SUPERFLUID He: A LABORATORY MODEL SYSTEM FOR QUANTUM FIELD THEORY∗

The early Universe is believed to have undergone a sequence of rapid phase transitions. Defect formation in these transitions has been suggested as one possible source for the anisotropy in the cosmic background radiation and the large-scale structure in the distribution of visible mass. So far controlled laboratory experiments have not been performed on homogeneous second order phase transitions as a function of transition speed and a freeze-out of topological defects has not been convincingly demonstrated. Recently a new phenomenon was discovered in superfluid HeB: the formation of quantized vortices within bulk liquid in the presence of ionizing radiation. This “mini bang” allows one to explore the superfluid transition within the clean bulk medium on the microsecond time scale. Such experiments appear to provide the first quantitative test of the theories on defect formation in a time-dependent second order phase transition. Also other superfluid He experiments can be found which establish analogies to phenomena in high energy physics, such as baryogenesis by strings and by textures, and generation of primordial magnetic fields. Here and in most other cases it is quantized vortex lines and other topological defects which provide a connection to quantum field theory and its applications in cosmology. Their analogies in relativistic quantum field theory include such objects as Z and W cosmic strings, Alice strings, torsion and spinning strings, strings terminating on walls and walls terminating on strings, gravimagnetic monopoles, axion and pion strings, etc.