gamma-ray burst. The sensitivity is limited by the intrinsic time delay between
a GW and a photon at the source. In this paper, we extend the method to
distinguish the intrinsic time delay from the true signal caused by anomalous
GW speed with multiple events at cosmological distances, also considering the
redshift distribution of GW sources, redshift-dependent GW propagation speed,
and the statistics of intrinsic time delays. We show that an advanced GW
detector such as Einstein Telescope will constrain the GW propagation speed at
the precision of ~10^{-16}. We also discuss the optimal statistic to measure
the GW speed, performing numerical simulations.
| [
{
"created": "Wed, 6 Jan 2016 03:43:26 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Feb 2016 03:55:05 GMT",
"version": "v2"
}
] | 2016-06-22 | [
[
"Nishizawa",
"Atsushi",
""
]
] | In testing gravity a model-independent way, one of crucial tests is measuring the propagation speed of a gravitational wave (GW). In general relativity, a GW propagates with the speed of light, while in the alternative theories of gravity the propagation speed could deviate from the speed of light due to the modification of gravity or spacetime structure at a quantum level. Previously we proposed the method measuring the GW speed by directly comparing the arrival times between a GW and a photon from the binary merger of neutron stars or neutron star and black hole, assuming that it is associated with a short gamma-ray burst. The sensitivity is limited by the intrinsic time delay between a GW and a photon at the source. In this paper, we extend the method to distinguish the intrinsic time delay from the true signal caused by anomalous GW speed with multiple events at cosmological distances, also considering the redshift distribution of GW sources, redshift-dependent GW propagation speed, and the statistics of intrinsic time delays. We show that an advanced GW detector such as Einstein Telescope will constrain the GW propagation speed at the precision of ~10^{-16}. We also discuss the optimal statistic to measure the GW speed, performing numerical simulations. |
1302.2198 | K G Arun | K G Arun, Archana Pai | Tests of General Relativity and Alternative theories of gravity using
Gravitational Wave observations | Invited Review to International Journal of Modern Physics D (based on
a talk in ASTROD symposium, Bangalore) | International Journal of Modern Physics D, Vol. 22, 1341012 (2013) | 10.1142/S0218271813410125 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational Wave (GW) observations of coalescing compact binaries will be
unique probes of strong-field, dynamical aspects of relativistic gravity. We
present a short review of various schemes proposed in the literature to test
General Relativity (GR) and alternative theories of gravity using inspiral
waveforms. Broadly these schemes may be classified into two types: model
dependent and model independent. In the model dependent category, GW
observations are compared against a specific waveform model representative of a
particular theory or a class of theories like Scalar-Tensor theories, Dynamical
Chern-Simons theory and Massive graviton theories. Model independent tests are
attempts to write down a parametrised gravitational waveform where the free
parameters take different values for different theories and (at least some of)
which can be constrained by GW observations. We revisit some of the proposed
bounds in the case of downscaled LISA configuration (eLISA) and compare them
with the original LISA configuration. We also compare the expected bounds on
alternative theories of gravity from ground-based and space-based detectors and
find that space-based GW detectors can test GR and other theories of gravity
with unprecedented accuracies. We then focus on a recent proposal to use
singular value decomposition (SVD) of the Fisher information matrix to improve
the accuracies with which Post-Newtonian (PN) theory can be tested. We extend
those results to the case of space based detector eLISA and discuss its
implications.
| [
{
"created": "Sat, 9 Feb 2013 05:40:18 GMT",
"version": "v1"
}
] | 2015-06-15 | [
[
"Arun",
"K G",
""
],
[
"Pai",
"Archana",
""
]
] | Gravitational Wave (GW) observations of coalescing compact binaries will be unique probes of strong-field, dynamical aspects of relativistic gravity. We present a short review of various schemes proposed in the literature to test General Relativity (GR) and alternative theories of gravity using inspiral waveforms. Broadly these schemes may be classified into two types: model dependent and model independent. In the model dependent category, GW observations are compared against a specific waveform model representative of a particular theory or a class of theories like Scalar-Tensor theories, Dynamical Chern-Simons theory and Massive graviton theories. Model independent tests are attempts to write down a parametrised gravitational waveform where the free parameters take different values for different theories and (at least some of) which can be constrained by GW observations. We revisit some of the proposed bounds in the case of downscaled LISA configuration (eLISA) and compare them with the original LISA configuration. We also compare the expected bounds on alternative theories of gravity from ground-based and space-based detectors and find that space-based GW detectors can test GR and other theories of gravity with unprecedented accuracies. We then focus on a recent proposal to use singular value decomposition (SVD) of the Fisher information matrix to improve the accuracies with which Post-Newtonian (PN) theory can be tested. We extend those results to the case of space based detector eLISA and discuss its implications. |
1111.3535 | Thomas Cailleteau Mr | Thomas Cailleteau, Jakub Mielczarek, Aurelien Barrau and Julien Grain | Anomaly-free scalar perturbations with holonomy corrections in loop
quantum cosmology | 19 pages, 1 figure, v2, new comments and references added, minor
corrections | Class.Quantum Grav. 29 095010 2012 | 10.1088/0264-9381/29/9/095010 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Holonomy corrections to scalar perturbations are investigated in the loop
quantum cosmology framework. Due to the effective approach, modifications of
the algebra of constraints generically lead to anomalies. In order to remove
those anomalies, counter-terms are introduced. We find a way to explicitly
fulfill the conditions for anomaly freedom and we give explicit expressions for
the counter-terms. Surprisingly, the "new quantization scheme" naturally arises
in this procedure. The gauge invariant variables are found and equations of
motion for the anomaly-free scalar perturbations are derived. Finally, some
cosmological consequences are discussed qualitatively.
| [
{
"created": "Tue, 15 Nov 2011 14:35:03 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Dec 2011 09:32:39 GMT",
"version": "v2"
}
] | 2012-11-01 | [
[
"Cailleteau",
"Thomas",
""
],
[
"Mielczarek",
"Jakub",
""
],
[
"Barrau",
"Aurelien",
""
],
[
"Grain",
"Julien",
""
]
] | Holonomy corrections to scalar perturbations are investigated in the loop quantum cosmology framework. Due to the effective approach, modifications of the algebra of constraints generically lead to anomalies. In order to remove those anomalies, counter-terms are introduced. We find a way to explicitly fulfill the conditions for anomaly freedom and we give explicit expressions for the counter-terms. Surprisingly, the "new quantization scheme" naturally arises in this procedure. The gauge invariant variables are found and equations of motion for the anomaly-free scalar perturbations are derived. Finally, some cosmological consequences are discussed qualitatively. |
2309.14270 | Ivan Avramidi | Ivan G. Avramidi and Roberto Niardi | MOND via Matrix Gravity | 31 pages, minor corrections | null | null | null | gr-qc astro-ph.GA | http://creativecommons.org/licenses/by/4.0/ | MOND theory has arisen as a promising alternative to dark matter in
explaining the collection of discrepancies that constitute the so-called
missing mass problem. The MOND paradigm is briefly reviewed. It is shown that
MOND theory can be incorporated in the framework of the recently proposed
Matrix Gravity. In particular, we demonstrate that Matrix Gravity contains MOND
as a particular case, which adds to the validity of Matrix Gravity and proves
it is deserving of further inquiry.
| [
{
"created": "Mon, 25 Sep 2023 16:30:26 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Sep 2023 05:20:28 GMT",
"version": "v2"
},
{
"created": "Fri, 16 Feb 2024 16:43:02 GMT",
"version": "v3"
}
] | 2024-02-19 | [
[
"Avramidi",
"Ivan G.",
""
],
[
"Niardi",
"Roberto",
""
]
] | MOND theory has arisen as a promising alternative to dark matter in explaining the collection of discrepancies that constitute the so-called missing mass problem. The MOND paradigm is briefly reviewed. It is shown that MOND theory can be incorporated in the framework of the recently proposed Matrix Gravity. In particular, we demonstrate that Matrix Gravity contains MOND as a particular case, which adds to the validity of Matrix Gravity and proves it is deserving of further inquiry. |
gr-qc/0211044 | Mauricio Bellini | Mauricio Bellini (IFM, Michoacana University) | Fresh inflation with increasing cosmological parameter | 5 pages, 5 figures (accepted in Phys. Rev. D) | Phys.Rev. D67 (2003) 027303 | 10.1103/PhysRevD.67.027303 | null | gr-qc hep-ph | null | I study a fresh inflationary model with an increasing F-cosmological
parameter. The model provides sufficiently e-folds to solve the
flatness/horizon problem and the density fluctuations agree with experimental
values. The temperature increases during fresh inflation and reach its maximum
value when inflation ends. I find that entropy perturbations always remain
below $10^{-4}$ during fresh inflation and become negligible when fresh
inflation ends. Hence, the adiabatic fluctuations dominate the primordial
spectrum at the end of fresh inflation.
| [
{
"created": "Tue, 12 Nov 2002 17:15:34 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Nov 2002 00:27:26 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Bellini",
"Mauricio",
"",
"IFM, Michoacana University"
]
] | I study a fresh inflationary model with an increasing F-cosmological parameter. The model provides sufficiently e-folds to solve the flatness/horizon problem and the density fluctuations agree with experimental values. The temperature increases during fresh inflation and reach its maximum value when inflation ends. I find that entropy perturbations always remain below $10^{-4}$ during fresh inflation and become negligible when fresh inflation ends. Hence, the adiabatic fluctuations dominate the primordial spectrum at the end of fresh inflation. |
gr-qc/0211093 | Stoytcho Yazadjiev | Stoytcho S. Yazadjiev (Sofia University) | A class of homogeneous scalar-tensor cosmologies with a radiation fluid | 7 pages, LaTex; v2 type mistakes corrected, comments added | Mod.Phys.Lett. A18 (2003) 1967-1974 | 10.1142/S0217732303011824 | null | gr-qc | null | We present a new class of exact homogeneous cosmological solutions with a
radiation fluid for all scalar-tensor theories. The solutions belong to Bianchi
type $VI_{h}$ cosmologies. Explicit examples of nonsingular homogeneous
scalar-tensor cosmologies are also given.
| [
{
"created": "Wed, 27 Nov 2002 12:52:03 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Jan 2003 07:06:06 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Yazadjiev",
"Stoytcho S.",
"",
"Sofia University"
]
] | We present a new class of exact homogeneous cosmological solutions with a radiation fluid for all scalar-tensor theories. The solutions belong to Bianchi type $VI_{h}$ cosmologies. Explicit examples of nonsingular homogeneous scalar-tensor cosmologies are also given. |
1901.09273 | Damiano Anselmi | Damiano Anselmi | Fakeons and the classicization of quantum gravity: the FLRW metric | 27 pages, 3 figures; v2: typos corrected and refs. updated, JHEP | J. High Energy Phys. 04 (2019) 61 | 10.1007/JHEP04(2019)061 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Under certain assumptions, it is possible to make sense of higher derivative
theories by quantizing the unwanted degrees of freedom as fakeons, which are
later projected away. Then the true classical limit is obtained by classicizing
the quantum theory. Since quantum field theory is formulated perturbatively,
the classicization is also perturbative. After deriving a number of properties
in a general setting, we consider the theory of quantum gravity that emerges
from the fakeon idea and study its classicization, focusing on the FLRW metric.
We point out cases where the fakeon projection can be handled exactly, which
include radiation, the vacuum energy density and the combination of the two,
and cases where it cannot, which include dust. Generically, the classical limit
shares many features with the quantum theory it comes from, including the
impossibility to write down complete, "exact" field equations, to the extent
that asymptotic series and nonperturbative effects come into play.
| [
{
"created": "Sat, 26 Jan 2019 20:08:38 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Apr 2019 15:12:58 GMT",
"version": "v2"
}
] | 2019-04-10 | [
[
"Anselmi",
"Damiano",
""
]
] | Under certain assumptions, it is possible to make sense of higher derivative theories by quantizing the unwanted degrees of freedom as fakeons, which are later projected away. Then the true classical limit is obtained by classicizing the quantum theory. Since quantum field theory is formulated perturbatively, the classicization is also perturbative. After deriving a number of properties in a general setting, we consider the theory of quantum gravity that emerges from the fakeon idea and study its classicization, focusing on the FLRW metric. We point out cases where the fakeon projection can be handled exactly, which include radiation, the vacuum energy density and the combination of the two, and cases where it cannot, which include dust. Generically, the classical limit shares many features with the quantum theory it comes from, including the impossibility to write down complete, "exact" field equations, to the extent that asymptotic series and nonperturbative effects come into play. |
1910.13217 | Avadhut Purohit | Avadhut V. Purohit | The status of geometry and matter in re-interpreted WdW equation | 6 pages | Phys. Sci. Forum 2023, 7(1), 37 | 10.3390/ECU2023-14097 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I have shown that the field defined by the Wheeler-DeWitt equation for
\textit{pure gravity} is neither a standard gravitational field nor the field
representing a particular universe. The theory offers a unified description of
geometry and matter, with geometry being fundamental. The quantum theory
possesses gravitational decoherence when the signature of $R^{(3)}$ changes.
The quantum theory resolves singularities dynamically. Application to the FLRW
$\kappa=0$ shows the creation of local geometries during quantum evolution. The
3-metric gets modified near the classical singularity in the case of the
Schwarzschild geometry.
| [
{
"created": "Tue, 29 Oct 2019 11:57:03 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Jul 2021 05:22:07 GMT",
"version": "v2"
},
{
"created": "Mon, 16 May 2022 12:47:14 GMT",
"version": "v3"
},
{
"created": "Wed, 27 Sep 2023 09:42:07 GMT",
"version": "v4"
}
] | 2023-09-28 | [
[
"Purohit",
"Avadhut V.",
""
]
] | I have shown that the field defined by the Wheeler-DeWitt equation for \textit{pure gravity} is neither a standard gravitational field nor the field representing a particular universe. The theory offers a unified description of geometry and matter, with geometry being fundamental. The quantum theory possesses gravitational decoherence when the signature of $R^{(3)}$ changes. The quantum theory resolves singularities dynamically. Application to the FLRW $\kappa=0$ shows the creation of local geometries during quantum evolution. The 3-metric gets modified near the classical singularity in the case of the Schwarzschild geometry. |
2108.04702 | Xiang-Hua Zhai | Rui Jiang, Rui-Hui Lin and Xiang-Hua Zhai | Superradiant instability of the Kerr-like black hole in
Einstein-bumblebee gravity | 18 pages, 3 figures, 1 table, version accepted for publication in
Physical Review D | null | 10.1103/PhysRevD.104.124004 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An exact Kerr-like solution has been obtained recently in Einstein-bumblebee
gravity model where Lorentz symmetry is spontaneously broken. In this paper, we
investigate the superradiant instability of the Kerr-like black hole under the
perturbation of a massive scalar field. We find the Lorentz breaking parameter
$L$ does not affect the superradiance regime or the regime of the bound states.
However, since $L$ appears in the metric and its effect cannot be erased by
redefining the rotation parameter $\tilde{a}=\sqrt{1+L}a$, it indeed affects
the bound state spectrum and the superradiance. We calculate the bound state
spectrum via the continued-fraction method and show the influence of $L$ on the
maximum binding energy and the damping rate. The superradiant instability could
occur since the superradiance condition and the bound state condition could be
both satisfied. Compared with Kerr black hole, the nature of the superradiant
instability of this black hole depends non-monotonously not only on the
rotation parameter of the black hole $\tilde{a}$ and the product of the black
hole mass $M$ and the field mass $\mu$, but also on the Lorentz breaking
parameter $L$. Through the Monte Carlo method, we find that for $l=m=1$ state
the most unstable mode occurs at $L=-0.79637$, $\tilde{a}/M=0.99884$ and
$M\mu=0.43920$, with the maximum growth rate of the field
$\omega_{I}M=1.676\times10^{-6}$, which is about 10 times of that in Kerr black
hole.
| [
{
"created": "Tue, 10 Aug 2021 14:02:50 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Nov 2021 12:39:30 GMT",
"version": "v2"
}
] | 2021-12-15 | [
[
"Jiang",
"Rui",
""
],
[
"Lin",
"Rui-Hui",
""
],
[
"Zhai",
"Xiang-Hua",
""
]
] | An exact Kerr-like solution has been obtained recently in Einstein-bumblebee gravity model where Lorentz symmetry is spontaneously broken. In this paper, we investigate the superradiant instability of the Kerr-like black hole under the perturbation of a massive scalar field. We find the Lorentz breaking parameter $L$ does not affect the superradiance regime or the regime of the bound states. However, since $L$ appears in the metric and its effect cannot be erased by redefining the rotation parameter $\tilde{a}=\sqrt{1+L}a$, it indeed affects the bound state spectrum and the superradiance. We calculate the bound state spectrum via the continued-fraction method and show the influence of $L$ on the maximum binding energy and the damping rate. The superradiant instability could occur since the superradiance condition and the bound state condition could be both satisfied. Compared with Kerr black hole, the nature of the superradiant instability of this black hole depends non-monotonously not only on the rotation parameter of the black hole $\tilde{a}$ and the product of the black hole mass $M$ and the field mass $\mu$, but also on the Lorentz breaking parameter $L$. Through the Monte Carlo method, we find that for $l=m=1$ state the most unstable mode occurs at $L=-0.79637$, $\tilde{a}/M=0.99884$ and $M\mu=0.43920$, with the maximum growth rate of the field $\omega_{I}M=1.676\times10^{-6}$, which is about 10 times of that in Kerr black hole. |
0812.3759 | Witold Chmielowiec | Witold Chmielowiec, Jerzy Kijowski | Hamiltonian description of radiation phenomena: Trautman-Bondi energy
and corner conditions | 16 pages, 1 figure | Rept.Math.Phys.64:223-240,2009 | 10.1016/S0034-4877(09)90028-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cauchy initial value problem on a hyperboloid is proved to define a
Hamiltonian system, provided the radiation data at null infinity are also taken
into account, as a part of Cauchy data. The "Trautman-Bondi mass", supplemented
by the "already radiated energy" assigned to radiation data, plays role of the
Hamiltonian function. This approach leads to correct description of the corner
conditions.
| [
{
"created": "Fri, 19 Dec 2008 11:47:03 GMT",
"version": "v1"
},
{
"created": "Mon, 30 Nov 2009 13:25:37 GMT",
"version": "v2"
}
] | 2010-03-04 | [
[
"Chmielowiec",
"Witold",
""
],
[
"Kijowski",
"Jerzy",
""
]
] | Cauchy initial value problem on a hyperboloid is proved to define a Hamiltonian system, provided the radiation data at null infinity are also taken into account, as a part of Cauchy data. The "Trautman-Bondi mass", supplemented by the "already radiated energy" assigned to radiation data, plays role of the Hamiltonian function. This approach leads to correct description of the corner conditions. |
1008.5023 | Brian Dolan | Brian P. Dolan | The cosmological constant and the black hole equation of state | 20 pages, 4 figures: some typos corrected in v5 | Class.Quant.Grav.28:125020,2011 | 10.1088/0264-9381/28/12/125020 | DIAS-STP-10-10 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The thermodynamics of black holes in various dimensions are described in the
presence of a negative cosmological constant which is treated as a
thermodynamic variable, interpreted as a pressure in the equation of state. The
black hole mass is then identified with the enthalpy, rather than the internal
energy, and heat capacities are calculated at constant pressure not at constant
volume. The Euclidean action is associated with a bridge equation for the Gibbs
free energy and not the Helmholtz free energy. Quantum corrections to the
enthalpy and the equation of state of the BTZ black hole are studied.
| [
{
"created": "Mon, 30 Aug 2010 08:41:58 GMT",
"version": "v1"
},
{
"created": "Thu, 5 May 2011 15:42:07 GMT",
"version": "v2"
},
{
"created": "Wed, 17 Aug 2011 15:21:19 GMT",
"version": "v3"
},
{
"created": "Fri, 21 Dec 2012 16:23:47 GMT",
"version": "v4"
}
] | 2012-12-24 | [
[
"Dolan",
"Brian P.",
""
]
] | The thermodynamics of black holes in various dimensions are described in the presence of a negative cosmological constant which is treated as a thermodynamic variable, interpreted as a pressure in the equation of state. The black hole mass is then identified with the enthalpy, rather than the internal energy, and heat capacities are calculated at constant pressure not at constant volume. The Euclidean action is associated with a bridge equation for the Gibbs free energy and not the Helmholtz free energy. Quantum corrections to the enthalpy and the equation of state of the BTZ black hole are studied. |
2312.09908 | Sreekanth Harikumar | Sreekanth Harikumar, Laur J\"arv, Margus Saal, Aneta Wojnar, Marek
Biesiada | Propagation and lensing of gravitational waves in Palatini $f(\hat R)$
gravity | null | null | 10.1103/PhysRevD.109.124014 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Accelerated expansion of the Universe prompted searches of modified gravity
theory beyond general relativity, instead of adding a mysterious dark energy
component with exotic physical properties. One such alternative gravity
approach is metric-affine Palatini $f(\hat{R})$ theory. By now routine
gravitational wave detections have opened a promising avenue of searching for
modified gravity effects. Future expected cases of strong lensing of
gravitational waves will enhance this opportunity further. In this paper, we
present a systematic study of the propagation and gravitational lensing of
gravitational waves in Palatini $f(\hat R)$ gravity and compare it with general
relativity. Using the WKB approximation we explore the geometric-optical limit
of lensing and derive the corrections to the measured luminosity distance of
the gravitational source. In addition, we study the lensing by the Singular
Isothermal Sphere lens model and show that Palatini $f(\hat{R})$ modifies the
lensing potential and hence the deflection angle. Then we show that the lens
model and chosen theory of gravity influences the rotation of the gravitational
wave polarization plane through the deflection angle. To be more specific we
discuss the $f(\hat R)=\hat R+\alpha \hat R^2$ gravity theory and find that the
modifications comparing to general relativity are negligible if the upper bound
of $\alpha \sim 10^{9} \, $m$^2$ suggested in the literature is adopted.
