arXiv subjects

J. Osorio Morales

Publications and source records attributed to J. Osorio Morales.

4 recordsLinked to original sources

arXiv2022

About apparent superluminal drives in generic gravity theories

As is well known, there exists warp drives in GR, such as the Alcubierre bubbles, which achieve an apparent faster than light travel \cite{alcubierre}. A result due to Gao and Wald \cite{gaowald} suggests that such a travel is unlikely for GR with matter satisfying both the Null Energy and the Null Generic Conditions. There exists a generalization of this statement due to Galloway, that ensures that the Gao-Wald result is true regardless the underlying gravity model, unless there exists at least one inextendible null geodesic with achronal image in the space time (a null line). The proof of this proposition is based on techniques of causal theories, and has never been released. In the present work an independent proof of this result is presented by use of the Raychaudhuri equation, and avoiding several technical complications described along the text. Some consequences of these affirmations are discussed at last section, in particular their potential use in problems of causality.

gr-qc↗

arXiv2019

About the Cauchy problem in Stelle's quadratic gravity

The focus of the present work is on the Cauchy problem for the quadratic gravity models introduced in \cite{stelle}-\cite{stelle2}. These are renormalizable higher order derivative models of gravity, but at cost of ghostly states propagating in the phase space. A previous work on the subject is \cite{noakes}. The techniques employed here differ slightly from those in \cite{noakes}, but the main conclusions agree. Furthermore, the analysis of the initial value formulation in \cite{noakes} is enlarged and the use of harmonic coordinates is clarified. In particular, it is shown that the initial constraints found \cite{noakes} include a redundant one. In other words, this constraint is satisfied when the equations of motion are taken into account. In addition, some terms that are not specified in \cite{noakes} are derived explicitly. This procedure facilitates application of some of the mathematical theorems given in \cite{ringstrom}. As a consequence of these theorems, the existence of both $C^\infty$ solutions and maximal globally hyperbolic developments is proved. The obtained equations may be relevant for the stability analysis of the solutions under small perturbations of the initial data.

hep-th↗

arXiv2018

The existence of smooth solutions in q-theories

The q-models are scenarios that may explain the smallness of the cosmological constant [1]-[7]. The vacuum in these theories is presented as a self-sustainable medium and include a new degree of freedom, the q-variable, which stablish the equilibrium of the quantum vacuum. In the present work, the Cauchy formulation for these models is studied. It has been already noted that there exist some limits where these theories are described by an F(R) model, which posses a well formulated Cauchy problem. This paper shows that the Cauchy problem is well posed even not reaching this limit. By use of some mathematical theorems about second order non linear systems, it is shown that these scenarios admit a smooth solution for at least a finite time when some specific type of initial conditions are imposed. Some technical conditions of [11] play an important role in this discussion.

gr-qc↗

arXiv2018

Gauss-Bonnet models with cosmological constant and non zero spatial curvature in $D=4$

In the present paper the possibility of eternal universes in Gauss-Bonnet theories of gravity in four dimensions is analysed. It is shown that, for zero spatial curvature and zero cosmological constant, if the coupling is such that $0<f'(ϕ)\leq c \exp(\frac{\sqrt{8}}{\sqrt{10}}ϕ)$, then there are solutions that are eternal. Similar conclusions are found when a cosmological constant turned on. These conclusions are not generalized for the case when the spatial curvature is present, but we are able to find some general results about the possible nature of the singularities. The presented results correct some dubious arguments in [54], although the same conclusions are reached. On the other hand, these past results are considerably generalized to a wide class of situations which were not considered in [54].

gr-qc↗