The Gauged WZNW Model Perturbed by the Sigma Model Term

Abstract

We discuss special perturbations of the gauged level $k$ WZNW model inspired by the $\sigma$-model perturbation of the nonunitary WZNW model. In the large $k$ limit there is a second conformal point in the vicinity of the ultarviolet fixed point. At the second critical point the conformal model has a rational Virasoro central charge which no longer corresponds to a coset construction. In spite of this fact the perturbative conformal model appears to be a unitary system as long as the underlying coset construction at the ultraviolet critical point is unitary.