Extensions of automorphisms and gauge symmetries

We characterize the automorphisms of a C*-algebra A which extend to automorphisms 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 automorphisms commuting with the dual action is also treated. These results are applied to the analysis of broken gauge symmetries in Quantum Field Theory to draw conclusions on the structure of the degenerate vacua on the field algebra