Two-loop QED bound-state calculations and squared decay rates

Abstract

We discuss the ε method as used in various recent QED bound-state calculations by considering mathematical-model examples. Recently obtained results for higher order self-energy binding corrections at the two-loop level are reviewed. Problems associated with the interpretation of squared decay rates as radiative bound-state energy-level shifts are discussed. We briefly expand on the relation of squared decay rates to nonresonant and radiative corrections to the Lorentzian line shape, including their dependence on the experimental process under study. PACS Nos.: 31.15-p, 12.20Ds