Superfluid densities in neutron-star matter

The superfluid densities in a mixture of neutron and proton superfluids are discussed within Fermi-liquid theory. There are the usual diagonal densities rho(nn) and rho(pp) but also off-diagonal densities rho(np) and rho(pn) which represent coupling between the two species. We express these quantities solely in terms of the Fermi momenta and the Landau parameter f(l)(pn) in a way that explicitly satisfies the Galilean invariance constraints rho(pp)+rho(pn)=m(p)n(p) and rho(nn)+rho(pn)=m(n)n(n)(.) The results are of astrophysical interest, e.g., in a discussion of the damping of gravitational instability in rapidly rotating neutron stars or of post-glitch relaxation of pulsars.