A next-to-next-to-leading-order pp -> pp pi(0) transition operator in chiral perturbation theory

We present a systematic analysis of next-to-next-to-leading-order diagrams that contribute to the pp --> pp pi(o) production at threshold. Analytic ex pressions are given for the effective transition operators, and the relativ e importance of various types of diagrams is discussed. The vertex-correcti on-type graphs are found to give only small corrections to lower order grap hs in conformity with expectations. By contrast, we find very large contrib utions from two-pion exchange graphs that can be interpreted as a part of e ffective sigma-meson exchange diagrams. The recoil correction to the pion r escattering diagram also turns out to be large. (C) 1999 Published by Elsev ier Science B.V. All rights reserved.