Latest Papers in General Relativity

General Relativity And Quantum Cosmology

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Holographic derivation of a class of short range correlation functions (1901.11002v1)

Hai Lin, Haoxin Wang

2019-01-30

We construct a class of backgrounds with a warp factor and anti-de Sitter asymptotics, which are dual to boundary systems that have a ground state with a short-range two-point correlation function. The solutions of probe scalar fields on these backgrounds are obtained by means of confluent hypergeometric functions. The explicit analytical expressions of a class of short-range correlation functions on the boundary and the correlation lengths are derived from gravity computation. The two-point function calculated from gravity side is explicitly shown to exponentially decay with respect to separation in the infrared. Such feature inevitably appears in confining gauge theories and certain strongly correlated condensed matter systems.

The Big Bang is a Coordinate Singularity for Inflationary FLRW Spacetimes (1810.06789v2)

Eric Ling

2018-10-16

We show the big bang is a coordinate singularity for a large class of inflationary FLRW spacetimes which we have dubbed 'Milne-like.' By introducing a new set of coordinates, the big bang appears as a past boundary of the universe where the metric is no longer degenerate. In fact this past boundary is just the future lightcone at the origin of a spacetime conformal to Minkowski space. Similar to how investigating the geometrical properties of the event horizon in Schwarzschild led to a better understanding of black holes, we believe that investigating the geometrical properties of the big bang coordinate singularity for Milne-like spacetimes will lead to a better understanding of cosmology. We show how the mathematics of these spacetimes may help illuminate certain issues associated with dark energy, dark matter, and the universe's missing antimatter.

Soft gravitational radiation from ultra-relativistic collisions at sub- and sub-sub-leading order (1901.10986v1)

Andrea Addazi, Massimo Bianchi, Gabriele Veneziano

2019-01-30

Using soft-graviton theorems a well-known zero-frequency limit (ZFL) for the gravitational radiation flux is re-derived and extended to order and for arbitrary massless multi-particle collisions. The (angle-integrated, unpolarized) correction to the flux turns out to be absent in the case of two-particle elastic collisions. The correction is instead non-vanishing and takes a simple general expression which is then applied to bremsstrahlung from two-particle elastic collisions. For a tree-level process the outcome is finite and consistent with expectations. Instead, if the tree-level form of the soft theorems is used at sub-sub-leading order even when the elastic amplitude needs an all-loop (eikonal) resummation, an unphysical infrared singularity occurs. Its origin can be traced to the infinite Coulomb phase of gravitational scattering in four dimensions. We briefly discuss how to get rid, in principle, of the unwanted divergences and indicate --without carrying out-- a possible procedure to find the proper correction to the naive soft theorems. Nevertheless, if a simple recipe recently proposed for handling these divergences is adopted, we find surprisingly good agreement with results obtained independently via the eikonal approach to transplanckian-energy scattering at large (small) impact parameter (deflection angle), where such Coulomb divergences explicitly cancel out.

The finite volume method on a Schwarzschild background (1901.10973v1)

Shijie Dong, Philippe G. LeFloch

2019-01-30

We introduce a class of nonlinear hyperbolic conservation laws on a Schwarzschild black hole background and derive several properties satisfied by (possibly weak) solutions. Next, we formulate a numerical approximation scheme which is based on the finite volume methodology and takes the curved geometry into account. An interesting feature of our model is that no boundary conditions is required at the black hole horizon boundary. We establish that this scheme converges to an entropy weak solution to the initial value problem and, in turn, our analysis also provides us with a theory of existence and stability for a new class of conservation laws.

Tunneling through bridges: Bohmian non-locality from higher-derivative gravity (1901.10969v1)

Gregory S. Duane

2019-01-30

A classical origin for the Bohmian quantum potential, as that potential term arises in the quantum mechanical treatment of black holes and Einstein-Rosen (ER) bridges, can be based on 4th-order extensions of Einstein's equations. The required 4th-order extension of general relativity is given by adding quadratic curvature terms with coefficients that maintain a fixed ratio, as their magnitudes approach zero, with classical general relativity as a singular limit. If entangled particles are connected by a Planck-width ER bridge, as conjectured by Maldacena and Susskind, then a connection by a traversable Planck-scale wormhole, allowed in 4th-order gravity, describes such entanglement in the ontological interpretation. It is hypothesized that higher-derivative gravity can account for the nonlocal part of the quantum potential generally.

