MASSLESS FACTORIZED SCATTERING AND SIGMA-MODELS WITH TOPOLOGICAL TERMS

We propose two massless non-diagonal scattering theories with SU(2) isotopic symmetry. While being identical in the right- and left-moving sectors, they differ in the right-left scattering. The first theory has reflectionless resonance right-left amplitudes and exhibits two independent (right and left) SU(2) symmetries. It is suggested as a scattering theory of the SU(2) x SU(2) principal chiral model with the Wess-Zumino term of level k = 1. In the second scattering theory only one SU(2) group survives at finite distances. We interpret this one as corresponding to the O(3) sigma model with the theta = pi-topological term. In both the cases the thermodynamic Bethe ansatz equations are derived.