Relativistic effects, the deuteronD-state, and backwardp−dscattering

The question of relativistic effects in backward-angle $p-d$ scattering is examined by evaluating the nucleon-exchange contribution to the elastic cross section and tensor polarization as a Feynman diagram. By means of a well-known approximation procedure, the invariant amplitudes in the $d-n-p$ vertex function are identified with nonrelativistic wave functions. Above 500 MeV proton energy, the calculated polarization agrees neither with earlier nonrelativistic calculations nor with experiment. Moreover, it is found that the aforementioned approximation procedure gives rise to large ambiguities in the tensor alignment, due to an intimate connection between nucleon negative-energy components and the deuteron $D$ state.