Nucleon-nucleon Bremsstrahlung: off-energy-shell effects and meson-exchange currents

Nucleon-nucleon bremsstrahlung, NNγ, is fundamental process, which involves the strong and electromagnetic fields acting simultaneously. Since the electromagnetic interaction is well known, NNγ provides a calculable tool for comparing off-energy-shell (OES) effects from different two-nucleon potentials compared to experiment and also provides a simple testing ground, which is sensitive to meson-exchange-current (MEC) contributions that are so important in electronuclear physics. MEC effects, which are included by requiring gauge invariance of the complete npγ amplitude and which increase the cross section by a factor greater than two, are shown to order K degree in the photon momentum at 200 MeV. ppγ calculations are compared to the 280 MeV experimental results from TRIUMF, which use a polarized proton beam, and which contain ''large'' OES effects. Potentials with different short-range radial behavior are compared in order to examine the penetration of the photon radiation. Rather good agreement with experiment for the Bonn potential is achieved without the arbitrary normalization of 2/3 applied to the TRIUMF cross-section data. The rescattering included in our work accounts for an increase of up to approximately 20% in the cross section, and it contributes up to a factor of 2.5 in the analyzing power