Stückelberg axions and the effective action of anomalous Abelian models. A SU(3)C×SU(2)W×U(1)Y×U(1)B model and its signature at the LHC

We elaborate on an extension of the Standard Model with a gauge structure enlarged by a single anomalous U(1), where the presence of a Wess-Zumino term is motivated by the Green-Schwarz mechanism of string theory. The additional gauge interaction is anomalous and requires an axion for anomaly cancelation. The pseudoscalar implements the Stückelberg mechanism and undergoes mixing with the standard Higgs sector to render the additional U(1) massive. We consider a 2-Higgs doublet model. We show that the anomalous effective vertices involving neutral currents are potentially observable. We clarify their role in the case of simple processes such as Z∗→γγ, which are at variance with respect to the Standard Model. A brief discussion of the implications of these studies for the LHC is included.