General Relativity and Quantum Cosmology

New submissions

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New submissions for Thu, 22 Aug 19

[1]
Title: Some physical implications of regularization ambiguities in SU(2) gauge-invariant loop quantum cosmology
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

The way physics of loop quantum gravity is affected by the underlying quantization ambiguities is an open question. We address this issue in the context of loop quantum cosmology using gauge-covariant fluxes. Consequences are explored for two choices of regularization parameters: $\mu_0$ and $\bar \mu$ in presence of a positive cosmological constant, and two choices of regularizations of the Hamiltonian constraint in loop quantum cosmology: the standard and the Thiemann regularization. We show that novel features of singularity resolution and bounce, occurring due to gauge-covariant fluxes, exist also for Thiemann-regularized dynamics. The $\mu_0$-scheme is found to be unviable as in standard loop quantum cosmology when a positive cosmological constant is included. Our investigation brings out a surprising result that the nature of emergent matter in the pre-bounce regime is determined by the choice of regulator in the Thiemann regularization of the scalar constraint whether or not one uses gauge-covaraint fluxes. Unlike $\bar \mu$-scheme where the emergent matter is a cosmological constant, the emergent matter in $\mu_0$-scheme behaves as a string gas.

[2]
Title: Inflationary Phenomenology of Einstein Gauss-Bonnet Gravity Compatible with GW170817
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

In this work we shall study Einstein Gauss-Bonnet theories and we investigate when these can have their gravitational wave speed equal to the speed of light, which is unity in natural units, thus becoming compatible with the striking event GW170817. We demonstrate how this is possible and we show that if the scalar coupling to the Gauss-Bonnet invariant is constrained to satisfy a differential equation, the gravitational wave speed becomes equal to one. Accordingly, we investigate the inflationary phenomenology of the resulting restricted Einstein Gauss-Bonnet model, by assuming that the slow-roll conditions hold true. As we demonstrate, the compatibility with the observational data coming from the Planck 2018 collaboration, can be achieved, even for a power-law potential. We restricted ourselves to the study of the power-law potential, due to the lack of analyticity, however more realistic potentials can be used, in this case though the calculations are not easy to be performed analytically. We also pointed out that a string-corrected extension of the Einstein Gauss-Bonnet model we studied, containing terms of the form $\sim \xi(\phi) G^{ab}\partial_a\phi \partial_b \phi$ can also provide a theory with gravity waves speed $c_T^2=1$ in natural units, if the function $\xi(\phi)$ is appropriately constrained, however in the absence of the Gauss-Bonnet term $\sim \xi(\phi) \mathcal{G}$ the gravity waves speed can never be $c_T^2=1$. Finally, we discuss which extensions of the above models can provide interesting cosmologies, since any combination of $f(R,X,\phi)$ gravities with the above string-corrected Einstein Gauss-Bonnet models can yield $c_T^2=1$, with $X=\frac{1}{2}\partial_{\mu}\phi\partial^{\mu}\phi$.

[3]
Title: The cosmological phase space of generalized hybrid metric-Palatini theories of gravity
Comments: 20 pages, 3 figures, 6 tables
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

In this work, we study the cosmological phase space of the generalized hybrid metric-Palatini gravity theory, characterized by the functions $f\left(R,\mathcal R\right)$, using a dynamical system approach. We formulate the propagation equations of the suitable dimensionless variables that describe FLRW universes as an autonomous system. The fixed points are obtained for four different forms of the function $f\left(R,\mathcal R\right)$ and the behavior of the scale factor is computed. We show that due to the structure of the system, no global attractors can be present and also that two different classes of solutions for the scale factor exist. In addition, using a redefinition of the dynamic variables, we also compute solutions for static universes.

[4]
Title: Six-dimensional Myers-Perry rotating black hole cannot be overspun
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Theory (hep-th)

Though under non-linear accretion, all black holes in four and higher dimensions obey the weak Cosmic Censorship Conjecture, however they generally violate it for the linear test particle accretion with the exception of five dimensional rotating black hole with a single rotation. In dimension greater than five, there exists no extremal condition for black hole with single rotation and hence it can never be overspun. However it does exist for two rotations of five dimensional rotating black hole and then black hole could indeed be overspun under linear accretion. In this paper we study the case of six dimensional rotating black hole with two rotations and show that unlike the five dimensional black hole it cannot be overspun under linear accretion. We would conjecture that so should also be the case in all dimensions greater than six. Thus CCC may always be obeyed for rotating black hole in all dimensions greater than five.

