Microscopic construction of the two-fluid model for superfluid helium-4

Using a system of Heisenberg’s equation of motion for both the normal and the anomalous correlation functions a two-fluid hydrodynamics for superfluid helium-4 was constructed. The method is based on a gradient expansion of the exact equations of motion for correlation functions about a local equilib-rium together with explicit use of the local equilibrium statistical operator for superfluid helium in the frame of reference, where condensate is rest