# General Relativity and Quantum Cosmology

## New submissions

[ total of 34 entries: 1-34 ]
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### New submissions for Thu, 21 Sep 17

[1]
Comments: 6 pages, 2 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

The superradiant instability can lead to the generation of extremely dense axion clouds around rotating black holes. We show that, despite the long lifetime of the QCD axion with respect to spontaneous decay into photon pairs, stimulated decay becomes significant above a minimum axion density and leads to extremely bright lasers. The lasing threshold can be attained for axion masses $\mu \gtrsim 10^{-8}\ \mathrm{eV}$, which implies superradiant instabilities around spinning primordial BHs with mass $\lesssim 0.01M_\odot$. We further show that lasing can be quenched by Schwinger pair production, which produces a critical electron-positron plasma within the axion cloud. Lasing can nevertheless restart once annihilation lowers the plasma density sufficiently, resulting in multiple laser bursts that repeat until the black hole spins down sufficiently to quench the superradiant instability. In particular, axions with a mass $\sim 10^{-5}\ \mathrm{eV}$ and primordial black holes with mass $\sim 10^{24}$ kg, which may account for all the dark matter in the Universe, lead to millisecond-bursts in the GHz radio-frequency range, with peak luminosities $\sim 10^{42}$ erg/s, suggesting a possible link to the observed fast radio bursts.

[2]
Title: Neutron star mergers as a probe of modifications of general relativity with finite-range scalar forces
Comments: 22 pages, 8 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

Observations of gravitational radiation from compact binary systems provide an unprecedented opportunity to test General Relativity in the strong field dynamical regime. In this paper, we investigate how future observations of gravitational radiation from binary neutron star mergers might provide constraints on finite-range forces from a universally coupled massive scalar field. Such scalar degrees of freedom are a characteristic feature of many extensions of General Relativity. For concreteness, we work in the context of metric $f(R)$ gravity, which is equivalent to General Relativity and a universally coupled scalar field with a non-linear potential whose form is fixed by the choice of $f(R)$. In theories where neutron stars (or other compact objects) obtain a significant scalar charge, the resulting attractive finite-range scalar force has implications for both the inspiral and merger phases of binary systems. We first present an analysis of the inspiral dynamics in Newtonian limit, and forecast the constraints on the mass of the scalar and charge of the compact objects for the Advanced LIGO gravitational wave observatory. We then perform a comparative study of binary neutron star mergers in General Relativity with those of a one-parameter model of $f(R)$ gravity using fully relativistic hydrodynamical simulations. These simulations elucidate the effects of the scalar on the merger and post-merger dynamics. We comment on the utility of the full waveform (inspiral, merger, post-merger) to probe different regions of parameter space for both the particular model of $f(R)$ gravity studied here and for finite-range scalar forces more generally.

[3]
Title: Radial oscillations of strange quark stars admixed with condensed dark matter
Comments: 6 pages, 2 figures, to appear in PRD. arXiv admin note: substantial text overlap with arXiv:1706.07272
Subjects: General Relativity and Quantum Cosmology (gr-qc)

We compute the 20 lowest frequency radial oscillation modes of strange stars admixed with condensed dark matter. We assume a self-interacting bosonic dark matter, and we model dark matter inside the star as a Bose-Einstein condensate. In this case the equation of state is a polytropic one with index $1+1/n=2$ and a constant $K$ that is computed in terms of the mass of the dark matter particle and the scattering length. Assuming a mass and a scattering length compatible with current observational bounds for self-interacting dark matter, we have integrated numerically first the Tolman-Oppenheimer-Volkoff equations for the hydrostatic equilibrium, and then the equations for the perturbations $\xi=\Delta r/r$ and $\eta=\Delta P/P$. For a compact object with certain mass and radius we have considered here three cases, namely no dark matter at all and two different dark matter scenarios. Our results show that i) the separation between consecutive modes increases with the amount of dark matter, and ii) the effect is more pronounced for higher order modes. These effects are relevant even for a strange star made of 5\% dark matter.

