  We consider the 4D effective theory for the light Kaluza-Klein (KK) modes.
The heavy KK mode contribution is generally needed to reproduce the correct
physical predictions: an equivalence, between the effective theory and the
D-dimensional (or geometrical) approach to spontaneous symmetry breaking (SSB),
emerges only if the heavy mode contribution is taken into account. This happens
even if the heavy mode masses are at the Planck scale. In particular, we
analyze a 6D Einstein-Maxwell model coupled to a charged scalar and fermions.
Moreover, we briefly review non-Abelian and supersymmetric extensions of this
theory.
