Calculable neutrino Dirac mass matrix and one-loop $\bar \theta$ in the minimal left-right symmetric model

TL;DR

This paper calculates the neutrino Dirac mass matrix and one-loop contributions to the strong CP parameter in a minimal left-right symmetric model, deriving sterile neutrino mass limits relevant for collider and decay experiments.

Contribution

It introduces a new parametrization of the right-handed neutrino mixing matrix and constructs the heavy neutrino mass matrix to maintain Hermiticity of the Dirac mass matrix.

Findings

Upper limits on sterile neutrino masses derived from strong CP constraints.

The parametrization is applicable to various phenomenological studies.

Sterile neutrino masses are within reach of current experimental searches.

Abstract

We revisit the contribution to the strong CP parameter $\bar \theta$ from leptonic CP violation at one-loop level in the minimal left-right symmetric model in the case of generalized parity as the left-right symmetry. The Hermitian neutrino Dirac mass matrix $M_D$ can be calculated using the light and heavy neutrino masses and mixings. We propose a parametrization of the right-handed neutrino mixing matrix $V_R$ and construct the heavy neutrino mass that maintains the Hermiticity of $M_D$. We further apply it to evaluate the one-loop $\bar\theta$, denoted as $\bar \theta_{loop}$, as a function of the sterile neutrino masses for explicit examples of $V_R$. By requiring the magnitude of $\bar \theta_{loop}\lesssim 10^{-10}$, we derive the upper limits on the sterile neutrino masses, which are within reach of direct searches at the Large Hadron Collider and neutrinoless double beta decay experiments. Furthermore, our parametrization is pertinent for other phenomenological investigations.