A next-to-next-to-leading order pp -> ppπ⁰ transition operator in chiral perturbation theory

We discuss the results of a systematic calculation of the next-to-next-to-leading order amplitude for the pp -> pp\pi^0 S-wave production at the threshold in heavy-baryon chiral perturbation theory. We find six new diagrams, two of which can be viewed as vertex corrections, of 15 - 20 %, to the pion-exchange graph, whereas the rest are much larger, one exceeding 900 %. We discuss the reasons for this enhancement, as well as the steps necessary to be taken before the final comparison with experiment.