Dyonic AdS_4 black hole entropy and attractors via entropy function

Abstract

Using the Sen's entropy function formalism, we compute the entropy for the extremal dyonic black hole solutions of theories in the presence of dilaton field coupled to the field strength and a dilaton potential. We solve the attractor equations analytically and determine the near horizon metric, the value of the scalar fields and the electric field on the horizon, and consequently the entropy of these black holes. The attractor mechanism plays a very important role for these systems, and after studying the simplest systems involving dilaton fields, we propose a general ansatz for the value of the scalar field on the horizon, which allows us to solve the attractor equations for gauged supergravity theories in $AdS_4$ spaces. In particular, we derive an expression for the dyonic black hole entropy for the $\mathcal{N}=8$ gauged supergravity in 4 dimensions which does not contain explicitly the gauge parameter of the potential.