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Comparing an analytical spacetime metric for a merging binary to a fully non-linear numerical evolution using curvature scalarsFeb 08 2018We introduce a new geometrically invariant prescription for comparing two different spacetimes based on geodesic deviation. We use this method to compare a family of recently introduced analytical spacetime representing inspiraling black-hole binaries ... More

A curvature bound from gravitational catalysisFeb 08 2018We determine bounds on the curvature of local patches of spacetime from the requirement of intact long-range chiral symmetry. The bounds arise from a scale-dependent analysis of gravitational catalysis and its influence on the effective potential for ... More

Noncommutative Heisenberg algebra in the neighbourhood of a generic null surfaceFeb 08 2018We show that the diffeomorphisms, which preserve the null nature for a generic null metric very near to the null surface, incorporate {\it noncommutative} Heisenberg algebra. This is the generalization of the earlier work (Phys. Rev. D95, 044020 (2017)) ... More

Selfgravitating axially symmetric disks in general-relativistic rotationFeb 08 2018We integrate numerically axially symmetric stationary Einstein equations describing self-gravitating disks around spinless black holes. The numerical scheme is based on a method developed by Shibata, but contains important new ingredients. We derive a ... More

Aspects of braneworld cosmology and holographyFeb 08 2018In a holographic braneworld universe a cosmological fluid occupies a 3+1 dimensional brane located at the boundary of the asymptotic AdS$_5$ bulk. The AdS/CFT correspondence and the second Randall-Sundrum model are combined to establish a relationship ... More

A dark energy scenario consistent with GW170817 in theories beyond HorndeskiFeb 08 2018The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are the general scheme of scalar-tensor theories allowing the possibility for realizing the tensor propagation speed $c_t$ equivalent to 1 on the isotropic cosmological background. ... More

Does the black hole shadow probe the event horizon geometry?Feb 07 2018There is an exciting prospect of obtaining the shadow of astrophysical black holes (BHs) in the near future with the Event Horizon Telescope. As a matter of principle, this justifies asking how much one can learn about the BH horizon itself from such ... More

Gravitation in terms of observablesFeb 07 2018In the 1960's, Mandelstam proposed a new approach to gauge theories and gravity based on loops. The program for gauge theories was completed for Yang--Mills theories by Gambini and Trias in the 1980's. Gauge theories could be understood as representations ... More

On Non-slow Roll Inflationary RegimesFeb 07 2018We summarize our work on constant roll inflationary models. It was understood recently that constant roll inflation, in a regime beyond the slow roll approximation, can give models that are in agreement with the observational constraints. We describe ... More

Quantum edge modes in 3d gravity and 2+1d topological phases of matterFeb 07 2018We analyze the edge mode structure of Euclidean three dimensional gravity from within the quantum theory as embodied by a Ponzano-Regge-Turaev-Viro discrete state sum with Gibbons-=-Hawking-York boundary conditions. This structure is encoded in a pair ... More

Detecting Stellar Lensing of Gravitational Waves with Ground-Based ObservatoriesFeb 07 2018We investigate the ability of ground based gravitational wave observatories to detect gravitational wave lensing events caused by stellar mass lenses. We show that LIGO and Virgo possess the sensitivities required to detect lenses with masses as small ... More

Minimally modified theories of gravity: a playground for testing the uniqueness of general relativityFeb 07 2018In a recent paper [1], it was introduced a new class of gravitational theories with two local degrees of freedom. The existence of these theories apparently challenges the unique role of general relativity as the unique non-linear theory of massless spin-2 ... More

Exact Solution of a Strongly Coupled Gauge Theory in 0+1 DimensionsFeb 07 2018Gauged tensor models are a class of strongly coupled quantum mechanical theories. We present the exact analytic solution of a specific example of such a theory: namely the smallest colored tensor model due to Gurau and Witten that exhibits non-linearities. ... More

Asymptotically Locally Euclidean/Kaluza-Klein Stationary Vacuum Black Holes in 5 DimensionsFeb 07 2018We produce new examples, both explicit and analytical, of bi-axisymmetric stationary vacuum black holes in 5 dimensions. A novel feature of these solutions is that they are asymptotically locally Euclidean in which spatial cross-sections at infinity have ... More

