Neutrinoless double beta decay in type I+II seesaw models

Abstract

We study neutrinoless double beta decay in left-right symmetric extension of the standard model with type I and type II seesaw origin of neutrino masses. Due to the enhanced gauge symmetry as well as extended scalar sector, there are several new physics sources of neutrinoless double beta decay in this model. Ignoring the left-right gauge boson mixing and heavy-light neutrino mixing, we first compute the contributions to neutrinoless double beta decay for type I and type II dominant seesaw separately and compare with the standard light neutrino contributions. We then repeat the exercise by considering the presence of both type I and type II seesaw, having non-negligible contributions to light neutrino masses and show the difference in results from individual seesaw cases. Assuming the new gauge bosons and scalars to be around a TeV, we constrain different parameters of the model including both heavy and light neutrino masses from the requirement of keeping the new physics contribution to neutrinoless double beta decay amplitude below the upper limit set by the GERDA experiment and also satisfying bounds from lepton flavor violation, cosmology and colliders.

Charged lepton flavour violcxmation and neutrinoless double beta decay in left-right symmetric models with type I+II seesaw

“…To be more specific, the authors of [57] showed that for heaviest right handed neutrino mass as low as 400 GeV, the triplet scalars are allowed to be as low as around 800 GeV for right handed charged gauge boson mass 3.5 TeV. Here we extend both these works [56,57] by considering more general type I and type II seesaw terms with comparable strength and study their implications in LFV processes µ → 3e, µ → eγ and LNV process like 0νββ. Instead of considering any specific mass matrix structure for either type I or type II seesaw mass matrix, we consider a very general mass matrix for one of the seesaw terms.…”

“…More recently, the authors of [32,52,53] studied the new physics contributions to 0νββ process for TeV scale MLRSM with dominant type II seesaw. There have also been several works [54][55][56][57] where type I seesaw limit was also included into the computation of 0νββ in MLRSM. Some more detailed analyses incorporating left-right gauge mixing were discussed in the works [58][59][60][61][62].…”

“…However, if both the seesaw terms are sizeable then one has more freedom to tune the individual seesaw terms in a way that their combination gives the effective light neutrino masses and mixing. In a recent work [56], we considered equally dominant type I and type II seesaw, with the type I seesaw mass matrix possessing a µ − τ symmetry, or, more specifically, Tri-Bimaximal or TBM type mixing. We then studied the new physics contributions to 0νββ amplitude by taking experimental constraints on LFV process µ → 3e, masses of triplet scalars, new gauge bosons and right handed neutrinos.…”

“…We call it democratic type Itype II seesaw scenario. One can also assume some specific structure of one of these mass matrices as was done in [56] to reduce the number of free parameters. However, in the absence of additional flavour symmetries, such realisations are ad-hoc to some extent and hence we intend to do a more general study in this work.…”

Observable lepton number violation with predominantly Dirac nature of active neutrinos

“…A more recent work [90] showed the possibility of lighter triplet scalars M i /M ∆ ≈ 0.5. In a subsequent work [91], it was shown that one can also have the possibility of M i /M ∆ > 1 if we consider the new physics contribution to the above-mentioned decay processes within a framework of equally dominant type I and type II seesaw, earlier studied in this context by [92]. Due to a different way of generating leading order neutrino mass in the present model, these bounds may however change as we discuss in the upcoming sections with further details.…”