Relativistic analysis of proton-proton bremsstrahlung

A microscopic calculation of pp bremsstrahlung based on a relativistic one boson exchange model for the nucleon-nucleon interaction is reviewed. For small photon momenta, gauge invariance imposes an important constraint on the single nucleon current contribution. Within the dynamical model it is found, that the pair term is compensated to a large extent by the rescattering contribution. Polarization predictions are in good agreement with the experimental data. Another approach to ppgamma is the soft photon approximation. It is based on a low energy expansion. Current conservation is satisfied by the introduction of an e.m. contact term. For one kinematics a large difference is found between the two approaches. We discuss this in some detail. In particular, it shown that the dynamical model predictions are very sensitive to the low energy NN interaction. Fitting to the pp data agreement is found with the observed ppgamma cross section.