Semi Concurrent vector fields in Finsler geometryFeb 07 2018In the present paper, we introduce and investigate the notion of a semi concurrent vector field on a Finsler manifold. We show that some special Finsler manifolds admitting such vector fields turn out to be Riemannian. We prove that Tachibana's characterization ... More

Dynamical analysis on $f(R,\mathcal{G})$ cosmologyFeb 07 2018We use a dynamical system approach to study the cosmological viability of $f(R,\mathcal{G})$ gravity theories. The method consists of formulating the evolution equations as an autonomous system of ODEs, using suitable variables. The formalism is applied ... More

Compact stars in Energy-Momentum Squared GravityFeb 07 2018A simple generalization to Einstein's general relativity (GR) was recently proposed which allows a correction term $T_{\alpha\beta}T^{\alpha\beta}$ in the action functional of the theory. This theory is called Energy-Momentum Squared Gravity (EMSG) and ... More

Strong Lensing of a Regular Black Hole with an Electrodynamics SourceFeb 07 2018In this paper we have investigated the gravitational lensing phenomenon in the strong field regime for a regular, charged, static, non-linear black hole having a electrodynamics source. We have obtained the angle of deflection and compared it to a Schwarzschild ... More

Structure formation in $f(T)$ gravity and a solution for $H_0$ tensionFeb 07 2018We investigate the evolution of scalar perturbations in $f(T)$ teleparallel gravity and its effects on the cosmic microwave background (CMB) anisotropy. The $f(T)$ gravity generalizes the teleparallel gravity which is formulated on the Weitzenb\"ock spacetime, ... More

Algorithms for the explicit computation of Penrose diagramsFeb 06 2018An algorithm is given for explicitly computing Penrose diagrams for spacetimes of the form $ds^2 = -f(r)\, dt^2 + f(r)^{-1} \, dr^2 + r^2 \, d\Omega^2$. The resulting diagram coordinates are shown to extend the metric continuously and nondegenerately ... More

Model Selection Using Cosmic Chronometers with Gaussian ProcessesFeb 06 2018The use of Gaussian Processes with a measurement of the cosmic expansion rate based solely on the observation of cosmic chronometers provides a completely cosmology-independent reconstruction of the Hubble constant H(z) suitable for testing different ... More

Semiclassical Self Consistent Treatment of the Emergence of Seeds of Cosmic Structure. The second order constructionFeb 06 2018In this work we extend the results of [1] where, Semiclassical Selfconsistent Configurations (SSC) formalism was introduced. The scheme combines quantum field theory on a background space-time, semiclassical treatment of gravitation and spontaneous collapse ... More

Why Is There Something, Rather Than Nothing?Feb 06 2018It seems natural to ask why the universe exists at all. Modern physics suggests that the universe can exist all by itself as a self-contained system, without anything external to create or sustain it. But there might not be an absolute answer to why it ... More

Building a linear equation of state for trapped gravitons from finite size effects and the Schwarzschild black hole caseFeb 06 2018In this paper we continue the investigations present in \cite{1} and \cite{2} concerning the spectrum of trapped gravitons in a spherical box, and in particular inside a Schwarzschild black hole (BH). We explore the possibility that, due to finite size ... More

Wormholes in conformal gravityFeb 06 2018We present a new class of solutions for static spherically symmetric wormhole spacetimes in conformal gravity and outline a detailed method for their construction. As an explicit example, we construct a class of traversable and non-traversable wormholes ... More

The First Hours of the GW170817 Kilonova and the Importance of Early Optical and Ultraviolet Observations for Constraining Emission ModelsFeb 06 2018The kilonova associated with GW170817 displayed early blue emission which has been interpreted as a signature of either radioactive decay in low-opacity ejecta, relativistic boosting of radioactive decay in high-velocity ejecta, the cooling of material ... More

Deformation of extremal black holes from stringy interactionsFeb 06 2018Black holes are a powerful setting for studying general relativity and theories beyond GR. However, analytical solutions for rotating black holes in beyond-GR theories are difficult to find because of the complexity of such theories. In this paper, we ... More

Hamiltonian formalism for f(T) gravityFeb 06 2018We present the Hamiltonian formalism for $f(T)$ gravity, and prove that the theory has $\frac{n(n-3)}{2}+1$ degrees of freedom in $n$ dimensions. We start from a scalar-tensor action for the theory, that represents a scalar field minimally coupled with ... More

