Fourth-Order Corrections to the Scattering of Pions by Nonrelativistic Nucleons

Abstract

Fourth-order corrections to the field theoretical phase shifts for pion nucleon scattering have been calculated for a linear and extended coupling and no nucleon recoil. The results support the use of the "Dancoff approximation," since those processes passing through intermediate states which contain three pions turn out to be much less important than processes involving only one and two pions.