Higher-order field effects in pion absorption on two nucleons

We estimate the importance of rescattering diagrams involving intrinsically third-order effects in the pionic field for the process of pion absorption at rest on a pair of nucleons. The calculation is performed using a chiral bag model adapted for the correct description of higher-order pionic effects. The model provides the form factors needed in order to achieve a convergent result. The third-order diagrams cancel in part; nevertheless, the net result is as important as the conventional second-order s-wave rescattering mechanism for reasonable bag radii R1 fm and becomes dominant for bag radii R20.7 fm for internucleon distances less than about 2 fm. NUCLEAR REACTIONS (,2N), pion absorption, chiral bag models.