Merging of photons in the field of a multielectron atom: Higher orders of perturbation theory

Abstract

The contribution of higher orders of relativistic quantum perturbation theory to the differential cross section for the merging of three X-ray photons into one photon in the field of a multielectron atom has been studied in the Tamm–Dankov approximation. It has been shown that higher orders do not change the physical results obtained in the leading (second) order of perturbation theory.