Phantom fluid supporting traversable wormholes in alternative gravity with extra material termsFeb 06 2018Wormholes are tunnels connecting different regions in space-time. They were obtained originally as a solution for Einstein's General Relativity theory and according to this theory they need to be filled by an exotic kind of anisotropic matter. In the ... More

Constraints on energy-momentum squared gravity from neutron stars and its cosmological implicationsFeb 06 2018Deviations from the predictions of general relativity due to energy-momentum squared gravity (EMSG) are expected to become pronounced in the high density cores of neutron stars. We derive the hydrostatic equilibrium equations in EMSG and solve them numerically ... More

Are gravitational wave ringdown echoes always equal-interval ?Feb 06 2018Feb 07 2018Gravitational wave (GW) ringdown waveforms may contain "echoes" that encode new physics in the strong gravity regime. It is commonly assumed that the new physics gives rise to the GW echoes whose intervals are constant. We point out that this assumption ... More

Testing modified gravity with globular clusters: the case of NGC 2419Feb 06 2018The dynamics of globular clusters has been studied in great detail in the context of general relativity as well as with modifications of gravity that strongly depart from the standard paradigm such as MOND. However, at present there are no studies that ... More

Classical motion on hyperbolic spacetimes of any dimensionsFeb 06 2018The geosesics on de Sitter and anti-de Sitter spacetimes of any dimensions are derived in terms of conserved quantities. With their help the mesoscopic systems on these manifolds are studied finding the general solutions of the Boltzmann-Marle model in ... More

Vortex Solution of the Gravitational Field Equation of a Twisted Skyrme StringsFeb 06 2018We construct non-linear sigma model plus Skyrme term (Skyrme model) with a twist in the gravitational field. To simplify the solution, first we examine non-linear sigma model without Skyrme term, in particular with a twist, which comprises a vortex solution ... More

Group theoretical formulation of free fall and projectile motionFeb 06 2018In this work we formulate the group theoretical description of free fall and projectile motion. For that purpose we first construct a phase space with coordinates $(y,V)$, where $y$ and $V$ denote the position and velocity of a particle in free fall. ... More

Motion and collision of particles in rotating linear dilaton black holeFeb 06 2018We study the motion of particles in the background of a four-dimensional linear dilaton black hole. We solve analytically the equations of motion of the test particles and we describe their motion. We show that the dilaton black hole acts as a particle ... More

Renormalization for a Scalar Field in an External Scalar PotentialFeb 05 2018The Pauli--Villars regularization procedure confirms and sharpens the conclusions reached previously by covariant point splitting. The divergences in the stress tensor of a quantized scalar field interacting with a static scalar potential are isolated ... More

Towards a bulk description of higher spin SYKFeb 05 2018We consider on the bulk side extensions of the Sachdev--Ye--Kitaev (SYK) model to Yang--Mills and higher spins. To this end we study generalizations of the Jackiw--Teitelboim (JT) model in the BF formulation. Our main goal is to obtain generalizations ... More

Non-conservative unimodular type gravityFeb 05 2018In unimodular gravity the cosmological constant $\Lambda$ appears naturally as an integration constant when deriving the field equations of the theory and using the conservation of the matter components. Therefore, the unimodular approach seems to naturally ... More

Anisotropic strange stars in the Einstein-Maxwell spacetimeFeb 05 2018We present here a detailed analysis on the effects of charge on the anisotropic strange star candidates by considering a spherically symmetric interior spacetime metric. To obtain exact solution of the Einstein-Maxwell field equations we have considered ... More

Analytic Study of Cosmological Perturbations in a Unified Model of Dark Matter and Dark Energy with a Sharp TransitionFeb 05 2018We study cosmological perturbations in a model of unified dark matter and dark energy with a sharp transition in the late-time universe. The dark sector is described by a dark fluid which evolves from an early stage at redshifts $z > z_C$ when it behaves ... More

Unitarity issues in higher derivative field theoriesFeb 03 2018We analyze the unitarity properties of higher derivative quantum field theories which are free of ghosts and ultraviolet singularities. We point out that in spite of the absence of ghosts most of these theories are not unitary. This result confirms the ... More

Small sphere limit of the quasi-local energy with anti de-Sitter space referenceFeb 02 2018In [13], a new quasi-local energy is introduced for spacetimes with a non-zero cosmological constant. In this article, we study the small sphere limit of this newly defined quasi-local energy for spacetimes with a negative cosmological constant. For such ... More

