Electroweak bremsstrahlung from neutron-neutron scattering

Background: Nucleon-nucleon (NN) bremsstrahlung processes NN gamma (nn gamma, np gamma, and pp gamma) have been extensively investigated. Neutrino-pair bremsstrahlung processes from nucleon-nucleon scattering NN nu(nu) over bar (nn nu(nu) over bar, np nu(nu) over bar, and pp nu(nu) over bar) have recently attracted attention in studies of neutrino emission in neutron stars. The calculated NN nu(nu) over bar cross sections (or emissivities) are found to be sensitive to the two-nucleon dynamical model used in the calculations. Purpose and Method: A realistic one-boson-exchange (ROBE) model for NN interactions is used to construct the electroweak bremsstrahlung amplitudes using the well-known nucleon electromagnetic and weak interaction vertices. The constructed nn gamma and nn nu(nu) over bar amplitudes are investigated by applying them to calculate nn gamma and nn nu(nu) over bar cross sections, respectively. Results: (i) The 190-MeV ROBE nn gamma cross sections agree well with those calculated using the TuTts amplitude, but they are in disagreement with those calculated using the Low amplitude. (ii) The calculated nn nu(nu) over bar cross sections using the ROBE amplitude at the neutrino-pair energy omega = 1 MeV are in quantitative agreement with those calculated by Timmermans et al. [Phys. Rev. C 65, 064007 (2002)], who used the leading-order term of the soft neutrino-pair bremsstrahlung amplitude. Conclusions: The nn gamma amplitude in the ROBE approach, which obeys the soft-photon theorem, has a predictive power similar to that of the TuTts amplitude. The nn nu(nu) over bar amplitude in the ROBE approach, which is consistent with the soft neutrino-pair bremsstrahlung theorem, has a predictive power similar to that of the soft neutrino-pair bremsstrahlung amplitude of Timmermans et al. in the low neutrino-pair energy region.