title: Bound states in the transfer matrix spectrum for general lattice ferromagnetic spin systems at high temperature
abstract: We obtain different properties of general d dimensional lattice ferromagnetic spin systems with nearest neighbor interactions in the high temperature region (beta<<1). Each model is characterized by a single site a priori spin distribution, taken to be even. We state our results in terms of the parameter alpha=<s(4)>-3<s(2)>(2) where <s(k)> denotes the kth moment of the a priori distribution. Associated with the model is a lattice quantum field theory that is known to contain particles. We show that for alpha>0, beta small, there exists a bound state with mass below the two-particle threshold. For alpha<0, bound states do not exist. The existence of the bound state has implications on the decay of correlations, i.e., the four-point function decays at a slower rate than twice that of the two-point function. These results are obtained using a lattice version of the Bethe-Salpeter equation in the ladder approximation. The existence and nonexistence results generalize to N-component models with rotationally invariant a priori spin distributions.
authors.affiliation: Departamento de Fisica ICEx, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.initials: RS
authors.lastname: Schor
authors.initials: M
authors.lastname: O'Carroll