Analysis of the gamma N Delta and pion N Delta interactions for pion photoproduction

Abstract

In this paper we analyze for the first time the γNΔ excitation vertex from the point of view of the dynamics of the Δ field, ѱ. That is, we look for the value of the Z parameter, present in all contact invariant Δ-field interaction Lagrangians and usually regarded as redundant, and shift it to contact background non-Δ resonant amplitudes (in this sense it is called “redundant”) by imposing that ѱ_0 the has no dynamics, instead of readjusting the background coupling constants.