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In this work, we study the existence of asymptotically Lifshitz black holes in Critical Gravity in four dimensions with a negative cosmological constant under two scenarios: First, including dilatonic fields as the matter source, where we find an asymptotically Lifshitz solution for a fixed value of the dynamical exponent $z=4$. As a second case, we also added a non-minimally coupled scalar field $\Phi$ with a potential given by a mass term and a quartic term. Using this approach, we found a solution for $z$ defined in the interval $(1,4)$, recovering the Schwarzchild-Anti-de Sitter case with planar base manifold in the isotropic limit. Moreover, when we analyzed the limiting case $z=4$, we found that there exists an additional solution that can be interpreted as a stealth configuration in which the stealth field is overflying the $z=4$ solution without the non-minimally coupled field $\Phi$. Finally, we studied the non-trivial thermodynamics of these new anisotropic solutions and found that they all satisfy the First Law of Thermodynamics as well as the Smarr relation. We were also able to determine that the non-stealth configuration is thermodynamically preferred in this case., Comment: 9 pages, 4 figures. Accepted for publication in Physical Review D

We study the propagation of exact gravitational waves in the ghost-free bimetric theory. Our focus is on type N spacetimes compatible with the cosmological constants provided by the bigravity interaction potential, and particularly in the single class known by allowing at least a Killing symmetry: the AdS waves. They have the advantage of being represented by a generalized Kerr-Schild transformation from AdS spacetime. This means a notorious simplification in bigravity by allowing to straightforwardly compute any power of its interaction square root matrix, opening the door to explore physically meaningful exact configurations. For these exact gravitational waves the complex dynamical structure of bigravity decomposes into elementary exact massless or massive excitations propagating on AdS. We use a complexified formulation of the Euler-Darboux equations to provide for the first time the general solutions to the massive version of the Siklos equation which rules the resulting AdS-waves dynamics, using an integral representation originally due to Poisson. Inspired in this progress we tackle the subtle problem on how matter couples to bigravity and concretely if this occurs through a composite metric, which is hard to handle in a general setting. Surprisingly, the Kerr-Schild ansatz brings again a huge simplification in how the related energy-momentum tensors are calculated. This allows us to explicitly characterize AdS waves supported in one case by a massless free scalar field and by a wavefront-homogeneous Maxwell field in another. Considering the most general allowed Maxwell source instead is a highly nontrivial task, that we accomplish by exploiting again the complexified Euler-Darboux description and taking advantage of the classical Riemann method. In fact, this allow us to find at the end the most general configurations for any matter source., Comment: 25 pages

We develop a geometric criterion that unambiguously characterizes and also provides a systematic and effective computational procedure for finding all the residual symmetries of any gravitational Ansatz . We apply the criterion to several examples starting with the Collinson Ansatz for circular stationary axisymmetric spacetimes. We reproduce the residual symmetries already known for this Ansatz including their conformal symmetry, for which we identify the corresponding infinite generators spanning the two related copies of the Witt algebra. We also consider the noncircular generalization of this Ansatz and show how the noncircular contributions on the one hand break the conformal invariance and on the other hand enhance the standard translations symmetries of the circular Killing vectors to supertranslations depending on the direction along which the circularity is lost. As another application of the method, the well-known relation defining conjugate gravitational potentials introduced by Chandrasekhar, that makes possible the derivation of the Kerr black hole from a trivial solution of the Ernst equations, is deduced as a special point of the general residual symmetry of the Papapetrou Ansatz. We emphasize how the election of Weyl coordinates, which determines the Papapetrou Ansatz, breaks also the conformal freedom of the stationary axisymmetric spacetimes. Additionally, we study AdS waves for any dimension generalizing the residual symmetries already known for lower dimensions and exhibiting a very complex infinite-dimensional Lie algebra containing three families: two of them span the semidirect sum of the Witt algebra and scalar supertranslations and the third generates vector supertranslations. We manage to comprehend that the infinite connected group is the precise diffeomorphisms subgroup allowing to locally deform the AdS background into AdS waves., Comment: Affiliations have been updated