Peripheral NN-scattering: role of delta-excitation, correlated two-pion and vector meson exchange

Abstract

Abstract We evaluate, within one-loop chiral perturbation theory, the two-pion exchange diagrams with single and double delta-isobar excitation contributing to elastic NN-scattering. We find that virtual Δ-excitation processes (in the static limit) produce the correct amount of isoscalar central attraction as needed in the peripheral partial waves with L ⩾ 3. Furthermore we compute the two-loop diagrams involving the ππ-interaction (so-called correlated 2π-exchange). Contrary to common believe these processes lead to negligibly small and repulsive corrections to the NN-potential. The exchange of vector mesons (ϱ, ω) turns out to be important for the F-wave phase shifts above Tlab = 150 Mev. Without adjustable parameters we are able to reproduce the empirical NN phase shifts up to 350 MeV for L ⩾ 3 and up to about (50–80) MeV for the D-waves. This is therefore the characteristic window in which the NN-interaction is basically governed by chiral symmetry. Not surprisingly, the lower partial waves require non-perturbative methods and additional short-distance parametrizations of the NN-dynamics.