  Extensions of the Standard Model with extra neutral currents due to
additional anomalous abelian gauge factors are considered. We summarize the
main features of the effective action associated to these theories. They are
characterized by an axion-like particle (the {\em axi-higgs}) which can be
(almost) massless, with its mass generated non-perturbatively in the QCD vacuum
as for an ordinary Peccei-Quinn axion, but that can also mix with the scalars
of the Higgs sector, becoming a heavy axion. We briefly describe the interplay
between the electroweak and the QCD sectors in these types of theories, which
emerge either from special vacua of string/brane theory; from partial
decoupling of a heavier fermion sector or from an anomaly inflow in the context
of models with extra dimensions.
