Rigorous theory of spectra and radiation for a model in quantum electrodynamics

Abstract

We study rigorously the problem of the lamb shift and the spontaneous emission of light in a framework of nonrelativistic quantum electrodynamics by using an exactly soluble model of a harmonic oscillator atom interacting with a quantized electromagnetic field. We show that, under the perturbation of the electromagnetic field, all the point spectra corresponding to the excited states of the unperturbed atom disappear. This means that the ‘‘energy level shifts’’ (Lamb shifts) of the excited states of the atom cannot be described simply in terms of shifts of point spectra. Then, we give a rigorous mathematical meaning to both formal perturbation theories for the ‘‘energy level shifts’’ and for the transitions of the excited states due to the spontaneous emission of light, showing that the ‘‘energy level shifts’’ and the ‘‘decay probabilities’’ of the excited states of the atom are characterized in terms of the resonance pole of the S-matrix for the photon scattering by the atom. We also discuss broken symmetry aspects and infinite mass-renormalization of the model.