Entropy entrainment and dissipation in superfluid

We discuss finite temperature effects in superfluid Helium, providing a direct demonstration that a model based on treating the excitations in the system as a massless “entropy” fluid is equivalent to the traditional two-fluid approach. In particular, we demonstrate how the entropy entrainment is related to the “normal fluid density”. We also show how the superfluid constraint of irrotationality reduces the number of dissipation coefficients in the system. This analysis provides insight into the more general problem when vortices are present in the superfluid, and we discuss how the so-called mutual friction force can be accounted for. The end product is a formalism for finite temperature effects in a single condensate that can be applied to Helium in the low temperature regime. It can also be used to describe (to a certain extent) colour-flavour locked quark superconductors that may be present at the extreme densities in a neutron star core. Entropy entrainment and dissipation in superfluid Helium 2