# General Relativity and Quantum Cosmology

## New submissions

[ total of 20 entries: 1-20 ]
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### New submissions for Thu, 22 Feb 18

[1]
Title: Effective stability against superradiance of Kerr black holes with synchronised hair
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Theory (hep-th)

Kerr black holes with synchronised hair [arXiv:1403.2757, arXiv:1603.02687] are a counter example to the no hair conjecture, in General Relativity minimally coupled to simple matter fields (with mass $\mu$) obeying all energy conditions. Since these solutions have, like Kerr, an ergoregion it has been a lingering possibility that they are afflicted by the superradiant instability, the same process that leads to their dynamical formation from Kerr. A recent breakthrough [arXiv:1711.08464] confirmed this instability and computed the corresponding timescales for a sample of solutions. We discuss how these results and other observations support two conclusions: $1)$ starting from the Kerr limit, the increase of hair for fixed coupling $\mu M$ (where $M$ is the BH mass) increases the timescale of the instability; $2)$ there are hairy solutions for which this timescale, for astrophysical black hole masses, is larger than the age of the Universe. The latter conclusion introduces the limited, but physically relevant concept of effective stability. The former conclusion, allows us to identify an astrophysically viable domain of such effectively stable hairy black holes, occurring, conservatively, for $M\mu \lesssim 0.25$. These are hairy BHs that form dynamically, from the superradiant instability of Kerr, within an astrophysical timescale, but whose own superradiant instability occurs only in a cosmological timescale.

[2]
Title: Remarks on cosmological gravitational waves
Authors: P. Valtancoli
Subjects: General Relativity and Quantum Cosmology (gr-qc)

We study the propagation of a gravitational wave in an Ads spacetime. We find that, in presence of the cosmological constant, the graviton mass cannot be measured with higher precision than the square root of the cosmological constant.

[3]
Title: Gravitational Wave Opacity from Gauge Field Dark Energy
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We show that astrophysical gravitational waves can undergo absorption and re-emission when propagating through cosmic gauge field dark energy. A sufficiently strong effect would impact the use of gravitational wave standard sirens to constrain the expansion history of the Universe. We investigate a particular model of dark energy based on a non-Abelian gauge field, and show that at early times it behaves like dark radiation, whereas a novel interaction causes it to drive cosmic acceleration at late times. Joint constraints on the cosmological scenario due to type 1a supernovae, baryon acoustic oscillations, and cosmic microwave background data are presented. We show that standard siren luminosity distances in the redshift range 0.5 < z < 1.5 would suffer at most a 1% absorption.

[4]
Title: Rotating effects on the scalar field in the cosmic string spacetime, in the spacetime with space-like dislocation and in the spacetime with a spiral dislocation
Comments: 12 pages, no figure. To be published in The European Physical Journal C
Subjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)

In the interface between general relativity and relativistic quantum mechanics, we analyse rotating effects on the scalar field subject to a hard-wall confining potential. We consider three different scenarios of general relativity given by the cosmic string spacetime, the spacetime with space-like dislocation and the spacetime with a spiral dislocation. Then, by searching for a discrete spectrum of energy, we analyse analogues effects of the Aharonov-Bohm effect for bound states and the Sagnac effect.

[5]
Title: Cosmological screening and the phantom braneworld model
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We study the first order scalar and vector cosmological perturbations in the phantom braneworld model for our current universe. We derive the perturbation equations valid at all length scales. Next, by ignoring the backreaction effects due to the peculiar velocities and also the bulk cosmological constant, we derive the expressions for the gravitational potentials. We show that there exist four characteristic screening lengths instead of the single one of the $\Lambda$-cold dark matter ($\Lambda{\rm CDM}$) model, with the latter obtained as an appropriate limit of this model. In particular, we find an upper bound on the parameter $\Omega_l$ characterizing the extra dimension of this model, $\Omega_l \lesssim 0.05$, by utilising the simple requirement that the metric is real. This bound seems to be an improvement of the one found earlier by analysing various cosmological data.

