Neutrino-pair bremsstrahlung by electrons in neutron star crusts

Neutrino-pair bremsstrahlung by relativistic degenerate electrons in a neut ron-star crust at densities 10(9) gem (-3) less than or similar to rho less than or similar to 1.5 x 10(14) g cm(-3) is analyzed. The processes taken into account are neutrino emission due to Coulomb scattering of electrons b y atomic nuclei in a Coulomb liquid, and electron-phonon scattering (the ph onon contribution) and Bragg diffraction (the static-lattice contribution) in a Coulomb crystal. The static-lattice contribution is calculated includi ng the electron band-structure effects for cubic Coulomb crystals of differ ent types and also for the liquid crystal phases composed of rod- and plate -like nuclei near the bottom of the neutron-star crust (1014 g cm(-3) less than or similar to rho less than or similar to 1.5 X 10(14) g cm(-3)). The phonon contribution is evaluated with proper treatment of the multi-phonon processes which removes a jump in the neutrino bremsstrahlung emissivity at the melting point obtained in previous works. Generally, bremsstrahlung in the solid phase does not differ significantly from that in the liquid. At rho less than or similar to 10(13) g cm(-3), the results are rather insensi tive to the nuclear form factor, but results for the solid state near the m elting point are affected significantly by the Debye-Waller factor and mult i-phonon processes. At higher densities the Debye-Waller factor and multi-p honon processes become less important but the nuclear form factor becomes m ore significant. With growing rho, the phonon contribution becomes smaller. Near the bottom of the neutron star crust bremsstrahlung becomes less effi cient due to the reduction of the effective electron-nucleus matrix element by the electron band-structure effects and the nuclear form factor. A comp arison of the various neutrino generation mechanisms in neutron star crusts shows that electron bremsstrahlung is among the most important ones.