Modification of the topological expansion of the O(3) sigma model

Abstract

We show that the one-instanton sector moduli-space divergence of the O(3) sigma model leads to an unacceptable dependence of Green functions on the arbitrary way that the field is split into a quantum fluctuation about a classical background. In particular the rotational symmetry of the model is spoilt. Since the divergence is associated with the degeneration of field configurations to those of the zero-instanton sector this arbitrariness may be cancelled by modifying the zero-instanton functional integral. We explicitly construct this modification.