In the last few years, an interesting new subject, the study of topological quantum fluids, has emerged. Examples of topological quantum fluids inclu… - Anthony Zee

In a course on nonrelativistic quantum mechanics you learned about the Pauli exclusion principle2 and its later generalization stating that particles with half integer spins, such as electrons, obey Fermi-Dirac statistics and want to stay apart, while in contrast particles with integer spins, such as photons or pairs of electrons, obey Bose-Einstein statistics and love to stick together. From the microscopic structure of atoms to the macroscopic structure of neutron stars, a dazzling wealth of physical phenomena would be incomprehensible without this spin-statistics rule. Many elements of condensed matter physics, for instance, band structure, Fermi liquid theory, superfluidity, superconductivity, quantum Hall effect, and so on and so forth, are consequences of this rule.

We show that the introduction of a charged scalar particle into the standard theory leads to numerous phenomenological consequences. In particular, muon-neutrino scattering on electron can resonate in the s-channel, a fact which is potentially important in high-energy neutrino experiments and conceivably relevant in explaining the recently reported underground muon events from Cygnus X-3. We focus on the violation of various quantum numbers, including electron, muon, and tauon numbers.

Although group theory is certainly relevant for nineteenth-century physics, it really started to play an important role with the work of Lorentz and Poincaré, and became essential with quantum mechanics. Heisenberg opened up an entirely new world with his vision of an internal symmetry, the exploration of which continues to this day in one form or another. Beginning in the 1950s, group theory has come to play a central role in several areas of physics, perhaps none more so than in what I call fundamental physics ...