Sterile Neutrinos for Warm Dark Matter and the Reactor Anomaly in Flavor Symmetry Models

TL;DR

This paper develops a flavor symmetry model using the A_4 group to explain keV-scale warm dark matter and eV-scale sterile neutrinos, analyzing their mixing and stability within the seesaw mechanism.

Contribution

It introduces a novel A_4 flavor symmetry framework that accommodates both keV and eV sterile neutrinos with stable mixing properties and discusses the impact of higher-order corrections.

Findings

Sterile neutrinos can serve as warm dark matter and explain the reactor anomaly.

Mixing angles of active neutrinos receive significant corrections, while sterile-active mixing remains stable.

Higher-order effects influence neutrino mass and mixing, consistent with experimental constraints.

Abstract

We construct a flavor symmetry model based on the tetrahedral group A_4 in which the right-handed neutrinos from the seesaw mechanism can be both keV warm dark matter particles and eV-scale sterile neutrinos. This is achieved by giving the right-handed neutrinos appropriate charges under the same Froggatt-Nielsen symmetry responsible for the hierarchy of the charged lepton masses. We discuss the effect of next-to-leading order corrections to deviate the zeroth order tri-bimaximal mixing. Those corrections have two sources: (i) higher order seesaw terms, which are important when the seesaw particles are eV-scale, and (ii) higher-dimensional effective operators suppressed by additional powers of the cut-off scale of the theory. Whereas the mixing angles of the active neutrinos typically receive corrections of the same order, the mixing of the sterile neutrinos with the active ones is rather stable as it is connected with a hierarchy of mass scales. We also modify an effective A_4 model to incorporate keV-scale sterile neutrinos.