However, this bound is not firmly established and can be updated in the future.
Therefore, the results we obtained could be valuable for further metric-affine
gravity vs. general relativity tests involving lensing of gravitational waves
and comparison of luminosity distances measured from electromagnetic and
gravitational wave sources.
| [
{
"created": "Fri, 15 Dec 2023 16:12:28 GMT",
"version": "v1"
},
{
"created": "Sat, 8 Jun 2024 08:10:37 GMT",
"version": "v2"
}
] | 2024-06-11 | [
[
"Harikumar",
"Sreekanth",
""
],
[
"Järv",
"Laur",
""
],
[
"Saal",
"Margus",
""
],
[
"Wojnar",
"Aneta",
""
],
[
"Biesiada",
"Marek",
""
]
] | Accelerated expansion of the Universe prompted searches of modified gravity theory beyond general relativity, instead of adding a mysterious dark energy component with exotic physical properties. One such alternative gravity approach is metric-affine Palatini $f(\hat{R})$ theory. By now routine gravitational wave detections have opened a promising avenue of searching for modified gravity effects. Future expected cases of strong lensing of gravitational waves will enhance this opportunity further. In this paper, we present a systematic study of the propagation and gravitational lensing of gravitational waves in Palatini $f(\hat R)$ gravity and compare it with general relativity. Using the WKB approximation we explore the geometric-optical limit of lensing and derive the corrections to the measured luminosity distance of the gravitational source. In addition, we study the lensing by the Singular Isothermal Sphere lens model and show that Palatini $f(\hat{R})$ modifies the lensing potential and hence the deflection angle. Then we show that the lens model and chosen theory of gravity influences the rotation of the gravitational wave polarization plane through the deflection angle. To be more specific we discuss the $f(\hat R)=\hat R+\alpha \hat R^2$ gravity theory and find that the modifications comparing to general relativity are negligible if the upper bound of $\alpha \sim 10^{9} \, $m$^2$ suggested in the literature is adopted. However, this bound is not firmly established and can be updated in the future. Therefore, the results we obtained could be valuable for further metric-affine gravity vs. general relativity tests involving lensing of gravitational waves and comparison of luminosity distances measured from electromagnetic and gravitational wave sources. |
gr-qc/9807058 | Perjes Zoltan | Michael Bradley, Gyula Fodor, L\'aszl\'o \'A. Gergely, Mattias
Marklund and Zolt\'an Perj\'es | Rotating perfect fluid sources of the NUT metric | 8 pages, latex | Class.Quant.Grav. 16 (1999) 1667-1675 | 10.1088/0264-9381/16/6/301 | null | gr-qc | null | Locally rotationally symmetric perfect fluid solutions of Einstein's
gravitational equations are matched along the hypersurface of vanishing
pressure with the NUT metric. These rigidly rotating fluids are interpreted as
sources for the vacuum exterior which consists only of a stationary region of
the Taub-NUT space-time. The solution of the matching conditions leaves
generally three parameters in the global solution. Examples of perfect fluid
sources are discussed.
| [
{
"created": "Tue, 21 Jul 1998 14:37:51 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Bradley",
"Michael",
""
],
[
"Fodor",
"Gyula",
""
],
[
"Gergely",
"László Á.",
""
],
[
"Marklund",
"Mattias",
""
],
[
"Perjés",
"Zoltán",
""
]
] | Locally rotationally symmetric perfect fluid solutions of Einstein's gravitational equations are matched along the hypersurface of vanishing pressure with the NUT metric. These rigidly rotating fluids are interpreted as sources for the vacuum exterior which consists only of a stationary region of the Taub-NUT space-time. The solution of the matching conditions leaves generally three parameters in the global solution. Examples of perfect fluid sources are discussed. |
1504.02112 | Maria J. Rodriguez | Samuel E. Gralla and Alexandru Lupsasca and Maria J. Rodriguez | Note on Bunching of Field Lines in Black Hole Magnetospheres | 4 pages, 1 figure v2: minor changes | Phys. Rev. D 92, 044053 (2015) | 10.1103/PhysRevD.92.044053 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Numerical simulations of Blandford-Znajek energy extraction at high spin have
revealed that field lines tend to bunch near the poles of the event horizon. We
show that this behavior can be derived analytically from the assumption of
fixed functional dependence of current and field line rotation on magnetic
flux. The argument relies crucially on the existence of the Znajek condition,
which offers non-trivial information about the fields on the horizon without
requiring a full force-free solution. We also provide some new analytic
expressions for the parabolic field configuration.
| [
{
"created": "Wed, 8 Apr 2015 20:11:42 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Sep 2015 23:16:53 GMT",
"version": "v2"
}
] | 2015-09-15 | [
[
"Gralla",
"Samuel E.",
""
],
[
"Lupsasca",
"Alexandru",
""
],
[
"Rodriguez",
"Maria J.",
""
]
] | Numerical simulations of Blandford-Znajek energy extraction at high spin have revealed that field lines tend to bunch near the poles of the event horizon. We show that this behavior can be derived analytically from the assumption of fixed functional dependence of current and field line rotation on magnetic flux. The argument relies crucially on the existence of the Znajek condition, which offers non-trivial information about the fields on the horizon without requiring a full force-free solution. We also provide some new analytic expressions for the parabolic field configuration. |
gr-qc/0106002 | Stefano Liberati | Carlos Barcelo, Matt Visser and Stefano Liberati | Einstein Gravity as an emergent phenomenon? | 8 pages, Essay awarded an honorable mention in the year 2001 Gravity
Research Foundation essay competition | Int.J.Mod.Phys.D10:799-806,2001 | 10.1142/S0218271801001591 | null | gr-qc | null | In this essay we marshal evidence suggesting that Einstein gravity may be an
emergent phenomenon, one that is not ``fundamental'' but rather is an almost
automatic low-energy long-distance consequence of a wide class of theories.
Specifically, the emergence of a curved spacetime ``effective Lorentzian
geometry'' is a common generic result of linearizing a classical scalar field
theory around some non-trivial background. This explains why so many different
``analog models'' of general relativity have recently been developed based on
condensed matter physics; there is something more fundamental going on. Upon
quantizing the linearized fluctuations around this background geometry, the
one-loop effective action is guaranteed to contain a term proportional to the
Einstein--Hilbert action of general relativity, suggesting that while classical
physics is responsible for generating an ``effective geometry'', quantum
physics can be argued to induce an ``effective dynamics''. This physical
picture suggests that Einstein gravity is an emergent low-energy long-distance
phenomenon that is insensitive to the details of the high-energy short-distance
physics.
| [
{
"created": "Fri, 1 Jun 2001 20:23:44 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Barcelo",
"Carlos",
""
],
[
"Visser",
"Matt",
""
],
[
"Liberati",
"Stefano",
""
]
] | In this essay we marshal evidence suggesting that Einstein gravity may be an emergent phenomenon, one that is not ``fundamental'' but rather is an almost automatic low-energy long-distance consequence of a wide class of theories. Specifically, the emergence of a curved spacetime ``effective Lorentzian geometry'' is a common generic result of linearizing a classical scalar field theory around some non-trivial background. This explains why so many different ``analog models'' of general relativity have recently been developed based on condensed matter physics; there is something more fundamental going on. Upon quantizing the linearized fluctuations around this background geometry, the one-loop effective action is guaranteed to contain a term proportional to the Einstein--Hilbert action of general relativity, suggesting that while classical physics is responsible for generating an ``effective geometry'', quantum physics can be argued to induce an ``effective dynamics''. This physical picture suggests that Einstein gravity is an emergent low-energy long-distance phenomenon that is insensitive to the details of the high-energy short-distance physics. |
1508.06231 | Lorenzo Iorio | Lorenzo Iorio | Accurate characterization of the stellar and orbital parameters of the
exoplanetary system WASP-33 b from orbital dynamics | LaTex2e, 1 figure, 1 table, 8 pages. Finale version accepted for
publication in Monthly Notices of the Royal Astronomical Society (MNRAS) | Mon.Not.Roy.Astron.Soc.455:207-213,2016 | 10.1093/mnras/stv2328 | null | gr-qc astro-ph.EP physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | By using the most recently published Doppler tomography measurements and
accurate theoretical modeling of the oblateness-driven orbital precessions, we
tightly constrain some of the physical and orbital parameters of the planetary
system hosted by the fast rotating star WASP-33. In particular, the
measurements of the orbital inclination $i_{\rm p}$ to the plane of the sky and
of the sky-projected spin-orbit misalignment $\lambda$ at two epochs about six
years apart allowed for the determination of the longitude of the ascending
node $\Omega$ and of the orbital inclination $I$ to the apparent equatorial
plane at the same epochs. As a consequence, average rates of change
$\dot\Omega_{\rm exp},~\dot I_{\rm exp}$ of this two orbital elements, accurate
to a $\approx 10^{-2}~{\rm deg}~{\rm yr}^{-1}$ level, were calculated as well.
By comparing them to general theoretical expressions $\dot\Omega_{J_2},~\dot
I_{J_2}$ for their precessions induced by an oblate star whose symmetry axis is
arbitrarily oriented, we were able to determine the angle $i^{\star}$ between
the line of sight the star's spin $S^{\star}$ and its first even zonal harmonic
$J_2^{\star}$ obtaining $i^{\star} = 142^{+10}_{-11}~{\rm deg},~J_2^{\star} =
(2.1^{+0.8}_{-0.5})\times 10^{-4}.$ As a by-product, the angle between
$S^{\star}$ and the orbital angular momentum $L$ is as large as about $\psi
\approx 100$ deg $(\psi^{2008} = 99^{+5}_{-4}~{\rm deg},~\psi^{2014} =
103^{+5}_{-4}~{\rm deg})$, and changes at a rate $\dot\psi =
0.7^{+1.5}_{-1.6}~{\rm deg}~{\rm yr}^{-1}$. The predicted general relativistic
Lense-Thirring precessions, or the order of $\approx 10^{-3}~{\rm deg}~{\rm
yr}^{-1}$, are, at present, about one order of magnitude below the
measurability threshold.
| [
{
"created": "Tue, 25 Aug 2015 17:44:46 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Aug 2015 13:06:00 GMT",
"version": "v2"
},
{
"created": "Sat, 29 Aug 2015 13:14:07 GMT",
"version": "v3"
},
{
"created": "Sat, 12 Sep 2015 20:50:26 GMT",
"version": "v4"
},
{
"c... | 2015-11-05 | [
[
"Iorio",
"Lorenzo",
""
]
] | By using the most recently published Doppler tomography measurements and accurate theoretical modeling of the oblateness-driven orbital precessions, we tightly constrain some of the physical and orbital parameters of the planetary system hosted by the fast rotating star WASP-33. In particular, the measurements of the orbital inclination $i_{\rm p}$ to the plane of the sky and of the sky-projected spin-orbit misalignment $\lambda$ at two epochs about six years apart allowed for the determination of the longitude of the ascending node $\Omega$ and of the orbital inclination $I$ to the apparent equatorial plane at the same epochs. As a consequence, average rates of change $\dot\Omega_{\rm exp},~\dot I_{\rm exp}$ of this two orbital elements, accurate to a $\approx 10^{-2}~{\rm deg}~{\rm yr}^{-1}$ level, were calculated as well. By comparing them to general theoretical expressions $\dot\Omega_{J_2},~\dot I_{J_2}$ for their precessions induced by an oblate star whose symmetry axis is arbitrarily oriented, we were able to determine the angle $i^{\star}$ between the line of sight the star's spin $S^{\star}$ and its first even zonal harmonic $J_2^{\star}$ obtaining $i^{\star} = 142^{+10}_{-11}~{\rm deg},~J_2^{\star} = (2.1^{+0.8}_{-0.5})\times 10^{-4}.$ As a by-product, the angle between $S^{\star}$ and the orbital angular momentum $L$ is as large as about $\psi \approx 100$ deg $(\psi^{2008} = 99^{+5}_{-4}~{\rm deg},~\psi^{2014} = 103^{+5}_{-4}~{\rm deg})$, and changes at a rate $\dot\psi = 0.7^{+1.5}_{-1.6}~{\rm deg}~{\rm yr}^{-1}$. The predicted general relativistic Lense-Thirring precessions, or the order of $\approx 10^{-3}~{\rm deg}~{\rm yr}^{-1}$, are, at present, about one order of magnitude below the measurability threshold. |
gr-qc/9906073 | Kerstin E. Kunze | Kerstin E. Kunze | Asymptotic Behaviour of Inhomogeneous String Cosmologies | 15 pages, Latex | Class.Quant.Grav.16:3795-3806,1999 | 10.1088/0264-9381/16/12/303 | ETH-TH/99-18 | gr-qc hep-th | null | The asymptotic behaviour at late times of inhomogeneous axion-dilaton
cosmologies is investigated. The space-times considered here admit two abelian
space-like Killing vectors. These space-times evolve towards an anisotropic
universe containing gravitational radiation. Furthermore, a peeling-off
behaviour of the Weyl tensor and the antisymmetric tensor field strength is
found. The relation to the pre-big-bang scenario is briefly discussed.
| [
{
"created": "Thu, 17 Jun 1999 10:58:17 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Kunze",
"Kerstin E.",
""
]
] | The asymptotic behaviour at late times of inhomogeneous axion-dilaton cosmologies is investigated. The space-times considered here admit two abelian space-like Killing vectors. These space-times evolve towards an anisotropic universe containing gravitational radiation. Furthermore, a peeling-off behaviour of the Weyl tensor and the antisymmetric tensor field strength is found. The relation to the pre-big-bang scenario is briefly discussed. |
1012.1582 | Larry Ford | Jen-Tsung Hsiang, L. H. Ford, Da-Shin Lee and Hoi-Lai Yu | Quantum Modifications to Gravity Waves in de Sitter Spacetime | 13 pages, no figures | Phys.Rev.D83:084027,2011 | 10.1103/PhysRevD.83.084027 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We treat a model in which tensor perturbations of de~Sitter spacetime,
represented as a spatially flat model, are modified by the effects of the
vacuum fluctuations of a massless conformally invariant field, such as the
electromagnetic field. We use the semiclassical theory of gravity with the
expectation value of the conformal field stress tensor as a source. We first
study the stability of de~Sitter spacetime by searching for growing, spatially
homogeneous modes, and conclude that it is stable within the limits of validity
of the semiclassical theory. We next examine the modification of linearized
plane gravity waves by the effects of the quantum stress tensor. We find a
correction term which is of the same form as the original wave, but displaced
in phase by -\pi/2, and with an amplitude which depends upon the duration of
inflation. The magnitude of this effect is proportional to the change in scale
factor during inflation. So long as the energy scale of inflation and the
proper frequency of the mode at the beginning of inflation are well below the
Planck scale, the fractional correction is small. However, modes which are
transplanckian at the onset of inflation can undergo a significant correction.
The increase in amplitude can potentially have observable consequences through
a modification of the power spectrum of tensor perturbations in inflationary
cosmology. This enhancement of the power spectrum depends upon the duration of
inflation and is greater for shorter wavelengths.
| [
{
"created": "Tue, 7 Dec 2010 19:22:02 GMT",
"version": "v1"
}
] | 2011-05-05 | [
[
"Hsiang",
"Jen-Tsung",
""
],
[
"Ford",
"L. H.",
""
],
[
"Lee",
"Da-Shin",
""
],
[
"Yu",
"Hoi-Lai",
""
]
] | We treat a model in which tensor perturbations of de~Sitter spacetime, represented as a spatially flat model, are modified by the effects of the vacuum fluctuations of a massless conformally invariant field, such as the electromagnetic field. We use the semiclassical theory of gravity with the expectation value of the conformal field stress tensor as a source. We first study the stability of de~Sitter spacetime by searching for growing, spatially homogeneous modes, and conclude that it is stable within the limits of validity of the semiclassical theory. We next examine the modification of linearized plane gravity waves by the effects of the quantum stress tensor. We find a correction term which is of the same form as the original wave, but displaced in phase by -\pi/2, and with an amplitude which depends upon the duration of inflation. The magnitude of this effect is proportional to the change in scale factor during inflation. So long as the energy scale of inflation and the proper frequency of the mode at the beginning of inflation are well below the Planck scale, the fractional correction is small. However, modes which are transplanckian at the onset of inflation can undergo a significant correction. The increase in amplitude can potentially have observable consequences through a modification of the power spectrum of tensor perturbations in inflationary cosmology. This enhancement of the power spectrum depends upon the duration of inflation and is greater for shorter wavelengths. |
1209.6349 | Tanja Hinderer | Alessandra Buonanno, Guillaume Faye, Tanja Hinderer | Spin effects on gravitational waves from inspiraling compact binaries at
second post-Newtonian order | 15 pages, expressions available in mathematica format upon request | Phys. Rev. D 87, 044009 (2013) | 10.1103/PhysRevD.87.044009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We calculate the gravitational waveform for spinning, precessing compact
binary inspirals through second post-Newtonian order in the amplitude. When
spins are collinear with the orbital angular momentum and the orbits are
quasi-circular, we further provide explicit expressions for the
gravitational-wave polarizations and the decomposition into spin-weighted
spherical-harmonic modes. Knowledge of the second post-Newtonian spin terms in
the waveform could be used to improve the physical content of analytical
templates for data analysis of compact binary inspirals and for more accurate
comparisons with numerical-relativity simulations.
| [
{
"created": "Thu, 27 Sep 2012 19:55:09 GMT",
"version": "v1"
},
{
"created": "Mon, 18 Mar 2013 15:30:15 GMT",
"version": "v2"
}
] | 2013-03-19 | [
[
"Buonanno",
"Alessandra",
""
],
[
"Faye",
"Guillaume",
""
],
[
"Hinderer",
"Tanja",
""
]
] | We calculate the gravitational waveform for spinning, precessing compact binary inspirals through second post-Newtonian order in the amplitude. When spins are collinear with the orbital angular momentum and the orbits are quasi-circular, we further provide explicit expressions for the gravitational-wave polarizations and the decomposition into spin-weighted spherical-harmonic modes. Knowledge of the second post-Newtonian spin terms in the waveform could be used to improve the physical content of analytical templates for data analysis of compact binary inspirals and for more accurate comparisons with numerical-relativity simulations. |
1709.10458 | Filipe Mena | Irene Brito, M. F. A. da Silva, Filipe C. Mena, N. O. Santos | Cylindrically symmetric inhomogeneous dust collapse with a zero
expansion component | 18 pages, 2 figures | null | 10.1088/1361-6382/aa8aa8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate a class of cylindrically symmetric inhomogeneous
$\Lambda$-dust spacetimes which have a regular axis and some zero expansion
component. For $\Lambda\ne 0$, we obtain new exact solutions to the Einstein
equations and show that they are unique, within that class. For $\Lambda=0$, we
recover the Senovilla-Vera metric and show that it can be locally matched to an
Einstein-Rosen type of exterior. Finally, we explore some consequences of the
matching, such as trapped surface formation and gravitational radiation in the
exterior.
| [
{
"created": "Fri, 29 Sep 2017 15:36:15 GMT",
"version": "v1"
}
] | 2017-10-11 | [
[
"Brito",
"Irene",
""
],
[
"da Silva",
"M. F. A.",
""
],
[
"Mena",
"Filipe C.",
""
],
[
"Santos",
"N. O.",
""
]
] | We investigate a class of cylindrically symmetric inhomogeneous $\Lambda$-dust spacetimes which have a regular axis and some zero expansion component. For $\Lambda\ne 0$, we obtain new exact solutions to the Einstein equations and show that they are unique, within that class. For $\Lambda=0$, we recover the Senovilla-Vera metric and show that it can be locally matched to an Einstein-Rosen type of exterior. Finally, we explore some consequences of the matching, such as trapped surface formation and gravitational radiation in the exterior. |
0704.1109 | Patricio S. Letelier | Valeria M. Rosa and Patricio S. letelier | Spinning Strings, Black Holes and Stable Closed Timelike Geodesics | 5 pages, RevTex4, some corrections and new material added | Int.J.Theor.Phys.49:316-323,2010 | 10.1007/s10773-009-0204-x | null | gr-qc | null | The existence and stability under linear perturbation of closed timelike
curves in the spacetime associated to Schwarzschild black hole pierced by a
spinning string are studied. Due to the superposition of the black hole, we
find that the spinning string spacetime is deformed in such a way to allow the
existence of closed timelike geodesics.
| [
{
"created": "Mon, 9 Apr 2007 14:45:43 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Jan 2008 20:15:01 GMT",
"version": "v2"
}
] | 2014-11-18 | [
[
"Rosa",
"Valeria M.",
""
],
[
"letelier",
"Patricio S.",
""
]
] | The existence and stability under linear perturbation of closed timelike curves in the spacetime associated to Schwarzschild black hole pierced by a spinning string are studied. Due to the superposition of the black hole, we find that the spinning string spacetime is deformed in such a way to allow the existence of closed timelike geodesics. |
gr-qc/9902036 | Luis O. Pimentel | Luis O. Pimentel | Inhomogeneous String Cosmology Solutions with Regular Spacetime
Curvature | LaTeX, 6 pges | Mod.Phys.Lett. A14 (1999) 43-50 | 10.1142/S0217732399000079 | UAMI-GA-990031 | gr-qc | null | In this work cosmological models are considered for the low energy string
cosmological effective action (tree level) in the absence of dilaton potential.
