Stochastic motion of vortex filaments in He II under random force

Abstract

Langevin dynamics are applied to describe the stochastic motion of vortex filaments in He II under random force. The article describes a functional formalism, which is a modification of the method developed earlier by Migdal to deal with the stochastic dynamics of classical vortex filaments. In particular, starting with the Langevin-type equation, the functional Fokker–Planck equation for the characteristic functional was obtained. Based on this equation, and under the assumption that the random force correlator satisfies the fluctuation-dissipation theorem, thermodynamic equilibrium in a system of chaotic quantized vortices was investigated. Additionally, the case of stationary helium and the case of counterflow with the constant relative velocity of the normal and superfluid components were considered. Some physical consequences of the results obtained are also discussed.