Up-Down Unification, Neutrino Masses and Rare Lepton Decays

TL;DR

This paper explores how supersymmetric left-right models with the seesaw mechanism can naturally unify up-down fermion Yukawa couplings, fit neutrino data, predict observable rare lepton decays, and generate baryon asymmetry.

Contribution

It extends previous work on fermion unification to the leptonic sector, analyzing neutrino masses, rare decay predictions, and baryogenesis within supersymmetric left-right models.

Findings

Neutrino data constrains Majorana-Yukawa couplings.

Predicts $ au o \mu+\gamma$ decay within experimental reach.

Model consistent with baryon asymmetry generation.

Abstract

In a recent paper, we showed that tree level up-down unification of fermion Yukawa couplings is a natural consequence of a large class of supersymmetric models. They can lead to viable quark masses and mixings for moderately large values of $\tan\beta$ with interesting and testable predictions for CP violation in the hadronic sector. In this letter, we extend our discussion to the leptonic sector focusing on one particular class of these models, the supersymmetric left-right model with the seesaw mechanism for neutrino masses. We show that fitting the solar and the atmospheric neutrino data considerably restricts the Majorana-Yukawa couplings of the leptons in this model and leads to predictions for the decay $\tau\to \mu +\gamma$, which is found to be accessible to the next generation of rare decay searches. We also show that the resulting parameter space of the model is consistent with the requirements of generating adequate baryon asymmetry through lepton-number violating decays of the right-handed neutrino.