Hyperon bulk viscosity is the most significant transport coefficient affecting the growth or decay of any neutron-star mode of oscillation which has, even to second order in its amplitude, a periodic density fluctuation. This paper evaluates both the direct Urca and strangeness-changing four-baryon weak-interaction terms in the coefficient.

• Received 14 March 2001

DOI:https://doi.org/10.1103/PhysRevD.64.084003