The three-body collision operator in quantum mechanics. II. Renormalization and quasiparticles

We analyze in detail the structure of the three-body collision operator that appears in the transport equation of a moderately dense gas. Using a binary scattering matrix expansion, we show that this three-body operator can be decomposed into three parts: the first one describes a renormalization of the two-body Boltzmann operator, the second corresponds to genuine three-body collisions between free incident particles; the interpretation of the last part is more complicated and takes a simple form only when the two-particle scattering matrix is energy independent: it corresponds then to a description of transport phenomena in terms of quasiparticles, similar to those obtained recently in the weakly coupled case. © 1957.SCOPUS: ar.j