eta-meson photoproduction off protons and deuterons

We present a unitary and gauge-invariant model with coupled channels, which provides a consistent description of pion photoproduction off nucleons in the E0+ channel and eta-meson photoproduction off protons and deuterons. An effective field theory with hadrons and photons is constructed, which includes non-resonant Born terms as well as the S-11(1535) and S-11(1650) baryon resonances. Due to the coupling between the channels, the production of eta-mesons is strongly affected by the S-11(1650) although its direct coupling to the eta N channel is negligible. The rho- and omega-meson exchange terms are important for achieving a consistent description of both pion- and photon-induced reactions. (C) 1997 Elsevier Science B.V.