Abstract
This work deals with investigation of the helicity dependence of the gamma -> d -> -* pi NN reaction channels near threshold and its implication to the helicity E-asymmetry and the Gerasimov-DrellHearn sum rule. Our formalism based on the one loop corrections to the impulse approximation due to nucleon and pion rescattering, uses the realistic Paris NN potential model for the deuteron wave function and the unitary isobar MAID-2007 model for the elementary gamma N -* pi N amplitude. We present results for the doubly polarized differential and total cross sections for parallel and antiparallel helicity states, the deuteron spin asymmetry, the helicity E-asymmetry, and the deuteron GDH integral in the near-threshold region. The influence of NN and pi N final-state rescattering on the estimated results has been discussed. It is shown that the inclusion of NN rescattering is important, and its inclusion strongly affected the estimated results in both pi +/-- and pi 0-production channels. The inclusion of pi N rescattering is found to be insignificant in pi +/--production, but it has a non- negligible contribution in the case of pi 0-production. A comparison with predictions of other theoretical models is given.