Effect of large light-heavy neutrino mixing and natural type-II seesaw dominance to lepton flavor violation and neutrinoless double beta decay

TL;DR

This paper investigates how large light-heavy neutrino mixing within a TeV scale left-right symmetric model influences lepton flavor violation and neutrinoless double beta decay, emphasizing a natural type-II seesaw dominance for neutrino mass generation.

Contribution

It introduces a framework where large light-heavy neutrino mixing is compatible with a natural type-II seesaw mechanism, analyzing its effects on lepton flavor violation and neutrinoless double beta decay.

Findings

Large light-heavy neutrino mixing can significantly enhance charged lepton flavor violation signals.

The model's neutrino mass is predominantly explained by the type-II seesaw mechanism despite large mixing.

Constraints from beta decay, double beta decay, and cosmology are consistent with the model's parameters.

Abstract

We derive the lower bound on the absolute scale of lightest neutrino mass for normal hierarchy and inverted hierarchy pattern of light neutrinos by studying the new physics contributions to charged lepton flavour violations in the framework of a TeV scale left-right symmetric model. In the model, the fermion sector comprises the usual quarks and leptons plus a fermion singlet per generation and the scalar sector consists of isospin doublets, triplets and a bidoublet. The framework allows large light-heavy neutrino mixing where the light neutrino mass formula is governed by a natural type-II seesaw mechanism, unlike the generic type-II seesaw dominance which assumes suppressed light-heavy neutrino mixing. We demonstrate how sizeable loop-induced contribution to light neutrino mass is kept under control such that the light neutrino mass formula is dominantly explained by the type-II seesaw mechanism. We examine the heavy neutrino contributions with large light-heavy neutrino mixing to charged lepton flavour violating processes like $\mu \to e \gamma$, $\mu \to 3 e$ and $\mu \to e$ conversion inside a nucleus. We present a complementary study between neutrinoless double beta decay and charged lepton flavour violation taking into account single beta decay bound, double beta decay bound and cosmology bounds on the sum of light neutrino masses.