POTTS-MODEL ON THE BETHE LATTICE WITH MIXED INTERACTIONS

A q-state Potts model on a Bethe lattice is considered in which the bonds at a given site may all have different interaction strengths, but in which all sites remain equivalent. We calculate the susceptibility of the system and hence the location of second-order phase transitions. The presence of first-order transitions is detemined directly from the free energy. The formalism is then specialised to the case of a model crystalline random copolymer, in which the interchain interactions are weaker than the randomly varying intrachain interaction strengths. A comparison of the results of this treatment is made with the results of the mean-held theory of Lin et al. [Phys. Rev. E 47, 981 (1993)].