Some comments on unitarity gauge

Abstract

A pedagogical discussion on the unitarity gauge within the context of Hamiltonian path integral formalism is presented. A model based on the group $O(N)$, spontaneously broken down to the subgroup $O(N-1)$, is used to illustrate the main aspects of this gauge--fixing procedure. Among the issues, discussed with some extent, are: (1) the structure of model's constraints following the Dirac's method, (2) the gauge--fixing procedure, using the unitarity gauge for the massive gauge fields and the Coulomb one for the massless gauge fields, (3) the absence of BRST symmetry in this gauge--fixing procedure and its implications on the renormalizability of the theory, and (4) the static role of the ghost and anti--ghost fields associated with the massive gauge fields and how their contributions can be eliminated by using the dimensional regularization scheme.