Efimov effect and the third cluster coefficient of binary mixtures

Because of the Efimov effect the three-body bound state contribution to the cluster coefficients diverges, if the pair interaction develops a zero energy two-body bound state. It is shown for a quantum Lorentz gas model and a Born-Oppenheimer model of a gas mixture that this divergence is cancelled by the continuum contribution. The behaviour of the third cluster coefficient of the Lorentz gas at extreme temperatures is discussed.