A two parametric non-diagonal family of analytic solutions is found. The
curvature is non singular, however the string coupling diverges exponentially.
| [
{
"created": "Thu, 11 Feb 1999 19:00:46 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Pimentel",
"Luis O.",
""
]
] | In this work cosmological models are considered for the low energy string cosmological effective action (tree level) in the absence of dilaton potential. A two parametric non-diagonal family of analytic solutions is found. The curvature is non singular, however the string coupling diverges exponentially. |
gr-qc/9801057 | Alessandro D. A. M. Spallicci | Alessandro D.A.M. Spallicci (Univ. Salerno at Benvento, Gravitation
Research Group) & (Univ. Leiden, Fac. Math. & Nat. Sc., Dept. Phys. & Astr.,
Kamerlingh Onnes Lab.) | On the perturbed Schwarzschild geometry for determination of particle
motion | Second Amaldi Conference on Gravitational Waves, 1-4 July 1997, CERN
Geneve | null | null | null | gr-qc | null | A novel method for calculation of the motion and radiation reaction for the
two-body problem (body plus particle, the small parameter m/M being the ratio
of the masses) is presented. In the background curvature given by the
Schwarzschild geometry rippled by gravitational waves, the geodesic equations
insure the presence of radiation reaction also for high velocities and strong
field. The method is generally applicable to any orbit, but radial fall is of
interest due to the non-adiabatic regime (equality of radiation reaction and
fall time scales), in which the particle locally and immediately reacts to the
emitted radiation. The energy balance hypothesis is only used (emitted
radiation equal to the variation in the kinetic energy) for determination of
the 4-velocity via the Lagrangian and normalization of divergencies. The
solution in time domain of the Regge-Wheeler-Zerilli-Moncrief radial wave
equation determines the metric tensor expressing the polar perturbations, in
terms of which the geodesic equations are written and shown herein.
| [
{
"created": "Fri, 16 Jan 1998 17:56:03 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Spallicci",
"Alessandro D. A. M.",
"",
"Univ. Salerno at Benvento, Gravitation\n Research Group"
]
] | A novel method for calculation of the motion and radiation reaction for the two-body problem (body plus particle, the small parameter m/M being the ratio of the masses) is presented. In the background curvature given by the Schwarzschild geometry rippled by gravitational waves, the geodesic equations insure the presence of radiation reaction also for high velocities and strong field. The method is generally applicable to any orbit, but radial fall is of interest due to the non-adiabatic regime (equality of radiation reaction and fall time scales), in which the particle locally and immediately reacts to the emitted radiation. The energy balance hypothesis is only used (emitted radiation equal to the variation in the kinetic energy) for determination of the 4-velocity via the Lagrangian and normalization of divergencies. The solution in time domain of the Regge-Wheeler-Zerilli-Moncrief radial wave equation determines the metric tensor expressing the polar perturbations, in terms of which the geodesic equations are written and shown herein. |
2004.00479 | Vasilis Oikonomou | S.D. Odintsov, V.K. Oikonomou | Swampland Implications of GW170817-compatible Einstein-Gauss-Bonnet
Gravity | Revised version, PLB Accepted | null | 10.1016/j.physletb.2020.135437 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revisit the Einstein-Gauss-Bonnet theory in view of the GW170817 event,
which compels that the gravitational wave speed is equal to $c_T^2=1$ in
natural units. We use an alternative approach compared to one previous work of
ours, which enables us to express all the slow-roll indices and the
observational indices as functions of the scalar field. Using our formalism we
investigate if the Swampland criteria are satisfied for the
Einstein-Gauss-Bonnet theory and as we demonstrate, the Swampland criteria are
satisfied for quite general forms of the potential and the Gauss-Bonnet
coupling function $\xi (\phi)$, if the slow-roll conditions are assumed to hold
true.
| [
{
"created": "Wed, 1 Apr 2020 14:50:43 GMT",
"version": "v1"
},
{
"created": "Sun, 19 Apr 2020 15:51:27 GMT",
"version": "v2"
}
] | 2020-04-22 | [
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | We revisit the Einstein-Gauss-Bonnet theory in view of the GW170817 event, which compels that the gravitational wave speed is equal to $c_T^2=1$ in natural units. We use an alternative approach compared to one previous work of ours, which enables us to express all the slow-roll indices and the observational indices as functions of the scalar field. Using our formalism we investigate if the Swampland criteria are satisfied for the Einstein-Gauss-Bonnet theory and as we demonstrate, the Swampland criteria are satisfied for quite general forms of the potential and the Gauss-Bonnet coupling function $\xi (\phi)$, if the slow-roll conditions are assumed to hold true. |
1702.06263 | Carlos A. S. Almeida | D. F. S. Veras and C. A. S. Almeida | Corrections to Newton's law of gravitation in the context of
codimension-1 warped thick braneworlds | 24 pages, 15 figures. Replaced in order to match the modified version
accepted to PRD. Minor text modifications | Phys. Rev. D 95, 104032 (2017) | 10.1103/PhysRevD.95.104032 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we compute the corrections in the Newton's law of gravitation
due to Kaluza-Klein gravitons in codimension-1 warped thick braneworld
scenarios. We focus in some models recently proposed in the literature, the
so-called asymmetric hybrid brane and compact brane. Such models are
deformations of the $\phi^4$ and sine-Gordon topological defects, respectively.
Therefore we consider the branes engendered by such defects and we also compute
the corrections in their cases. We use suitable numerical techniques to attain
the mass spectrum and its corresponding eigenfunctions which are the essential
quantities for computing the correction to the Newtonian potential. Moreover,
we discuss that the existence of massive modes is necessary for building a
braneworld model with a phenomenology involved. We find that the odd
eigenfunctions have non-trivial contributions and the first eigenstate of the
Kaluza-Klein tower has the highest contribution. The calculation of slight
deviations in the gravitational potential may be used as a selection tool for
braneworld scenarios matching with future experimental measurements in high
energy collisions.
| [
{
"created": "Tue, 21 Feb 2017 04:49:17 GMT",
"version": "v1"
},
{
"created": "Mon, 15 May 2017 20:35:31 GMT",
"version": "v2"
}
] | 2017-05-31 | [
[
"Veras",
"D. F. S.",
""
],
[
"Almeida",
"C. A. S.",
""
]
] | In this work, we compute the corrections in the Newton's law of gravitation due to Kaluza-Klein gravitons in codimension-1 warped thick braneworld scenarios. We focus in some models recently proposed in the literature, the so-called asymmetric hybrid brane and compact brane. Such models are deformations of the $\phi^4$ and sine-Gordon topological defects, respectively. Therefore we consider the branes engendered by such defects and we also compute the corrections in their cases. We use suitable numerical techniques to attain the mass spectrum and its corresponding eigenfunctions which are the essential quantities for computing the correction to the Newtonian potential. Moreover, we discuss that the existence of massive modes is necessary for building a braneworld model with a phenomenology involved. We find that the odd eigenfunctions have non-trivial contributions and the first eigenstate of the Kaluza-Klein tower has the highest contribution. The calculation of slight deviations in the gravitational potential may be used as a selection tool for braneworld scenarios matching with future experimental measurements in high energy collisions. |
0911.0177 | Anil Yadav dr | Anil Kumar Yadav | Bianchi Type V Matter Filled Universe with Varying Lambda Term in
General Relativity | 16 pages, 3 figures | EJTP 10: 169 - 182, 2013 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bianchi type V matter filled universe with varying lambda in general
relativity are investigated by using the law of variation for the generalized
mean Hubble parameter. This yields the constant value of deceleration parameter
and generates two types of solutions for the average scale factor one is of
power law type and other is of exponential type. The cosmological constant is
found to be a decreasing function of time, which is supported by results from
recent type Ia supernovae observations. Also it has been found that
cosmological constant affects entropy. Some physical and geometric behaviour of
the models are discussed.
| [
{
"created": "Sun, 1 Nov 2009 16:19:32 GMT",
"version": "v1"
}
] | 2013-01-15 | [
[
"Yadav",
"Anil Kumar",
""
]
] | Bianchi type V matter filled universe with varying lambda in general relativity are investigated by using the law of variation for the generalized mean Hubble parameter. This yields the constant value of deceleration parameter and generates two types of solutions for the average scale factor one is of power law type and other is of exponential type. The cosmological constant is found to be a decreasing function of time, which is supported by results from recent type Ia supernovae observations. Also it has been found that cosmological constant affects entropy. Some physical and geometric behaviour of the models are discussed. |
1201.1697 | Glenn D. Starkman | Glenn D. Starkman | Modifying Gravity: You Can't Always Get What You Want | A talk given at the Royal Society Discussion Session "Gravity,"
Chicheley Hall, UK Feb. 2011 | Phil. Trans. R. Soc. A 28 December 2011 vol. 369 no. 1957
5018-5041 | 10.1098/rsta.2011.0292 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The combination of GR and the Standard Model disagrees with numerous
observations on scales from our Solar System up. In the concordance model of
cosmology, these contradictions are removed or alleviated by the introduction
of three completely independent new components of stress-energy -- the
inflaton, dark matter, and dark energy. Each of these in its turn is meant to
have (or to currently) dominate the dynamics of the universe. There is still no
non-gravitational evidence for any of these dark sectors; nor for the required
extensions of the standard model. An alternative is to imagine that GR itself
must be modified. Certain coincidences of scale even suggest that one might
expect not to have to make three independent. Because they must address the
most different types of data, attempts to replace dark matter with modified
gravity are the most controversial. A phenomenological model (or family of
models), Modified Newtonian Dynamics, has, over the last few years seen several
covariant realizations. We discuss a number of challenges that any model that
seeks to replace dark matter with modified gravity must face: the loss of
Birkhoff's Theorem, and the calculational simplifications it implies; the
failure to explain clusters, whether static or interacting, and the consequent
need to introduce dark matter of some form, whether hot dark matter neutrinos,
or dark fields that arise in new sectors of the modified gravity theory; the
intrusion of cosmological expansion into the modified force law, that arises
precisely because of the coincidence in scale between the centripetal
acceleration at which Newtonian gravity fails in galaxies, and the cosmic
acceleration. We conclude with the observation that, although modified gravity
may indeed manage to replace dark matter, it is likely to do so by becoming or
incorporating, a dark matter theory itself.
| [
{
"created": "Mon, 9 Jan 2012 06:46:26 GMT",
"version": "v1"
}
] | 2012-01-10 | [
[
"Starkman",
"Glenn D.",
""
]
] | The combination of GR and the Standard Model disagrees with numerous observations on scales from our Solar System up. In the concordance model of cosmology, these contradictions are removed or alleviated by the introduction of three completely independent new components of stress-energy -- the inflaton, dark matter, and dark energy. Each of these in its turn is meant to have (or to currently) dominate the dynamics of the universe. There is still no non-gravitational evidence for any of these dark sectors; nor for the required extensions of the standard model. An alternative is to imagine that GR itself must be modified. Certain coincidences of scale even suggest that one might expect not to have to make three independent. Because they must address the most different types of data, attempts to replace dark matter with modified gravity are the most controversial. A phenomenological model (or family of models), Modified Newtonian Dynamics, has, over the last few years seen several covariant realizations. We discuss a number of challenges that any model that seeks to replace dark matter with modified gravity must face: the loss of Birkhoff's Theorem, and the calculational simplifications it implies; the failure to explain clusters, whether static or interacting, and the consequent need to introduce dark matter of some form, whether hot dark matter neutrinos, or dark fields that arise in new sectors of the modified gravity theory; the intrusion of cosmological expansion into the modified force law, that arises precisely because of the coincidence in scale between the centripetal acceleration at which Newtonian gravity fails in galaxies, and the cosmic acceleration. We conclude with the observation that, although modified gravity may indeed manage to replace dark matter, it is likely to do so by becoming or incorporating, a dark matter theory itself. |
2209.05749 | Souvik Ghose | Anirban Chanda and Arpan Krishna Mitra and Souvik Ghose and Sagar Dey
and Bikash Chandra Paul | Barrow Holographic Dark Energy in Brane World Cosmology | uses article class, 30 pages, 25 figures, 2 tables (v4) typo
corrected, new figure, analysis and reference added, matches the published
version(class. Quant. Grav.) | Class. Quantum Grav. 41 035004 (2024) | 10.1088/1361-6382/ad1af3 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Cosmological features of Barrow Holographic Dark Energy (BHDE), a recent
generalization of original Holographic dark energy with a richer structure, are
studied in the context of DGP brane, RS II brane-world, and the cyclic
universe. It is found that a flat FRW scenario with pressure less dust and a
dark energy component described as BHDE can accommodate late time acceleration
with Hubble horizon considered as infrared cut off even in the absence of
interaction between the dark sectors. Statefinder diagnostic reveals that these
model resemble $\Lambda CDM$ cosmology in future. It is found that BHDE
parameter $\Delta$, despite its theoretically constrained range of values, is
significant in describing the evolution of the universe, however, a classically
stable cosmological model cannot be obtained in the RS-II and DGP brane.
Viability of the models is also probed with observed Hubble data.
| [
{
"created": "Tue, 13 Sep 2022 06:28:06 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Sep 2022 07:33:09 GMT",
"version": "v2"
},
{
"created": "Thu, 6 Jul 2023 11:41:12 GMT",
"version": "v3"
},
{
"created": "Sat, 20 Jan 2024 06:11:43 GMT",
"version": "v4"
}
] | 2024-01-23 | [
[
"Chanda",
"Anirban",
""
],
[
"Mitra",
"Arpan Krishna",
""
],
[
"Ghose",
"Souvik",
""
],
[
"Dey",
"Sagar",
""
],
[
"Paul",
"Bikash Chandra",
""
]
] | Cosmological features of Barrow Holographic Dark Energy (BHDE), a recent generalization of original Holographic dark energy with a richer structure, are studied in the context of DGP brane, RS II brane-world, and the cyclic universe. It is found that a flat FRW scenario with pressure less dust and a dark energy component described as BHDE can accommodate late time acceleration with Hubble horizon considered as infrared cut off even in the absence of interaction between the dark sectors. Statefinder diagnostic reveals that these model resemble $\Lambda CDM$ cosmology in future. It is found that BHDE parameter $\Delta$, despite its theoretically constrained range of values, is significant in describing the evolution of the universe, however, a classically stable cosmological model cannot be obtained in the RS-II and DGP brane. Viability of the models is also probed with observed Hubble data. |
1605.02005 | Anuj Kumar Dubey Mr. | Anuj Kumar Dubey and A. K. Sen | Frame-Dragging from Charged Rotating Body | arXiv admin note: text overlap with arXiv:0811.2471 by other authors | J. Phys.: Conf. Ser. 759, 1, 012065 ( 2016) | 10.1088/1742-6596/759/1/012065 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present paper, we have considered the three parameters: mass, charge
and rotation to discuss their combined effect on frame dragging for a charged
rotating body. If we consider the ray of light which is emitted radially
outward from a rotating body then the frame dragging shows a periodic nature
with respect to coordinate $\phi$ (azimuthal angle). It has been found that the
value of frame dragging obtains a maximum at, $ \phi =\frac{\pi}{2}$ and a
minimum at $ \phi =\frac{3 \pi}{2}$.
| [
{
"created": "Fri, 6 May 2016 17:03:29 GMT",
"version": "v1"
}
] | 2016-11-15 | [
[
"Dubey",
"Anuj Kumar",
""
],
[
"Sen",
"A. K.",
""
]
] | In the present paper, we have considered the three parameters: mass, charge and rotation to discuss their combined effect on frame dragging for a charged rotating body. If we consider the ray of light which is emitted radially outward from a rotating body then the frame dragging shows a periodic nature with respect to coordinate $\phi$ (azimuthal angle). It has been found that the value of frame dragging obtains a maximum at, $ \phi =\frac{\pi}{2}$ and a minimum at $ \phi =\frac{3 \pi}{2}$. |
1510.08552 | Bo-Qiang Ma | Bofeng Wu, Bo-Qiang Ma | Spherically symmetric solution of $f(R,\mathcal{G})$ gravity at low
energy | 14 latex files, 11 figures | Phys.Rev. D92 (2015) 4, 044012 | 10.1103/PhysRevD.92.044012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The weak-field and slow-motion limit of $f(R,\mathcal{G})$ gravity is
developed up to $(v/c)^{4}$ order in a spherically symmetric background.
Considering the Taylor expansion of a general function $f$ around vanishing
values of $R$ and $\mathcal{G}$, we present general vacuum solutions up to
$(v/c)^{4}$ order for the gravitational field generated by a ball-like source.
