Neutrino-Pair Bremsstrahlung Due to Electromagnetic Collisions in Neutron Star Cores Revisited

We reconsider the problem of neutrino-pair bremsstrahlung emission originating from the electromagnetic collisions of charged particles in nucleonic (npeμ) neutron star cores. Two limiting cases are considered: (i) protons in the normal state and (ii) protons in the superconducting state. In both cases, the dominant contribution to the bremsstrahlung emissivity QBrem comes from the transverse part of in-medium electromagnetic interactions. For non-superconducting matter, we obtain an unusual QBrem∝T23/3 temperature dependence due to the dynamical character of plasma screening in the transverse channel, but these are considerably smaller values of QBrem than in previous studies, rendering the considered process unimportant in practice. In contrast, for superconducting and superfluid matter, the neutrino emission processes involving nucleons are suppressed and QBrem due to lepton collisions provides the residual contribution to the neutrino emissivity of neutron star core matter. In the superconducting case, the plasma screening becomes static and the standard QBrem∝T8 temperature scaling is restored. Simple analytical expressions for QBrem in both limiting cases are provided.