Delta--Excitation and Exchange Corrections for NN--Bremsstrahlung

The role of the relativistic amplitudes for a number of ${\cal O}(k)$ processes usually neglected in potential model calculations of NN--bremsstrahlung is investigated. In particular, we consider the $\Delta$--excitation pole contributions related to the one--pion and one--rho exchange and in addition include the exchange contributions induced by the radiative $\omega,\,\rho \to \pi \gamma$ decays. The contributions are calculated from relativistic Born amplitudes fitted to $\Delta$--production and absorption data in the energy range up to 1 GeV and then used to supplement potential model and soft photon calculations for nucleon--nucleon bremsstrahlung. The effects on $NN\gamma$--observables, although moderate in general, are found to be important in some kinematic domains.