In Part I the kinetic theory of excitations in flowing liquid He IIis developed to a higher order than that carried out previously, byLandau and Khalatnikov, in order to demonstrate the existence ofnon-equilibrium terms of a new nature in the hydrodynamic equations.It is then shown that these terms can lead to spontaneous destabilizationin counter currents when the relative velocity of the normaland super fluids exceeds a critical value that depends on the temperature,but not on geometry. There are no adjustable parametersin the theory. The critical velocities are estimated to be in the14-20 m/sec range for T ≤2.0° K, but tend to zero as T → T_λ. Thepossibility that these critical velocities may be related to the experimentally observed "intrinsic" critical velocities is discussed.
Part II consists of a semi-classical investigation of rotonquantizedvortex line interactions. An essentially classical modelis used for the collision and the behavior of the roton in the vortexfield is investigated in detail. From this model it is possible toderive the HVBK mutual friction terms that appear in the phenomenalogicalequations of motion for rotating liquid He II. Estimates ofthe Hall and Vinen B and B' coefficients are in good agreement withexperiments. The claim is made that the theory does not containany arbitrary adjustable parameters.
