Significance of zero modes in path--integral quantization of solitonic   theories with BRST invariance
  The significance of zero modes in the path-integral quantization of some solitonic models is investigated. In particular a Skyrme-like theory with topological vortices in (1+2) dimensions is studied, and with a BRST invariant gauge fixing a well defined transition amplitude is obtained in the one loop approximation. We also present an alternative method which does not necessitate evoking the time-dependence in the functional integral, but is equivalent to the original one in dealing with the quantization in the background of the static classical solution of the non-linear field equations. The considerations given here are particularly useful in - but also limited to - the one-loop approximation. 
J.-G. Zhou, F. Zimmerschied, J.-Q. Liang, H.J.W. Mueller-Kirsten and   D.H. Tchrakian