Probing $0\nu \beta \beta$ and $\mu \to e\gamma$ via Fully Determined Dirac Mass Terms in LRSM with Double Seesaw

Abstract

Neutrinoless double beta decay ($0\nu \beta \beta$) and charged lepton flavor violation (cLFV) experiments provide promising avenues to probe new physics contributions from extended neutrino sectors in beyond Standard Model (BSM) scenarios. We consider a Left-Right Symmetric Model (LRSM) extended with three generations of sterile neutrinos to realize a double type-I seesaw mechanism for light neutrino mass generation. The double seesaw induces maximal lepton number violation in the right-handed sector and facilitates enhanced Majorana masses for right-handed neutrinos, thereby leading to their dominant contributions in both cLFV and $0\nu \beta \beta$ processes. We perform a comprehensive exploration of the parameter space for new-physics contributions to the cLFV decay $\mu \to e\gamma$ and to $0\nu \beta \beta$, considering two different textures for the Dirac mass matrices: (i) a symmetry-motivated limit with $M_D\propto 1$, and (ii) a texture fully determined by the model framework. A detailed analysis of the common parameter regions accessible to current experiments like KamLAND-Zen and LEGEND-200, and upcoming experiments, such as MEG-II and LEGEND-1000, is presented, underscoring the phenomenological relevance of this framework. Our results aim to provide optimistic benchmarks for future searches targeting right-handed current-mediated neutrino interactions.

Comments: 67 pages, 13 figures, 15 tables, version accepted in JHEP on 18th Dec 2025