Inspirals into a charged black holeFeb 02 2018We model the quasi-circular inspiral of a compact object into a more massive charged black hole. Extreme and intermediate mass-ratio inspirals are considered through a small mass-ratio approximation. Reissner-Nordstr$\ddot{\text{o}}$m spacetime is used ... More

Gravitational Lensing of a star by a rotating black holeFeb 02 2018The gravitational lensing of a finite star moving around a rotating Kerr black hole has been numerically calculated. Calculations for the direct image of the star and for the first and second light echoes have been performed for the star moving with an ... More

Maximally Rotating Supermassive Stars at the Onset of Collapse: The Perturbative Effects of Gas Pressure, Magnetic Fields, Dark Matter and Dark EnergyFeb 02 2018The discovery of quasars at increasingly large cosmological redshifts may favor "direct collapse" as the most promising evolutionary route to the formation of supermassive black holes. In this scenario, supermassive black holes form when their progenitors ... More

Numerically solving the relativistic Grad-Shafranov equation in Kerr spacetimes: Numerical techniquesFeb 02 2018The study of the electrodynamics of static, axisymmetric and force-free Kerr magnetospheres relies vastly on solutions of the so called relativistic Grad-Shafranov equation (GSE). Different numerical approaches to the solution of the GSE have been introduced ... More

Translation of Cylinders in General RelativityFeb 02 2018We obtain the general vacuum metric solution to a cylindrical translating source. We show that its metric is geometrically related to the vacuum field produced by a stationary cylindrical source. However, this result is not trivial, as for instance, in ... More

Lorentz Distributed Noncommutative $F(T,T_G)$ Wormhole SolutionsFeb 02 2018The aim of this paper is to study static spherically symmetric noncommutative $F(T,T_G)$ wormhole solutions along with Lorentzian distribution. Here, $T$ and $T_G$ are torsion scalar and teleparallel equivalent Gauss-Bonnet term, respectively. We take ... More

Mode solutions for a Klein-Gordon field in anti-de Sitter with dynamical boundary conditions of Wentzell typeFeb 01 2018We study a real, massive Klein-Gordon field in the Poincar\'e fundamental domain of the $(d+1)$-dimensional anti-de Sitter (AdS) spacetime, subject to a particular choice of dynamical boundary conditions of generalized Wentzell type, whereby the boundary ... More

Entanglement Entropy for Open Bosonic Strings on $Dp$-branesFeb 01 2018We study the entanglement entropy for open bosonic strings on multiple $Dp$-branes by using the covariant open string field theory. Choosing one of the spatial coordinates which are tangential to the hyperplane on which $Dp$-branes are located, we divide ... More

Scalar fields as sources for wormholes and regular black holesJan 31 2018We review nonsingular static, spherically solutions of general relativity with a minimally coupled scalar field $\phi$ as a source. Considered are wormholes and regular black holes without a center, including black universes (black holes with an expanding ... More

A Galerkin-Collocation domain decomposition method: application to the evolution of cylindrical gravitational wavesJan 31 2018We present an innovative Galerkin-Collocation domain decomposition algorithm applied to the evolution of cylindrical unpolarized gravitational waves. We display how the domain decomposition effectiveness was successfully implemented for those initial ... More

Holographic studies of Einsteinian cubic gravityJan 31 2018Einsteinian cubic gravity provides an holographic toy model of a nonsupersymmetric CFT in three dimensions, analogous to the one defined by Quasi-topological gravity in four. The theory admits explicit non-hairy AdS$_4$ black holes and allows for numerous ... More

Anisotropic compact stars in general relativityJan 31 2018We present model of an asisotropic fluid sphere under Einstein's general theory of relativity. For this we employ the Tolman-Kuchowicz~\cite{Tolman1939,Kuchowicz1968} metric which provides a class of singularity free solutions. The set of solutions satisfies ... More

Can the cosmological dark sector be modeled by a single scalar field?Jan 31 2018In a previous paper it was shown that a minimally coupled scalar field of mass $M \sim H_0$ can describe both components of the dark sector in a unified way. In the solution found, the dark energy component decays linearly with the Hubble parameter, with ... More

