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,
Matematica, Universita' di Roma 2
Via della Ricerca Scientifica