[6]
Title: On a Modified Klein-Gordon Equation with Vacuum-Energy Contributions
Subjects: General Relativity and Quantum Cosmology (gr-qc)

We define a modified Klein-Gordon equation containing quantum vacuum contributions arising from the coupling of matter's potential to its background spacetime. Generalized commutation relations and Energy-Momentum relations are characterized as a result of a conformal factor. A representation theorem is introduced suggesting that one can equally modify the spacetime structure or the momentum operator in defining a generalized quantum mechanical formalism. Additionally, we show that the presumed conformal factor acts as a renormalization procedure which can potentially eliminate the ultraviolet divergences in Feynman amplitudes. Finally, we suggest a modified Lagrangian density, containing the proposed feedback term, for $U(1)$ symmetric fields.

[7]
Title: Gravitational lensing by wormholes supported by electromagnetic, scalar, and quantum effects
Subjects: General Relativity and Quantum Cosmology (gr-qc)

Wormholes are one of the most interesting topological features in spacetime, offering a rat run between two vastly separated regions of the universe. In this paper, we study the deflection angle of light by wormholes, which are supported by electric charge, magnetic charge, and scalar fields in the weak field limit approximation. To this end, we apply new geometric methods -- the Gauss-Bonnet theorem and the optical geometry -- to compute the deflection angles. We also verify our findings by using the well-known geodesics method. There exists a similarity between the charge and the quantum corrections on a black hole solution, which has been recently discussed in the context of the relativistic Bohmian quantum mechanics. By replacing classical geodesics with Bohmian trajectories, we introduce a new wormhole solution, whose having matter sources and anisotropic pressure supported by Bohmian quantum effects. The problem of fulfillment of the energy conditions of the Morris-Thorne traversable wormhole is also discussed.

### Cross-lists for Thu, 22 Feb 18

[8]  arXiv:1802.07267 (cross-list from hep-th) [pdf, ps, other]
Title: Analysis of constraints and their algebra in bimetric theory
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)

We perform a canonical analysis of the bimetric theory in the metric formulation, computing the constraints and their algebra explicitly. In particular, we compute a secondary constraint, that has been argued to exist earlier, and show that it has the correct form to eliminate the ghost. We also identify a set of four first class constraints that generate the algebra of general covariance. This algebra naturally determines a spacetime metric for the theory. However, in bimetric theory, this metric is not unique but depends on how the first class constraints are identified.

[9]  arXiv:1802.07275 (cross-list from hep-th) [pdf, other]
Title: Phase transitions in 3D gravity and fractal dimension
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); Geometric Topology (math.GT)

We show that for three dimensional gravity with higher genus boundary conditions, if the theory possesses a sufficiently light scalar, there is a second order phase transition where the scalar field condenses. This three dimensional version of the holographic superconducting phase transition occurs even though the pure gravity solutions are locally AdS$_3$. This is in addition to the first order Hawking-Page-like phase transitions between different locally AdS$_3$ handlebodies. This implies that the R\'enyi entropies of holographic CFTs will undergo phase transitions as the R\'enyi parameter is varied, as long as the theory possesses a scalar operator which is lighter than a certain critical dimension. We show that this critical dimension has an elegant mathematical interpretation as the Hausdorff dimension of the limit set of a quotient group of AdS$_3$, and use this to compute it, analytically near the boundary of moduli space and numerically in the interior of moduli space. We compare this to a CFT computation generalizing recent work of Belin, Keller and Zadeh, bounding the critical dimension using higher genus conformal blocks, and find a surprisingly good match.

[10]  arXiv:1802.07278 (cross-list from hep-th) [pdf, other]
Title: Exactly solvable gravitating perfect fluid solitons in (2+1) dimensions
Comments: Latex file, 35 pages, 13 figures
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)

The Bogomolnyi-Prasad-Sommerfield (BPS) baby Skyrme model coupled to gravity is considered. We show that in an asymptotically flat space-time the model still possesses the BPS property, i.e., admits a BPS reduction to first order Bogomolnyi equations, which guarantees that the corresponding proper energy is a linear function of the topological charge. We also find the mass-radius relation as well as the maximal mass and radius. All these results are obtained in an analytical manner, which implies the complete solvability of this selfgravitating matter system. If a cosmological constant is added, then the BPS property is lost. In de Sitter (dS) space-time both extremal and non-extremal solutions are found, where the former correspond to finite positive pressure solutions of the flat space-time model. For the asymptotic anti-de Sitter (AdS) case, extremal solutions do not exist as there are no negative pressure BPS baby Skyrmions in flat space-time. Non-extremal solutions with AdS asymptotics do exist and may be constructed numerically. We found, however, strong evidence that there are no stable multi-soliton solutions in the AdS background space-time. Finally, we elaborate on the implications of these findings for certain three-dimensional models of holographic QCD.

