Relativistic effects in the two-nucleon system

The Gross approximation to the Bethe-Salpeter equation is investigated using a one-boson-exchange model for the nucleon-nucleon interaction. In particular, it is shown that the inclusion of corrections from the two-pion direct-box diagram to the driving force in general does not yield phase shifts closer to those obtained from the Bethe-Salpeter equation. Moreover, the cross-box contributions lead in the quasipotential approach to a non-Hermitian interaction at all energies. The electromagnetic form factors of the deuteron are calculated for various sets of potential parameters which give reasonable scattering parameters. A detailed analysis is presented of the relativistic and mesonic exchange current corrections to the nonrelativistic limit. As a result it is shown that the usual treatment of mesonic exchange currents for both pseudovector and pseudoscalar pion-nucleon interaction is not correct since other non-negligible contributions should be taken into account