The spatial behaviors at $(v/c)^{2}$ order are the same for $f(R,\mathcal{G})$
gravity and $f(R)$ gravity, and their corresponding real valued static
behaviors are presented and compared with the one in general relativity. The
static Yukawa-like behavior is proved to be compatible with the previous result
of the most general fourth-order theory. At $(v/c)^{4}$ order, the static
corrections to the Yukawa-like behavior for $f(R,\mathcal{G})$ gravity, $f(R)$
gravity, and the Starobinsky gravity are presented and compared with the one in
general relativity.
| [
{
"created": "Thu, 29 Oct 2015 02:56:34 GMT",
"version": "v1"
}
] | 2015-11-05 | [
[
"Wu",
"Bofeng",
""
],
[
"Ma",
"Bo-Qiang",
""
]
] | The weak-field and slow-motion limit of $f(R,\mathcal{G})$ gravity is developed up to $(v/c)^{4}$ order in a spherically symmetric background. Considering the Taylor expansion of a general function $f$ around vanishing values of $R$ and $\mathcal{G}$, we present general vacuum solutions up to $(v/c)^{4}$ order for the gravitational field generated by a ball-like source. The spatial behaviors at $(v/c)^{2}$ order are the same for $f(R,\mathcal{G})$ gravity and $f(R)$ gravity, and their corresponding real valued static behaviors are presented and compared with the one in general relativity. The static Yukawa-like behavior is proved to be compatible with the previous result of the most general fourth-order theory. At $(v/c)^{4}$ order, the static corrections to the Yukawa-like behavior for $f(R,\mathcal{G})$ gravity, $f(R)$ gravity, and the Starobinsky gravity are presented and compared with the one in general relativity. |
1506.06032 | Richard O'Shaughnessy | Brandon Miller (1), Richard O'Shaughnessy (1), Tyson B. Littenberg
(2), Ben Farr (3) ((1) CCRG, Rochester Institute of Technology, (2) CIERA,
Northwestern University, (3) Enrico Fermi Institute, University of Chicago) | Rapid gravitational wave parameter estimation with a single spin:
Systematic uncertainties in parameter estimation with the SpinTaylorF2
approximation | Submitted to PRD. (12 pages, 9 figures) | Phys. Rev. D 92, 044056 (2015) | 10.1103/PhysRevD.92.044056 | LIGO DCC P1500090 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Reliable low-latency gravitational wave parameter estimation is essential to
target limited electromagnetic followup facilities toward astrophysically
interesting and electromagnetically relevant sources of gravitational waves. In
this study, we examine the tradeoff between speed and accuracy. Specifically,
we estimate the astrophysical relevance of systematic errors in the posterior
parameter distributions derived using a fast-but-approximate waveform model,
SpinTaylorF2 (STF2), in parameter estimation with lalinference_mcmc. Though
efficient, the STF2 approximation to compact binary inspiral employs
approximate kinematics (e.g., a single spin) and an approximate waveform (e.g.,
frequency domain versus time domain). More broadly, using a large
astrophysically-motivated population of generic compact binary merger signals,
we report on the effectualness and limitations of this single-spin
approximation as a method to infer parameters of generic compact binary
sources. For most low-mass compact binary sources, we find that the STF2
approximation estimates compact binary parameters with biases comparable to
systematic uncertainties in the waveform. We illustrate by example the effect
these systematic errors have on posterior probabilities most relevant to
low-latency electromagnetic followup: whether the secondary is has a mass
consistent with a neutron star; whether the masses, spins, and orbit are
consistent with that neutron star's tidal disruption; and whether the binary's
angular momentum axis is oriented along the line of sight.
| [
{
"created": "Fri, 19 Jun 2015 14:45:22 GMT",
"version": "v1"
}
] | 2015-09-09 | [
[
"Miller",
"Brandon",
""
],
[
"O'Shaughnessy",
"Richard",
""
],
[
"Littenberg",
"Tyson B.",
""
],
[
"Farr",
"Ben",
""
]
] | Reliable low-latency gravitational wave parameter estimation is essential to target limited electromagnetic followup facilities toward astrophysically interesting and electromagnetically relevant sources of gravitational waves. In this study, we examine the tradeoff between speed and accuracy. Specifically, we estimate the astrophysical relevance of systematic errors in the posterior parameter distributions derived using a fast-but-approximate waveform model, SpinTaylorF2 (STF2), in parameter estimation with lalinference_mcmc. Though efficient, the STF2 approximation to compact binary inspiral employs approximate kinematics (e.g., a single spin) and an approximate waveform (e.g., frequency domain versus time domain). More broadly, using a large astrophysically-motivated population of generic compact binary merger signals, we report on the effectualness and limitations of this single-spin approximation as a method to infer parameters of generic compact binary sources. For most low-mass compact binary sources, we find that the STF2 approximation estimates compact binary parameters with biases comparable to systematic uncertainties in the waveform. We illustrate by example the effect these systematic errors have on posterior probabilities most relevant to low-latency electromagnetic followup: whether the secondary is has a mass consistent with a neutron star; whether the masses, spins, and orbit are consistent with that neutron star's tidal disruption; and whether the binary's angular momentum axis is oriented along the line of sight. |
1301.1485 | Sunil Maharaj | S. Thirukkanesh, S. S. Rajah, S. D. Maharaj | Shearing radiative collapse with expansion and acceleration | 16 pages, To appear in J. Math. Phys | J. Math. Phys. 53: 032506, 2012 | 10.1063/1.3698286 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the behaviour of a relativistic spherically symmetric
radiative star with an accelerating, expanding and shearing interior matter
distribution in the presence of anisotropic pressures. The junction condition
can be written in standard form in three cases: linear, Bernoulli and Riccati
equations. We can integrate the boundary condition in each case and three
classes of new solutions are generated. For particular choices of the metric we
investigate the physical properties and consider the limiting behaviour for
large values of time. The causal temperature can also be found explicitly.
| [
{
"created": "Tue, 8 Jan 2013 10:57:37 GMT",
"version": "v1"
}
] | 2015-06-12 | [
[
"Thirukkanesh",
"S.",
""
],
[
"Rajah",
"S. S.",
""
],
[
"Maharaj",
"S. D.",
""
]
] | We investigate the behaviour of a relativistic spherically symmetric radiative star with an accelerating, expanding and shearing interior matter distribution in the presence of anisotropic pressures. The junction condition can be written in standard form in three cases: linear, Bernoulli and Riccati equations. We can integrate the boundary condition in each case and three classes of new solutions are generated. For particular choices of the metric we investigate the physical properties and consider the limiting behaviour for large values of time. The causal temperature can also be found explicitly. |
gr-qc/0204007 | Paola Zizzi | P. A. Zizzi | Quantum Computing Spacetime | 12 pages, 5 figures | null | null | null | gr-qc quant-ph | null | A causal set C can describe a discrete spacetime, but this discrete spacetime
is not quantum, because C is endowed with Boolean logic, as it does not allow
cycles. In a quasi-ordered set Q, cycles are allowed. In this paper, we
consider a subset QC of a quasi-ordered set Q, whose elements are all the
cycles. In QC, which is endowed with quantum logic, each cycle of maximal
outdegree N in a node, is associated with N entangled qubits. Then QC describes
a quantum computing spacetime. This structure, which is non-local and
non-casual, can be understood as a proto-spacetime. Micro-causality and
locality can be restored in the subset U of Q whose elements are unentangled
qubits which we interpret as the states of quantum spacetime. The mapping of
quantum spacetime into proto-spacetime is given by the action of the XOR gate.
Moreover, a mapping is possible from the Boolean causal set into U by the
action of the Hadamard gate. In particular, the causal order defined on the
elements of U induces the causal evolution of spin networks.
| [
{
"created": "Tue, 2 Apr 2002 08:13:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Zizzi",
"P. A.",
""
]
] | A causal set C can describe a discrete spacetime, but this discrete spacetime is not quantum, because C is endowed with Boolean logic, as it does not allow cycles. In a quasi-ordered set Q, cycles are allowed. In this paper, we consider a subset QC of a quasi-ordered set Q, whose elements are all the cycles. In QC, which is endowed with quantum logic, each cycle of maximal outdegree N in a node, is associated with N entangled qubits. Then QC describes a quantum computing spacetime. This structure, which is non-local and non-casual, can be understood as a proto-spacetime. Micro-causality and locality can be restored in the subset U of Q whose elements are unentangled qubits which we interpret as the states of quantum spacetime. The mapping of quantum spacetime into proto-spacetime is given by the action of the XOR gate. Moreover, a mapping is possible from the Boolean causal set into U by the action of the Hadamard gate. In particular, the causal order defined on the elements of U induces the causal evolution of spin networks. |
1812.08663 | Fredy Dubeibe | F. L. Dubeibe, J. D. Arias H. and J. E. Alfonso | Geodesic dynamics in Chazy-Curzon spacetimes | 13 pages, 9 figures, Accepted for publication in The Indian Journal
of Physics | Indian J Phys (December 2019) 93(12):1635-1641 | 10.1007/s12648-019-01416-8 | null | gr-qc math.DS nlin.CD | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the last decades, the dynamical studies around compact objects became a
subject of active research, partially motivated by the observed differences in
the profiles of the gravitational waves depending on the dynamics of the
system. In this work, via the Poincar\'e section method, we conduct a thorough
numerical analysis of the dynamical behavior of geodesics around Chazy-Curzon
metrics. As the main result, we find only regular motions for the geodesics in
all cases, which suggest the existence of the so-called Carter's constant in
this kind of exact solutions. Moreover, our simulations indicate that in the
two-particle Chazy-Curzon solution, some oscillatory motions take place as in
the classical MacMillan problem.
| [
{
"created": "Thu, 20 Dec 2018 16:09:58 GMT",
"version": "v1"
}
] | 2020-03-12 | [
[
"Dubeibe",
"F. L.",
""
],
[
"H.",
"J. D. Arias",
""
],
[
"Alfonso",
"J. E.",
""
]
] | In the last decades, the dynamical studies around compact objects became a subject of active research, partially motivated by the observed differences in the profiles of the gravitational waves depending on the dynamics of the system. In this work, via the Poincar\'e section method, we conduct a thorough numerical analysis of the dynamical behavior of geodesics around Chazy-Curzon metrics. As the main result, we find only regular motions for the geodesics in all cases, which suggest the existence of the so-called Carter's constant in this kind of exact solutions. Moreover, our simulations indicate that in the two-particle Chazy-Curzon solution, some oscillatory motions take place as in the classical MacMillan problem. |
1111.2867 | Etera R. Livine | Etera R. Livine, Mercedes Mart\'in-Benito | Classical Setting and Effective Dynamics for Spinfoam Cosmology | 38 pages, v2: Link with discretized loop quantum gravity made
explicit and emphasized | Class. Quantum Grav. 30 (2013) 035006 | 10.1088/0264-9381/30/3/035006 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explore how to extract effective dynamics from loop quantum gravity and
spinfoams truncated to a finite fixed graph, with the hope of modeling
symmetry-reduced gravitational systems. We particularize our study to the
2-vertex graph with N links. We describe the canonical data using the recent
formulation of the phase space in terms of spinors, and implement a
symmetry-reduction to the homogeneous and isotropic sector. From the canonical
point of view, we construct a consistent Hamiltonian for the model and discuss
its relation with Friedmann-Robertson-Walker cosmologies. Then, we analyze the
dynamics from the spinfoam approach. We compute exactly the transition
amplitude between initial and final coherent spin networks states with support
on the 2-vertex graph, for the choice of the simplest two-complex (with a
single space-time vertex). The transition amplitude verifies an exact
differential equation that agrees with the Hamiltonian constructed previously.
Thus, in our simple setting we clarify the link between the canonical and the
covariant formalisms.
| [
{
"created": "Fri, 11 Nov 2011 21:13:38 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Jul 2013 15:23:01 GMT",
"version": "v2"
}
] | 2013-07-09 | [
[
"Livine",
"Etera R.",
""
],
[
"Martín-Benito",
"Mercedes",
""
]
] | We explore how to extract effective dynamics from loop quantum gravity and spinfoams truncated to a finite fixed graph, with the hope of modeling symmetry-reduced gravitational systems. We particularize our study to the 2-vertex graph with N links. We describe the canonical data using the recent formulation of the phase space in terms of spinors, and implement a symmetry-reduction to the homogeneous and isotropic sector. From the canonical point of view, we construct a consistent Hamiltonian for the model and discuss its relation with Friedmann-Robertson-Walker cosmologies. Then, we analyze the dynamics from the spinfoam approach. We compute exactly the transition amplitude between initial and final coherent spin networks states with support on the 2-vertex graph, for the choice of the simplest two-complex (with a single space-time vertex). The transition amplitude verifies an exact differential equation that agrees with the Hamiltonian constructed previously. Thus, in our simple setting we clarify the link between the canonical and the covariant formalisms. |
gr-qc/0611041 | Jose Edgar Madriz Aguilar | Jose Edgar Madriz Aguilar | Gravitational Waves generated during inflation from a 5D vacuum theory
of gravity in a de Sitter expansion | null | Phys.Lett.B645:6-11,2007 | 10.1016/j.physletb.2006.11.051 | null | gr-qc astro-ph hep-th | null | In this letter we study the generation of gravitational waves during
inflation from a 5D vacuum theory of gravity. Within this formalism, on an
effective 4D de Sitter background, we recover the typical results obtained with
4D inflationary theory in general relativity, for the amplitude of
gravitational waves generated during inflation. We also obtain a range of
values for the amplitude of tensor to scalar ratio which is in agreement with
COBE observations.
| [
{
"created": "Mon, 6 Nov 2006 20:25:27 GMT",
"version": "v1"
},
{
"created": "Wed, 31 Jan 2007 15:29:07 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Aguilar",
"Jose Edgar Madriz",
""
]
] | In this letter we study the generation of gravitational waves during inflation from a 5D vacuum theory of gravity. Within this formalism, on an effective 4D de Sitter background, we recover the typical results obtained with 4D inflationary theory in general relativity, for the amplitude of gravitational waves generated during inflation. We also obtain a range of values for the amplitude of tensor to scalar ratio which is in agreement with COBE observations. |
1108.0744 | Shahar Hod | Shahar Hod | Hyperentropic systems and the generalized second law of thermodynamics | 5 pages | Phys.Lett.B700:75-78,2011 | 10.1016/j.physletb.2011.04.048 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The holographic bound asserts that the entropy $S$ of a system is bounded
from above by a quarter of the area ${\cal A}$ of a circumscribing surface
measured in Planck areas: $S\leq {\cal A}/4{\ell^2_P}$. This bound is widely
regarded a desideratum of any fundamental theory. Moreover, it was argued that
the holographic bound is necessary for the validity of the generalized second
law (GSL) of thermodynamics. However, in this work we explicitly show that
hyperentropic systems (those violating the holographic entropy bound) do exist
in higher-dimensional spacetimes. We resolve this apparent violation of the GSL
and derive an upper bound on the area of hyperentropic objects.
| [
{
"created": "Wed, 3 Aug 2011 05:30:05 GMT",
"version": "v1"
}
] | 2011-08-04 | [
[
"Hod",
"Shahar",
""
]
] | The holographic bound asserts that the entropy $S$ of a system is bounded from above by a quarter of the area ${\cal A}$ of a circumscribing surface measured in Planck areas: $S\leq {\cal A}/4{\ell^2_P}$. This bound is widely regarded a desideratum of any fundamental theory. Moreover, it was argued that the holographic bound is necessary for the validity of the generalized second law (GSL) of thermodynamics. However, in this work we explicitly show that hyperentropic systems (those violating the holographic entropy bound) do exist in higher-dimensional spacetimes. We resolve this apparent violation of the GSL and derive an upper bound on the area of hyperentropic objects. |
1809.01961 | Emilio Elizalde | Emilio Elizalde, Martiros Khurshudyan, Shin'ichi Nojiri | Cosmological singularities in interacting dark energy models with an
$\omega(q)$ parametrization | 20 pages, to appear in IJMPD | null | 10.1142/S0218271819500196 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Future singularities arising in a family of models for the expanding
Universe, characterized by sharing a convenient parametrization of the energy
budget in terms of the deceleration parameter, are classified. Finite-time
future singularities are known to appear in many cosmological scenarios, in
particular, in the presence of viscosity or non-gravitational interactions, the
last being known to be able to suppress or just change in some cases the type
of the cosmological singularity. Here, a family of models with a
parametrization of the energy budget in terms of the deceleration parameter are
studied in the light of Gaussian processes using reconstructed data from
$40$-value $H(z)$ datasets. Eventually, the form of the possible
non-gravitational interaction between dark energy and dark matter is
constructed from these smoothed $H(z)$ data. Using phase space analysis, it is
shown that a non-interacting model with dark energy $\omega_\mathrm{de} =
\omega_{0} + \omega_{1}q$ ($q$ being the deceleration parameter) may evolve,
after starting from a matter dominated unstable state, into a de Sitter
Universe (the solution being in fact a stable node). Moreover, for a model with
interaction term $Q = 3 H b \rho_\mathrm{dm}$ ($b$ is a parameter and $H$ the
Hubble constant) three stable critical points are obtained, what may have
important astrophysical implications. In addition, part of the paper is devoted
to a general discussion of the finite-time future singularities obtained from
direct numerical integration of the field equations, since they appear in many
cosmological scenarios and could be useful for future extended studies of the
models here introduced. Numerical solutions for the new models, produce
finite-time future singularities of Type I or Type III, or an
$\omega$-singularity, provided general relativity describes the background
dynamics.
| [
{
"created": "Thu, 6 Sep 2018 13:11:16 GMT",
"version": "v1"
}
] | 2019-01-23 | [
[
"Elizalde",
"Emilio",
""
],
[
"Khurshudyan",
"Martiros",
""
],
[
"Nojiri",
"Shin'ichi",
""
]
] | Future singularities arising in a family of models for the expanding Universe, characterized by sharing a convenient parametrization of the energy budget in terms of the deceleration parameter, are classified. Finite-time future singularities are known to appear in many cosmological scenarios, in particular, in the presence of viscosity or non-gravitational interactions, the last being known to be able to suppress or just change in some cases the type of the cosmological singularity. Here, a family of models with a parametrization of the energy budget in terms of the deceleration parameter are studied in the light of Gaussian processes using reconstructed data from $40$-value $H(z)$ datasets. Eventually, the form of the possible non-gravitational interaction between dark energy and dark matter is constructed from these smoothed $H(z)$ data. Using phase space analysis, it is shown that a non-interacting model with dark energy $\omega_\mathrm{de} = \omega_{0} + \omega_{1}q$ ($q$ being the deceleration parameter) may evolve, after starting from a matter dominated unstable state, into a de Sitter Universe (the solution being in fact a stable node). Moreover, for a model with interaction term $Q = 3 H b \rho_\mathrm{dm}$ ($b$ is a parameter and $H$ the Hubble constant) three stable critical points are obtained, what may have important astrophysical implications. In addition, part of the paper is devoted to a general discussion of the finite-time future singularities obtained from direct numerical integration of the field equations, since they appear in many cosmological scenarios and could be useful for future extended studies of the models here introduced. Numerical solutions for the new models, produce finite-time future singularities of Type I or Type III, or an $\omega$-singularity, provided general relativity describes the background dynamics. |
gr-qc/0010110 | Takahiro Tanaka | Takahiro Tanaka and T. P. Singh | Analytic derivation of the map of null rays passing near a naked
singularity | 4 pages, submitted to Phys. Rev. D | Phys.Rev. D63 (2001) 124021 | 10.1103/PhysRevD.63.124021 | YITP-00-57 | gr-qc | null | Recently the energy emission from a naked singularity forming in spherical
dust collapse has been investigated. This radiation is due to the particle
creation in a curved spacetime. In this discussion, the central role is played
by the mapping formula between the incoming and the outgoing null coordinates.
For the self-similar model, this mapping formula has been derived analytically.
But for the model with $C^{\infty}$ density profile, the mapping formula has
been obtained only numerically. In the present paper, we argue that the
singular nature of the mapping is determined by the local geometry around the
point at which the singularity is first formed. If this is the case, it would
be natural to expect that the mapping formula can be derived analytically. In
the present paper, we analytically rederive the same mapping formula for the
model with $C^{\infty}$ density profile that has been earlier derived using a
numerical technique.
| [
{
"created": "Tue, 31 Oct 2000 03:18:40 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Tanaka",
"Takahiro",
""
],
[
"Singh",
"T. P.",
""
]
] | Recently the energy emission from a naked singularity forming in spherical dust collapse has been investigated. This radiation is due to the particle creation in a curved spacetime. In this discussion, the central role is played by the mapping formula between the incoming and the outgoing null coordinates. For the self-similar model, this mapping formula has been derived analytically. But for the model with $C^{\infty}$ density profile, the mapping formula has been obtained only numerically. In the present paper, we argue that the singular nature of the mapping is determined by the local geometry around the point at which the singularity is first formed. If this is the case, it would be natural to expect that the mapping formula can be derived analytically. In the present paper, we analytically rederive the same mapping formula for the model with $C^{\infty}$ density profile that has been earlier derived using a numerical technique. |
2107.06551 | Masaru Siino | Masaru Siino | Black hole shadow and Wandering null geodesics | 15 pages, 3figures, One of main results (prop.2) has been corrected.
Some inappropriate sentences are removed | null | 10.1103/PhysRevD.106.044020 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The role of the wandering null geodesic is studied in a black hole spacetime.
