INTEGRABLE PERTURBATIONS OF CFT WITH COMPLEX PARAMETER - THE M(3 5) MODEL AND ITS GENERALIZATIONS/

By using the thermodynamic Bethe ansatz, approach, we give evidence of the existence of both massive and massless behaviors for the phi(2,1) perturbation of the M(3,5) nonunitary minimal model, thus resolving a pparent contradictions in the previous literature. The two behaviors c orrespond to changing the perturbing bare coupling constant from real values to imaginary ones. Generalizations of this picture to the whole class of nonunitary minimal models M(p,2p+/-1), perturbed by their fe ast relevant operator, lead to a cascade of flows similar to that of u nitary minimal models perturbed by phi(1,3). Various aspects and gener alizations of this phenomenon and the links with the Izergin-Korepin m odel are discussed.