Pion photo- and electroproduction and the partially conserved axial current

The relevance of the axial current for pion production processes off the nu cleon with real or virtual photons is revisited. Employing the hypothesis o f a partially conserved axial current (PCAC), it is shown that, when all of the relevant contributions are taken into account, PCAC does not provide a ny additional constraint for threshold production processes that goes beyon d the Goldberger-Treiman relation. In particular, it is shown that pion ele ctroproduction processes at threshold cannot be used to extract any informa tion regarding the weak axial form factor. The relationships found in previ ous investigations are seen to be an accident of the approximations usually made in this context.