[4]
Title: Dynamical deformation of 2+1 dimensional double torus universe
Authors: Masaru Siino
Comments: 19pages, 9 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)

In (2+1)-dimensional pure gravity with cosmological constant, the dynamics of double torus universe with pinching parameter is investigated. Each mode of affine stretching deformation is illustrated in the context of horizontal foliation along the holomorphic quadratic differential. The formulation of the Einstein Hilbert action for the parameters of the affine stretching is developed. Then the dynamics along one holomorphic quadratic differential will be solved concretely.

[5]
Title: Is exponential gravity a viable description for the whole cosmological history?
Comments: 19 pages, 6 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

Here we analysed a particular type of F(R) gravity, the so-called exponential gravity which includes an exponential function of the Ricci scalar in the action. Such term represents a correction to the usual Hilbert-Einstein action. By using Supernovae Ia, Barionic Acoustic Oscillations, Cosmic Microwave Background and H(z) data, the free parameters of the model are well constrained. The results show that such corrections to General Relativity become important at cosmological scales and at late-times, providing an alternative to the dark energy problem. In addition, the fits do not determine any significant difference statistically with respect to the LCDM model. Finally, such model is extended to include the inflationary epoch in the same gravitational Lagrangian. As shown in the paper, the additional terms can reproduce the inflationary epoch and satisfy the constraints from Planck data.

[6]
Title: Critical behavior and phase transition of dilaton black holes with nonlinear electrodynamics
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

In this paper, we take into account the dilaton black hole solutions of Einstein gravity in the presence of logarithmic and exponential forms of nonlinear electrodynamics. At first, we consider the cosmological constant and nonlinear parameter as thermodynamic quantities which can vary. We obtain thermodynamic quantities of the system such as pressure, temperature and Gibbs free energy in an extended phase space. We complete the analogy of the nonlinear dilaton black holes with Van der Waals liquid-gas system. We work in the canonical ensemble and hence we treat the charge of the black hole as an external fixed parameter. Moreover, we calculate the critical values of temperature, volume and pressure and show they depend on dilaton coupling constant as well as nonlinear parameter. We also investigate the critical exponents and find that they are universal and independent of the dilaton and nonlinear parameters, which is an expected result. {Finally, we explore the phase transition of nonlinear dilaton black holes by studying the Gibbs free energy of the system. We find that in case of $T>T_c$, we have no phase transition. When $T=T_c$, the system admits a second order phase transition, while for $T=T_{\rm f}<T_c$ the system experiences a first order transition. Interestingly, for $T_{\rm f}<T<T_c$ we observe a \textit{zeroth order} phase transition in the presence of dilaton field. This novel \textit{zeroth order} phase transition is occurred due to a finite jump in Gibbs free energy which is generated by dilaton-electromagnetic coupling constant, $\alpha$, for a certain range of pressure.}

[7]
Title: Evolution of Compact Stars and Dark Dynamical Variables
Comments: 18 pages, 4 figures, version accepted for publication in European Physical Journal C
Subjects: General Relativity and Quantum Cosmology (gr-qc)

This work is aimed to explore the dark dynamical effects of $f(R,T)$ modified gravity theory on the dynamics of compact celestial star. We have taken the interior geometry as spherical star which is filled with imperfect fluid distribution. The modified field equations are explored by taking a particular form of $f(R,T)$ model, i.e., $f(R,T)=f_1(R)+f_2(R)f_3(T)$. These equations are then utilized to formulate the well-known structure scalars under the dark dynamical effects of this higher order gravity theory. Also, the evolution equations for expansion and shear are formulated with the help of these scalar variables. Further, all this analysis have been made under the condition of constant $R$ and $T$. We found a crucial significance of dark source terms and dynamical variables on the evolution and density inhomogeneity of compact objects.

