Strong CP Problem and the Natural Hierarchy of Yukawa Couplings

TL;DR

This paper proposes a supersymmetric vectorlike model that naturally solves the strong CP problem without an axion by leveraging spontaneous P-C-T-breaking to ensure a zero theta angle at tree level, stable against radiative corrections.

Contribution

It introduces a novel supersymmetric vectorlike framework with spontaneous P-C-T-breaking that maintains a zero theta angle, offering an alternative to axion-based solutions.

Findings

Yukawa matrices' structure is crucial for theta=0

Theta remains stable against radiative corrections

Model provides a natural solution without axions

Abstract

A possible solution to the strong CP problem is presented without using an axion. The model is based on the framework of the supersymmetric vectorlike theory with the spontaneous breakdown of the P-C-T-invariance. It is shown that the characteristic structure of the Yukawa coupling matrices that results from the spontaneous P-C-T-breaking plays the essential role in naturally realizing $\theta=0$ at the tree level. It is argued that $\theta=0$ will not be affected by the radiative corrections.