Rate of the weak reactions+u→u+din quark matter

The weak reaction $s+u\to u+d$ and its inverse play important roles in the attempts to detect strangelets from relativistic heavy-ion collisions, in the burning of neutron stars into strange stars, in the formation and evaporation of quark nuggets in the early Universe, and, through the bulk viscosity, in determining the stability properties and maximum rotation velocity of neutron stars and/or strange stars. Exact expressions for these rates are given in the case of zero temperature and strange quark mass, and numerical calculations and fits to analytic approximations are given for the general case. Pauli blocking and finite-temperature effects are crucial. There is no "typical" time scale for the reactions.