Charged Lepton Flavour Violation and Neutrinoless Double Beta Decay in Left-Right Symmetric Models with Type I+II Seesaw

TL;DR

This paper investigates how left-right symmetric models with combined type I and II seesaw mechanisms influence neutrinoless double beta decay and lepton flavor violation, expanding the viable parameter space and contrasting previous models.

Contribution

It introduces a comprehensive analysis of the minimal left-right symmetric model with combined type I+II seesaw, showing increased allowed parameter space and novel mass relations.

Findings

Allowed scalar masses $M_{\Delta}$ can be smaller than right-handed neutrino masses $M_N$.

The combined type I+II seesaw broadens the parameter space compared to individual seesaw models.

Experimental bounds constrain the model parameters within the TeV scale.

Abstract

We study the new physics contributions to neutrinoless double beta decay ($0\nu\beta \beta$) half-life and lepton flavour violation (LFV) amplitude within the framework of the minimal left-right symmetric model (MLRSM). Considering all possible new physics contributions to $0\nu\beta \beta$ and charged lepton flavour violation $\mu \rightarrow e \gamma, \mu \rightarrow 3e$ in MLRSM, we constrain the parameter space of the model from the requirement of satisfying existing experimental bounds. Assuming the breaking scale of the left-right symmetry to be $\mathcal{O}(1)$ TeV accessible at ongoing and near future collider experiments, we consider the most general type I+II seesaw mechanism for the origin of tiny neutrino masses. Choosing the relative contribution of the type II seesaw term allows us to calculate the right handed neutrino mass matrix as well as Dirac neutrino mass matrix as a function of the model parameters, required for the calculation of $0\nu\beta \beta$ and LFV amplitudes. We show that such a general type I+II seesaw structure results in more allowed parameter space compared to individual type I or type II seesaw cases considered in earlier works. In particular, we show that the doubly charged scalar masses $M_{\Delta}$ are allowed to be smaller than the heaviest right handed neutrino mass $M_N$ from the present experimental bounds in these scenarios which is in contrast to earlier results with individual type I or type II seesaw showing $M_{\Delta} > M_N$.