Relativistic effects in proton-proton bremsstrahlung

The ppγ reaction at intermediate energies is investigated using a modern relativistic meson-exchange potential model. Both the single-scattering and rescattering terms are treated including relativistic corrections. It is shown that for energetic photons in the region near the end-point energy the relativistic spin correction is very large and reduces the ppγ cross section by a factor of ∼2. This large correction is dynamical in origin and can be traced in a very simple way to the strong energy dependence of the ${}_{}{}^1{}_{}{}^{}$ ${\mathit{S}}_0$ state contribution. It is also shown that, under these kinematical conditions, the rescattering term reduces the cross section, which amplifies the relativistic effects on the ppγ reaction. For the kinematical conditions of the recent TRIUMF experiment at ${\mathit{T}}_{\mathrm{lab}}$=280 MeV the rescattering contribution enhances the cross section and reduces the discrepancy between the data and the calculation.