Black holes and the phase space of supersymmetric solutions

Abstract

Supergravity BPS solutions in six dimensions are richer than their four and five dimensional counterparts and the full determination of their phase space remains an open problem. We study here the phase space of supersymmetric solutions of minimal 6D supergravity, which have a stringy microscopic realization in terms of F-theory. We centre our attention on a class of solutions with certain isometries, for which an Sp(6,R) group of endomorphisms was recently discovered. This group can be used to generate new backgrounds, and its physical role is still unclear. We study in particular a solution obtained by acting on AdS3xS3 with one of its generators. The transformation changes the geometry noticeably, giving a singularity and a squashed event horizon in the new solution, as well as non-trivial asymptotics and metric signature changes. We show that it is actually a particular limit of a family of solutions with S3xS1 horizon topology and local AdS3xS3 near-horizon geometry. On another note, the singularity happens to be naked for a certain region of the parameter space of the solution. We attempt to give an explanation to this fact in terms of type IIB superstring theory with negative branes.