The abstract Hilbert space generalization of Feenberg’s perturbation theory—A new method of quantum field theory

A rigorous generalization of Feenberg’s perturbation theory to the calculation of thermodynamic Green’s functions is outlined. This method offers an algorithm for calculating correlation functions and propagators for any Hamiltonian, bounded or unbounded, and is exact and tractable in the thermodynamic limit. The method is defined and its use is illustrated by several brief examples.