THRESHOLD PION ELECTROPRODUCTION IN CHIRAL PERTURBATION-THEORY

Electroproduction of pions on the nucleon near the threshold is analyzed within the framework of baryon chiral perturbation theory. We give a thorough discussion of the low-energy theorems related to charged and neutral electropionproduction. It is shown how the axial radius of the nucleon can be related to the S-wave multipoles E(0+)((-)) and L(0+)((-)). The chiral perturbation theory calculations of the gamma*p --> pi(0)p reaction are found to be in good agreement with the recent near threshold data. We also discuss the influence of some isospin-breaking effects in this channel. For future experimental tests of the underlying chiral dynamics, extensive predictions of differential cross sections and multipole amplitudes are presented.