Statistical Entropy of Magnetic Black Holes from Near--Horizon Geometry

Abstract

Four-dimensional magnetic black holes including dilaton and abelian gauge fields which are solutions of supergravity can also be obtained by dimensional reduction of the Einstein-Maxwell gravity in five dimensions. In the extremal case the five-dimensional solutions have horizon and their near-horizon geometry is $AdS_3\times S^2 $. In the non-extremal case the near-horizon geometry is shown to be the product of the three-dimensional Ba\~nados-Teitelboim-Zanelli black hole and $S^2$. This allows to perform microscopic counting of statistical entropy of magnetic black holes. Exact agreement with the geometric entropy is found. The microstates responsible for statistical entropy are located in the near-horizon region.