The Reconstruction of $f(φ)R$ and Mimetic Gravity from Viable Slow-roll InflationJan 31 2018In this work, we extend the bottom-up reconstruction framework of $F(R)$ gravity to other modified gravities, and in particular for $f(\phi)R$ and mimetic $F(R)$ gravities. We investigate which are the important conditions in order for the method to work, ... More

Mapping Ricci-based theories of gravity into general relativityJan 31 2018We show that the space of solutions of a wide family of Ricci-based metric-affine theories of gravity can be put into correspondence with the space of solutions of general relativity (GR). This allows us to use well-established methods and results from ... More

Late-time acceleration with steep exponential potentialsJan 31 2018In this letter, we study the cosmological dynamics of steeper potential than exponential. Our analysis shows that a simple extension of an exponential potential allows to capture late-time cosmic acceleration and retain the tracker behavior. We also perform ... More

Stellar Tidal Disruption Events in General RelativityJan 30 2018A tidal disruption event (TDE) ensues when a star passes too close to the supermassive black hole (SMBH) in a galactic center and is ripped apart by the tidal field of the SMBH. The gaseous debris produced in a TDE can power a bright electromagnetic flare ... More

Rotating Kinky BraneworldsJan 30 2018Cylindrical braneworlds have been used in the literature as a convenient way to resolve co-dimension-two branes. They are prevented from collapsing by a massless worldvolume field with non-trivial winding, but here we discuss another way of preventing ... More

Nonlinear evolution of the AdS$_4$ black hole bombJan 29 2018The superradiant instability of rotating black holes with negative cosmological constant is studied by numerically solving the full 3+1-dimensional Einstein equations. We find evidence for an epoch dominated by a solution with a single helical Killing ... More

Strong cosmic censorship in de Sitter spaceJan 29 2018Recent work indicates that the strong cosmic censorship hypothesis is violated by nearly extremal Reissner-Nordstrom-de Sitter black holes. It was argued that perturbations of such a black hole decay sufficiently rapidly that the perturbed spacetime can ... More

GUP impact onto black holes information flux and the sparsity of Hawking radiationJan 29 2018We investigate the Generalized Uncertainty Principle (GUP) corrections to the entropy content and the information flux of black holes, as well as the corrections to the sparsity of the Hawking radiation at the late stages of evaporation. We find that ... More

Gravitational Energy and the Gauge Theory PerspectiveJan 29 2018Gravity, and the puzzle regarding its energy, can be understood from a gauge theory perspective. Gravity, i.e., dynamical spacetime geometry, can be considered as a local gauge theory of the symmetry group of Minkowski spacetime: the Poincare group. The ... More

Primordial Black Holes from Inflation and non-GaussianityJan 29 2018Primordial black holes may owe their origin to the small-scale enhancement of the comoving curvature perturbation generated during inflation. Their mass fraction at formation is markedly sensitive to possible non-Gaussianities in such large, but rare ... More

The LArase Satellites Spin mOdel Solutions (LASSOS): a comprehensive model for the spin evolution of the LAGEOS and LARES satellitesJan 27 2018The two LAGEOS and LARES are laser-ranged satellites tracked with the best accuracy ever achieved. Using their range measurements many geophysical parameters were calculated and some General Relativity effects were directly observed. To obtain precise ... More

Testing general relativity with compact-body orbits: A modified Einstein-Infeld-Hoffmann frameworkJan 26 2018We describe a general framework for analyzing orbits of systems containing compact objects (neutron stars or black holes) in a class of Lagrangian-based alternative theories of gravity that also admit a global preferred reference frame. The framework ... More

Bardeen regular black hole as a quantum-corrected Schwarzschild black holeJan 26 2018Bardeen regular black hole is commonly considered as a solution of general relativity coupled to a nonlinear electrodynamics. In this letter, it is shown that Bardeen solution may be interpreted as a quantum-corrected Schwarzschild black hole. This new ... More

BPS Kerr-AdS Time MachinesJan 25 2018It was recently observed that Kerr-AdS metrics with negative mass describe smooth spacetimes that have a region with naked closed time-like curves, bounded by a velocity of light surface. Such spacetimes are sometimes known as time machines. In this paper ... More

Density perturbations for running vacuum: a successful approach to structure formation and to the $σ_8$-tensionJan 25 2018Recent studies suggest that dynamical dark energy (DDE) provides a better fit to the rising affluence of modern cosmological observations than the concordance model ($\Lambda$CDM) with a rigid cosmological constant, $\Lambda$. Such is the case with the ... More

