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Dirac particle in a magnetic field: Symmetries and their breaking by monopole singularities

Journal Article · · Phys. Rev., D; (United States)

Some rules governing motion of a charged particle obeying the Dirac equation are assembled, including exact helicity conservation for scattering on an arbitrary finite magnetic field configuration. The singularity at the location of a magnetic monopole invalidates the derivation of the rules mentioned, leaving the Dirac Hamiltonian H undefined for the lowest angular momentum state of the electron in the field of the pole. Specifying the behavior of H under the discrete P, T, and C symmetries determines it almost uniquely. One result is that H may possess a bound state of zero energy, contrary to assertions in early papers on the subject. Zero-energy bound states which violate the superselection rule for electric charge are also studied, including one which is the point limit of a solution for a fermion multiplet interacting with a finite-energy soliton monopole. Implications of such a bound state for second quantization have been considered previously by others and are further analyzed here. The suggestion that monopoles may possess half-integral fermion number is shown to be unwarranted by present evidence.

Research Organization:
Institute for Theoretical Physics, State University of New York at Stony Brook, Stony Brook, New York 11794
OSTI ID:
5441383
Journal Information:
Phys. Rev., D; (United States), Journal Name: Phys. Rev., D; (United States) Vol. 16:6; ISSN PRVDA
Country of Publication:
United States
Language:
English