  This thesis work analyzes basic field theoretical aspects of a class of
models motivated by orientifold vacua of string theory and some of their
phenomenological applications at the Large Hadron Collider. They extend the
gauge structure of the Standard Model by anomalous extra U(1) symmetries, which
involve Stuckelberg axions for anomaly cancellation and are accompanied by
Chern-Simons interactions. In particular, these effective actions are
characterized by a physical pseudoscalar (the axi-Higgs) in the CP-odd
spectrum, which has the properties of a generalized Peccei-Quinn axion, with
independent mass and couplings to the gauge fields. Amplitudes mediated by
anomalous gauge interactions are studied at the new collider in some specific
channels such as Drell-Yan and double prompt-photon and shown to be small.
Finally, we address the problem of the relation between the Green-Schwarz and
the Wess-Zumino mechanism(s) for anomaly cancellations in effective lagrangeans
involving anomalous gauge interactions, with their gauge symmetry restored
either with local or non-local counterterms and identify some unitarity bounds
in the Wess-Zumino case. These are due to the presence of anomaly poles in
scattering amplitudes mediated by the anomaly (BIM amplitudes) and whose
cancellation requires necessarly non-local counterterms. While the axi-Higgs
appears in the Wess-Zumino case, two axion-like particles are needed for the
cancellation of the gauge anomalies at all scales, one of them being a ghost.
