Non-Abelian Boltzmann Equation for Mixing and Decoherence
  We consider particle oscillations and their damping in second-quantized form. We find that the damping or "decoherence" may be described by a Boltzmann-like collision integral with "non-abelian blocking factors" (fermions). Earlier results are generalized in that the momentum degrees of freedom are included and that the mixing equations become intrinsically non-linear at high densities. 
G. Raffelt, G. Sigl, and L. Stodolsky