Based on the continuity of the solution of the geodesic equation, the wandering
null geodesics commonly exist and explain the typical phenomena of the optical
observation of event horizons. Moreover, a new concept of `black room' is
investigated to relate the wandering null geodesic to the black hole shadow
more closely.
| [
{
"created": "Wed, 14 Jul 2021 08:34:55 GMT",
"version": "v1"
},
{
"created": "Thu, 19 May 2022 08:23:57 GMT",
"version": "v2"
}
] | 2022-08-31 | [
[
"Siino",
"Masaru",
""
]
] | The role of the wandering null geodesic is studied in a black hole spacetime. Based on the continuity of the solution of the geodesic equation, the wandering null geodesics commonly exist and explain the typical phenomena of the optical observation of event horizons. Moreover, a new concept of `black room' is investigated to relate the wandering null geodesic to the black hole shadow more closely. |
gr-qc/0404012 | L. Arturo Urena-Lopez | Octavio Obregon, L. Arturo Urena-Lopez and Franz E. Schunck | Oscillatons formed by non linear gravity | Revtex file, 6 pages, 3 eps figure; matches version published in PRD | Phys.Rev. D72 (2005) 024004 | 10.1103/PhysRevD.72.024004 | null | gr-qc | null | Oscillatons are solutions of the coupled Einstein-Klein-Gordon (EKG)
equations that are globally regular and asymptotically flat. By means of a
Legendre transformation we are able to visualize the behaviour of the
corresponding objects in non-linear gravity where the scalar field has been
absorbed by means of the conformal mapping.
| [
{
"created": "Thu, 1 Apr 2004 20:17:16 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Aug 2005 18:44:47 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Obregon",
"Octavio",
""
],
[
"Urena-Lopez",
"L. Arturo",
""
],
[
"Schunck",
"Franz E.",
""
]
] | Oscillatons are solutions of the coupled Einstein-Klein-Gordon (EKG) equations that are globally regular and asymptotically flat. By means of a Legendre transformation we are able to visualize the behaviour of the corresponding objects in non-linear gravity where the scalar field has been absorbed by means of the conformal mapping. |
0812.2406 | Marco Pizzi | Marco Pizzi, Armando Paolino | Intersections of self-gravitating charged shells in a Reissner-Nordstrom
field | 21 pages, 1 figure;v3 added references | Int.J.Mod.Phys.D18:1955-1975,2009 | 10.1142/S0218271809015047 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe the equation of motion of two charged spherical shells with
tangential pressure in the field of a central Reissner-Nordstrom (RN) source.
We solve the problem of determining the motion of the two shells \textsl{after}
the intersection by solving the related Einstein-Maxwell equations and by
requiring a physical continuity condition on the shells velocities.
We consider also four applications: post-Newtonian and ultra-relativistic
approximations, a test-shell case, and the ejection mechanism of one shell.
This work is a direct generalization of Barkov-Belinski-Bisnovati-Kogan
paper.
| [
{
"created": "Fri, 12 Dec 2008 16:02:00 GMT",
"version": "v1"
},
{
"created": "Sat, 13 Dec 2008 14:12:13 GMT",
"version": "v2"
},
{
"created": "Mon, 26 Jan 2009 13:23:11 GMT",
"version": "v3"
}
] | 2010-01-06 | [
[
"Pizzi",
"Marco",
""
],
[
"Paolino",
"Armando",
""
]
] | We describe the equation of motion of two charged spherical shells with tangential pressure in the field of a central Reissner-Nordstrom (RN) source. We solve the problem of determining the motion of the two shells \textsl{after} the intersection by solving the related Einstein-Maxwell equations and by requiring a physical continuity condition on the shells velocities. We consider also four applications: post-Newtonian and ultra-relativistic approximations, a test-shell case, and the ejection mechanism of one shell. This work is a direct generalization of Barkov-Belinski-Bisnovati-Kogan paper. |
1305.4884 | T. Damour | Donato Bini and Thibault Damour | Analytical determination of the two-body gravitational interaction
potential at the 4th post-Newtonian approximation | 6 pages, no figures | null | 10.1103/PhysRevD.87.121501 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We complete the analytical determination, at the 4th post-Newtonian
approximation, of the main radial potential describing the gravitational
interaction of two bodies within the effective one-body formalism. The (non
logarithmic) coefficient a_5 (nu) measuring this 4th post-Newtonian interaction
potential is found to be linear in the symmetric mass ratio nu. Its
nu-independent part a_5 (0) is obtained by an analytical gravitational
self-force calculation that unambiguously resolves the formal infrared
divergencies which currently impede its direct post-Newtonian calculation. Its
nu-linear part a_5 (nu) - a_5 (0) is deduced from recent results of Jaranowski
and Sch\"afer, and is found to be significantly negative.
| [
{
"created": "Tue, 21 May 2013 17:06:02 GMT",
"version": "v1"
}
] | 2015-06-16 | [
[
"Bini",
"Donato",
""
],
[
"Damour",
"Thibault",
""
]
] | We complete the analytical determination, at the 4th post-Newtonian approximation, of the main radial potential describing the gravitational interaction of two bodies within the effective one-body formalism. The (non logarithmic) coefficient a_5 (nu) measuring this 4th post-Newtonian interaction potential is found to be linear in the symmetric mass ratio nu. Its nu-independent part a_5 (0) is obtained by an analytical gravitational self-force calculation that unambiguously resolves the formal infrared divergencies which currently impede its direct post-Newtonian calculation. Its nu-linear part a_5 (nu) - a_5 (0) is deduced from recent results of Jaranowski and Sch\"afer, and is found to be significantly negative. |
1607.03743 | Thomas Philbin | T.G. Philbin | An exact solution for the Hawking effect in a dispersive fluid | 18 pages, minor changes | Phys. Rev. D 94, 064053 (2016) | 10.1103/PhysRevD.94.064053 | null | gr-qc cond-mat.quant-gas | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the wave equation for sound in a moving fluid with a fourth-order
anomalous dispersion relation. The velocity of the fluid is a linear function
of position, giving two points in the flow where the fluid velocity matches the
group velocity of low-frequency waves. We find the exact solution for wave
propagation in the flow. The scattering shows amplification of classical waves,
leading to spontaneous emission when the waves are quantized. In the
dispersionless limit the system corresponds to a 1+1-dimensional black-hole or
white-hole binary and there is a thermal spectrum of Hawking radiation from
each horizon. Dispersion changes the scattering coefficients so that the
quantum emission is no longer thermal. The scattering coefficients were
previously obtained by Busch and Parentani in a study of dispersive fields in
de Sitter space [Phys. Rev. D 86, 104033 (2012)]. Our results give further
details of the wave propagation in this exactly solvable case, where our focus
is on laboratory systems.
| [
{
"created": "Wed, 13 Jul 2016 14:06:57 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Jul 2016 14:54:24 GMT",
"version": "v2"
},
{
"created": "Wed, 28 Sep 2016 15:24:46 GMT",
"version": "v3"
}
] | 2016-09-29 | [
[
"Philbin",
"T. G.",
""
]
] | We consider the wave equation for sound in a moving fluid with a fourth-order anomalous dispersion relation. The velocity of the fluid is a linear function of position, giving two points in the flow where the fluid velocity matches the group velocity of low-frequency waves. We find the exact solution for wave propagation in the flow. The scattering shows amplification of classical waves, leading to spontaneous emission when the waves are quantized. In the dispersionless limit the system corresponds to a 1+1-dimensional black-hole or white-hole binary and there is a thermal spectrum of Hawking radiation from each horizon. Dispersion changes the scattering coefficients so that the quantum emission is no longer thermal. The scattering coefficients were previously obtained by Busch and Parentani in a study of dispersive fields in de Sitter space [Phys. Rev. D 86, 104033 (2012)]. Our results give further details of the wave propagation in this exactly solvable case, where our focus is on laboratory systems. |
2401.09737 | Salvatore Capozziello | Salvatore Capozziello and Carmen Ferrara | The Equivalence Principle as a Noether Symmetry | 10 pages, to appear in International Journal of Geometric Methods in
Modern Physics | null | 10.1142/S0219887824400140 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | The Equivalence Principle is considered in the framework of metric-affine
gravity. We show that it naturally emerges as a Noether symmetry starting from
a general non-metric theory. In particular, we discuss the Einstein Equivalence
Principle and the Strong Equivalence Principle showing their relations with the
non-metricity tensor. Possible violations are also discussed pointing out the
role of non-metricity in this debate.
| [
{
"created": "Thu, 18 Jan 2024 05:36:35 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Jan 2024 14:22:53 GMT",
"version": "v2"
},
{
"created": "Thu, 20 Jun 2024 06:52:32 GMT",
"version": "v3"
}
] | 2024-06-21 | [
[
"Capozziello",
"Salvatore",
""
],
[
"Ferrara",
"Carmen",
""
]
] | The Equivalence Principle is considered in the framework of metric-affine gravity. We show that it naturally emerges as a Noether symmetry starting from a general non-metric theory. In particular, we discuss the Einstein Equivalence Principle and the Strong Equivalence Principle showing their relations with the non-metricity tensor. Possible violations are also discussed pointing out the role of non-metricity in this debate. |
1007.5371 | Edwin J. Son | Edwin J. Son and Wontae Kim | Note on nonsingular cyclic universes in the deformed Horava-Lifshitz
gravity | 10 pages, 2 figures | Mod.Phys.Lett.A26:719-725,2011 | 10.1142/S0217732311035237 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform the phase space analysis in terms of the linearization technique
in the Ho\v{r}ava-Lifshitz gravity with the softly broken detailed balance
condition. It can be shown that the bouncing universe appears only for the
positive spatial curvature of $k=+1$, and it is possible to obtain oscillating
universe with the help of the negative dark radiation and the negative
cosmological constant.
| [
{
"created": "Fri, 30 Jul 2010 05:39:59 GMT",
"version": "v1"
},
{
"created": "Sun, 17 Apr 2011 23:16:01 GMT",
"version": "v2"
}
] | 2011-04-21 | [
[
"Son",
"Edwin J.",
""
],
[
"Kim",
"Wontae",
""
]
] | We perform the phase space analysis in terms of the linearization technique in the Ho\v{r}ava-Lifshitz gravity with the softly broken detailed balance condition. It can be shown that the bouncing universe appears only for the positive spatial curvature of $k=+1$, and it is possible to obtain oscillating universe with the help of the negative dark radiation and the negative cosmological constant. |
1709.09033 | Douglas A. Singleton | Preston Jones, Andri Gretarsson and Douglas Singleton | Low frequency electromagnetic radiation coming from gravitational waves
generated by neutron stars | 16 pages revtex, no figures, 1 table. Version published in PRD | Phys. Rev. D 96, 124030 (2017) | 10.1103/PhysRevD.96.124030 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the possibility of observing very low frequency (VLF)
electromagnetic radiation produced from the vacuum by gravitational waves. We
review the calculations leading to the possibility of vacuum conversion of
gravitational waves into electromagnetic waves and show how this process evades
the well-known prohibition against particle production from gravitational
waves. Using Newman-Penrose scalars, we estimate the luminosity of this
proposed electromagnetic counterpart radiation coming from gravitational waves
produced by neutron star oscillations. The detection of electromagnetic
counterpart radiation would provide an indirect way of observing gravitational
radiation with future spacecraft missions, especially lunar orbiting probes.
| [
{
"created": "Sat, 23 Sep 2017 21:08:09 GMT",
"version": "v1"
},
{
"created": "Fri, 29 Dec 2017 22:14:09 GMT",
"version": "v2"
}
] | 2018-01-03 | [
[
"Jones",
"Preston",
""
],
[
"Gretarsson",
"Andri",
""
],
[
"Singleton",
"Douglas",
""
]
] | We investigate the possibility of observing very low frequency (VLF) electromagnetic radiation produced from the vacuum by gravitational waves. We review the calculations leading to the possibility of vacuum conversion of gravitational waves into electromagnetic waves and show how this process evades the well-known prohibition against particle production from gravitational waves. Using Newman-Penrose scalars, we estimate the luminosity of this proposed electromagnetic counterpart radiation coming from gravitational waves produced by neutron star oscillations. The detection of electromagnetic counterpart radiation would provide an indirect way of observing gravitational radiation with future spacecraft missions, especially lunar orbiting probes. |
2306.14581 | Chevarra Hansraj | Jonathan Hakata, Rituparno Goswami, Chevarra Hansraj, Sunil D. Maharaj | What makes a shear-free spherical perfect fluid be inhomogeneous with
tidal effects? | 8 pages, 2 figures | General Relativity and Gravitation (2023) 55:119 | 10.1007/s10714-023-03161-0 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | This is an important and natural question as the spacetime shear,
inhomogeneity and tidal effects are all intertwined via the Einstein field
equations. However, as we show in this paper, such scenarios are possible for
limited classes of equations of state that are solutions to a highly non-linear
and fourth order differential equation. To show this, we use a covariant
semitetrad spacetime decomposition and present a novel geometrical
classification of shear-free Locally Rotationally Symmetric (LRS-II) perfect
fluid self-gravitating systems, in terms of the covariantly defined fluid
acceleration and the fluid expansion. Noteworthily, we deduce the governing
differential equation that gives the possible limited equations of state of
matter.
| [
{
"created": "Mon, 26 Jun 2023 10:48:17 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Aug 2023 14:34:15 GMT",
"version": "v2"
}
] | 2024-06-18 | [
[
"Hakata",
"Jonathan",
""
],
[
"Goswami",
"Rituparno",
""
],
[
"Hansraj",
"Chevarra",
""
],
[
"Maharaj",
"Sunil D.",
""
]
] | This is an important and natural question as the spacetime shear, inhomogeneity and tidal effects are all intertwined via the Einstein field equations. However, as we show in this paper, such scenarios are possible for limited classes of equations of state that are solutions to a highly non-linear and fourth order differential equation. To show this, we use a covariant semitetrad spacetime decomposition and present a novel geometrical classification of shear-free Locally Rotationally Symmetric (LRS-II) perfect fluid self-gravitating systems, in terms of the covariantly defined fluid acceleration and the fluid expansion. Noteworthily, we deduce the governing differential equation that gives the possible limited equations of state of matter. |
1912.10448 | Philip D. Mannheim | Matthew G. Phelps, Asanka Amarasinghe and Philip D. Mannheim | Three-dimensional and four-dimensional scalar, vector, tensor
cosmological fluctuations and the cosmological decomposition theorem | 61 pages | null | 10.1007/s10714-020-02757-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In cosmological perturbation theory it is convenient to use the scalar,
vector, tensor (SVT) basis as defined according to how these components
transform under 3-dimensional rotations. In attempting to solve the fluctuation
equations that are automatically written in terms of gauge-invariant
combinations of these components, the equations are taken to break up into
separate SVT sectors, the decomposition theorem. Here, without needing to
specify a gauge, we solve the fluctuation equations exactly for some standard
cosmologies, to show that in general the various gauge-invariant combinations
only separate at a higher-derivative level. To achieve separation at the level
of the fluctuation equations themselves one has to assume boundary conditions
for the higher-derivative equations. While asymptotic conditions suffice for
fluctuations around a dS background or a $k=0$ RW background, for fluctuations
around a $k\neq 0$ RW background one additionally has to require that the
fluctuations be well-behaved at the origin. We show that in certain cases the
gauge-invariant combinations themselves involve both scalars and vectors. For
such cases there is no decomposition theorem for the individual SVT components
themselves, but for the gauge-invariant combinations there still can be. Given
the lack of manifest covariance in defining a basis with respect to
3-dimensional rotations, we introduce an alternate SVT basis whose components
are defined according to how they transform under 4-dimensional general
coordinate transformations. With this basis the fluctuation equations greatly
simplify, and while one can again break them up into separate gauge-invariant
sectors at the higher-derivative level, in general we find that even with
boundary conditions we do not obtain a decomposition theorem in which the
fluctuations separate at the level of the fluctuation equations themselves.
| [
{
"created": "Sun, 22 Dec 2019 13:40:00 GMT",
"version": "v1"
}
] | 2021-04-14 | [
[
"Phelps",
"Matthew G.",
""
],
[
"Amarasinghe",
"Asanka",
""
],
[
"Mannheim",
"Philip D.",
""
]
] | In cosmological perturbation theory it is convenient to use the scalar, vector, tensor (SVT) basis as defined according to how these components transform under 3-dimensional rotations. In attempting to solve the fluctuation equations that are automatically written in terms of gauge-invariant combinations of these components, the equations are taken to break up into separate SVT sectors, the decomposition theorem. Here, without needing to specify a gauge, we solve the fluctuation equations exactly for some standard cosmologies, to show that in general the various gauge-invariant combinations only separate at a higher-derivative level. To achieve separation at the level of the fluctuation equations themselves one has to assume boundary conditions for the higher-derivative equations. While asymptotic conditions suffice for fluctuations around a dS background or a $k=0$ RW background, for fluctuations around a $k\neq 0$ RW background one additionally has to require that the fluctuations be well-behaved at the origin. We show that in certain cases the gauge-invariant combinations themselves involve both scalars and vectors. For such cases there is no decomposition theorem for the individual SVT components themselves, but for the gauge-invariant combinations there still can be. Given the lack of manifest covariance in defining a basis with respect to 3-dimensional rotations, we introduce an alternate SVT basis whose components are defined according to how they transform under 4-dimensional general coordinate transformations. With this basis the fluctuation equations greatly simplify, and while one can again break them up into separate gauge-invariant sectors at the higher-derivative level, in general we find that even with boundary conditions we do not obtain a decomposition theorem in which the fluctuations separate at the level of the fluctuation equations themselves. |
gr-qc/9905069 | Mark J. Hadley | Tammo Diemer and Mark J Hadley | Charge and the topology of spacetime | Accepted by Class. Quantum Grav. More explanation added as advised by
the referee. 13 pages | Class.Quant.Grav. 16 (1999) 3567-3577 | 10.1088/0264-9381/16/11/308 | null | gr-qc | null | A new class of electrically charged wormholes is described in which the outer
two sphere is not spanned by a compact coorientable hypersurface. These
wormholes can therefore display net electric charge from the source free
Maxwell's equation. This extends the work of Sorkin on non-space orientable
manifolds, to spacetimes which do not admit a time orientation. The work is
motivated by the suggestion that quantum theory can be explained by modelling
elementary particles as regions of spacetime with non-trivial causal structure.
The simplest example of an electrically charged spacetime carries a spherical
symmetry.
| [
{
"created": "Wed, 19 May 1999 09:18:58 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Sep 1999 09:22:11 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Diemer",
"Tammo",
""
],
[
"Hadley",
"Mark J",
""
]
] | A new class of electrically charged wormholes is described in which the outer two sphere is not spanned by a compact coorientable hypersurface. These wormholes can therefore display net electric charge from the source free Maxwell's equation. This extends the work of Sorkin on non-space orientable manifolds, to spacetimes which do not admit a time orientation. The work is motivated by the suggestion that quantum theory can be explained by modelling elementary particles as regions of spacetime with non-trivial causal structure. The simplest example of an electrically charged spacetime carries a spherical symmetry. |
1612.00632 | Andrea Addazi AndAdd | Andrea Addazi, Stephon Alexander, Yi-Fu Cai and Antonino Marciano | Dark matter and baryogenesis in the Fermi-bounce curvaton mechanism | some phrases are changed, one reference was added, results and
conclusions are the same; 16 pages, 1 figure | Chinese Physics C Vol. 42, No. 6 (2018) 065101 | 10.1088/1674-1137/42/6/065101 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We elaborate on a toy-model of matter bounce, in which the matter content is
constituted by two fermion species endowed with four fermion interaction term.
