Yukawa Black Holes from Interacting Vacuum

In this paper we obtain an exact solution of Einstein field equations assuming an interaction between a vacuum component and the Maxwell field. The key feature of such interaction refers to a simple stress exchange so that the electromagnetic field naturally incorporates the Yukawa potential. It is shown that the resulting spacetime thus obtained can either be a naked singularity or a black hole with an inner Cauchy horizon $R_-$ and an exterior event horizon $R_+$. For this latter configuration we examine the group velocity of test photons in the region $R>R_+$. Beyond a lower bound for the frequency we show that superluminal velocities arise in a neighbourhood of the event horizon and that the coupling parameter of the interaction is actually connected to a nonvanishing rest mass for the photon.