The quasiclassical approach to superfluid 3He

We develop the quasiclassical theory for normal and superfluid liquid ³He using a systematic expansion in small parameters such as δ/E_F, ?₀^?1/k_F, etc., and paying particular attention to the high-energy renormalizations of the external pertubations and observables. We apply the general formalism to a number of more specific problems including the derivation of the non-linear quantum kinetic equation for normal ³He, the weak-coupling and strong-coupling free energies and static response functions for superfluid ³He, and the low-frequency and high-frequency dynamics of the superfluid phases. We also discuss extensions of the quasiclassical framework to cover strong short-ranged pertubations such as walls and ions, review recent phenomenological models for the quasiparticle scattering amplitude, and present a brief but self-contained derivation of the Keldysh perturbation theory for real-time Green's functions.