Answers are grounded in this paper and cite their sources.
If physics is stable with respect to a class of perturbations of the spacetime metric, including that of "small" constant four-dimensional curvature, then it may be shown that (1) left-handed and right-handed neutrinos are distinguished by a superselection rule; (2) magnetic monopoles cannot exist; (3) the conformal symmetry associated with the field equations for massless particles with spin 0, {}, and 1 is spontaneously broken---except in the case of neutrinos with fixed chirality.
No takes yet. Share an insight, caveat, or question.
C. Frønsdal (1975) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: