Light Sterile Neutrino in the Minimal Extended Seesaw

TL;DR

This paper proposes a minimal extension to the type-I seesaw model by adding a singlet fermion, naturally producing an eV-scale sterile neutrino with significant active-sterile mixing, and demonstrates a flavor model realization.

Contribution

It introduces a minimal extended seesaw model that naturally generates an eV-scale sterile neutrino without fine-tuning, including a concrete flavor symmetry implementation.

Findings

Predicts active-sterile mixing of about 0.1

Provides a flavor A_4 model realization

Discusses potential for keV sterile neutrino dark matter

Abstract

Motivated by the recent observations on sterile neutrinos, we present a minimal extension of the canonical type-I seesaw by adding one extra singlet fermion. After the decoupling of right-handed neutrinos, an eV-scale mass eigenstate is obtained without the need of artificially inserting tiny mass scales or Yukawa couplings for sterile neutrinos. In particular, the active-sterile mixing is predicted to be of the order of 0.1. Moreover, we show a concrete flavor A_4 model, in which the required structures of the minimal extended seesaw are realized. We also comment on the feasibility of accommodating a keV sterile neutrino as an attractive candidate for warm dark matter.