Kelvin Helmholtz Instability and Circulation Transfer at an Isotropic-Anisotropic Superfluid Interface in a Neutron Star

A recent laboratory experiment (Blaauwgeers et al. 2003) suggests that a Kelvin-Helmholtz (KH) instability at the interface between two superfluids, one rotating and anisotropic, the other stationary and isotropic, may trigger sudden spin-up of the stationary superfluid. This result suggests that a KH instability at the crust-core ($^1S_0$-$^3P_2$-superfluid) boundary of a neutron star may provide a trigger mechanism for pulsar glitches. We calculate the dispersion relation of the KH instability involving two different superfluids including the normal fluid components and their effects on stability, particularly entropy transport. We show that an entropy difference between the core and crust superfluids reduces the threshold differential shear velocity and threshold crust-core density ratio. We evaluate the wavelength of maximum growth of the instability for neutron star parameters and find the resultant circulation transfer to be within the range observed in pulsar glitches.