Lorentz invariance and origin of symmetries - art. no. 091601

We reconsider the role of Lorentz invariance in the dynamical generation of the observed internal symmetries. We argue that, generally, Lorentz invari ance can be imposed only in the sense that all Lorentz noninvariant effects caused by the spontaneous breakdown of Lorentz symmetry are physically uno bservable. The application of this principle to the most general relativist ic ally invariant Lagrangian, with arbitrary couplings for all the fields i nvolved, leads to the appearance of a symmetry and, what is more, to the ma ssless vector fields gauging this symmetry in both Abelian and non-Abelian cases. In contrast, purely global symmetries are generated only as accident al consequences of the gauge symmetry.