Nelson-Barr Models with Vector-Like Quark Doublets

Abstract

We investigate Nelson--Barr solutions to the strong CP problem in which spontaneous CP violation is transmitted to the Standard Model through mixing with a vector-like partner of the SM quark doublet. We show that these constructions constitute compelling and phenomenologically viable alternatives to the more widely studied singlet-based NB models. A key result of our analysis is that an accidental symmetry of the renormalizable theory delays the leading contributions to \bar{\theta} until three loops, naturally suppressing hadronic CP violation. We outline the main phenomenological constraints, including future EDM experiments, as well as the main differences between these scenarios and generic models with doublet vector-like quarks.