We discuss the possibility of enforcing a massless Majorana neutrino in the direct and semi-direct approaches to lepton mixing, in which the PMNS matrix is partly predicted by subgroups of a discrete family symmetry, extending previous group searches up to order 1535. We find a phenomenologically viable scheme for the semi-direct approach based on Q(648) which contains ∆(27) and the quaternion group as subgroups. This leads to novel predictions for the first column of the PMNS matrix corresponding to a normal neutrino mass hierarchy with m 1 = 0, and sum rules for the mixing angles and phase which are characterised by the solar angle being on the low side θ 12 ̃ 31° and the Dirac (oscillation) CP phase δ being either about ±45° or ±π.
Journal of High Energy Physics
- Pub Date:
- June 2016
- Global Symmetries;
- Neutrino Physics;
- High Energy Physics - Phenomenology
- 18 pages, 1 figure, small comments added in introduction and section 3, one reference added, version matches publication in JHEP