Scattering of vector mesons off nucleons

We construct a relativistic and unitary approach to 'high' energy pion- and photon-nucleon reactions taking the piN, piDelta, rhoN, omegaN, etaN, KLambda, KSigma final states into account. Our scheme dynamically generates the s- and d-wave nucleon resonances N(1535), N(1650) and N(1520) and isobar resonances Delta(1620) and Delta(1700) in terms of quasi-local interaction vertices. The description of photon-induced processes is based on a generalized vector-meson dominance assumption which directly relates the electromagnetic quasi-local four-point interaction vertices to the corresponding vertices involving the rho and omega fields. We obtain a satisfactory description of the elastic and inelastic pion- and photon-nucleon scattering data in the channels considered. The resulting s-wave rho- and omega-nucleon scattering amplitudes are presented. Using these amplitudes we compute the leading density modification of the rho and omega energy distributions in nuclear matter. We find a repulsive energy shift for the omega meson at small nuclear density but predict considerable strength in resonance-hole like omega-meson modes. Compared to previous calculations our result for the rho-meson spectral function shows a significantly smaller in-medium effect. This reflects a fairly small coupling strength of the N(1520) resonance to the rhoN channel. (C) 2002 Elsevier Science B.V. All rights reserved.