Comparison of exchange mechanisms in pi N to rho N and pion photo- and electroproduction

Rho-, photo- and electroproduction are compared and contrasted from a t-channel exchange point of view. A common exchange mechanism is evident. Systematic differences associated with the variable mass of the vector particle are found-in particular, the mass dependence of the non-pole-like contributions is reminiscent of that seen in higher mass resonance production. Naive vector meson dominance arguments which do not allow for these mass-dependent effects are shown to disagree both qualitatively and quantitatively with the data. The implications of this, and similar studies, are emphasised for an understanding of absorption effects in two-body scattering. (31 refs).