We describe the curvaton mechanism that is forth generated, and then argue that
one of the two fermionic species may realize baryogenesis, while the other
(lighter) one is compatible with constrains on extra hot dark matter particles.
| [
{
"created": "Fri, 2 Dec 2016 11:10:20 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Dec 2016 14:24:20 GMT",
"version": "v2"
}
] | 2018-05-29 | [
[
"Addazi",
"Andrea",
""
],
[
"Alexander",
"Stephon",
""
],
[
"Cai",
"Yi-Fu",
""
],
[
"Marciano",
"Antonino",
""
]
] | We elaborate on a toy-model of matter bounce, in which the matter content is constituted by two fermion species endowed with four fermion interaction term. We describe the curvaton mechanism that is forth generated, and then argue that one of the two fermionic species may realize baryogenesis, while the other (lighter) one is compatible with constrains on extra hot dark matter particles. |
0809.2590 | Tomasz Pawlowski | Wojciech Kaminski, Jerzy Lewandowski, Tomasz Pawlowski | Physical time and other conceptual issues of QG on the example of LQC | Revtex4, 19 pages, 1 figure, revised to match the version published
in CQG | Class.Quant.Grav.26:035012,2009 | 10.1088/0264-9381/26/3/035012 | IGC-08/9-1 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Several conceptual aspects of quantum gravity are studied on the example of
the homogeneous isotropic LQC model. In particular: $(i)$ The proper time of
the co-moving observers is showed to be a quantum operator {and} a quantum
spacetime metric tensor operator is derived. $(ii)$ Solutions of the quantum
scalar constraint for two different choices of the lapse function are compared
and contrasted. In particular it is shown that in case of model with masless
scalar field and cosmological constant $\Lambda$ the physical Hilbert spaces
constructed for two choices of lapse are the same for $\Lambda<0$ while they
are significantly different for $\Lambda>0$. $(iii)$ The mechanism of the
singularity avoidance is analyzed via detailed studies of an energy density
operator, whose essential spectrum was shown to be an interval $[0,\rhoc]$,
where $\rhoc\approx 0.41\rho_{\Pl}$. $(iv)$ The relation between the
kinematical and the physical quantum geometry is discussed on the level of
relation between observables.
| [
{
"created": "Mon, 15 Sep 2008 19:20:21 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Jan 2009 10:55:58 GMT",
"version": "v2"
}
] | 2009-01-27 | [
[
"Kaminski",
"Wojciech",
""
],
[
"Lewandowski",
"Jerzy",
""
],
[
"Pawlowski",
"Tomasz",
""
]
] | Several conceptual aspects of quantum gravity are studied on the example of the homogeneous isotropic LQC model. In particular: $(i)$ The proper time of the co-moving observers is showed to be a quantum operator {and} a quantum spacetime metric tensor operator is derived. $(ii)$ Solutions of the quantum scalar constraint for two different choices of the lapse function are compared and contrasted. In particular it is shown that in case of model with masless scalar field and cosmological constant $\Lambda$ the physical Hilbert spaces constructed for two choices of lapse are the same for $\Lambda<0$ while they are significantly different for $\Lambda>0$. $(iii)$ The mechanism of the singularity avoidance is analyzed via detailed studies of an energy density operator, whose essential spectrum was shown to be an interval $[0,\rhoc]$, where $\rhoc\approx 0.41\rho_{\Pl}$. $(iv)$ The relation between the kinematical and the physical quantum geometry is discussed on the level of relation between observables. |
0905.3900 | Wlodzimierz Piechocki | Przemyslaw Malkiewicz and Wlodzimierz Piechocki | Dirac quantization of membrane in time dependent orbifold | 16 pages, no figures, version accepted for publication in Journal of
High Energy Physics | JHEP 1008:054,2010 | 10.1007/JHEP08(2010)054 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present quantum theory of a membrane propagating in the vicinity of a time
dependent orbifold singularity. The dynamics of a membrane, with the parameters
space topology of a torus, winding uniformly around compact dimension of the
embedding spacetime is mathematically equivalent to the dynamics of a closed
string in a flat FRW spacetime. The construction of the physical Hilbert space
of a membrane makes use of the kernel space of self-adjoint constraint
operators. It is a subspace of the representation space of the constraints
algebra. There exist non-trivial quantum states of a membrane evolving across
the singularity.
| [
{
"created": "Sun, 24 May 2009 13:37:44 GMT",
"version": "v1"
},
{
"created": "Sat, 29 Aug 2009 11:38:32 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Aug 2010 13:34:15 GMT",
"version": "v3"
}
] | 2014-11-20 | [
[
"Malkiewicz",
"Przemyslaw",
""
],
[
"Piechocki",
"Wlodzimierz",
""
]
] | We present quantum theory of a membrane propagating in the vicinity of a time dependent orbifold singularity. The dynamics of a membrane, with the parameters space topology of a torus, winding uniformly around compact dimension of the embedding spacetime is mathematically equivalent to the dynamics of a closed string in a flat FRW spacetime. The construction of the physical Hilbert space of a membrane makes use of the kernel space of self-adjoint constraint operators. It is a subspace of the representation space of the constraints algebra. There exist non-trivial quantum states of a membrane evolving across the singularity. |
gr-qc/9405023 | null | Ignati Grigentch and D.V.Vassilevich | Reduced phase space quantization of Ashtekar's gravity on de Sitter
background | 9, CEBAF-TH-94-07 | Int.J.Mod.Phys.D4:581-588,1995 | 10.1142/S0218271895000405 | null | gr-qc | null | We solve perturbative constraints and eliminate gauge freedom for Ashtekar's
gravity on de Sitter background. We show that the reduced phase space consists
of transverse, traceless, symmetric fluctuations of the triad and of
transverse, traceless, symmetric fluctuations of the connection. A part of
gauge freedom corresponding to the conformal Killing vectors of the
three-manifold can be fixed only by imposing conditions on Lagrange multiplier.
The reduced phase space is equivalent to that of ADM gravity on the same
background.
| [
{
"created": "Mon, 9 May 1994 18:23:58 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Grigentch",
"Ignati",
""
],
[
"Vassilevich",
"D. V.",
""
]
] | We solve perturbative constraints and eliminate gauge freedom for Ashtekar's gravity on de Sitter background. We show that the reduced phase space consists of transverse, traceless, symmetric fluctuations of the triad and of transverse, traceless, symmetric fluctuations of the connection. A part of gauge freedom corresponding to the conformal Killing vectors of the three-manifold can be fixed only by imposing conditions on Lagrange multiplier. The reduced phase space is equivalent to that of ADM gravity on the same background. |
0801.1726 | S Habib Mazharimousavi | S. Habib Mazharimousavi and M. Halilsoy | Higher dimensional Yang-Mills black holes in third order Lovelock
gravity | 14 pages, 3 figures, to appear in Phys. Lett. B | Phys.Lett.B665:125-130,2008 | 10.1016/j.physletb.2008.06.007 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | By employing the higher (N\TEXTsymbol{>}5) dimensional version of the Wu-Yang
Ansatz we obtain magnetically charged new black hole solutions in the
Einstein-Yang-Mills-Lovelock (EYML) theory with second ($\alpha_{2}$) and third
($\alpha_{3}$)order parameters. These parameters, where $\alpha_{2}$ is also
known as the Gauss-Bonnet parameter, modify the horizons (and the resulting
thermodynamical properties) of the black holes. It is shown also that
asymptotically ($r\to \infty $), these parameters contribute to an effective
cosmological constant -without cosmological constant- so that the solution
behaves de-Sitter (Anti de-Sitter) like.
| [
{
"created": "Fri, 11 Jan 2008 07:32:36 GMT",
"version": "v1"
},
{
"created": "Fri, 13 Jun 2008 08:20:09 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Mazharimousavi",
"S. Habib",
""
],
[
"Halilsoy",
"M.",
""
]
] | By employing the higher (N\TEXTsymbol{>}5) dimensional version of the Wu-Yang Ansatz we obtain magnetically charged new black hole solutions in the Einstein-Yang-Mills-Lovelock (EYML) theory with second ($\alpha_{2}$) and third ($\alpha_{3}$)order parameters. These parameters, where $\alpha_{2}$ is also known as the Gauss-Bonnet parameter, modify the horizons (and the resulting thermodynamical properties) of the black holes. It is shown also that asymptotically ($r\to \infty $), these parameters contribute to an effective cosmological constant -without cosmological constant- so that the solution behaves de-Sitter (Anti de-Sitter) like. |
2207.01694 | Sanjar Shaymatov | Ayyesha K. Ahmed, Sanjar Shaymatov, Bobomurat Ahmedov | Weak cosmic censorship conjecture for the (2+1)-dimensional charged BTZ
black hole in the Einstein-Gauss-Bonnet Gravity | 8 pages, no figures | Physics of the Dark Universe 37, 101082 (2022) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well known that ($2+1$) dimensional charged BTZ (Banados, Teitelboim,
Zanelli) black hole can be overcharged by a charged scalar field and a charged
particle in contrast to their analogues in ($3+1$) and higher dimensions. In
this regard, it may play an important role to understand more deeply the
properties of the ($2+1$)-dimensional charged black hole in the
Einstein-Gauss-Bonnet (EGB) gravity. In this paper, we test the validity of the
weak cosmic censorship conjecture for the ($2+1$)-dimensional charged black
hole in novel EGB theory derived recently by Henniger et. al (2021). We show
that the minimum energy that particle can have at the horizon becomes negative
for both an extremal and nearly-extremal BTZ black holes in EGB gravity. It is
proven that both extremal and nearly-extremal $(2+1)$ dimensional BTZ black
hole could be overcharged in EGB theory, leading to the violation of the weak
cosmic censorship conjecture (WCCC), which is in good agreement with the
results obtained for the classical BTZ black hole.
| [
{
"created": "Mon, 4 Jul 2022 19:46:37 GMT",
"version": "v1"
}
] | 2022-07-06 | [
[
"Ahmed",
"Ayyesha K.",
""
],
[
"Shaymatov",
"Sanjar",
""
],
[
"Ahmedov",
"Bobomurat",
""
]
] | It is well known that ($2+1$) dimensional charged BTZ (Banados, Teitelboim, Zanelli) black hole can be overcharged by a charged scalar field and a charged particle in contrast to their analogues in ($3+1$) and higher dimensions. In this regard, it may play an important role to understand more deeply the properties of the ($2+1$)-dimensional charged black hole in the Einstein-Gauss-Bonnet (EGB) gravity. In this paper, we test the validity of the weak cosmic censorship conjecture for the ($2+1$)-dimensional charged black hole in novel EGB theory derived recently by Henniger et. al (2021). We show that the minimum energy that particle can have at the horizon becomes negative for both an extremal and nearly-extremal BTZ black holes in EGB gravity. It is proven that both extremal and nearly-extremal $(2+1)$ dimensional BTZ black hole could be overcharged in EGB theory, leading to the violation of the weak cosmic censorship conjecture (WCCC), which is in good agreement with the results obtained for the classical BTZ black hole. |
1701.05257 | Abraham Harte | Abraham I. Harte | Metric-independence of vacuum and force-free electromagnetic fields | 5 pages, minor additional comments | Phys. Rev. Lett. 118, 141101 (2017) | 10.1103/PhysRevLett.118.141101 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Electromagnetic fields which solve the vacuum Maxwell equations in one
spacetime are well-known to also be solutions in all spacetimes with
conformally-related metrics. This provides a sense in which electromagnetism
alone cannot be used to measure certain aspects of geometry. We show that there
is actually much more which cannot be so measured; relatively little of a
spacetime's geometry is in fact imprinted in any particular electromagnetic
field. This is demonstrated by finding a much larger class of metric
transformations---involving five free functions---which preserve Maxwell
solutions both in vacuum, without local currents, and also for the force-free
electrodynamics associated with a tenuous plasma. One consequence of this is
that many of the exact force-free fields which have previously been found
around Schwarzschild and Kerr black holes are also solutions in
appropriately-identified flat backgrounds. As a more direct application, we use
our metric transformations to write down a large class of electromagnetic waves
which remain unchanged by a large class of gravitational waves propagating "in
the same direction."
| [
{
"created": "Wed, 18 Jan 2017 23:25:14 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Apr 2017 10:04:34 GMT",
"version": "v2"
}
] | 2017-04-13 | [
[
"Harte",
"Abraham I.",
""
]
] | Electromagnetic fields which solve the vacuum Maxwell equations in one spacetime are well-known to also be solutions in all spacetimes with conformally-related metrics. This provides a sense in which electromagnetism alone cannot be used to measure certain aspects of geometry. We show that there is actually much more which cannot be so measured; relatively little of a spacetime's geometry is in fact imprinted in any particular electromagnetic field. This is demonstrated by finding a much larger class of metric transformations---involving five free functions---which preserve Maxwell solutions both in vacuum, without local currents, and also for the force-free electrodynamics associated with a tenuous plasma. One consequence of this is that many of the exact force-free fields which have previously been found around Schwarzschild and Kerr black holes are also solutions in appropriately-identified flat backgrounds. As a more direct application, we use our metric transformations to write down a large class of electromagnetic waves which remain unchanged by a large class of gravitational waves propagating "in the same direction." |
gr-qc/9905098 | Claus Kiefer | A. Barvinsky, A. Kamenshchik, C. Kiefer | Origin of the inflationary Universe | LATEX, 6 pages, selected for honorable mention in the 1999 Essay
Competition of the Gravity Research Foundation. To appear in Mod. Phys. Lett.
A | Mod.Phys.Lett. A14 (1999) 1083 | 10.1142/S0217732399001164 | Freiburg THEP-99/6 | gr-qc | null | We give a consistent description of how the inflationary Universe emerges in
quantum cosmology. This involves two steps: Firstly, it is shown that a
sensible probability peak can be obtained from the cosmological wave function.
This is achieved by going beyond the tree level of the semiclassical expansion.
Secondly, due to decoherence interference terms between different semiclassical
branches are negligibly small. The results give constraints on the particle
content of a unified theory.
| [
{
"created": "Thu, 27 May 1999 12:29:17 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Barvinsky",
"A.",
""
],
[
"Kamenshchik",
"A.",
""
],
[
"Kiefer",
"C.",
""
]
] | We give a consistent description of how the inflationary Universe emerges in quantum cosmology. This involves two steps: Firstly, it is shown that a sensible probability peak can be obtained from the cosmological wave function. This is achieved by going beyond the tree level of the semiclassical expansion. Secondly, due to decoherence interference terms between different semiclassical branches are negligibly small. The results give constraints on the particle content of a unified theory. |
2004.12549 | Andreas Doll | Antonio De Felice, Andreas Doll, Shinji Mukohyama | A theory of type-II minimally modified gravity | 18 pages | JCAP09(2020)034 | 10.1088/1475-7516/2020/09/034 | YITP-20-55, IPMU20-0040 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a modified gravity theory that propagates only two local
gravitational degrees of freedom and that does not have an Einstein frame.
According to the classification in JCAP 01 (2019) 017 [arXiv:1810.01047
[gr-qc]], this is a type-II minimally modified gravity theory. The theory is
characterized by the gravitational constant $G_{\rm N}$ and a function
$V(\phi)$ of a non-dynamical auxiliary field $\phi$ that plays the role of dark
energy. Once one fixes a homogeneous and isotropic cosmological background, the
form of $V(\phi)$ is determined and the theory no longer possesses a free
parameter or a free function, besides $G_{\rm N}$. For $V'(\phi) = 0$ the
theory reduces to general relativity (GR) with $G_N$ being the Newton's
constant and $V=const.$ being the cosmological constant. For $V'(\phi) \ne 0$,
it is shown that gravity behaves differently from GR but that GR with $G_{\rm
N}$ being the Newton's constant is recovered for weak gravity at distance and
time scales sufficiently shorter than the scale associated with $V(\phi)$.
Therefore this theory provides the simplest framework of cosmology in which
deviations from GR can be tested by observational data.
| [
{
"created": "Mon, 27 Apr 2020 02:27:05 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Sep 2020 16:13:19 GMT",
"version": "v2"
}
] | 2020-09-17 | [
[
"De Felice",
"Antonio",
""
],
[
"Doll",
"Andreas",
""
],
[
"Mukohyama",
"Shinji",
""
]
] | We propose a modified gravity theory that propagates only two local gravitational degrees of freedom and that does not have an Einstein frame. According to the classification in JCAP 01 (2019) 017 [arXiv:1810.01047 [gr-qc]], this is a type-II minimally modified gravity theory. The theory is characterized by the gravitational constant $G_{\rm N}$ and a function $V(\phi)$ of a non-dynamical auxiliary field $\phi$ that plays the role of dark energy. Once one fixes a homogeneous and isotropic cosmological background, the form of $V(\phi)$ is determined and the theory no longer possesses a free parameter or a free function, besides $G_{\rm N}$. For $V'(\phi) = 0$ the theory reduces to general relativity (GR) with $G_N$ being the Newton's constant and $V=const.$ being the cosmological constant. For $V'(\phi) \ne 0$, it is shown that gravity behaves differently from GR but that GR with $G_{\rm N}$ being the Newton's constant is recovered for weak gravity at distance and time scales sufficiently shorter than the scale associated with $V(\phi)$. Therefore this theory provides the simplest framework of cosmology in which deviations from GR can be tested by observational data. |
1912.05314 | Astrid Eichhorn | Astrid Eichhorn, Johannes Lumma, Antonio D. Pereira, Arslan Sikandar | Universal critical behavior in tensor models for four-dimensional
quantum gravity | 10 pages | null | 10.1007/JHEP02(2020)110 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Four-dimensional random geometries can be generated by statistical models
with rank-4 tensors as random variables. These are dual to discrete building
blocks of random geometries. We discover a potential candidate for a continuum
limit in such a model by employing background-independent coarse-graining
techniques where the tensor size serves as a pre-geometric notion of scale. A
fixed point candidate which features two relevant directions is found. The
possible relevance of this result in view of universal results for quantum
gravity and a potential connection to the asymptotic-safety program is
discussed.
| [
{
"created": "Wed, 11 Dec 2019 13:55:01 GMT",
"version": "v1"
}
] | 2020-03-18 | [
[
"Eichhorn",
"Astrid",
""
],
[
"Lumma",
"Johannes",
""
],
[
"Pereira",
"Antonio D.",
""
],
[
"Sikandar",
"Arslan",
""
]
] | Four-dimensional random geometries can be generated by statistical models with rank-4 tensors as random variables. These are dual to discrete building blocks of random geometries. We discover a potential candidate for a continuum limit in such a model by employing background-independent coarse-graining techniques where the tensor size serves as a pre-geometric notion of scale. A fixed point candidate which features two relevant directions is found. The possible relevance of this result in view of universal results for quantum gravity and a potential connection to the asymptotic-safety program is discussed. |
gr-qc/0402103 | Stephane Fay | Stephane Fay | Scalar fields properties for flat galactic rotation curves | 10 pages | Astron.Astrophys.413:799,2004; Astron.Astrophys.413:799-805,2004 | 10.1051/0004-6361:20031540 | null | gr-qc astro-ph | null | The whole class of minimally coupled and massive scalar fields which may be
responsible for flattening of galactic rotation curves is found. An interesting
relation with a class of scalar-tensor theories able to isotropise anisotropic
models of Universe is shown. The resulting metric is found and its stability
and scalar field properties are tested with respect to the presence of a second
scalar field or a small perturbation of the rotation velocity at galactic outer
radii.
| [
{
"created": "Tue, 24 Feb 2004 14:34:12 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Fay",
"Stephane",
""
]
] | The whole class of minimally coupled and massive scalar fields which may be responsible for flattening of galactic rotation curves is found. An interesting relation with a class of scalar-tensor theories able to isotropise anisotropic models of Universe is shown. The resulting metric is found and its stability and scalar field properties are tested with respect to the presence of a second scalar field or a small perturbation of the rotation velocity at galactic outer radii. |
gr-qc/0409105 | Matteo Luca Ruggiero | Guido Rizzi, Matteo Luca Ruggiero, Alessio Serafini | Synchronization Gauges and the Principles of Special Relativity | 56 pages, 3 eps figures, invited paper; to appear in Foundations of
Physics (Special Issue to honor Prof. Franco Selleri on his 70th birthday) | Found.Phys. 34 (2005) 1835-1887 | 10.1007/s10701-004-1624-3 | null | gr-qc | null | The axiomatic bases of Special Relativity Theory (SRT) are thoroughly
re-examined from an operational point of view, with particular emphasis on the
status of Einstein synchronization in the light of the possibility of arbitrary
synchronization procedures in inertial reference frames. Once correctly and
explicitly phrased, the principles of SRT allow for a wide range of `theories'
that differ from the standard SRT only for the difference in the chosen
synchronization procedures, but are wholly equivalent to SRT in predicting
empirical facts. This results in the introduction, in the full background of
SRT, of a suitable synchronization gauge. A complete hierarchy of
synchronization gauges is introduced and elucidated, ranging from the useful
Selleri synchronization gauge (which should lead, according to Selleri, to a
multiplicity of theories alternative to SRT) to the more general Mansouri-Sexl
synchronization gauge and, finally, to the even more general
Anderson-Vetharaniam-Stedman's synchronization gauge. It is showed that all
these gauges do not challenge the SRT, as claimed by Selleri, but simply lead
to a number of formalisms which leave the geometrical structure of Minkowski
spacetime unchanged. Several aspects of fundamental and applied interest
related to the conventional aspect of the synchronization choice are discussed,
encompassing the issue of the one-way velocity of light on inertial and
rotating reference frames, the GPS's working, and the recasting of Maxwell
equations in generic synchronizations. Finally, it is showed how the gauge
freedom introduced in SRT can be exploited in order to give a clear explanation
of the Sagnac effect for counter-propagating matter beams.