[8]
Title: Relativistic effects due to gravimagnetic moment of a rotating body
Subjects: General Relativity and Quantum Cosmology (gr-qc)

We compute exact Hamiltonian (and corresponding Dirac brackets) for spinning particle with gravimagnetic moment $\kappa$ in an arbitrary gravitational background. $\kappa=0$ corresponds to the Mathisson-Papapetrou-Tulczyjew-Dixon (MPTD) equations. $\kappa=1$ leads to modified MPTD equations with reasonable behavior in the ultrarelativistic limit. So we study the modified equations in the leading post-Newtonian approximation. Rotating body with unit gravimagnetic moment has qualitatively different behavior as compared with MPTD body: A) If a number of gyroscopes with various rotation axes are freely traveling together, the angles between the axes change with time. B) For specific binary systems, gravimagnetic moment gives a contribution to frame-dragging effect with the magnitude, that turns out to be comparable with that of Schiff frame dragging.

[9]
Title: Rotating and spatially twisting Locally Rotationally Symmetric Spacetimes in f(R)-Gravity: a No-Go theorem
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)

Recently, in a series of papers, we established the existence and found a general solution for the simultaneously rotating and twisting locally rotationally symmetric spacetimes in general relativity, which can model inhomogeneous and dynamic astrophysical bodies. However, these spacetimes necessarily require imperfect fluids with entropy flux. Therefore, in this paper, we investigate the existence of these spacetimes in generic f(R)-gravity models, where the entropy flux is generated purely by higher order curvature effects, while the standard matter still remains a perfect fluid. However, we transparently demonstrate here, that the symmetries of these spacetimes force the theory to be general relativity. This is a novel study that shows how the geometrical properties of a spacetime can be used to restrict the theories of gravity.

### Cross-lists for Thu, 21 Sep 17

[10]  arXiv:1709.06576 (cross-list from astro-ph.CO) [pdf, other]
Title: The merger rate of primordial-black-hole binaries
Authors: Yacine Ali-Haïmoud (1), Ely D. Kovetz (2), Marc Kamionkowski (2) ((1) NYU, (2) JHU)
Comments: 17 pages, 7 figures, comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

Primordial black holes (PBHs) have long been a candidate for the elusive dark matter (DM), and remain poorly constrained in the ~20-100 Msun mass range. PBH binaries were recently suggested as the possible source of LIGO's first detections. In this paper, we thoroughly revisit existing estimates of the merger rate of PBH binaries. We compute the probability distribution of orbital parameters for PBH binaries formed in the early Universe, accounting for tidal torquing by all other PBHs, as well as standard large-scale adiabatic perturbations. We then check whether the orbital parameters of PBH binaries formed in the early Universe can be significantly affected between formation and merger. Our analytic estimates indicate that the tidal field of halos and interactions with other PBHs, as well as dynamical friction by unbound standard DM particles, do not do significant work on nor torque PBH binaries. We estimate the torque due to baryon accretion to be much weaker than previous calculations, albeit possibly large enough to significantly affect the eccentricity of typical PBH binaries. We also revisit the PBH-binary merger rate resulting from gravitational capture in present-day halos, accounting for Poisson fluctuations. If binaries formed in the early Universe survive to the present time, as suggested by our analytic estimates, they dominate the total PBH merger rate. Moreover, this merger rate would be orders of magnitude larger than LIGO's current upper limits if PBHs make a significant fraction of the dark matter. As a consequence, LIGO would constrain ~10-300 Msun PBHs to constitute no more than ~1% of the dark matter. To make this conclusion fully robust, though, numerical study of several complex astrophysical processes - such as the formation of the first PBH halos and how they may affect PBH binaries, as well as the accretion of gas onto an extremely eccentric binary - is needed.

