Bulk viscosity of superfluid hyperon stars

We calculate the bulk viscosity due to nonequilibrium weak processes in superfluid nucleon-hyperon matter of neutron stars. For that, the dissipative relativistic hydrodynamics, formulated eariler [M. E. Gusakov, Phys. Rev. D 76, 083001 (2007).] for superfluid mixtures, is extended to the case when both nucleons and hyperons are superfluid. It is demonstrated that in the most general case (when neutrons, protons, $\ensuremath{\Lambda}$, and ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ hyperons are superfluid), nonequilibrium weak processes generate 16 bulk viscosity coefficients, with only three of them being independent. In addition, we correct an inaccuracy in a widely used formula for the bulk viscosity of nonsuperfluid nucleon-hyperon matter.

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