A CHARACTERIZATION OF GIBBS-STATES OF LATTICE BOSON SYSTEMS

We consider lattice boson systems interacting via potentials which are superstable and regular. By using the Wiener integral formalism and t he concept of conditional reduced density matrices we are able to give a characterization of Gibbs (equilibrium) states. It turns out that t he space of Gibbs states is non-empty, convex, and also weak-compact i f the interactions are of finite range. We give a brief discussion on the uniqueness of Gibbs states and the existence of phase transitions in our formalism,