Spontaneous CP Violation and the Strong CP Problem in Left-Right Symmetric Theories

TL;DR

This paper explores how spontaneous CP violation in left-right symmetric theories can address the strong CP problem, proposing a novel mechanism involving Higgs fields and vectorlike quarks, with implications for phenomenology and testability.

Contribution

It introduces a new approach combining spontaneous CP violation with a Nelson-Barr type mechanism within left-right symmetric models, including an ultraviolet complete trinification framework.

Findings

A complex vacuum expectation value breaks CP symmetry.

Heavy vectorlike quarks induce known CP violation.

Loop-level effects generate a small QCD vacuum angle.

Abstract

We study spontaneous CP violation as a solution to the strong CP problem in left-right symmetric theories. The discrete CP symmetry is broken by a complex vacuum expectation value of a right-handed Higgs doublet. Heavy vectorlike down-type quarks mix with the Standard Model quarks introducing the known CP violation - realizing a variant of the Nelson-Barr mechanism. A nonvanishing QCD vacuum angle is generated at loop level. The implementation in the ultraviolet complete theory of trinification at low scales is discussed. We further comment on the phenomenology and future testability of the model.