Covariant approach to deuteron photodisintegration and gauge invariance

Gauge invariant amplitudes of the #betta#d → np reaction have been obtained in the pole approximation with the d-, N-pole and contact diagrams. Helicity amplitudes have been calculated at the threshold. It is shown that the A coupling at the dnp-vertex (the u UCu2 structure, where U is the polarization vector of the deuteron) makes a dominant contribution to the photodisintegration cross-section at the threshold. The angular distribution at E -20 MeV and the energy dependence of dσ/dΩ(theta=0) (theta is the angle between the proton and photon momenta in the c. m. s.) calculated using this coupling are in good agreement with experiments