Analyticity in Hubbard models
  The Hubbard model describes a lattice system of quantum particles with local (on-site) interactions. Its free energy is analytic when \beta t is small, or \beta t^2/U is small; here, \beta is the inverse temperature, U the on-site repulsion and t the hopping coefficient.   For more general models with Hamiltonian H = V + T where V involves local terms only, the free energy is analytic when \beta ||T|| is small, irrespectively of V. The Gibbs state exists in the thermodynamic limit, is exponentially clustering and thermodynamically stable. These properties are rigorously established in this paper. 
Daniel Ueltschi