Counting Higher Genus Curves with Crosscaps in Calabi-Yau Orientifolds
  We compute all loop topological string amplitudes on orientifolds of local Calabi-Yau manifolds, by using geometric transitions involving SO/Sp Chern-Simons theory, localization on the moduli space of holomorphic maps with involution, and the topological vertex. In particular we count Klein bottles and projective planes with any number of handles in some Calabi-Yau orientifolds. 
Vincent Bouchard, Bogdan Florea, Marcos Marino