A higher-dimensional origin of the inverted mass hierarchy for neutrinos

We present successful lepton mass matrices with an inverted mass hierarchy for neutrinos, which follow from a geometrical structure of a (1+5)-dimensional space-time where two extra dimensions are compactified on the T2/Z3 orbifold. A 5∗ and a right-handed neutrino N in each family are localized on each of the equivalent three fixed points of the orbifold while three 10's and Higgs doublets Hu and Hd live in the bulk. An S3 family symmetry is assumed on three 5∗'s and on three N's, since the three fixed points are equivalent to one another. The Higgs field ϕ responsible for the B-L breaking is localized on one of the three fixed points, which generates the inverted hierarchy for the neutrino masses. The baryon asymmetry is well explained in the non-thermal leptogenesis via inflaton decay. We emphasize that the present model predicts the effective neutrino mass, 〈m〉ee, responsible for neutrinoless double beta decays as 〈m〉ee≃50meV. This will be accessible to future experiments.