Shear viscosity in a CFL quark star

We compute the mean free path and shear viscosity in the color-flavor locked(CFL) phase of dense quark matter at low temperature T, when the contributionsof mesons, quarks and gluons to the transport coefficients are Boltzmannsuppressed. CFL quark matter displays superfluid properties, and transportphenomena in such cold regime are dominated by phonon-phonon scattering. Westudy superfluid phonons within thermal field theory and compute the mean freepath associated to their most relevant collision processes. Small-angleprocesses turn out to be more efficient in slowing transport phenomena in theCFL matter, while the mean free path relevant for the shear viscosity is lesssensitive to collinear scattering due to the presence of zero modes in theBoltzmann equation. In analogy with superfluid He4, we find the same T powerlaw for the superfluid phonon damping rate and mean free path. Our results arerelevant for the study of rotational properties of compact stars, and correctwrong estimates existing in the literature.Comment: 22 pages, 3 figures; it matches the published versio