[11]  arXiv:1709.06766 (cross-list from hep-th) [pdf, other]
Title: On actions for (entangling) surfaces and DCFTs
Comments: v1: 71pp, 1fig
Subjects: High Energy Physics - Theory (hep-th); Soft Condensed Matter (cond-mat.soft); General Relativity and Quantum Cosmology (gr-qc); Mathematical Physics (math-ph)

The dynamics of surfaces and interfaces describe many physical systems, including fluid membranes, entanglement entropy and the coupling of defects to quantum field theories. Based on the formulation of submanifold calculus developed by Carter, we introduce a new variational principle for (entangling) surfaces. This principle captures all diffeomorphism constraints on surface/interface actions and their associated spacetime stress tensor. The different couplings to the geometric tensors appearing in the surface action are interpreted in terms of linear response coefficients within elasticity theory. An example of a surface action with edges at the two-derivative level is studied, including both the parity-even and parity-odd sectors. Its conformally invariant counterpart restricts the type of conformal anomalies that can appear in two-dimensional submanifolds with boundaries. Analogously to hydrodynamics, it is shown that classification methods can be used to constrain the stress tensor of (entangling) surfaces at a given order in derivatives. This analysis reveals a purely geometric parity-odd contribution to the Young modulus of a thin elastic membrane. Extending this novel variational principle to BCFTs and DCFTs in curved spacetimes allows to obtain the Ward identities for diffeomorphism and Weyl transformations. In this context, we provide a formal derivation of the contact terms in the stress tensor and of the displacement operator for a broad class of actions.

[12]  arXiv:1709.06798 (cross-list from math.DG) [pdf, ps, other]
Title: Scalar conformal invariants of weight zero
Comments: This work was presented for the first time at the Spanish-Portuguese Relativity Meeting -- EREP 2017 held in M\'alaga (Spain), 12-15 September 2017. 7 pages, 1 table
Subjects: Differential Geometry (math.DG); General Relativity and Quantum Cosmology (gr-qc)

In the class of metrics of a generic conformal structure there exists a distinguishing metric. This was noticed by Albert Einstein in a lesser-known paper of 1921. There he also announced that it is possible to add an scalar equation to the field equations of General Relativity. We explore this suggestion from a geometrical point of view. Then, we obtain a family of scalar conformal invariants of weight 0 for generic pseudo-Riemannian conformal structures $[g]$ in more than three dimensions. In particular, we define the conformal scalar curvature of $[g]$ and calculate it for some well-known conformal spacetimes, comparing the results with the Ricci scalar and the Kretschmann scalar.

