A study on a minimally broken residual TBM-Klein symmetry with its implications on flavoured leptogenesis and ultra high energy neutrino flux ratios

TL;DR

This paper explores minimally broken residual TBM-Klein symmetry in neutrino mass matrices, analyzing implications for flavoured leptogenesis and ultra high energy neutrino flux ratios, with a focus on phenomenological viability and experimental predictions.

Contribution

It introduces a specific minimally perturbed TBM mixing model with detailed numerical analysis, linking residual symmetry breaking to leptogenesis and neutrino flux predictions.

Findings

Large symmetry breaking (>45%) is needed for phenomenological viability.

Non-maximal mixing is preferred due to small breaking constraints.

The model predicts specific neutrino flux ratios at IceCube.

Abstract

We present a systematic study on minimally perturbed neutrino mass matrices which at the leading order give rise to Tri-BiMaximal (TBM) mixing due to a residual $\mathbb{Z}_2\times \mathbb{Z}_2^{\mu\tau}$ Klein symmetry in the neutrino mass term of the low energy effective seesaw Lagrangian. Considering only the breaking of $\mathbb{Z}_2^{\mu\tau}$ with two relevant breaking parameters ($\epsilon_{4,6}^\prime$), after a comprehensive numerical analysis, we show that the phenomenologically viable case in this scenario is a special case of TM1 mixing. For this class of models, from the phenomenological perspective, one always needs large breaking (more than $ 45\%$) in one of the breaking parameters. However, to be consistent the maximal mixing of $\theta_{23}$, while more than $ 35\%$ breaking is needed in the other, a range $49.4^\circ-53^\circ$ and $38^\circ-40^\circ$ could be probed allowing breaking up to $ 25\%$ in the same parameter. Thus though this model cannot distinguish the octant of $\theta_{23}$, non-maximal mixing is preferred from the viewpoint of small breaking. The model is also interesting from leptogenesis perspective. Unlike the standard $N_1$-leptogenesis scenario, here all the RH neutrinos contribute to lepton asymmetry due to the small mass splitting controlled by the $\mathbb{Z}_2^{\mu\tau}$ breaking parameters. Inclusion of flavour coupling effects (In general, which have been partially included in all the leptogenesis studies in perturbed TBM framework) makes our analysis and results pertaining to a successful leptogenesis more accurate than any other studies in existing literature. Finally, in the context of recent discovery of the ultra high energy (UHE) neutrino events at IceCube, assuming UHE neutrinos originate from purely astrophysical sources, we obtain prediction on the neutrino flux ratios at neutrino telescopes.