Pauli-Zeldovich cancellation of the vacuum energy divergences, auxiliary fields and supersymmetryJan 25 2018We have considered the Pauli-Zeldovich mechanism for the cancellation of the ultraviolet divergences in vacuum energy. This mechanism arises because bosons and fermions give contributions of the opposite signs. In contrast with the preceding papers devoted ... More

Dynamical System Analysis of a Five-Dimensional Cosmological ModelJan 25 2018A five-dimensional cosmological model including a single perfect fluid is studied in the framework of dynamical system analysis. All the critical points of the system with their stability properties are listed and some representative phase diagrams are ... More

Linear potentials in galaxy halos by Asymmetric WormholesJan 25 2018In this letter we study the spherically symmetric space-time for a diffusive two measures theory. It is demonstrated that by imposing an asymmetric wormhole geometry, one gets a metric coefficient which for galactic distances has a linear term and from ... More

Hamilton Geometry - Phase Space Geometry from Modified Dispersion RelationsJan 24 2018Quantum gravity phenomenology suggests an effective modification of the general relativistic dispersion relation of freely falling point particles caused by an underlying theory of quantum gravity. Here we analyse the consequences of modifications of ... More

Current and future constraints on extended Bekenstein-type models for a varying fine-structure constantJan 24 2018There is a growing interest in astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\alpha$, as an optimal probe of new physics. The imminent arrival of the ESPRESSO spectrograph will soon enable ... More

Regularity of high energy photon events from gamma ray burstsJan 24 2018Feb 06 2018The effect of Quantum Gravity (QG) may bring a tiny light speed variation as $v(E)=c(1-E/E_{\rm LV})$, where $E$ is the photon energy and $E_{\rm LV}$ is a Lorentz violation scale. A remarkable regularity was suggested in previous studies to look for ... More

Energy-parity from a bicomplex algebraJan 24 2018By replacing the field of complex numbers with the commutative ring of bicomplex numbers, we attempt to construct interacting scalar quantum field theories that feature both positive- and negative-energy states. This work places the tentative ideas proposed ... More

Constraints on two accretion disks centered on the equatorial plane of a Kerr SMBHJan 24 2018The possibility that two toroidal accretion configurations may be orbiting around a~super--massive Kerr black hole has been addressed. Such tori may be formed during different stages of the Kerr attractor accretion history. We consider the relative rotation ... More

Discovering intermediate-mass black hole lenses through gravitational wave lensingJan 24 2018Intermediate-mass black holes are the missing link that connects supermassive and stellar-mass black holes and are key to understanding galaxy evolution. Gravitational waves, like photons, can be lensed by these objects. In the diffraction limit a gravitational ... More

Mad-Dog Everettianism: Quantum Mechanics at Its Most MinimalJan 23 2018To the best of our current understanding, quantum mechanics is part of the most fundamental picture of the universe. It is natural to ask how pure and minimal this fundamental quantum description can be. The simplest quantum ontology is that of the Everett ... More

dRGT Massive Gravity is not UniqueJan 23 2018With the realization that dRGT has difficulties to provide dynamical cosmological solutions, the interest of current research in massive gravity has significantly decreased. The reason for that is not least because it is commonly believed that the dRGT ... More

Magnetic Seed and Cosmology as Quantum Hall EffectJan 23 2018In the framework of a bimetric model, we discuss a relation between the (modified) Friedmann equations and a mechanical system similar to the quantum Hall effect problem. Firstly, we show how these modified Friedmann equations are mapped to an anisotropic ... More

Hawking radiation and the Bloom-Gilman dualityJan 23 2018The decay widths of the quantum black hole precursors, determined from the poles of the resummed graviton propagator, are matched to the expected lifetime given by the Hawking decay. In this way, we impose a sort of duality between a perturbative description ... More

Large-scale messengers from arbitrary spin fieldsJan 22 2018We show that nonperturbative production of arbitrary spin fields from vacuum will accompany the generation of non-vanishing macroscopic energy-momentum tensor correlators. This argument is based on the general causal field formalism, which gives a manifestly ... More

A Local First Law of GravityJan 22 2018We find a local first law of thermodynamics, $\Delta E = T \Delta S - W$, connecting gravitational entropy, $S$, with matter energy and work. For Einstein gravity $S$ is the Bekenstein-Hawking entropy, while for more general theories of gravity $S$ is ... More

