Bulk viscosity in superfluid neutron star cores. III. Effects of ${\mathrm{\Sigma }}^{-}$ hyperons

Bulk viscosity of neutron star cores containing hyperons is studied taking into account non-equilibrium weak process $n+n\rightleftharpoons p+{\mathrm{\Sigma }}^{-}$. Rapid growth of the bulk viscosity within the neutron star core associated with switching on new reactions (modified Urca process, direct Urca process, hyperon reactions) is analyzed. The suppression of the bulk viscosity by superfluidity of baryons is considered and found out to be very important.