It is widely known that the genus g topological string partition function computes gravitational couplings in string theroy which are encoded in a class of higher derivative F-terms. In the field theory limit, they reduce to the partition function of N=2 gauge theory in the Omega background, in the limit where one of its paramaters is switched off. In this talk, I will describe a set of generalized couplings capturing the full Omega background which can be computed exactly at one loop in the Heterotic string theory. The new deformation parameter turns out to be interpreted in terms of a geometric modulus of the K3xT2 compactification.

CERN