Projecting a non-Abelian SU(2) vacuum gauge field---a pure gauge constructed from the group element U---onto a fixed (electromagnetic) direction in isospace gives rise to a nontrivial magnetic field, with nonvanishing magnetic helicity, which coincides with the winding number of U. Although the helicity is not conserved under Maxwell (vacuum) evolution, it retains one-half its initial value at infinite time.
No takes yet. Share an insight, caveat, or question.
Jackiw et al. (2000) studied this question.
Synapse has enriched 3 closely related papers on similar clinical questions. Consider them for comparative context: