Unitary theory of the deuteron photodisintegration

The deuteron photodisintegration in the Δ-resonance region is calculated within a unitary theory of the NN-NΔ-πNN system coupled to the photon. The photoexcitation amplitude of the Δ is deduced from the $M_{1+}$((3/2) pion photoproduction amplitude consistently with its background term and the πN interaction. The NN-NΔ transition amplitude is obtained from the coupled equations for the NN-NΔ-πNN system. The one-pion-exchange currents as well as the normal single-nucleon current are included. The polarization parameters are reproduced quantitatively, but the cross section is slightly underestimated. Comparison of our results with those of the NN-NΔ coupled-channel model is made. Effects of relativistic corrections and gauge-invariance constraints are discussed.