Canonical solution of a system of long-range interacting rotators on a lattice

The canonical partition function of a system of rotators (classical X-Y spi ns) on a lattice, coupled by terms decaying as the inverse of their distanc e to the power alpha, is analytically computed. It is also shown how to com pute a rescaling function that allows us to reduce the model, for any d-dim ensional lattice and for any alpha<d, to the mean-field (alpha=0) model.