Electroweak instantons at non-zero Weinberg angle

Previous calculations of instanton effects in electroweak theory have concentrated on the case of zero Weinberg angle θw, where the U(1) hypercharge field decouples. In this paper we extend the instanton calculation to non-zero θw, by constructing a perturbation expansion. This allows for the first time the study of photon production at B and L number violating vertices. We find that the orientation of the instanton solution in isospin space has to be carefully considered to avoid unphysical results.