On the theory of vortex quantum tunnelling in the dense Bose superfluid   helium II
  The quantum tunnelling and nucleation theory of vortices in helium II is reviewed. Arguments are given that the only reliable method to calculate tunnelling probabilities in this highly correlated, strongly interacting many-body system is the semiclassical, large scale approach for evaluation of the tunnelling exponent, which does not make any assumptions about the unknown dynamical behaviour of the fluid on microscopic scales. The geometric implications of this semiclassical theory are represented in some detail and its relevance for the interpretation of experimental data is discussed. 
Uwe R. Fischer