Abstract :
An effective field theory calculation of the np→dγ cross section accurate to 1% for center of mass energies E≲1 MeV is presented. At these energies, which are relevant for big-bang nucleosynthesis, isovector magnetic dipole transitions M1 View the MathML source and isovector electric dipole transitions E1 View the MathML source give the dominant contributions. The M1 View the MathML source amplitude is calculated up to next-to-next-to-leading order (N 2 LO), and the contribution from the associated four-nucleon–one-photon operator is determined from the cold neutron capture rate. The E1 View the MathML source amplitude is calculated up to N 4 LO. The four-nucleon–one-photon operator contribution to E1 View the MathML source is determined from the related deuteron photodisintegration reaction γd→np .
