Abstract:
The idea that isolated magnetic poles (or monopoles) exist has long been fascinating. While monopoles have yet to be discovered experimentally, many particle physicists believe that they must exist because monopoles are ubiquitous in Grand Unified Theories of particle physics. One of the most puzzling properties of monopoles was discovered by J.J. Thomson in 1904: a system with an electric and a magnetic charge has non-zero angular momentum even when both particles are at rest. The existence of this angular momentum has a number of important consequences, such as the quantization of electric charge. However, one of these consequences leads to a paradox: a theory with magnetically charged particles seems to require the existence of "half-particles" such as half-electrons and half-quarks (dubbed semitons by Curtis Callan, who discovered this feature). In this talk, I will discuss the physics of charge-monopole systems and describe a resolution of the Callan paradox.