SPIN POLARIZATION BY EXTERNAL MAGNETIC FIELDS, AHARONOV-BOHM FLUX STRINGS, AND CHIRAL SYMMETRY BREAKING IN QED3

Abstract

In the first part, the induced vacuum spin around an Aharonov-Bohm flux string in massless three-dimensional QED is computed explicitly and the result is shown to agree with a general index theorem. A previous observation in the literature, that the presence of induced vacuum quantum numbers which are not periodic in the flux make an integral-flux AB string visible, is reinforced. In the second part, a recent discussion of chiral symmetry breaking by external magnetic fields in parity-invariant QED 3 and its relation to the induced spin in parity-noninvariant QED 3 is further elaborated. Finally, other vacuum polarization effects around flux tubes in different variants of QED, in three and four dimensions are mentioned.