Speaker
Description
Strong interactions can potentially violate Charge Parity (CP) symmetry, but experimentally there has been no evidence for it. The Peccei-Quinn (PQ) mechanism which assumes a global U(1) symmetry provides an elegant solution to this "strong CP problem", in terms of a light particle, the axion. However, global symmetries, such as the ones employed in the PQ mechanism, are not respected by quantum gravity, which could destabilize the PQ solution. In this talk I will suggest a variety of models that solves this "axion quality problem" through a gauged U(1) symmetry, which is safe from gravity corrections. The QCD axion that solves the strong CP problem arises automatically in these models. A unified SO(10) model will be presented, which has a high quality axion of a hybrid nature, which interpolates between two popular (DFSZ and KSVZ) models. Other classes of models will be presented, including one with a gauged flavor symmetry which also explains the hierarchical structure of quark and lepton masses. Possible ways to test these models in axion physics will be outlined.