Role of correlated two-pion exchange in K+ N scattering

A dynamical model for S- and P-wave correlated 2π (and K K) exchange between a kaon and a nucleon is presented, starting from corresponding N N →K K amplitudes in the pseudophysical region, which have been constructed from nucleon, Δ-isobar and hyperon (Λ, Σ) exchange Born terms and a realistic meson exchange model of the ππ→K K and K K →K K amplitude. The contribution in the s-channel is then obtained by performing a dispersion relation over the unitarity cut. In the ρ-channel, considerable ambiguities exist, depending on how the dispersion integral is performed. Our model, supplemented by short range interaction terms, is able to describe empirical K+ N data below pion production threshold in a satisfactory way. (orig.)