Threshold pion photoproduction and chiral models of the nucleon

Abstract

We present calculations of the chiral and isospin symmetry-breaking corrections to the threshold pion photoproduction amplitude E 0+. The calculations are based on two chiral models of the nucleon: the chiral bag model and the non-topological soliton model. We find that ΔE 0+ from explicit chiral-symmetry breaking is substantial, but not sufficient to explain the discrepancy between the measured γp → π 0p threshold amplitude and its predicted value based on the chiral low-energy theorem.