High-energy low-temperature physics: Production of phase transitions and topological defects by energetic particles in superfluid ³He

I review three sets of experiments conducted in the last decade, in which superfluid ³ He was irradiated with high-energy particles and the nucleation either of vorticity or of the A-B phase transition reported. I consider how far the known atomic physics constrains possible scenarios for such nucleation, and comment on two such scenarios which have appeared in the literature, namely the "baked-Alaska" and "cosmological" (Kibble-Zurek-Volovik) models. I point out that there is a fundamental difference between the problems of nucleation of vorticity on the one hand and the B phase on the other: and that as a result, it is by no means necessary that the same scenario should describe both phenomena. In an appendix I discuss possible sinks of energy in the calorimetric (Grenoble-Lancaster) experiment, with the conclusion that it is entirely consistent with the data to assume that no vorticity at all was produced in this experiment.