Geometric expansion of the log-partition function of the anisotropic Heisenberg model

We study the asymptotic expansion of the log-partition function of the anisotropic Heisenberg model in a bounded domain as this domain is dilated to infinity. Using the Ginibre's representation of the anisotropic Heisenberg model as a gas of interacting trajectories of a compound Poisson process, we find all the non-decreasing terms of this expansion. They are given explicitly in terms of functional integrals. As the main technical tool, we use the cluster expansion method. (C) 2015 AIP Publishing LLC.