EFFECTS OF RELATIVITY IN PROTON-PROTON BREMSSTRAHLUNG

We investigate the influence of negative-energy states in proton-proto n bremsstrahlung in a fully relativistic framework using the T matrix of Fleischer and Tjon. The contribution from negative-energy states in the single-scattering diagrams is shown to be large, indicating that relativistic effects are important. The rescattering contribution comp ensates some of the effect, which is shown to be a consequence of a lo w-energy theorem. The net effect of negative-energy states nevertheles s is of the order of 20% at higher energies. We investigate retardatio n effects in the nucleon-nucleon (NN) interaction by means of a one-pi on exchange model, which gives effects of the order of 15% at the pion -production threshold. We furthermore modify the NN T matrix tb incorp orate some of these effects, and find that on the level of single-scat tering contributions they are of the order of 10%. We show predictions at incoming proton energy T-lab=190 MeV, where high accuracy measurem ents are being done at KVI, and conclude that even at these relatively low energies off-shell effects in the NN interaction and contribution s from negative-energy states clearly show up.