Experimental and theoretical evidence of universality in superfluid vortex reconnections

Stasiak, P.Z. and Xing, Y. and Alihosseini, Y. and Barenghi, C.F. and Baggaley, A. and Guo, W. and Galantucci, L. and Krstulovic, G. (2025) Experimental and theoretical evidence of universality in superfluid vortex reconnections. Proceedings of the National Academy of Sciences of the United States of America, 122 (21): e242606412. ISSN 0027-8424

Abstract

The minimum separation between reconnecting vortices in fluids and superfluids obeys a universal scaling law with respect to time. The prereconnection and the postreconnection prefactors of this scaling law are different, a property related to irreversibility and to energy transfer and dissipation mechanisms. In the present work, we determine the temperature dependence of these prefactors in superfluid helium from experiments and a numeric model which fully accounts for the coupled dynamics of the superfluid vortex lines and the thermal normal fluid component. At all temperatures, we observe a pre- and postreconnection asymmetry similar to that observed in other superfluids and in classical viscous fluids, indicating that vortex reconnections display a universal behavior independent of the small-scale regularizing dynamics. We also numerically show that each vortex reconnection event represents a sudden injection of energy in the normal fluid. Finally we argue that in a turbulent flow, these punctuated energy injections can sustain the normal fluid in a perturbed state, provided that the density of superfluid vortices is large enough.