S. Hohenegger (ETH Zurich)
I will describe a new class of $N=2$ topological amplitudes that compute certain BPS terms in the low energy effective supergravity action. The novel feature of these terms is that they depend both on the vector and hypermultiplet moduli. Their BPS nature implies that they satisfy a holomorphicity condition with respect to vector moduli and a harmonicity condition as well as a second order differential equation with respect to hypermultiplet moduli. However, an explicit study in heterotic string theory reveals that these relations are only satisfied up to anomalous boundary terms in the world-sheet moduli space. In particular I will explain that the obstruction to the holomorphicity arises from the one loop threshold correction to the gauge couplings.
Arnold Sommerfeld Center