Diffusion model of evolution of superthermal high-energy particles under   scaling in the early Universe
  The evolution of a superthermal relic component of matter is studied on the basis of non-equilibrium model of Universe and the Fokker-Planck type kinetic equation offered by one of the authors. 
Yu.G.Ignatyev, R.A.Ziatdinov
gr-qc hep-ph