Neutrino and axion emissivities of neutron stars from nucleon–nucleon scattering data

Neutrino and axion production in neutron stars occurs mainly as bremsstrahlung from nucleon–nucleon (NN) scattering. The energy radiated via neutrinos or axions is typically very small compared to other scales in the two-nucleon system. The rate of emission of such “soft” radiation is directly related to the on-shell NN amplitude, and thereby to the NN experimental data. This facilitates the model-independent calculation of the neutrino and axion radiation rates which is presented here. We find that the resultant rates are roughly a factor of four below earlier estimates based on a one-pion-exchange NN amplitude.