Soft L_e-L_mu-L_tau flavour symmetry breaking and sterile neutrino keV Dark Matter

TL;DR

This paper presents a model where a softly broken $L_e-L_-L_ au$ flavour symmetry explains active neutrino properties and predicts keV sterile neutrinos as Warm Dark Matter, with testable neutrino mass spectrum.

Contribution

It introduces the first model applying flavour symmetries to both active and sterile neutrinos to simultaneously explain neutrino properties and Dark Matter.

Findings

Predicts vanishing 13 and maximal 23 mixing angles.

Predicts an exact neutrino mass spectrum.

Identifies a keV sterile neutrino as Dark Matter candidate.

Abstract

We discuss how a $L_e-L_\mu-L_\tau$ flavour symmetry that is softly broken leads to keV sterile neutrinos, which are a prime candidate for Warm Dark Matter. This is to our knowledge the first model where flavour symmetries are applied simultaneously to active and sterile neutrinos explaining at the same time active neutrino properties and this peculiar Dark Matter scenario. The essential point is that different scales of the symmetry breaking and the symmetry preserving entries in the mass matrix lead to one right-handed neutrino which is nearly massless compared to the other two. Furthermore, we naturally predict vanishing $\theta_{13}$ and maximal $\theta_{23}$, while the correct value of $\theta_{12}$ must come from the mixing of the charged leptons. We can furthermore predict an exact mass spectrum for the light neutrinos, which will be testable in the very near future.