Title: High-temperature cluster expansion for quantum spin lattice systems

Abstract: We develop a novel cluster expansion for finite-spin lattice systems subject to multi-body quantum —and, in particular, classical— interactions. Our approach is based on the use of the M ̈obius transform instead of the usual “±1 trick”, introduced by Mayer. Our treatment is inspired by work by Park, but leads to explicit expansions in a β-dependent effective fugacity, instead of a Kirwood-Salzburg system of equations. The resulting series provide an explicit perturbative evaluation of free energy and correlation functions at small β which leads to improved estimations of their range of analyticity.
Jointly with Nguyen Tong Xuan (NYU Shanghai)