### Replacements for Thu, 21 Sep 17

[13]  arXiv:1403.4110 (replaced) [pdf, ps, other]
Title: On galaxy rotation curves from a continuum mechanics approach to modified gravity
Comments: 8 pages; v2 11 pages, heavily revised version, new title; v3 13 pages final version
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[14]  arXiv:1505.04392 (replaced) [pdf, ps, other]
Title: Inflationary universe in the presence of a minimal measurable length
Comments: 19 pages, 4 figures, Published version in Annals of Physics
Journal-ref: Annals Phys. 385 (2017) 214
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[15]  arXiv:1505.04730 (replaced) [pdf, other]
Title: What is Dynamics in Quantum Gravity?
Comments: 14 pages, 6 figures
Journal-ref: Class. Quantum Grav. 34 (2017) 205001
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[16]  arXiv:1606.09644 (replaced) [pdf, ps, other]
Title: Forced Fluid Dynamics from Blackfolds in General Supergravity Backgrounds
Comments: v2: 47pp, typos corrected, presentation improved, matches published version in JHEP
Journal-ref: JHEP 1610 (2016) 154
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
[17]  arXiv:1607.06329 (replaced) [pdf, other]
Title: Universal features of quantum bounce in loop quantum cosmology
Comments: revtex4, 7 figures, 1 table. Further corrected some typos. Phys. Lett. B773 (2017) 196-202
Journal-ref: Phys. Lett. B773 (2017) 196-202
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
[18]  arXiv:1609.08220 (replaced) [pdf, other]
Title: Probing dark energy with braneworld cosmology in the light of recent cosmological data
Comments: 19 pages, 5 figures, 4 Tables. Accepted for publication in IJMPD
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
[19]  arXiv:1612.05795 (replaced) [pdf, other]
Title: What is the magnetic field distribution for the equation of state of magnetized neutron stars?
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
[20]  arXiv:1703.10479 (replaced) [pdf, ps, other]
Title: Accretion onto a noncommutative geometry inspired black hole
Comments: Published in EPJC
Journal-ref: Eur. Phys. J. C (2017) 77:577
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[21]  arXiv:1704.08925 (replaced) [pdf, other]
Title: Dynamics of cosmological perturbations in modified Brans-Dicke cosmology with matter-scalar field interaction
Comments: 20 pages, 5 figues. Version 2 with minor revisions to match manuscript accepted by PRD
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
[22]  arXiv:1705.01099 (replaced) [pdf, ps, other]
Title: Nonsingular universe in massive gravity's rainbow
Comments: 13 pages, published
Journal-ref: Phys. Dark Universe 16 (2017) 26
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[23]  arXiv:1705.03654 (replaced) [pdf, ps, other]
Title: Scalar perturbations of nonsingular nonrotating black holes in conformal gravity
Comments: 10 pages, 5 figures, 3 tables
Journal-ref: Phys. Rev. D 96, 064028 (2017)
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[24]  arXiv:1705.08797 (replaced) [pdf, other]
Title: Conjoined constraints on modified gravity from the expansion history and cosmic growth
Comments: 11 pages, 3 figures, 5 tables, comments welcome. Changes match published version in PRD
Journal-ref: Phys.Rev. D96 (2017), 063517
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[25]  arXiv:1706.00436 (replaced) [pdf, ps, other]
Title: Soft Hair as a Soft Wig
Comments: One reference added and other references updated. To appear in Classical and Quantum Gravity, focus issue on BMS asymptotic symmetries
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
[26]  arXiv:1706.09833 (replaced) [pdf, other]
Title: Cosmological Effective Hamiltonian from full Loop Quantum Gravity Dynamics
Comments: 6 pages, 2 figures. Added references and a section with a toy model (example of the effective dynamics)
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th)
[27]  arXiv:1707.00984 (replaced) [pdf, other]
Title: Frame-dependence of higher-order inflationary observables in scalar-tensor theories
Comments: Title changed per journal request, typos fixed, a few comments and references added, to appear in PRD
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
[28]  arXiv:1707.06460 (replaced) [pdf, ps, other]
Title: Expansion of magnetic neutron stars in an energy (in)dependent spacetime
Comments: 15 pages, 8 figures, accepted for publication in Astrophys. J
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Theory (hep-th)
[29]  arXiv:1707.07333 (replaced) [pdf, other]
Title: From black holes to white holes: a quantum gravitational, symmetric bounce
Comments: 23 pages, 11 figs, Penrose-Carter diagram and references added, to appear in CQG
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[30]  arXiv:1708.05631 (replaced) [pdf, other]
Title: Are black holes about information?
Comments: 20 pages; forthcoming in Richard Dawid, Radin Dardashti, and Karim Th\'ebault (eds.), Epistemology of Fundamental Physics, Cambridge University Press; minor changes and additions of references
Subjects: History and Philosophy of Physics (physics.hist-ph); General Relativity and Quantum Cosmology (gr-qc)
[31]  arXiv:1708.08766 (replaced) [pdf, ps, other]
Title: Generalized plane waves in Poincaré gauge theory of gravity
Comments: 13 pages, Rextex, Paper is dedicated to Friedrich Hehl on the occasion of his 80th birthday, in appreciation of his contribution to the development of gauge theories of gravity. arXiv admin note: text overlap with arXiv:1702.05185
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[32]  arXiv:1709.03798 (replaced) [pdf, other]
Title: On the end stage of spherical gravitational collapse in a cosmological scenario
Comments: 24 Pages, 2 figures, minor modifications
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
[33]  arXiv:1709.03960 (replaced) [pdf, other]
Title: Natural Inflation from Polymer Quantization
Comments: 9 pages, 4 figures, references added
Subjects: General Relativity and Quantum Cosmology (gr-qc)
[34]  arXiv:1709.04293 (replaced) [pdf, other]
Title: Rotating black hole geometries in a two-dimensional photon superfluid
Subjects: Optics (physics.optics); General Relativity and Quantum Cosmology (gr-qc)
[ total of 34 entries: 1-34 ]
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