Precision calculation of γd↦πnn within chiral perturbation theory

Abstract.The reaction γd↦π+nn is calculated up to order χ5/2 in chiral perturbation theory, where χ denotes the ratio of the pion to the nucleon mass. Special emphasis is put on the role of nucleon recoil corrections that are the source of contributions with fractional power in χ. Using the known near-threshold production amplitude for γp↦π+n as the only input, the total cross-section for γd↦π+nn is described very well. A conservative estimate suggests that the theoretical uncertainty for the transition operator amounts to 3% for the computed amplitude near threshold.