Asymptotic scale invariance in two-dimensional theories: a massive Thirring model with bosons

The exact vanishing of all β functions of the Callan-Symanzik equation is proved in a two-dimensional model with Thirring and gradient couplings: (anti psiγsub(μ)psi)2, (anti psiγ5γsub(μ)psi)deltasup(μ)π and (anti psiγsub(μ)psi)deltasup(μ)sigma, where psi, π and sigma are fermion, pseudoscalar and scalar massive fields, respectively. The anomalous dimensions of scalar and pseudoscalar fields are also shown to be zero. Then it is demonstrated that in two-dimensional models including at most one fermion field, only these three couplings can give asymptotic scale invariance. (Auth.)