Five models for lepton mixing

Abstract

We produce five flavour models for the lepton sector. All five models fit perfectly well — at the 1σ level — the existing data on the neutrino mass-squared differences and on the lepton mixing angles. The models are based on the type I seesaw mechanism, on a ${{\mathbb{Z}}_2}$ symmetry for each lepton flavour, and either on a (spontaneously broken) symmetry under the interchange of two lepton flavours or on a (spontaneously broken) CP symmetry incorporating that interchange — or on both symmetries simultaneously. Each model makes definite predictions both for the scale of the neutrino masses and for the phase δ in lepton mixing; the fifth model also predicts a correlation between the lepton mixing angles θ ₁₂ and θ ₂₃.