EXTENSIONS OF AUTOMORPHISMS AND GAUGE SYMMETRIES

We characterize the automorphisms of a C-algebra A which extend to au tomorphisms of the crossed product B of A by a compact group dual. The case where the inclusion A subset-of B is equipped with a group of au tomorphisms commuting with the dual action is also treated. These resu lts are applied to the analysis of broken gauge symmetries in Quantum Field Theory to draw conclusions on the structure of the degenerate va cua on the field algebra.