Anomalous Violation of Conservation Laws in Minkowski Space:   Spontaneously Broken Gauge Theories
  We extend our previous results on the evolution of quantum fermi fields in Minkowski gauge field backgrounds to the case of spontaneously broken gauge theories. We obtain a selection rule which relates the amount of fermion number violation to the change in Higgs winding number of the configuration. This selection rule is applicable to any classical solution which dissipates at both early and late times. 
Thomas M. Gould and Stephen D.H. Hsu