2015/08/31 by Soumita Pramanick, Amitava Raychaudhuri
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Neutrino Physics Research #Particle physics theoretical and experimental studies #hep-ex #hep-ph
paper · pdf · doi:10.1103/physrevd.93.033007
published as Phys. Rev. D 93, 033007 (2016) · v2: 23 pages, 3 figures, Appendix on scalar potential minimization added, Matches with the published version
openalex publication_date 2016/02/16 · arxiv created 2016/03/03 · arxiv updated 2016/03/04 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We present an A4-based model where neutrino masses arise from a combination of see-saw mechanisms. The model is motivated by several small mixing and mass parameters indicated by the data. These are θ13, the solar mass splitting, and the small deviation of θ23 from maximal mixing (= π/4). We take the above as indications that at some level the small quantities are well-approximated by zero. In particular the mixing angles, to a zero order, should be either 0 or π/4. Accordingly, in this model the Type-II see-saw dominates and generates the larger atmospheric mass splitting and sets θ23 = π/4. The other mixing angles are vanishing as is the solar splitting. We show how the A4 assignment for the lepton doublets leads to this form. We also specify the A4 properties of the right-handed neutrinos which result in a smaller Type-I see-saw contribution that acts as a perturbation and shifts the angles θ12 and θ13 into the correct range and the desired value of Δm2solar is produced. The A4 symmetry results in relationships between these quantities as well as with a small deviation of θ23 from π/4. If the right-handed neutrino mass matrix, MR, is chosen real then there is no leptonic CP-violation and only Normal Ordering is admissible. If MR is complex then Inverted Ordering is also allowed with the proviso that the CP-phase, δ, is large, i.e., ∼ π/2 or -π/2. The preliminary results from NOνA favouring Normal Ordering and δ near -π/2 imply quasi-degenerate neutrino masses in this model.