Renormalisation Group Corrections to the Littlest Seesaw Model and Maximal Atmospheric Mixing

TL;DR

This paper investigates how renormalisation group corrections affect the predictions of the highly constrained Littlest Seesaw model, finding that the model's predictions for neutrino mixing angles, especially maximal atmospheric mixing, are quite stable under these corrections.

Contribution

It provides a detailed calculation of RG corrections to the Littlest Seesaw model, including threshold effects, and assesses their impact on neutrino mixing predictions, especially maximal atmospheric mixing.

Findings

RG corrections have minimal impact on neutrino mass ratios and mixing angles.

The model predicts near-maximal atmospheric mixing, close to 45°, with small deviations.

Predictions are generally stable under RG corrections, supporting the model's robustness.

Abstract

The Littlest Seesaw (LS) model involves two right-handed neutrinos and a very constrained Dirac neutrino mass matrix, involving one texture zero and two independent Dirac masses, leading to a highly predictive scheme in which all neutrino masses and the entire PMNS matrix is successfully predicted in terms of just two real parameters. We calculate the renormalisation group (RG) corrections to the LS predictions, with and without supersymmetry, including also the threshold effects induced by the decoupling of heavy Majorana neutrinos both analytically and numerically. We find that the predictions for neutrino mixing angles and mass ratios are rather stable under RG corrections. For example we find that the LS model with RG corrections predicts close to maximal atmospheric mixing, $\theta_{23}=45^\circ \pm 1^\circ$, in most considered cases, in tension with the latest NOvA results. The techniques used here apply to other seesaw models with a strong normal mass hierarchy.