Relaxation time hierarchy in a two-component quasiparticle gas

A quasiparticle description of various condensed media is a very popular tool in the study of their transport and thermodynamic properties. I present here a microscopic theory for the description of diffusion processes in a two-component gas of quasiparticles with arbitrary dispersion law and statistics. In particular, I analyze the role of interaction within each subsystem (i.e., between identical quasiparticles) in relaxation of the whole system. The approach for solving such kinetic problems allows one to study the most important limiting cases and to clarify their physical sense. Classical results for diffusion coefficients of light particles in a massive gas (Lorentz model) and of massive particles in a light gas (Rayleigh model) are obtained directly from the general solution without using artificial approaches, as was done earlier. This provides a possibility to generalize these popular models on quasiparticle systems.