Precision calculation of np → dγ cross section for big-bang nucleosynthesis

An effective field theory calculation of the np --> d gamma cross section accurate to 1% for center of mass energies E less than or similar to 1 MeV is presented. At these energies, which are relevant for big-bang nucleosynthesis, isovector magnetic dipole transitions M1(V) and isovector electric dipole transitions E1(V) give the dominant contributions. The M1(V) amplitude is calculated up to next-to-next-to-leading order ((NLO)-L-2), and the contribution from the associated four-nucleon-one-photon operator is determined from the cold neutron capture rate. The E1(V) amplitude is calculated up to (NLO)-L-4. The four-nucleon-one-photon operator contribution to E1(V) is determined from the related deuteron photodisintegration reaction gamma d --> np. (C) 2000 Elsevier Science B.V. All rights reserved.