Preserving the gauge invariance of meson production currents in the presence of explicit final-state interactions - art. no. 034605

A comprehensive formalism is developed to preserve the gauge invariance of currents describing the photo; or electroproduction of mesons off the nucle on when the final-state interactions of mesons and nucleons is taken into a ccount explicitly. Replacing exchange currents by auxiliary currents, it is found that all contributions due to explicit final-state interactions are purely transverse and do not contain a Kroll-Ruderman-type contact current. The relation of the present formulation to tree-level-type prescriptions i s shown.