  An effective field theory calculation of the n+p->d+gamma cross section
accurate to 1% for center of mass energy E up to ~1 MeV is presented. At these
energies, which are relevant for big-bang nucleosynthesis, isovector magnetic
transitions M1 and isovector electric transitions E1 give the dominant
contributions. The M1 amplitude is calculated up to next-to-next-to-leading
order (NNLO) and the contribution from the associated four-nucleon-one-photon
operator is determined from the cold neutron capture rate. The E1 amplitude is
calculated up to NNNNLO. The four-nucleon-one-photon operator contribution to
E1 is determined from the related deuteron photodisintegration reaction
gamma+d->n+p.
