Ameliorating the popular lepton mixings with A4 symmetry: A seesaw model for realistic neutrino masses and mixing

Abstract

A model for neutrino masses and mixing is presented using the see-saw mechanism. The model combines Type -I and Type-II see-saw contributions of which the latter dominates. The scalars and the leptons in the model are assigned A4 charges suitable to obtain the mass matrices required for the scheme. The Type -II see-saw accommodates atmospheric mass splitting and maximal mixing in the atmospheric sector (θ 23 = π/4). It is characterized by vanishing solar mass splitting and θ 13 whereas the third neutrino mixing angle can acquire any value, θ 0 12 . Particular alternatives of θ 0 12 viz. θ 0 12 = 35.3 • (tribimaximal), 45.0 • (bimaximal), 31.7 • (golden ratio) are accounted for. Another choice of θ 0 12 = 0 • (no solar mixing) is also considered. Incorporating the corrections provided by the subdominant Type-I see-saw involves degenerate perturbation theory due to vanishing solar splitting in the Type -II see-saw enabling the solar mixing angle to receive substantial corrections. Apart from amending the solar sector the Type-I see-saw also tunes all the neutrino oscillation parameters into the allowed ranges thus interrelating them all. Thus the model is testable in the light of future experimental data. As an example, θ 23 emerges in the first (second) octant for normal (inverted) ordering. CP-violation is controlled by phases present in the right-handed Majorana neutrino mass matrix, M νR . Only normal ordering is allowed if these phases are absent. If M νR is complex the Dirac CP-violating phase δ, can be large, i.e., ∼ ±π/2, and inverted ordering is also allowed. T2K and NOVA preliminary data favouring normal ordering and δ ∼ −π/2 predicts lightest neutrino mass to be 0.05 eV or more within the model framework. 1 Earlier attempts on neutrino mass models with some oscillation parameters much smaller than the others can be located in [4].

Using A4 to Ameliorate Popular Lepton Mixings: A Model for Realistic Neutrino Masses and Mixing Based on Seesaw

“…For detailed discussion of A4, see [1,6,7]. The particle spectrum of the model with their respective quantum numbers are shown in Tables 73.1 and 73.2.…”

“…The particle spectrum of the model with their respective quantum numbers are shown in Tables 73.1 and 73.2. An extensive study of the scalar potential arising out of the scalars in Table 73.2 can be found in the appendix of [1]. The SU (2) L × U (1) Y conserving Lagrangian that preserves A4 symmetry is given by…”

“…We call this basis as the flavour basis. For structures of all the mass matrices in flavour basis see [1].…”

“…This talk is based on [1]. A model with two-component Lagrangian formalism based on Type-I and Type-II seesaw mechanism is proposed for tree-level generation of realistic neutrino masses and mixing using the discrete flavour symmetry A4 in [1]. The Type-II seesaw is the dominant contribution, Type-I seesaw is the sub-dominant contribution.…”

Scotogenic S3 symmetric generation of realistic neutrino mixing

“…The popular mixings were amended at tree-level using a two-component Lagrangian with discrete symmetries A4, S3 in [10,11]. In these models, type II see-saw yielded the dominant component that gave the popular mixing, corrections to which were offered by type I see-saw sub-dominant component.…”