Self-similar critical geometries at horizon intersections and mergers
  We study topology-changing transitions in the space of higher-dimensional black hole solutions. Kol has proposed that these are conifold-type transitions controlled by self-similar double-cone geometries. We present an exact example of this phenomenon in the intersection between a black hole horizon and a cosmological deSitter horizon in D >= 6. We also describe local models for the critical geometries that control many transitions in the phase space of higher-dimensional black holes, such as the pinch-down of a topologically spherical black hole to a black ring or to a black p-sphere, or the merger between black holes and black rings in black Saturns or di-rings in D >= 6. 
Roberto Emparan, Nidal Haddad
hep-th