Abstract
Within the unitary πNN theory with Δ excitation, the effect of πd and πNN production channels on NN elastic scattering is examined. It is shown that the two-body coupled-channel method, which has been widely employed to study the Δ excitation in intermediate-energy NN scattering, is a valid approximation. Our results indicate that the difficulty encountered by the meson-exchange theory in understanding the NN data up to 1 GeV cannot be resolved within the model based on the one-pion-exchange Δ excitation mechanism.