Lagrangian quantum turbulence model based on alternating superfluid/ normal fluid stochastic dynamics

Inpired by recent measurements of the velocity and acceleration statistics of Lagrangian tracer particles embedded in a turbulent quantum liquid we propose a new superstatistical model for the dynamics of tracer particles in quantum turbulence. Our model consists of random sequences S/N/S/... where the particle spends some time in the superfluid (S) and some time in the normal fluid (N). This model leads to a superposition of power law distributions generated in the superfluid and Gaussian distributions in the normal liquid, in excellent agreement with experimental measurements. We include memory effects into our analysis and present analytic predictions for probability densities and correlation functions.Comment: 6 pages, 4 figure

Statistics of Lagrangian quantum turbulence

We consider the dynamics of small tracer particles in turbulent quantum fluids. The complicated interaction processes of vortex filaments, the quantum constraints on vorticity, and the varying influence of both the superfluid and the normal fluid on the tracer particle effectively lead to a superstatistical Langevin-like model that in a certain approximation can be solved analytically. An analytic expression for the probability density function of velocity v of the tracer particle is derived that exhibits not only the experimentally observed v⁻³ tails but also the correct behavior near the center of the distribution, in excellent agreement with experimental measurements and numerical simulations. Our results are universal and do not depend on details of the quantum fluid