INTEGRABLE DEFORMATIONS OF THE O(3) SIGMA-MODEL - THE SAUSAGE MODEL

We consider two one-parameter families of two-dimensional relativistic factorized scattering theories, which are deformations of the ones characteristic for the two-dimensional O(3) sigma models with theta = 0 and theta = pi. The Bethe ansatz technique is applied to these two families to justify their interpretation as the factorized scattering theories of certain O(2)-symmetric deformations of the O(3) sigma model (the sausage model). The result suggests that the sausage model is integrable at the topological angle values theta = 0 or theta = pi.