  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.

High Energy Physics - Phenomenology