A perturbative approach to the construction of initial data on compact manifoldsJan 22 2018We discuss the implementation of Butscher's method \cite{But06,But07} for the construction of solutions to the extended constraint equations, for the vacuum Einstein field equations, in the case of compact manifolds. The method is then applied to the ... More

Axisymmetric black holes allowing for separation of variables in the Klein-Gordon and Hamilton-Jacobi equationJan 22 2018Jan 23 2018We determine the class of axisymmetric and asymptotically flat black-hole spacetimes for which the test Klein-Gordon and Hamilton-Jacobi equations allow for the separation of variables. The known Kerr, Kerr-Newman, Kerr-Sen and some other black-hole metrics ... More

Cosmological Theories Of The Extra TermsJan 21 2018This paper purports to have: Introduced a new formulation of Quantum Mechanics, explained the apparent disconnect between Quantum Mechanics and General Relativity, explained the observed far field expansion of the Universe (Dark Energy), supplied an argument ... More

Exact ghost-free bigravitational wavesJan 21 2018We study the propagation of exact gravitational waves in the ghost-free bimetric theory. Our focus is on type N spacetimes compatible with the cosmological constants provided by the bigravity interaction potential, and particularly in the single class ... More

Gravitational wave speed: Implications for models without a mass scaleJan 20 2018The recent report that the gravitational wave speed equals the light speed puts strong constraints on the anisotropic stress parameter of many modified gravity models, a quantity that is directly observable through large-scale structure. We show here ... More

On the asymptotic behavior of static perfect fluidsJan 20 2018Static spherically symmetric solutions to the Einstein-Euler equations with prescribed central densities are known to exist, be unique and smooth for reasonable equations of state. Some criteria are also available to decide whether solutions have finite ... More

Scalar-torsion theories of gravity II: $L(T, X, Y, φ)$ theoryJan 19 2018We consider Lorentz invariant scalar-tensor teleparallel gravity theories with a Lagrangian built from the torsion scalar, a scalar field, its kinetic term and a derivative coupling between the torsion and the scalar field. The field equations of the ... More

Scalar-torsion theories of gravity III: analogue of scalar-tensor gravity and conformal invariantsJan 19 2018We discuss a class of teleparallel scalar-torsion theories of gravity, which is parametrized by five free functions of the scalar field. The theories are formulated covariantly using a flat, but non-vanishing spin connection. We show how the actions of ... More

Scalar-torsion theories of gravity I: general formalism and conformal transformationsJan 19 2018We discuss the most general class of teleparallel scalar-torsion theories of gravity in their covariant formulation. The only restrictions we impose are the invariance of the action under diffeomorphisms and local Lorentz transformations, as well as vanishing ... More

Scalar Casimir effect in a linearly expanding universeJan 18 2018We investigate quantum vacuum effects for a massive scalar field, induced by two planar boundaries in background of a linearly expanding spatially flat Friedmann-Robertson-Walker spacetime for an arbitrary number of spatial dimensions. For the Robin boundary ... More

Collisionless Magnetic Reconnection in Curved Spacetime and the Effect of Black Hole RotationJan 18 2018Magnetic reconnection in curved spacetime is studied by adopting a general relativistic magnetohydrodynamic model that retains collisionless effects for both electron-ion and pair plasmas. A simple generalization of the standard Sweet-Parker model allows ... More

Observers in Kerr spacetimes: the ergoregion on the equatorial planeJan 18 2018We perform a detailed analysis of the properties of stationary observers located on the equatorial plane of the ergosphere in a Kerr spacetime, including light-surfaces. This study highlights crucial differences between black hole and the super-spinner ... More

Imprints of the redshift evolution of double neutron star merger rate on the signal to noise ratio distributionJan 18 2018Proposed third generation gravitational wave (GW) interferometers such as Einstein Telescope will have the sensitivity to observe double neutron star (DNS) mergers up to a redshift of $\sim 2$ with good signal to noise ratios. We argue that the measurement ... More

Mimicking inflation with 2-fluid systems in a strong gradient magnetic fieldJan 17 2018In the standard cosmological picture the Universe underwent a brief period of near-exponential expansion, known as Inflation. This provides an explanation for structure formation through the amplification of perturbations by the rapid expansion of the ... More