Seesaw Limit of the Nelson-Barr Mechanism

TL;DR

This paper explores a seesaw limit of the Nelson-Barr mechanism, linking solutions to the strong CP problem with fermion mass hierarchies by introducing vector-like quarks to suppress CP violation and explain quark masses.

Contribution

It introduces the concept of a seesaw limit in the Nelson-Barr mechanism and demonstrates how adding vector-like quarks can address both the strong CP problem and fermion mass hierarchies.

Findings

Light quark masses are suppressed by large CP-violating terms.

Adding vector-like quarks can eliminate CP violation in the strong sector.

The observed quark mass hierarchy can be achieved simultaneously.

Abstract

We investigate how the solution to the strong CP problem and the explanation for the observed fermion mass hierarchies can be intrinsically related. Specifically, we explore the Nelson-Barr mechanism and identify its "seesaw limit", where light quark masses are suppressed by large CP-violating terms. Upon adding three (two) vector-like quarks that mix with the down-type (up-type) quark sector of the Standard Model, we demonstrate how the lack of CP violation in the strong sector and the observed quark mass hierarchy can be simultaneously achieved.