Some considerations on the Mac Dowell-Mansouri action

A precise relation is established between the Stelle-West formulation of the Mac Dowell-Mansouri approach to a gauge theory of gravity and the approach based on a gauged Wess-Zumino-Witten term. In particular, it is shown that a consistent truncation of the latter correspond to the former. A brief review of the Lovelock-Chern-Simons motivation behind the gauged WZW ones is also done.Comment: references adde

Four-dimensional Traversable Wormholes and Bouncing Cosmologies in Vacuum

In this letter we point out the existence of solutions to General Relativity with a negative cosmological constant in four dimensions, which contain solitons as well as traversable wormholes. The latter connect two asymptotically locally AdS$_{4}$ spacetimes. At every constant value of the radial coordinate the spacetime is a spacelike warped AdS$_{3}$. We compute the dual energy momentum tensor at each boundary showing that it yields different results. We also show that these vacuum wormholes can have more than one throat and that they are indeed traversable by computing the time it takes for a light signal to go from one boundary to the other, as seen by a geodesic observer. We generalize the wormholes to include rotation and charge. When the cosmological constant is positive we find a cosmology that is everywhere regular, has either one or two bounces and that for late and early times matches the Friedmann-Lema\^{\i}tre-Robertson-Walker metric with spherical topology.Comment: 12 pages, 2 figure

On the mechanical stability of asymptotically flat black holes with minimally coupled scalar hair

We show that the asymptotically flat hairy black holes, solutions of the Einstein field equations minimally coupled to a scalar field, previously discovered by one of us, present mode instability against linear radial perturbations. It is also shown that the number of unstable modes is finite and their frequencies can be made arbitrarily small.Comment: 11 pages, 6 figures, one reference fixe

Black holes in ω\omega-defomed gauged N=8N=8 supergravity

Motivated by the recently found 4-dimensional omega-deformed gauge supergravity, we investigate the black hole solutions within all the single scalar field consistent truncations of this theory. We construct black hole solutions that have spherical, toroidal, and hyperbolic horizon topology. The scalar field is regular everywhere outside the curvature singularity and the stress-energy tensor satisfies the null energy condition. When the parameter omega does not vanish, there is a degeneracy in the spectrum of black hole solutions for boundary conditions that preserve the asymptotic Anti-de Sitter symmetries. These boundary conditions correspond to multi-trace deformations in the dual field theory.Comment: 9 pages, no figures; v2: refs. added, typos fixe