Critical behaviour and ultrametricity of Ising spin-glass with long-range interactions

Ising spin-glass systems with long-range interactions (J(r) similar to r(-sigma))are considered. A numerical study of the critical behaviour is presented in the non-mean-field region together with an analysis of the probability distribution of the overlaps and of the ultrametric structure of the space of the equilibrium configurations in the frozen phase. Also. in the presence of diverging thermodynamical fluctuations at the critical point the behaviour of the model is shown to be of the replica symmetry breaking type and there are hints of a non-trivial ultrametric structure. The parallel tempering algorithm has been used to simulate the dynamical approach to equilibrium of such systems.