Integrable perturbations of CFT with complex parameter: The M3/5 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 φ2,1 perturbation of the M3,5 nonunitary minimal model, thus resolving apparent contradictions in the previous literature. The two behaviors correspond 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 Mp,2p±1, perturbed by their least relevant operator, lead to a cascade of flows similar to that of unitary minima] models perturbed by φ1,3. Various aspects and generalizations of this phenomenon and the links with the Izergin-Korepin model are discussed.