Massless black hole pairs in string theory
  We analyze the zero mass black holes that arise as classical solutions to low energy heterotic string theory. Though these solutions contain naked singularities, it has been conjectured that they should be allowed in the theory. We find a solution describing a pair of oppositely charged massless black holes in uniformly accelerated motion under no external force. By analytically continuing the solution to Euclidean time, we find an instanton mediating the pair production of these objects in Minkowski space. We analyze the creation rate, and discuss some consequences of the result. 
R. Emparan