Spacetime foam in twistor string theory
  We show how a Kahler spacetime foam in four dimensional conformal (super)gravity may be mapped to twistor spaces carrying the D1 brane charge of the B model topological string theory. The spacetime foam is obtained by blowing up an arbitrary number of points in $\C^2$ and can be interpreted as a sum over gravitational instantons. Some twistor spaces for blowups of $\C^2$ are known explicitly. In these cases we write down a meromorphic volume form and suggest a relation to a holomorphic superform on a corresponding super Calabi-Yau manifold. 
Sean A. Hartnoll, Giuseppe Policastro