Advances in a Field-Theoretic Understanding of Pion Production in Nucleon-Nucleon Collisions

We study the production amplitude for the reaction NN → NNπ up to next-to-leading order in chiral perturbation theory. We show that the irreducible chiral loops at this order exactly cancel those terms that arise from the off-shell parts of the πN rescattering vertex. This cancellation is required for formal consistency of the whole scheme. The net effect of the inclusion of all next-to-leading order loops is to enhance the leading rescattering amplitude by a factor of 4/3 compared to phenomenological studies, bringing its contribution to the cross section for pp → dπ+ close to the experimental value.