Feynman integral in regularized nonrelativistic quantum electrodynamics

Abstract

We express the unitary time evolution in nonrelativistic regularized quantum electrodynamics at zero and positive temperature by a Feynman integral defined in terms of a complex Brownian motion. An average over the quantum electromagnetic field determines the form of the quantum mechanics in an environment of a quantum black body radiation. In this nonperturbative formulation of quantum electrodynamics we prove the existence of the classical limit ℏ→0. We estimate an error to some approximations commonly applied in quantum radiation theory.