Long and short time quantum dynamics: II. Kinetic regime

Non-equilibrium Greenʹs functions reduce to quantum kinetic equations in the kinetic regime, that is, if the quasi-classical, quasi-particle picture is valid. The classical tool yielding the kinetic equations, the Kadanoff–Baym Ansatz, has been improved and generalized to a whole Ansatz family including the so-called extended quasi-particle approximation. Each Ansatz produces a quantum kinetic theory: a quasi-particle kinetic equation and a functional of the quasi-particle distribution returning the average values of observables. In the extended quasi-particle model, the theory is physically consistent: causal, gauge invariant and conserving. This model leads to kinetic equations for dense Fermi liquids which combine the Landau quasi-particle drift with non-local scattering integrals in the spirit of the Enskog equation.