Latest Papers in General Relativity

General Relativity And Quantum Cosmology

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Transport phenomena and Weyl correction in effective holographic theory of momentum dissipation (1902.03225v1)

Jian-Pin Wu

2019-02-08

We construct a higher derivative theory involving an axionic field and the Weyl tensor in four dimensional spacetime. Up to the first order of the coupling parameters, the charged black brane solution with momentum dissipation in a perturbative manner is constructed. Metal-insulator transitions are implemented when varying the system parameters at zero temperature. Also, we study the transports including DC conductivity and optical conductivity at zero charge density. We observe the exact particle-vortex duality for some specific momentum dissipation strength.

Hyper non-Gaussianities in inflation with strongly non-geodesic motion (1902.03221v1)

Jacopo Fumagalli, Sebastian Garcia-Saenz, Lucas Pinol, Sébastien Renaux-Petel, John Ronayne

2019-02-08

Several recent proposals to embed inflation into high-energy physics rely on inflationary dynamics characterized by a strongly non-geodesic motion in negatively curved field space. This naturally leads to a transient instability of perturbations on sub-Hubble scales, and to their exponential amplification. Supported by first-principle numerical computations, we demonstrate that a non-standard single-field effective field theory with imaginary speed of sound enables one to gain analytical insight into primordial non-Gaussianities in this type of models. We show that the bispectrum is enhanced in flattened configurations and, more importantly, that the trispectrum and all higher-order correlation functions are exponentially amplified. These "hyper non-Gaussianities", whose amplitude we can relate to the amplification of the tree-level power spectrum, can easily lead to a loss of perturbative control. For example our results exclude the recent proposal of hyperinflation in its most interesting incarnation that satisfies the de Sitter swampland conjecture. More generally we provide powerful model-independent constraints on non-standard inflationary attractors motivated by the search for ultraviolet completions of inflation.

Baryon acoustic oscillation, Hubble parameter, and angular size measurement constraints on the Hubble constant, dark energy dynamics, and spatial curvature (1902.03196v1)

Joseph Ryan, Yun Chen, Bharat Ratra

2019-02-08

In this paper we use all available baryon acoustic oscillation and Hubble parameter data to constrain six dark energy cosmological models, both spatially flat and non-flat. These data mildly favor (at 1.3-1.4) closed spatial hypersurfaces in the dynamical dark energy models, and favor dark energy dynamics (at -2, depending on the model) over a cosmological constant . They also favor, at 2.2 to , depending on the model, a lower Hubble constant than what is measured from the local expansion rate by Riess et al. (2018).

Regularization by ε-metric (1902.03152v1)

V. D. Ivashchuk

2019-02-08

The regularization of propagators by means of a complex metric is considered. (The paper is an English translation of the first of two articles in Russian published by the author in 1987-88: V.D. Ivashchuk, Regularization by {\epsilon}-metric. I, Izvestiya Akademii Nauk Moldavskoy SSR, Ser. Fiziko-tekhnicheskih i matematicheskih nauk, No 3, p. 8-17 (1987) [in Russian] .)

A hydrodynamic approach to the classical ideal gas (1902.03106v1)

Bartolomé Coll, Joan Josep Ferrando, Juan Antonio Sáez

2019-02-08

The necessary and sufficient condition for a conservative perfect fluid energy tensor to be the energetic evolution of a classical ideal gas is obtained. This condition forces the square of the speed of sound to have the form in terms of the hydrodynamic quantities, energy density and pressure , being the (constant) adiabatic index. The {\em inverse problem} for this case is also solved, that is, the determination of all the fluids whose evolutions are represented by a conservative energy tensor endowed with the above expression of , and it shows that these fluids are, and only are, those fulfilling a Poisson law. The relativistic compressibility conditions for the classical ideal gases and the Poisson gases are analyzed in depth and the values for the adiabatic index for which the compressibility conditions hold in physically relevant ranges of the hydrodynamic quantities are obtained. Some scenarios that model isothermal or isentropic evolutions of a classical ideal gas are revisited, and preliminary results are presented in applying our hydrodynamic approach to looking for perfect fluid solutions that model the evolution of a classical ideal gas or of a Poisson gas.

2+1D Loop Quantum Gravity on the Edge (1811.04360v3)

Laurent Freidel, Florian Girelli, Barak Shoshany

2018-11-11

We develop a new perspective on the discretization of the phase space structure of gravity in 2+1 dimensions as a piecewise-flat geometry in 2 spatial dimensions. Starting from a subdivision of the continuum geometric and phase space structure into elementary cells, we obtain the loop gravity phase space coupled to a collection of effective particles carrying mass and spin, which measure the curvature and torsion of the geometry. We show that the new degrees of freedom associated to the particle-like elements can be understood as edge modes, which appear in the decomposition of the continuum theory into subsystems and do not cancel out in the gluing of cells along codimension 2 defects. These new particle-like edge modes are gravitationally dressed in an explicit way. This provides a detailed explanation of the relations and differences between the loop gravity phase space and the one deduced from the continuum theory.

Thin-Shells and Thin-Shell Wormholes in New Massive Gravity (1812.05074v2)

S. Danial Forghani, S. Habib Mazharimousavi, M. Halilsoy

2018-12-12

Within 2+1-dimensional cosmological new massive gravity, we consider thin-shell and thin-shell wormhole construction. For this, we introduce first, the junction conditions apt for the fourth order terms in the action of the theory. Then, by employing some specific static solutions in new massive gravity, we study the characteristics of associated thin-shells and thin-shell wormholes. Our finding suggests that, firstly, there cannot exist any thin-shells regarding our chosen solutions of cosmological new massive gravity, and secondly, the constructed thin-shell wormhole does not need to be symmetric. More importantly, the thin-shell wormhole, if ever forms, possesses null energy density and null angular pressure on its throat which preferable to their negative-valued counterparts.

Natural discrete differential calculus in physics (1902.03026v1)

Carlo Rovelli, Václav Zatloukal

2019-02-08

We sharpen a recent observation by Tim Maudlin: differential calculus is a natural language for physics only if additional structure, like the definition of a Hodge dual or a metric, is given; but the discrete version of this calculus provides this additional structure for free.

Some Aspects of the Canonical Analysis of Reuter-Weyer RG Improved Einstein-Hilbert Action (1902.03014v1)

Gabriele Gionti, S. J

2019-02-08

A canonical analysis of RG improved action of the Einstein-Hilbert functional is performed. The gravitational and cosmological constants as function of the space-time coordinates are treated as external non-geometrical fields. Dirac's constraint analysis is performed, in the general case, up to secondary constraints. The constraints are second class and, in general, the problem appears to be technically complicated. This fact suggests studying the Dirac's constraint analysis of the related Brans-Dicke theory, which shows the Poisson Brackets between Hamiltonian-Hamiltonian constraints do not close. A simplified FLRW minisuperspace model based on the RG improved Einstein Hilbert action contains Bouncing and Emergent Universes for values of K=-1, 0, 1.

Harmonic maps with prescribed singularities and applications in general relativity (1902.01576v2)

Gilbert Weinstein

2019-02-05

This paper presents a general existence and uniqueness result for harmonic maps with prescribed singularities into non-positively curved targets, and surveys a number of applications to general relativity. It is based on a talk delivered by the author at The 11th Mathematical Society of Japan Seasonal Institute, The Role of Metrics in the Theory of Partial Differential Equations.

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