Hydrodynamics of the A-phase of superfluid He3

A complete set of hydrodynamics equations for the A-phase of superfluid He3 is derived on basis of the kinetic equation for the quasiparticle distribution function and from gauge invariance considerations. All thermodynamic quantities and, in the tau approximation, the kinetic coefficients entering the equations are determined and expressed in terms of the Fermi fluid parameters of the Landau theory. It is shown that within the limits of applicability of hydrodynamics, ω tau < < 1, there are two frequency ranges in which the equations of motion for the orbital moment vector are principally different. At low frequencies the equation is a diffusion-type equation and at higher frequencies it describes the propagation of weakly damped orbital waves with a linear dispersion law