[5]
Title: Bounding f(R,T) gravity by particle creation
Comments: Published online: Int. J. Geom. Methods Mod. Phys (2019)
Subjects: General Relativity and Quantum Cosmology (gr-qc)

We consider the possibility of the quantum vacuum states in f(R,T) gravity. Particularly, we study the Bogoliubov transformations associated to different vacuum states for some f(R,T) models. The method consists of fixing the f(R,T) free parameters by requiring the Bogoliubov coefficients to be minimized. In such a way, the particle production is related to the value of the Hubble parameter and also the given f(R,T) model.

[6]
Title: Glitching pulsars: unraveling the interactions of general relativity with quantum fields in the strong field regimes
Comments: 19 pages, 11 figures, research article
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)

We present a modification of our previous model for the mechanisms underlying the glitch phenomena in pulsars and young neutron stars. Accordingly, pulsars are born with embryonic cores comprising of purely incompressible superconducting gluon-quark superfluid (henceforth SuSu-cores). As the ambient medium cools and spins down due to emission of magnetic dipole radiation, the mass and size of SuSu-cores are set to grow discretely with time, in accordance with the Onsager-Feynmann analysis of superfluidity. Presently, we propose that the spacetime embedding glitching pulsars is dynamical and of bimetric nature: inside SuSu-cores the spacetime must be flat, whereas the surrounding region, where the matter is compressible and dissipative, the spacetime is Schwarzschild. It is further proposed that the topological change of spacetime is derived by the strong nuclear force, whose operating length scales is found to increase with time to reach O(1) cm at the end of the luminous lifetimes of pulsars. The model presented here model is in line with the recent radio and GW observations of pulsars and NSs.

Cross-lists for Thu, 22 Aug 19

[7]  arXiv:1908.07780 (cross-list from hep-th) [pdf]
Title: Casimir force in the Gödel space-time and its possible induced cosmological inhomogeneity
Journal-ref: Eur. Phys. J. C (2017) 77:454
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)

The Casimir force between two parallel plates in the G\"odel universe is computed for a scalar field at finite temperature. It is observed that when the plates separation is comparable with the scale given by the rotation of the space-time, the force becomes repulsive and then approaches zero. Since it has been shown previously that the universe may experience a Godel phase for a small period of time, the induced inhomogeneities from the Casimir force are also studied.

[8]  arXiv:1908.07823 (cross-list from physics.class-ph) [pdf, other]
Title: Sound waves move matter
Authors: Davison E. Soper
Comments: 6 pages with one figure
Subjects: Classical Physics (physics.class-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

A recent Letter has reported that sound waves can carry gravitational mass. I analyze this effect in a Hooke's law solid, considering a wave packet moving in the $z$ direction with an amplitude that is independent of $x$ and $y$. The analysis shows that, at second order in an expansion around small amplitude vibrations, there is a small net motion of material, and thus mass, in the direction opposite to the wave packet propagation. This is a straightforward consequence of Newton's laws.

[9]  arXiv:1908.07892 (cross-list from astro-ph.CO) [pdf, ps, other]
Title: Parametrizations for tests of gravity
Authors: Lucas Lombriser
Comments: 37 pages; published as part of the IJMPD special issue "Modified Gravity: Progresses and Outlook of Theories, Numerical Techniques and Observational Tests" edited by Baojiu Li and Kazuya Koyama
Journal-ref: International Journal of Modern Physics D, Vol. 27, No. 15, 1848002 (2018)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

With the increasing wealth of high-quality astronomical and cosmological data and the manifold departures from General Relativity in principle conceivable, the development of generalized parametrization frameworks that unify gravitational models and cover a wide range of length scales and a variety of observational probes to enable systematic high-precision tests of gravity has been a stimulus for intensive research. A review is presented here for some of the formalisms devised for this purpose, covering the cosmological large- and small-scale structures, the astronomical static weak-field regime as well as emission and propagation effects for gravitational waves. This includes linear and nonlinear parametrized post-Friedmannian frameworks, effective field theory approaches, the parametrized post-Newtonian expansion, the parametrized post-Einsteinian formalism as well as an inspiral-merger-ringdown waveform model among others. Connections between the different formalisms are highlighted where they have been established and a brief outlook is provided for general steps towards a unified global framework for tests of gravity and dark sector models.

