Speaker
Description
The neutron superfluid present in the inner crust and outer core of a neutron star is coupled to the rest of the star due to nondissipative entrainment effects of different nature. Such effects could play an important role in the dynamics of the star. In the crust, entrainment effects are measured in terms of the superfluid density, i.e. the density of neutrons that contribute to the superfluid motion, or equivalently in terms of an effective mass of crustal ions. Both are derived in the linear response theory within the Bardeen-Cooper-Schrieffer approximation. The superfluid density thus obtained leads to the same entrainment matrix as derived earlier in homogeneous neutron-proton superfluid mixture, thus providing a unified description of entrainment effects throughout the inner crust and outer core within the same microscopic framework. The superfluid density and effective ion mass are evaluated numerically in different regions of the crust from three-dimensional band-structure calculations, taking into account lattice vibrations. Results are compared to predictions from classical hydrodynamics with different prescriptions for the permeability of ions to superfluidity.