Testing CSL with neutron stars (1901.10963v1)

Stephen L. Adler, Angelo Bassi, Matteo Carlesso, Andrea Vinante

2019-01-30

A recent paper [arXiv:1901.05477] claims that the CSL model of spontaneous wave function collapse is ruled out by observations on heat flow from neutron stars. This type of system-a degenerate Fermi gas-is relevant as it represents the densest form of matter, potentially maximising CSL effects. As it turns out, this is not the case: to leading order, the CSL induced heating is the same as for ordinary matter, and neutron stars do not bound the CSL parameters significantly.

Avoiding instabilities in antisymmetric tensor driven inflation (1901.10959v1)

Sandeep Aashish, Abhilash Padhy, Sukanta Panda

2019-01-30

Models of inflation with antisymmetric tensor studied in the past are plagued with ghost instability even in an unperturbed FRW background. We show that it is possible to avoid ghosts by considering the most general kinetic term for antisymmetric tensor. The kinetic part acquires a new gauge symmetry violating term whose effect on perturbed modes is to prevent the appearance of nondynamical modes, and thus avoid ghosts. For completeness, we also perform a check for gradient instability when this new kinetic term is dominant and find that the perturbations are free of gradient instability.

Constraints on Hořava gravity from binary black hole observations (1811.07786v2)

Oscar Ramos, Enrico Barausse

2018-11-19

Ho\v{r}ava gravity breaks Lorentz symmetry by introducing a preferred spacetime foliation, which is defined by a timelike dynamical scalar field, the khronon. The presence of this preferred foliation makes black hole solutions more complicated than in General Relativity, with the appearance of multiple distinct event horizons: a matter horizon for light/matter fields, a spin-0 horizon for the scalar excitations of the khronon, a spin-2 horizon for tensorial gravitational waves, and even, at least in spherical symmetry, a universal horizon for instantaneously propagating modes appearing in the ultraviolet. We study how black hole solutions in Ho\v{r}ava gravity change when the black hole is allowed to move with low velocity relative to the preferred foliation. These slowly moving solutions are a crucial ingredient to compute black hole "sensitivities" and predict gravitational wave emission (and in particular dipolar radiation) from the inspiral of binary black hole systems. We find that for generic values of the theory's three dimensionless coupling constants, slowly moving black holes present curvature singularities at the universal horizon. Singularities at the spin-0 horizon also arise unless one waives the requirement of asymptotic flatness at spatial infinity. Nevertheless, we have verified that at least in a one-dimensional subset of the (three-dimensional) parameter space of the theory's coupling constants, slowly moving black holes are regular everywhere, even though they coincide with the general relativistic ones (thus implying in particular the absence of dipolar gravitational radiation). Remarkably, this subset of the parameter space essentially coincides with the one selected by the recent constraints from GW170817 and by solar system tests.

Peeling property and asymptotic symmetries with a cosmological constant (1705.00435v2)

Vee-Liem Saw, Freeman Chee Siong Thun

2017-05-01

This paper establishes two things in an asymptotically (anti-)de Sitter spacetime, by direct computations in the physical spacetime (i.e. with no involvement of spacetime compactification): (1) The peeling property of the Weyl spinor is guaranteed. In the case where there are Maxwell fields present, the peeling properties of both Weyl and Maxwell spinors similarly hold, if the leading order term of the spin coefficient when expanded as inverse powers of (where is the usual spherical radial coordinate, and is null infinity, ) has coefficient . (2) In the absence of gravitational radiation (a conformally flat ), the group of asymptotic symmetries is trivial, with no room for supertranslations.

From Scattering Amplitudes to Classical Potentials in the Post-Minkowskian Expansion (1808.02489v2)

Clifford Cheung, Ira Z. Rothstein, Mikhail P. Solon

2018-08-07

We combine tools from effective field theory and generalized unitarity to construct a map between on-shell scattering amplitudes and the classical potential for interacting spinless particles. For general relativity, we obtain analytic expressions for the classical potential of a binary black hole system at second order in the gravitational constant and all orders in velocity. Our results exactly match all known results up to fourth post-Newtonian order, and offer a simple check of future higher order calculations. By design, these methods should extend to higher orders in perturbation theory.

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