Replacements for Thu, 22 Aug 19

[10]  arXiv:1801.03353 (replaced) [pdf, other]
Title: Bohmian quantum gravity and cosmology
Comments: 45 pages, 6 figures, PDFLaTeX; written for "Applied Bohmian Mechanics: From Nanoscale Systems to Cosmology", edited by Xavier Oriols Pladevall and Jordi Mompart; v2 typos corrected
Subjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
[11]  arXiv:1808.00901 (replaced) [pdf, other]
Title: Measuring the star formation rate with gravitational waves from binary black holes
Comments: 7 pages, 1 table, 4 figs
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[12]  arXiv:1902.00289 (replaced) [pdf, ps, other]
Title: Observational Constraints on Growth Index with Cosmography
Authors: Zhao-Yu Yin, Hao Wei
Comments: 14 pages, 4 figures, 5 tables, revtex4; v2: discussions added, Eur. Phys. J. C in press; v3: published version
Journal-ref: Eur. Phys. J. C 79 (2019) 698
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[13]  arXiv:1902.10716 (replaced) [pdf, ps, other]
Title: Gravitational Radiation from Close Binaries with Time-Varying Masses
Comments: 6 pages, 1 figure, accepted
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)
[14]  arXiv:1903.05924 (replaced) [pdf, other]
Title: Prospective constraints on the primordial black hole abundance from the stochastic gravitational-wave backgrounds produced by coalescing events and curvature perturbations
Comments: 14 pages, 8 figures. Corrections are included due to updated sensitivity curves of SKA and LISA (which were available when v1 was submitted)
Journal-ref: Phys. Rev. D 99, 103531 (2019)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[15]  arXiv:1903.09377 (replaced) [pdf, ps, other]
Title: Three-Dimensional Extended Newtonian (Super)Gravity
Comments: 5 pages v3: typos corrected in equations (21), (22) and (24); version appeared in JHEP
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
[16]  arXiv:1903.11211 (replaced) [pdf, ps, other]
Authors: John R. Klauder
Comments: 14 pages, a novel approach to quantizing general relativity, minor corrections; NEW RESULTS, SHARPER EXAMPLES; Important correction
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
[17]  arXiv:1904.08912 (replaced) [pdf, other]
Title: Axion-Dilaton Destabilization and the Hubble Tension
Comments: v1: 4 pages, 2 figures. v2: references added. v3: more references added, plots updated to show evolution as a function of redshift. v4: Additional references and clarifications added. v5: matches published version
Journal-ref: Physics Letters B 797 (2019)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
[18]  arXiv:1904.12390 (replaced) [pdf, other]
Title: Relativistic quantum clocks observe classical and quantum time dilation
Comments: Minor corrections and updates for clarity, including the normalization of Eq. (42) and plots in Figs. 2 and 3. Comments welcome
Subjects: Quantum Physics (quant-ph); General Relativity and Quantum Cosmology (gr-qc)
[19]  arXiv:1905.13019 (replaced) [pdf, other]
Title: Unraveling the origin of black holes from effective spin measurements with LIGO-Virgo
Journal-ref: JCAP 1908 (2019) 022
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[20]  arXiv:1905.13519 (replaced) [pdf, other]
Title: Charged anisotropic compact star in $f(R,\mathcal{T})$ gravity: A minimal geometric deformation gravitational decoupling approach
Comments: 18 figures, submitted in JCAP
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[21]  arXiv:1906.08265 (replaced) [pdf, other]
Title: The BTZ black hole violates strong cosmic censorship
Comments: 59 pages, 9 figures. Changes in v2: 1) a few discussions added/improved, 2) added Section 5.8 discussing the non-smoothness of the Hartle-Hawking state at the Cauchy horizon
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
[22]  arXiv:1908.02185 (replaced) [pdf, ps, other]
Title: On the initial geometry of a vacuum cosmological spacetime
Authors: John Lott
Subjects: Differential Geometry (math.DG); General Relativity and Quantum Cosmology (gr-qc)
[23]  arXiv:1908.03584 (replaced) [pdf, other]
Title: An Optically Targeted Search for Gravitational Waves emitted by Core-Collapse Supernovae during the First and Second Observing Runs of Advanced LIGO and Advanced Virgo
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[24]  arXiv:1908.03942 (replaced) [pdf, other]
Title: Primordial black holes from sound speed resonance in the inflaton-curvaton mixed scenario
Authors: Chao Chen, Yi-Fu Cai