Comments on worldsheet description of the Omega background

Abstract

Nekrasovʼs partition function is defined on a flat bundle of R 4 over S 1 called the Omega background. When the fibration is self-dual, the partition function is known to be equal to the topological string partition function, which computes scattering amplitudes of self-dual gravitons and graviphotons in type II superstring compactified on a Calabi–Yau manifold. We propose a generalization of this correspondence when the fibration is not necessarily self-dual.