PERTURBATION-THEORY IN TERMS OF CURRENTS AND RESTORATION OF CONTINUOUS SYMMETRY IN 2 DIMENSIONS

We discuss a formulation of perturbation theory for two-dimensional field theories which possess a spontaneous symmetry breaking at the classical level. It is useful to employ the formalism in terms of currents, and then one is able to restore the continuous symmetries which, according to general theorems, cannot be spontaneously broken at the full quantum level. As a prototype example we consider in detail the non-linear Schrodinger theory at finite density. Some observations concerning theories with non-Abelian symmetry are made. © 1978.