| [
{
"created": "Tue, 28 Sep 2004 10:25:49 GMT",
"version": "v1"
},
{
"created": "Mon, 18 Oct 2004 12:31:56 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Rizzi",
"Guido",
""
],
[
"Ruggiero",
"Matteo Luca",
""
],
[
"Serafini",
"Alessio",
""
]
] | The axiomatic bases of Special Relativity Theory (SRT) are thoroughly re-examined from an operational point of view, with particular emphasis on the status of Einstein synchronization in the light of the possibility of arbitrary synchronization procedures in inertial reference frames. Once correctly and explicitly phrased, the principles of SRT allow for a wide range of `theories' that differ from the standard SRT only for the difference in the chosen synchronization procedures, but are wholly equivalent to SRT in predicting empirical facts. This results in the introduction, in the full background of SRT, of a suitable synchronization gauge. A complete hierarchy of synchronization gauges is introduced and elucidated, ranging from the useful Selleri synchronization gauge (which should lead, according to Selleri, to a multiplicity of theories alternative to SRT) to the more general Mansouri-Sexl synchronization gauge and, finally, to the even more general Anderson-Vetharaniam-Stedman's synchronization gauge. It is showed that all these gauges do not challenge the SRT, as claimed by Selleri, but simply lead to a number of formalisms which leave the geometrical structure of Minkowski spacetime unchanged. Several aspects of fundamental and applied interest related to the conventional aspect of the synchronization choice are discussed, encompassing the issue of the one-way velocity of light on inertial and rotating reference frames, the GPS's working, and the recasting of Maxwell equations in generic synchronizations. Finally, it is showed how the gauge freedom introduced in SRT can be exploited in order to give a clear explanation of the Sagnac effect for counter-propagating matter beams. |
1411.5454 | Kokubu Takafumi | Takafumi Kokubu and Tomohiro Harada | Negative tension branes as stable thin shell wormholes | 24pages, 6 figures | Class.Quant.Grav. 32 (2015) 20, 205001 | 10.1088/0264-9381/32/20/205001 | RUP-14-17 | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate negative tension branes as stable thin shell wormholes in
Reissner-Nordstrom-(anti) de Sitter spacetimes in $d$ dimensional Einstein
gravity. Imposing Z2 symmetry, we construct and classify traversable static
thin shell wormholes in spherical, planar (or cylindrical) and hyperbolic
symmetries. In spherical geometry, we find the higher dimensional counterpart
of Barcelo and Visser's wormholes, which are stable against spherically
symmetric perturbations. We also find the classes of thin shell wormholes in
planar and hyperbolic symmetries with a negative cosmological constant, which
are stable against perturbations preserving symmetries. In most cases, stable
wormholes are found with the combination of an electric charge and a negative
cosmological constant. However, as special cases, we find stable wormholes even
with vanishing cosmological constant in spherical symmetry and with vanishing
electric charge in hyperbolic symmetry.
| [
{
"created": "Thu, 20 Nov 2014 06:46:17 GMT",
"version": "v1"
}
] | 2015-12-29 | [
[
"Kokubu",
"Takafumi",
""
],
[
"Harada",
"Tomohiro",
""
]
] | We investigate negative tension branes as stable thin shell wormholes in Reissner-Nordstrom-(anti) de Sitter spacetimes in $d$ dimensional Einstein gravity. Imposing Z2 symmetry, we construct and classify traversable static thin shell wormholes in spherical, planar (or cylindrical) and hyperbolic symmetries. In spherical geometry, we find the higher dimensional counterpart of Barcelo and Visser's wormholes, which are stable against spherically symmetric perturbations. We also find the classes of thin shell wormholes in planar and hyperbolic symmetries with a negative cosmological constant, which are stable against perturbations preserving symmetries. In most cases, stable wormholes are found with the combination of an electric charge and a negative cosmological constant. However, as special cases, we find stable wormholes even with vanishing cosmological constant in spherical symmetry and with vanishing electric charge in hyperbolic symmetry. |
0901.0394 | Alan Coley | A. Coley, S. Hervik, G. Papadopoulos, N. Pelavas | Kundt Spacetimes | 40 pages. to appear CQG | Class.Quant.Grav.26:105016,2009 | 10.1088/0264-9381/26/10/105016 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Kundt spacetimes are of great importance in general relativity in 4
dimensions and have a number of topical applications in higher dimensions in
the context of string theory. The degenerate Kundt spacetimes have many special
and unique mathematical properties, including their invariant curvature
structure and their holonomy structure. We provide a rigorous geometrical
kinematical definition of the general Kundt spacetime in 4 dimensions;
essentially a Kundt spacetime is defined as one admitting a null vector that is
geodesic, expansion-free, shear-free and twist-free. A Kundt spacetime is said
to be degenerate if the preferred kinematic and curvature null frames are all
aligned. The degenerate Kundt spacetimes are the only spacetimes in 4
dimensions that are not $\mathcal{I}$-non-degenerate, so that they are not
determined by their scalar polynomial curvature invariants. We first discuss
the non-aligned Kundt spacetimes, and then turn our attention to the degenerate
Kundt spacetimes. The degenerate Kundt spacetimes are classified algebraically
by the Riemann tensor and its covariant derivatives in the aligned kinematic
frame; as an example, we classify Riemann type D degenerate Kundt spacetimes in
which $\nabla(Riem),\nabla^{(2)}(Riem)$ are also of type D. We discuss other
local characteristics of the degenerate Kundt spacetimes. Finally, we discuss
degenerate Kundt spacetimes in higher dimensions.
| [
{
"created": "Sun, 4 Jan 2009 19:29:38 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Mar 2009 22:40:43 GMT",
"version": "v2"
}
] | 2009-10-09 | [
[
"Coley",
"A.",
""
],
[
"Hervik",
"S.",
""
],
[
"Papadopoulos",
"G.",
""
],
[
"Pelavas",
"N.",
""
]
] | Kundt spacetimes are of great importance in general relativity in 4 dimensions and have a number of topical applications in higher dimensions in the context of string theory. The degenerate Kundt spacetimes have many special and unique mathematical properties, including their invariant curvature structure and their holonomy structure. We provide a rigorous geometrical kinematical definition of the general Kundt spacetime in 4 dimensions; essentially a Kundt spacetime is defined as one admitting a null vector that is geodesic, expansion-free, shear-free and twist-free. A Kundt spacetime is said to be degenerate if the preferred kinematic and curvature null frames are all aligned. The degenerate Kundt spacetimes are the only spacetimes in 4 dimensions that are not $\mathcal{I}$-non-degenerate, so that they are not determined by their scalar polynomial curvature invariants. We first discuss the non-aligned Kundt spacetimes, and then turn our attention to the degenerate Kundt spacetimes. The degenerate Kundt spacetimes are classified algebraically by the Riemann tensor and its covariant derivatives in the aligned kinematic frame; as an example, we classify Riemann type D degenerate Kundt spacetimes in which $\nabla(Riem),\nabla^{(2)}(Riem)$ are also of type D. We discuss other local characteristics of the degenerate Kundt spacetimes. Finally, we discuss degenerate Kundt spacetimes in higher dimensions. |
2012.11545 | Vladimir O. Soloviev | Vladimir O. Soloviev | The Canonical Structure of Bigravity | 11 pages, 1 table, based on a talk given at the Fourth Zeldovich
meeting, an international conference in honor of Ya. B. Zeldovich held in
Minsk, Belarus on September 7--11, 2020 | null | 10.1134/S1063772921100383 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work is motivated by an intention to make the theory of bigravity more
comprehensible. Bigravity is a modification of the General Relativity (GR),
maybe even the most natural one because it is based on the equivalence
principle. The Hamiltonian formalism in tetrad variables transparently
demonstrates the structure of bigravity
| [
{
"created": "Mon, 21 Dec 2020 18:27:41 GMT",
"version": "v1"
}
] | 2021-11-03 | [
[
"Soloviev",
"Vladimir O.",
""
]
] | This work is motivated by an intention to make the theory of bigravity more comprehensible. Bigravity is a modification of the General Relativity (GR), maybe even the most natural one because it is based on the equivalence principle. The Hamiltonian formalism in tetrad variables transparently demonstrates the structure of bigravity |
2002.01341 | Kimet Jusufi | Kimet Jusufi, Phongpichit Channuie, Mubasher Jamil | Traversable Wormholes Supported by GUP Corrected Casimir Energy | 14 pages, 18 figures. Accepted for publication in EPJC. arXiv admin
note: text overlap with arXiv:1112.2924 by other authors | Eur. Phys. J. C 80, 127 (2020) | 10.1140/epjc/s10052-020-7690-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we investigate the effect of the Generalized Uncertainty
Principle (GUP) in the Casimir wormhole spacetime recently proposed by
Garattini [Eur. Phys. J. C (2019) 79: 951]. In particular, we consider three
types of the GUP relations, firstly the Kempf, Mangano and Mann (KMM) model,
secondly the Detournay, Gabriel and Spindel (DGS) model, and finally the so
called type II model for GUP principle. To this end, we consider three specific
models of the redshift function along with two different EoS of state given by
$\mathcal{P}_r(r)=\omega_r(r) \rho(r)$ along with $\mathcal{P}_t(r)=\omega_t
(r)\mathcal{P}_r(r)$ and obtain a class of asymptotically flat wormhole
solutions supported by Casimir energy under the effect of GUP. Furthermore we
check the null, weak, and strong condition at the wormhole throat with a radius
$r_0$, and show that in general the classical energy condition are violated by
some arbitrary quantity at the wormhole throat. Importantly, we examine the
wormhole geometry with semi-classical corrections via embedding diagrams. We
also consider the ADM mass of the wormhole, the volume integral quantifier to
calculate the amount of the exotic matter near the wormhole throat, and the
deflection angle of light.
| [
{
"created": "Mon, 3 Feb 2020 11:43:52 GMT",
"version": "v1"
}
] | 2020-02-18 | [
[
"Jusufi",
"Kimet",
""
],
[
"Channuie",
"Phongpichit",
""
],
[
"Jamil",
"Mubasher",
""
]
] | In this paper, we investigate the effect of the Generalized Uncertainty Principle (GUP) in the Casimir wormhole spacetime recently proposed by Garattini [Eur. Phys. J. C (2019) 79: 951]. In particular, we consider three types of the GUP relations, firstly the Kempf, Mangano and Mann (KMM) model, secondly the Detournay, Gabriel and Spindel (DGS) model, and finally the so called type II model for GUP principle. To this end, we consider three specific models of the redshift function along with two different EoS of state given by $\mathcal{P}_r(r)=\omega_r(r) \rho(r)$ along with $\mathcal{P}_t(r)=\omega_t (r)\mathcal{P}_r(r)$ and obtain a class of asymptotically flat wormhole solutions supported by Casimir energy under the effect of GUP. Furthermore we check the null, weak, and strong condition at the wormhole throat with a radius $r_0$, and show that in general the classical energy condition are violated by some arbitrary quantity at the wormhole throat. Importantly, we examine the wormhole geometry with semi-classical corrections via embedding diagrams. We also consider the ADM mass of the wormhole, the volume integral quantifier to calculate the amount of the exotic matter near the wormhole throat, and the deflection angle of light. |
gr-qc/9705050 | Dharam V. Ahluwalia | D. V. Ahluwalia (Los Alamos, and ANSER, Inc.) | On a New Non-Geometric Element in Gravity | 1997 Gravity Research Foundation Essay (Fourth Prize), 11 pages | Gen.Rel.Grav.29:1491-1501,1997 | 10.1023/A:1018874111373 | LA-UR-97-864 | gr-qc quant-ph | null | In this essay a generalized notion of flavor-oscillation clocks is
introduced. The generalization contains the element that various superimposed
mass eigenstates may have different relative orientation of the component of
their spin with respect to the rotational axis of the the gravitational source.
It is found that these quantum mechanical clocks do not always redshift
identically when moved from the gravitational environment of a non-rotating
source to the field of a rotating source. The non-geometric contributions to
the redshifts may be interpreted as quantum mechanically induced fluctuations
over a geometric structure of space-time.
| [
{
"created": "Tue, 20 May 1997 19:20:45 GMT",
"version": "v1"
},
{
"created": "Wed, 21 May 1997 01:18:55 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Ahluwalia",
"D. V.",
"",
"Los Alamos, and ANSER, Inc."
]
] | In this essay a generalized notion of flavor-oscillation clocks is introduced. The generalization contains the element that various superimposed mass eigenstates may have different relative orientation of the component of their spin with respect to the rotational axis of the the gravitational source. It is found that these quantum mechanical clocks do not always redshift identically when moved from the gravitational environment of a non-rotating source to the field of a rotating source. The non-geometric contributions to the redshifts may be interpreted as quantum mechanically induced fluctuations over a geometric structure of space-time. |
2110.06247 | Harkirat Singh Sahota | Harkirat Singh Sahota and Kinjalk Lochan | Infrared signatures of quantum bounce in a minisuperspace analysis of
Lema\^{\i}tre-Tolman-Bondi dust collapse | 21 pages, 5 figures, Version published in Phys. Rev. D | Phys. Rev. D 104, 126027 (2021) | 10.1103/PhysRevD.104.126027 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the quantum treatment of collapsing matter, a viable mode analysis is
supposed to give information regarding emission during the collapse.
Nevertheless, partly owing to operator ordering ambiguities involved in a
typical quantum gravity analysis, the availability of such well-defined modes
is not guaranteed. We study the mode decomposition of the unitarily evolving
wave packet constructed for the quantum model of spherically symmetric dust
collapsing in a marginally bound Lema\^{\i}tre-Tolman-Bondi (LTB) model. We
identify the observable depicting mode decomposition, and using the freedom of
operator ordering ambiguity, we obtain the Hermitian extension of this operator
alongside the Hermitian Hamiltonian. After identifying incoming and outgoing
modes with this operator's eigenstates, we estimate their contributions to the
radiation profile. The infrared sector of this process demonstrates some
characteristic features which turn out to be highly sensitive to the
near-bounce dynamics of the dust cloud. Near the epoch of classical
singularity, there is a significant contribution from incoming/outgoing modes
of small wavenumber in the expanding/collapsing phase of the dust cloud, which
keeps on decreasing as one moves away from the singularity. The information of
the bounce is carried over to the infrared modes through a flip from largely
incoming to largely outgoing radiation as the evolution progresses from
collapsing to expanding phase, much before the information of bounce comes
about to any observer. In the infrared sector, the saturation value of the
amplitude marks the bounce radius. Thus, we argue that the information of the
short scale physics is essentially carried over to the longest wavelength in
this quantum gravity model, which we argue is rather more prominent for low
energy processes.
| [
{
"created": "Tue, 12 Oct 2021 18:03:12 GMT",
"version": "v1"
},
{
"created": "Tue, 28 Dec 2021 10:20:39 GMT",
"version": "v2"
}
] | 2021-12-30 | [
[
"Sahota",
"Harkirat Singh",
""
],
[
"Lochan",
"Kinjalk",
""
]
] | In the quantum treatment of collapsing matter, a viable mode analysis is supposed to give information regarding emission during the collapse. Nevertheless, partly owing to operator ordering ambiguities involved in a typical quantum gravity analysis, the availability of such well-defined modes is not guaranteed. We study the mode decomposition of the unitarily evolving wave packet constructed for the quantum model of spherically symmetric dust collapsing in a marginally bound Lema\^{\i}tre-Tolman-Bondi (LTB) model. We identify the observable depicting mode decomposition, and using the freedom of operator ordering ambiguity, we obtain the Hermitian extension of this operator alongside the Hermitian Hamiltonian. After identifying incoming and outgoing modes with this operator's eigenstates, we estimate their contributions to the radiation profile. The infrared sector of this process demonstrates some characteristic features which turn out to be highly sensitive to the near-bounce dynamics of the dust cloud. Near the epoch of classical singularity, there is a significant contribution from incoming/outgoing modes of small wavenumber in the expanding/collapsing phase of the dust cloud, which keeps on decreasing as one moves away from the singularity. The information of the bounce is carried over to the infrared modes through a flip from largely incoming to largely outgoing radiation as the evolution progresses from collapsing to expanding phase, much before the information of bounce comes about to any observer. In the infrared sector, the saturation value of the amplitude marks the bounce radius. Thus, we argue that the information of the short scale physics is essentially carried over to the longest wavelength in this quantum gravity model, which we argue is rather more prominent for low energy processes. |
2108.04234 | Debashis Gangopadhyay | Somnath Mukherjee, Debashis Gangopadhyay | An accelerated universe with negative equation of state parameter in
Inhomogeneous Cosmology with $k$-essence scalar field | 7 pages, latex. arXiv admin note: substantial text overlap with
arXiv:1602.01289 | Physics of The Dark Universe, Volume 32, May 2021, 100800 | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We obtain a scaling relation for spherically symmetric k-essence scalar
fields $\phi(r,t)$ for an inhomogeneous cosmology with the Lemaitre-Tolman-
Bondi (LTB) metric. We show that this scaling relation reduces to the known
relation for a homogeneous cosmology when the LTB metric reduces to the
Friedmann-Lemaitre-Robertson-Walker (FLRW) metric under certain identifications
of the metric functions. A k-essence lagrangian is set up and the
Euler-Lagrangian equations solved assuming $\phi(r,t)=\phi_{1}(r) +
\phi_{2}(t)$. The solutions enable the LBT metric functions to be related to
the fields. The LTB inhomogeneous universe exhibits accelerated expansion
i.e.cosmic acceleration driven by negative pressure.
| [
{
"created": "Sun, 8 Aug 2021 05:56:23 GMT",
"version": "v1"
}
] | 2021-08-21 | [
[
"Mukherjee",
"Somnath",
""
],
[
"Gangopadhyay",
"Debashis",
""
]
] | We obtain a scaling relation for spherically symmetric k-essence scalar fields $\phi(r,t)$ for an inhomogeneous cosmology with the Lemaitre-Tolman- Bondi (LTB) metric. We show that this scaling relation reduces to the known relation for a homogeneous cosmology when the LTB metric reduces to the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric under certain identifications of the metric functions. A k-essence lagrangian is set up and the Euler-Lagrangian equations solved assuming $\phi(r,t)=\phi_{1}(r) + \phi_{2}(t)$. The solutions enable the LBT metric functions to be related to the fields. The LTB inhomogeneous universe exhibits accelerated expansion i.e.cosmic acceleration driven by negative pressure. |
gr-qc/0508057 | Oleg Zaslavskii | O.B.Zaslavskii | Exactly solvable model of wormhole supported by phantom energy | 6 pages. Two references added, typos corrected. Accepted for
publication in Phys. Rev. D as Rapid Communication | Phys.Rev. D72 (2005) 061303 | 10.1103/PhysRevD.72.061303 | null | gr-qc astro-ph hep-th | null | We have found a simple exact solution of spherically-symmetrical Einstein
equations describing a wormhole for an inhomogeneous distribution of the
phantom energy. The equation of state is linear but highly anisotropic: while
the radial pressure is negative, the transversal one is positive. At infinity
the spacetime is not asymptotically flat and possesses on each side of the
bridge a regular cosmological Killing horizon with an infinite area,
impenetrable for any particles. This horizon does not arise if the wormhole
region is glued to the Schwarzschild region. In doing so, the wormhole can
enclose an arbitrary amount of the phantom energy. The configuration under
discussion has a limit in which the phantom energy turns into the string dust,
the areal radius tends to the constant. In this limit, the strong gravitational
mass defect is realized in that the gravitational active mass is finite and
constant while the proper mass integrated over the total manifold is infinite.
| [
{
"created": "Sat, 13 Aug 2005 08:18:35 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Sep 2005 17:22:03 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Zaslavskii",
"O. B.",
""
]
] | We have found a simple exact solution of spherically-symmetrical Einstein equations describing a wormhole for an inhomogeneous distribution of the phantom energy. The equation of state is linear but highly anisotropic: while the radial pressure is negative, the transversal one is positive. At infinity the spacetime is not asymptotically flat and possesses on each side of the bridge a regular cosmological Killing horizon with an infinite area, impenetrable for any particles. This horizon does not arise if the wormhole region is glued to the Schwarzschild region. In doing so, the wormhole can enclose an arbitrary amount of the phantom energy. The configuration under discussion has a limit in which the phantom energy turns into the string dust, the areal radius tends to the constant. In this limit, the strong gravitational mass defect is realized in that the gravitational active mass is finite and constant while the proper mass integrated over the total manifold is infinite. |
0709.0532 | Vitor Cardoso | Vitor Cardoso, Paolo Pani, Mariano Cadoni, Marco Cavaglia | Ergoregion instability of ultra-compact astrophysical objects | 14 pages, 8 Figures, 6 Tables. RevTeX4. v2: Shortened version,
published on PRD, focused on gravastars and boson stars. Sections on
wormholes and superspinars will appear elsewhere | Phys.Rev.D77:124044,2008 | 10.1103/PhysRevD.77.124044 | null | gr-qc astro-ph hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Most of the properties of black holes can be mimicked by horizonless compact
objects such as gravastars and boson stars. We show that these ultra-compact
objects develop a strong ergoregion instability when rapidly spinning.
