These lectures discuss the formulation of quantum mechanics with fractional spin and statistics in 2+1 dimensions in a relativistic setting, emphasizing the path-integral approach. The non-relativistic theory is reviewed from a path-integral viewpoint. The group-theoretical underpinnings of relativistic fractional spin are discussed, then the path-integral quantization of spin and of massive fermions without using spinors is reviewed. The path integral for a system of n relativistic particles with fractional spin is constructed, the spin-statistics relation and the Lorentz and Poincare' representation content of physical states are discussed. Some problems in formulating a field theory with fractional statistics are presented, and their resolution in the operator cocycle approach is reviewed.
We develop the relativistic quantum mechanics of particles with fractional spin and statistics in 2 + 1 dimensions in the path-integral approach. We endow the elementary excitations of the theory with fractional spin through the coupling of the particle number current with a topological term. We work out the dynamics of the spin degrees of freedom, and display the relation between the spin action and the knot invariants of the paths contributing to the path integral. We show that the explicit spin-changing interaction can be traded for multivaluedness of the wave function, and we relate this to the representation theory of the Lorentz and Poincaré groups in 2 + 1 dimensions. We discuss the multiparticle dynamics and derive the spin–statistics theorem.