Solving the strong CP problem via Wess-Zumino terms

GERARDO ALDAZABAL, LUIS E. IBÁÑEZ AND ANGEL M. URANGA

JOURNAL OF HIGH ENERGY PHYSICS - (Online)

Año: 2004 p. 1 - 18

1029-8479

We propose a new solution to the strong-CP problem. It involves the existence of an unbroken gauged U(1)X symmetry whose gauge boson gets a Stuckelberg mass term by combining with a pseudoscalar field η(x). The latter has axion-like couplings to FQCDFQCD. This system leads to mixed gauge anomalies and we argue that they are cancelled by the addition of an appropriate Wess-Zumino term, so that no SM fermions need to be charged under U(1)X. In this setup the axion and θ parameter can be rotated away using the symmetries of the system. We discuss scenarios in which the above set of fields and couplings appear. The mechanism is quite generic, but a natural possibility is that the the U(1)X symmetry arises from bulk gauge bosons in theories with extra dimensions or string models. We show that in certain D-brane type-II string models (with antisymmetric tensor field strength fluxes) higher dimensional Chern-Simons couplings give rise to the required D = 4 Wess-Zumino terms upon compactification. In one of the possible string realizations of the mechanism the U(1)X gauge boson comes from the Kaluza-Klein reduction of the eleven-dimensional metric in M-theory.