Spectral Representations in Perturbation Theory III The Scattering Amplitude with Two Complex Invariants

摘要

The partial Feynman amplitude corresponding to a particular fourth order diagram la examined as a function of energy and momentum transfer with both of these variables complex. The region of regularity of this function is found, and the types of singularities at the remaining points are determined. An approach which requires only elementary cal¬culations is developed.