Tadpoles and Symmetries in Higgs-Gauge Unification Theories
  In theories with extra dimensions the Standard Model Higgs fields can be identified with internal components of bulk gauge fields (Higgs-gauge unification). The bulk gauge symmetry protects the Higgs mass from quadratic divergences, but at the fixed points localized tadpoles can be radiatively generated if U(1) subgroups are conserved, making the Higgs mass UV sensitive. We show that a global symmetry, remnant of the internal rotation group after orbifold projection, can prevent the generation of such tadpoles. In particular we consider the classes of orbifold compactifications T^d/Z_N (d even, N>2) and T^d/Z_2 (arbitrary d) and show that in the first case tadpoles are always allowed, while in the second they can appear only for d=2 (six dimensions). 
C. Biggio, M. Quiros