FM 2003-02; mp_arc nlin/CD 0007???
versione 0.1 10/02/2003

Author: Vieri Mastropietro

Title: Ising models with four spin interaction at criticality

Abstract: We consider two bidimensional Ising models coupled by an interaction quartic in the spins. By Renormalization Group methods we write a convergent perturbative expansion for the specific heat and of the energy-energy correlation up to the critical temperature. A form of nonuniversality is proved, in the sense that the critical behaviour is described in terms of critical indices which are non trivial functions of the coupling. In particular the logarithmic behaviour of the specific heat in the Ising model is changed by the four spin interaction in a power law with non universal critical indices.

Key words: Ising models, vertex models, nonuniversality, Critical indices.

Vieri Mastropietro
Matematica, Universita' di Roma 2
Via della Ricerca Scientifica
Roma, Italia