A comparative study of type-II, inverse and linear seesaw mechanisms with $ A_{4} $ flavour symmetry

Abstract

In this work, we present a comparative study of the three of the seesaw models, viz., type II, inverse and linear seesaw models, to investigate about light neutrino masses and mixings, flavour structure, neutrinoless double beta decay (0νββ) and charged lepton flavour violation (cLFV) decay (µ → eγ). We consider the A 4 flavour symmetry, while some other symmetries, like U (1) X , Z 4 and Z 5 are also included to forbid unwanted terms in the Lagrangian. Taking into account the present experimental data for the known light neutrino parameters from recent global fit data, we compute the currently unknown neutrino parameters such as the lightest neutrino mass (m 1 ), CPV phase (Dirac and Majorana), and effective light neutrino mass in the neutrinoless double beta decay, by considering different VEV alignments of the triplet scalar flavon fields. We also elucidate on the octant of atmospheric neutrino mixing angle, θ 23 , in the light of our predicted results.Finally, we present the region of parameter spaces of m 1 , CPV phases, octant of θ 23 and effective mass measurable in of neutrino less double beta decay experiments, that can be tested in future experiments. We observe that the branching ratio of (µ → eγ) can help discriminate the three seesaw models. Further, the favoured Octant of the atmospheric mixing angle θ 23 changes with the VEV alignment of the triplet flavon field -i.e., the internal flavour structure of the neutrinos is reflected in their composition (mixing). We also find some interesting results in context of mass hierarchy-Octant degeneracy with reference to VEV of the triplet flavon field. The constant F determining the scale of flavour symmetry breaking, seesaw scale and coupling constants of the three seesaw models has also been computed, which puts a constraint among them allowed by the present experimental results. Interesting implications on dependence of scale of flavour symmetry breaking in the three seesaw models is also presented in discussion.

Flavour and CP symmetries in the inverse seesaw

“…For Case 3 b.1) all mixing angles turn out to depend on the parameter s and the free angle θ S , in addition to the two parameters n and m which we have fixed, see Eq. (72). In what follows we identify the areas in the (s/n − θ S ) plane in which the three mixing angles (individually and simultaneously) are in agreement with the experimental data at the 3 σ level [76].…”

“…As shown in the model-independent scenario, several simplifications of the formulae in Eqs. (72,73) can be made for m = n 2 (corresponding to m = 10 for the present case). In particular, two approximate sum rules are found, see Eq.…”

“…Flavour (and CP) symmetries have been studied in association with several scenarios of neutrino mass generation, see, e.g., [37][38][39][40][41][42][43][44][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73].…”

“…We focus on the socalled (3, 3) ISS framework, in which the SM field content is extended by 3+3 heavy sterile states, N i and S j . We note that different realisations of the ISS mechanism with flavour (and CP) symmetries have been considered in the literature, see, e.g., [63][64][65][66][67][68][69][70][71][72][73]. The main features of the present ISS framework are the following: left-handed (LH) lepton doublets, and the sterile states N i and S j all transform as irreducible triplets of G f , while right-handed (RH) charged leptons are assigned to singlets, so that the three different charged lepton masses can be easily accommodated.…”