Nucleon structure effects in proton-proton bremsstrahlung

The cross section for proton-proton bremsstrahlung depends on the electromagnetic structure of the protons through two form factors. It is found that if these are evaluated from dispersion relations assuming threshold dominance, the theoretical bremsstrahlung cross sections are incompatible with the available data, except at very low energies. This holds with any reasonable assumptions about the off-shell proton-proton interaction. Agreement with experiments can easily be obtained by abandoning the threshold-dominance assumption for one of the form factors. This makes it difficult to use bremsstrahlung data as tests for models of the proton-proton interaction.