Instability timescales can be of the order of 0.1 seconds to 1 week for objects
with mass M=1-10^6 solar masses and angular momentum J> 0.4 M^2. This provides
a strong indication that ultra-compact objects with large rotation are black
holes. Explosive events due to ergoregion instability have a well-defined
gravitational-wave signature. These events could be detected by next-generation
gravitational-wave detectors such as Advanced LIGO or LISA.
| [
{
"created": "Tue, 4 Sep 2007 20:25:29 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Jul 2008 20:28:11 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Cardoso",
"Vitor",
""
],
[
"Pani",
"Paolo",
""
],
[
"Cadoni",
"Mariano",
""
],
[
"Cavaglia",
"Marco",
""
]
] | Most of the properties of black holes can be mimicked by horizonless compact objects such as gravastars and boson stars. We show that these ultra-compact objects develop a strong ergoregion instability when rapidly spinning. Instability timescales can be of the order of 0.1 seconds to 1 week for objects with mass M=1-10^6 solar masses and angular momentum J> 0.4 M^2. This provides a strong indication that ultra-compact objects with large rotation are black holes. Explosive events due to ergoregion instability have a well-defined gravitational-wave signature. These events could be detected by next-generation gravitational-wave detectors such as Advanced LIGO or LISA. |
2305.10943 | Dnyaneshwar Tadas | S. P. Hatkar, D. P. Tadas, S. D. Katore | Non-interacting String and Holographic Dark Energy Cosmological Models
in f(R) Theory of Gravitation | 15 Pages, 07 Figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, a new class of string and holographic dark energy (HDE)
cosmological model in the context of f(R) theory of gravity using the Kasner
metric is considered. The exact solution of filed equations are obtained by
using the relation between average scale factor and the scalar function f(R).
It is observed that the universe is accelerating and expanding. The string
phase of the universe is present at early stage of evolution of the universe.
The universe is dominated by quintessence type HDE at present. Effect of the
curvature function f(R) is also observed on dynamical parameters.
| [
{
"created": "Thu, 18 May 2023 13:01:17 GMT",
"version": "v1"
}
] | 2023-05-19 | [
[
"Hatkar",
"S. P.",
""
],
[
"Tadas",
"D. P.",
""
],
[
"Katore",
"S. D.",
""
]
] | In this paper, a new class of string and holographic dark energy (HDE) cosmological model in the context of f(R) theory of gravity using the Kasner metric is considered. The exact solution of filed equations are obtained by using the relation between average scale factor and the scalar function f(R). It is observed that the universe is accelerating and expanding. The string phase of the universe is present at early stage of evolution of the universe. The universe is dominated by quintessence type HDE at present. Effect of the curvature function f(R) is also observed on dynamical parameters. |
2112.09950 | Juan M. Z\'arate Pretel | Jos\'e C. Jim\'enez, Juan M. Z. Pretel, Eduardo S. Fraga, Sergio E.
Jor\'as and Ribamar R. R. Reis | $R^2$-gravity quark stars from perturbative QCD | Accepted for publication in JCAP; 17 pages, 5 figures and minor
clarifications added | JCAP 07 (2022) 017 | 10.1088/1475-7516/2022/07/017 | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the structure of quark stars in the framework of $f(R)= R+
\alpha R^2$ gravity using an equation of state for cold quark matter obtained
from perturbative QCD, parametrized only by the renormalization scale. We show
that a considerably large range of the free parameter $\alpha$, within and even
beyond the constraints previously reported in the literature, yield
non-negligible modifications in the mass and radius of stars with large central
mass densities. Besides, their stability against baryon evaporation is analyzed
through the behavior of the associated total binding energies for which we show
that these energies are slightly affected by the modified gravity term in the
regime of high proper (baryon) masses.
| [
{
"created": "Sat, 18 Dec 2021 15:05:50 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Jan 2022 16:47:48 GMT",
"version": "v2"
},
{
"created": "Tue, 24 May 2022 14:49:40 GMT",
"version": "v3"
}
] | 2022-07-12 | [
[
"Jiménez",
"José C.",
""
],
[
"Pretel",
"Juan M. Z.",
""
],
[
"Fraga",
"Eduardo S.",
""
],
[
"Jorás",
"Sergio E.",
""
],
[
"Reis",
"Ribamar R. R.",
""
]
] | We investigate the structure of quark stars in the framework of $f(R)= R+ \alpha R^2$ gravity using an equation of state for cold quark matter obtained from perturbative QCD, parametrized only by the renormalization scale. We show that a considerably large range of the free parameter $\alpha$, within and even beyond the constraints previously reported in the literature, yield non-negligible modifications in the mass and radius of stars with large central mass densities. Besides, their stability against baryon evaporation is analyzed through the behavior of the associated total binding energies for which we show that these energies are slightly affected by the modified gravity term in the regime of high proper (baryon) masses. |
1202.6015 | Stefano Finazzi | Stefano Finazzi and Renaud Parentani | Hawking radiation in dispersive theories, the two regimes | 11 pages, 9 figures | Phys. Rev. D 85, 124027 (2012) | 10.1103/PhysRevD.85.124027 | null | gr-qc cond-mat.quant-gas hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compute the black hole radiation spectrum in the presence of
high-frequency dispersion in a large set of situations. In all cases, the
spectrum diverges like the inverse of the Killing frequency. When studying the
low-frequency spectrum, we find only two regimes: an adiabatic one where the
corrections with respect to the standard temperature are small, and an abrupt
one regulated by dispersion, in which the near-horizon metric can be replaced
by step functions. The transition from one regime to the other is governed by a
single parameter which also governs the net redshift undergone by dispersive
modes. These results can be used to characterize the quasiparticles spectrum of
recent and future experiments aiming to detect the analogue Hawking radiation.
They also apply to theories of quantum gravity which violate Lorentz
invariance.
| [
{
"created": "Mon, 27 Feb 2012 18:17:50 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Jun 2012 15:10:06 GMT",
"version": "v2"
}
] | 2012-06-15 | [
[
"Finazzi",
"Stefano",
""
],
[
"Parentani",
"Renaud",
""
]
] | We compute the black hole radiation spectrum in the presence of high-frequency dispersion in a large set of situations. In all cases, the spectrum diverges like the inverse of the Killing frequency. When studying the low-frequency spectrum, we find only two regimes: an adiabatic one where the corrections with respect to the standard temperature are small, and an abrupt one regulated by dispersion, in which the near-horizon metric can be replaced by step functions. The transition from one regime to the other is governed by a single parameter which also governs the net redshift undergone by dispersive modes. These results can be used to characterize the quasiparticles spectrum of recent and future experiments aiming to detect the analogue Hawking radiation. They also apply to theories of quantum gravity which violate Lorentz invariance. |
gr-qc/0602023 | Lev Prokhorov | Lev V. Prokhorov | Quantum mechanics and the cosmological constant | 9 pages; minor corrections | null | null | null | gr-qc hep-th quant-ph | null | It is shown that in the model [3,4] of quantum mechanics besides probability
amplitudes, the Planck constant and the Fock space, the cosmological constant
also appear in the natural way. The Poisson brackets are generalized for the
case of kinetics.
| [
{
"created": "Tue, 7 Feb 2006 09:22:19 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Feb 2006 18:40:04 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Prokhorov",
"Lev V.",
""
]
] | It is shown that in the model [3,4] of quantum mechanics besides probability amplitudes, the Planck constant and the Fock space, the cosmological constant also appear in the natural way. The Poisson brackets are generalized for the case of kinetics. |
gr-qc/9603007 | Vladimir Dzhunushaliev | V. D. Dzhunushaliev | 5D Kaluza - Klein's Wormhole Between Two Event Horizons | REVTEX, 3 pages | null | null | null | gr-qc hep-th | null | The solution of the 5D Kaluza-Klein's theory is obtained. This solution is a
Lorentzian wormhole between two event horizons. It is shown that this solution
can sew with (4D Reissner-Nordstr\"om's solution + Maxwell's electrical field)
on the event horizon. Such construction is composite wormhole connecting two
asymptotically flat region. From the viewpoint of infinite observer this
wormhole is an electrical charge. According to J. Wheeler terminology this is
"charge without charge".
| [
{
"created": "Thu, 7 Mar 1996 04:42:56 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Dzhunushaliev",
"V. D.",
""
]
] | The solution of the 5D Kaluza-Klein's theory is obtained. This solution is a Lorentzian wormhole between two event horizons. It is shown that this solution can sew with (4D Reissner-Nordstr\"om's solution + Maxwell's electrical field) on the event horizon. Such construction is composite wormhole connecting two asymptotically flat region. From the viewpoint of infinite observer this wormhole is an electrical charge. According to J. Wheeler terminology this is "charge without charge". |
2006.04272 | Deborah Ferguson | Deborah Ferguson, Karan Jani, Pablo Laguna, and Deirdre Shoemaker | Assessing the Readiness of Numerical Relativity for LISA and 3G
Detectors | 7 pages, 5 figures | Phys. Rev. D 104, 044037 (2021) | 10.1103/PhysRevD.104.044037 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Future detectors such as LISA promise signal-to-noise ratios potentially in
the thousands and data containing simultaneous signals. Accurate numerical
relativity waveforms will be essential to maximize the science return. A
question of interest to the broad gravitational wave community is: Are the
numerical relativity codes ready to face this challenge? Towards answering this
question, we provide a new criteria to identify the minimum resolution a
simulation must have as a function of signal-to-noise ratio in order for the
numerical relativity waveform to be indistinguishable from a true signal. This
criteria can be applied to any finite-differencing numerical relativity code
with multiple simulations of differing resolutions for the desired binary
parameters and waveform length. We apply this criteria to binary systems of
interest with the fourth-order MAYA code to obtain the first estimate of the
minimum resolution a simulation must have to be prepared for next generation
detectors.
| [
{
"created": "Sun, 7 Jun 2020 21:32:18 GMT",
"version": "v1"
},
{
"created": "Fri, 9 Jul 2021 18:57:16 GMT",
"version": "v2"
},
{
"created": "Wed, 8 Dec 2021 22:35:14 GMT",
"version": "v3"
}
] | 2021-12-10 | [
[
"Ferguson",
"Deborah",
""
],
[
"Jani",
"Karan",
""
],
[
"Laguna",
"Pablo",
""
],
[
"Shoemaker",
"Deirdre",
""
]
] | Future detectors such as LISA promise signal-to-noise ratios potentially in the thousands and data containing simultaneous signals. Accurate numerical relativity waveforms will be essential to maximize the science return. A question of interest to the broad gravitational wave community is: Are the numerical relativity codes ready to face this challenge? Towards answering this question, we provide a new criteria to identify the minimum resolution a simulation must have as a function of signal-to-noise ratio in order for the numerical relativity waveform to be indistinguishable from a true signal. This criteria can be applied to any finite-differencing numerical relativity code with multiple simulations of differing resolutions for the desired binary parameters and waveform length. We apply this criteria to binary systems of interest with the fourth-order MAYA code to obtain the first estimate of the minimum resolution a simulation must have to be prepared for next generation detectors. |
1812.01909 | Roderich Tumulka | Roderich Tumulka | The Problem of Boltzmann Brains and How Bohmian Mechanics Helps Solve It | 7 pages, 2 figures (1 figure file). Written for the Proceedings of
the 15th Marcel Grossmann Meeting on General Relativity (Rome 2018), edited
by E. Battistelli, R.T. Jantzen, and R. Ruffini | null | null | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Most versions of classical physics imply that if the 4-volume of the entire
space-time is infinite or at least extremely large, then random fluctuations in
the matter will by coincidence create copies of us in remote places, so called
"Boltzmann brains." That is a problem because it leads to the wrong prediction
that _we_ should be Boltzmann brains. The question arises, how can any theory
avoid making this wrong prediction? In quantum physics, it turns out that the
discussion requires a formulation of quantum theory that is more precise than
the orthodox interpretation. Using Bohmian mechanics for this purpose, we point
out a possible solution to the problem based on the phenomenon of "freezing" of
configurations.
| [
{
"created": "Wed, 5 Dec 2018 10:46:57 GMT",
"version": "v1"
}
] | 2018-12-06 | [
[
"Tumulka",
"Roderich",
""
]
] | Most versions of classical physics imply that if the 4-volume of the entire space-time is infinite or at least extremely large, then random fluctuations in the matter will by coincidence create copies of us in remote places, so called "Boltzmann brains." That is a problem because it leads to the wrong prediction that _we_ should be Boltzmann brains. The question arises, how can any theory avoid making this wrong prediction? In quantum physics, it turns out that the discussion requires a formulation of quantum theory that is more precise than the orthodox interpretation. Using Bohmian mechanics for this purpose, we point out a possible solution to the problem based on the phenomenon of "freezing" of configurations. |
0911.3519 | Alberto Rozas-Fernandez | Alberto Rozas-Fernandez | Holographic dilatonic model of dark energy | 7 pages, 3 figures, changed content, added references, accepted for
publication at Eur.Phys.J.C | Eur.Phys.J.C71:1536,2011 | 10.1140/epjc/s10052-010-1536-7 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a dilatonic description of the holographic dark energy by
connecting the holographic dark energy density with the dilaton scalar field
energy density in a flat Friedmann-Robertson-Walker universe. We show that this
model can describe the observed accelerated expansion of our universe with the
choice $c\geq1$ and reconstruct the kinetic term as well as the dynamics of the
dilaton scalar field.
| [
{
"created": "Wed, 18 Nov 2009 12:29:39 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Nov 2010 16:31:27 GMT",
"version": "v2"
}
] | 2011-03-03 | [
[
"Rozas-Fernandez",
"Alberto",
""
]
] | We present a dilatonic description of the holographic dark energy by connecting the holographic dark energy density with the dilaton scalar field energy density in a flat Friedmann-Robertson-Walker universe. We show that this model can describe the observed accelerated expansion of our universe with the choice $c\geq1$ and reconstruct the kinetic term as well as the dynamics of the dilaton scalar field. |
gr-qc/0208046 | Craig B. Markwardt | Craig B. Markwardt | Independent Confirmation of the Pioneer 10 Anomalous Acceleration | RevTeX, 29 pages, 5 figures, submitted to Phys Rev D | null | null | null | gr-qc astro-ph | null | I perform an independent analysis of radio Doppler tracking data from the
Pioneer 10 spacecraft for the time period 1987-1994. All of the tracking data
were taken from public archive sources, and the analysis tools were developed
independently by myself. I confirm that an apparent anomalous acceleration is
acting on the Pioneer 10 spacecraft, which is not accounted for by present
physical models of spacecraft navigation. My best fit value for the
acceleration, including corrections for systematic biases and uncertainties, is
(8.60 +/- 1.34) x 10^{-8} cm s^{-2}, directed towards the Sun. This value
compares favorably to previous results. I examine the robustness of my result
to various perturbations of the analysis method, and find agreement to within
+/- 5%. The anomalous acceleration is reasonably constant with time, with a
characteristic variation time scale of > 70 yr. Such a variation timescale is
still too short to rule out on-board thermal radiation effects, based on this
particular Pioneer 10 data set.
| [
{
"created": "Fri, 16 Aug 2002 21:41:28 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Markwardt",
"Craig B.",
""
]
] | I perform an independent analysis of radio Doppler tracking data from the Pioneer 10 spacecraft for the time period 1987-1994. All of the tracking data were taken from public archive sources, and the analysis tools were developed independently by myself. I confirm that an apparent anomalous acceleration is acting on the Pioneer 10 spacecraft, which is not accounted for by present physical models of spacecraft navigation. My best fit value for the acceleration, including corrections for systematic biases and uncertainties, is (8.60 +/- 1.34) x 10^{-8} cm s^{-2}, directed towards the Sun. This value compares favorably to previous results. I examine the robustness of my result to various perturbations of the analysis method, and find agreement to within +/- 5%. The anomalous acceleration is reasonably constant with time, with a characteristic variation time scale of > 70 yr. Such a variation timescale is still too short to rule out on-board thermal radiation effects, based on this particular Pioneer 10 data set. |
1707.02720 | Chopin Soo | Eyo Eyo Ita III, Chopin Soo, Hoi-Lai Yu | Intrinsic time gravity, heat kernel regularization, and emergence of
Einstein's theory | 8 pages; replaced with published version | Class. Quantum Grav. 38 035007 (2021) | 10.1088/1361-6382/abcb0e | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Hamiltonian of Intrinsic Time Gravity is elucidated. The theory describes
Schrodinger evolution of our universe with respect to the fractional change of
the total spatial volume. Gravitational interactions are introduced by
extending Klauder's momentric variable with similarity transformations, and
explicit spatial diffeomorphism invariance is enforced via similarity
transformation with exponentials of spatial integrals. In analogy with
Yang-Mills theory, a Cotton-York term is obtained from the Chern-Simons
functional of the affine connection. The essential difference is the
fundamental variable for geometrodynamics is the metric rather than a gauge
connection; in the case of Yang-Mills, there is also no analog of the integral
of the spatial Ricci scalar curvature. Heat kernel regularization is employed
to isolate the divergences of coincidence limits; apart from an additional
Cotton-York term, a prescription in which Einstein's Ricci scalar potential
emerges naturally from the positive-definite self-adjoint Hamiltonian of the
theory is demonstrated.
| [
{
"created": "Mon, 10 Jul 2017 07:13:51 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Nov 2017 06:34:04 GMT",
"version": "v2"
},
{
"created": "Wed, 2 Sep 2020 09:11:39 GMT",
"version": "v3"
},
{
"created": "Mon, 11 Jan 2021 00:18:44 GMT",
"version": "v4"
}
] | 2021-01-12 | [
[
"Ita",
"Eyo Eyo",
"III"
],
[
"Soo",
"Chopin",
""
],
[
"Yu",
"Hoi-Lai",
""
]
] | The Hamiltonian of Intrinsic Time Gravity is elucidated. The theory describes Schrodinger evolution of our universe with respect to the fractional change of the total spatial volume. Gravitational interactions are introduced by extending Klauder's momentric variable with similarity transformations, and explicit spatial diffeomorphism invariance is enforced via similarity transformation with exponentials of spatial integrals. In analogy with Yang-Mills theory, a Cotton-York term is obtained from the Chern-Simons functional of the affine connection. The essential difference is the fundamental variable for geometrodynamics is the metric rather than a gauge connection; in the case of Yang-Mills, there is also no analog of the integral of the spatial Ricci scalar curvature. Heat kernel regularization is employed to isolate the divergences of coincidence limits; apart from an additional Cotton-York term, a prescription in which Einstein's Ricci scalar potential emerges naturally from the positive-definite self-adjoint Hamiltonian of the theory is demonstrated. |
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