[11]  arXiv:1802.07505 (cross-list from astro-ph.HE) [pdf, other]
Title: Influence of toroidal magnetic field in multi-accreting tori
Comments: 15 pages, 7 multi-panels figures. To appear on MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

We analyzed the effects of a toroidal magnetic field in the formation of several magnetized accretion tori, dubbed as ringed accretion disks (RADs), orbiting around one central Kerr supermassive Black Hole (SMBH) in AGNs, where both corotating and counterotating disks are considered. Constraints on tori formation and emergence of RADs instabilities, accretion onto the central attractor and tori collision emergence, are investigated. The results of this analysis show that the role of the central BH spin-mass ratio, the magnetic field and the relative fluid rotation and tori rotation with respect the central BH, are crucial elements in determining the accretion tori features, providing ultimately evidence of a strict correlation between SMBH spin, fluid rotation and magnetic fields in RADs formation and evolution. More specifically we proved that magnetic field and disks rotation are in fact strongly constrained, as tori formation and evolution in RADs depend on the toroidal magnetic fields parameters. Eventually this analysis identifies specific classes of tori, for restrict ranges of magnetic field parameter, that can be observed around some specific SMBHs identified by their dimensionless spin.

### Replacements for Thu, 22 Feb 18

[12]  arXiv:1706.03430 (replaced) [pdf, other]
Title: Gravitational shockwaves on rotating black holes
Comments: 93 pages, no figures. v2: partial to covariant in Sec. 2.2; Killing vector in 2.84; "et al" to "et al." below 8.11 and in Ref. 32; "=" to \equiv in 2.100; "d\theta" in footnote 143. v3: \Psi_4* in Eq. 4.1; [] to () in B.19; () from 2.61; Overring to deg on "\beta" in 3.41; Removed prime from law for \beta'* in footnote 44; "palette" to "palate" in footnote 170; Tweaked 2.82 and 2.83
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[13]  arXiv:1709.05128 (replaced) [pdf, ps, other]
Title: Dark matter scenarios with multiple spin-2 fields
Comments: 30 pages, 4 figures; comments of referee implemented, matches published version
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[14]  arXiv:1710.10463 (replaced) [pdf, other]
Title: Role of pressure anisotropy on relativistic compact stars
Comments: 11 pages, 4 figures; v2:, texts are improved and updated to match journal version
Journal-ref: Phys.Rev. D 97, 044022 (2018)
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[15]  arXiv:1711.02414 (replaced) [pdf, other]
Title: Accurate ray tracing of realistic neutron star atmospheres for constraining their parameters
Comments: 17 pages, 13 figures; accepted in ApJ ; important updates in Section 2.2 and Fig. 2
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[16]  arXiv:1711.07290 (replaced) [pdf, other]
Title: Cosmological dynamics of mimetic gravity
Comments: 30 pages, 7 figures. Final version published in JCAP
Journal-ref: JCAP 02 (2018) 041
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[17]  arXiv:1712.04956 (replaced) [pdf, other]
Title: Higgs-Dilaton Cosmology: An inflation - dark energy connection and forecasts for future galaxy surveys
Comments: 17 pages, 7 figures, added forecasts for DESI - matches the published version
Journal-ref: Phys. Rev. D 97, 043520 (2018)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[18]  arXiv:1801.00161 (replaced) [pdf, ps, other]
Title: On the Cosmological Constant in a Conformally Transformed Einstein Equation
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[19]  arXiv:1802.02130 (replaced) [pdf, ps, other]
Title: Hamiltonian formalism for f(T) gravity