arXiv subjects

Guillermo Rubilar

Publications and source records attributed to Guillermo Rubilar.

3 recordsLinked to original sources

arXiv2024

Neutron stars in 4D Einstein-Gauss-Bonnet gravity

Since the derivation of a well-defined $D\to4$ limit for 4D Einstein-Gauss-Bonnet (4DEGB) gravity coupled to a scalar field, there has been considerable interest in testing it as an alternative to Einstein's general theory of relativity. Past work has shown that this theory hosts interesting compact star solutions which are smaller in radius than a Schwarzschild black hole of the same mass in general relativity (GR), though the stability of such objects has been subject to question. In this paper we solve the equations for radial perturbations of neutron stars in the 4DEGB theory with Skyrme Lyon (SLy)/Brussels-Montreal Skyrme functionals (BSk) class equations of state (EOSs), along with the M\"uller-Serot (MS2) EOS, and show that the coincidence of stability and maximum mass points in GR is still present in this modified theory, with the interesting additional feature of solutions re-approaching stability near the black hole solution on the mass-radius diagram. Besides this, as expected from past work, we find that larger values of the 4DEGB coupling $\alpha$ tend to increase the mass of neutron stars of the same radius (due to a larger $\alpha$ weakening gravity) and move the maximum mass points of the solution branches closer to the black hole horizon.

gr-qc↗

arXiv2024

Scalar probes on wormholes in Lovelock theories with unique vacuum

In this paper we present a new family of wormhole geometries in Lovelock theories with a unique vacuum, and study their stability under scalar field perturbations. As the solutions already known in the literature for Chern-Simons gravity on AdS, the new wormholes are characterized by a single integration constant $ρ_{0}$, that parameterizes the contribution to the mass coming from each boundary, which cancel each other, leading to a new example of "mass without mass". The stability of these new configurations, as well as other previously constructed in the literature is explored under scalar field perturbations. The stability is ensured provided the mass of the scalar perturbation is above a deformed Breitenlohner-Freedman bound which is sensitive to the value of $ρ_{0}$.

hep-th↗

arXiv2000

Wave propagation in linear electrodynamics

The Fresnel equation governing the propagation of electromagnetic waves for the most general linear constitutive law is derived. The wave normals are found to lie, in general, on a fourth order surface. When the constitutive coefficients satisfy the so-called reciprocity or closure relation, one can define a duality operator on the space of the two-forms. We prove that the closure relation is a sufficient condition for the reduction of the fourth order surface to the familiar second order light cone structure. We finally study whether this condition is also necessary.

gr-qc↗