Grand Unification of the Sterile Neutrino

The simplest way to simultaneously understand all existing indications of neutrino oscillations from solar and atmospheric neutrino deficits and the LSND experiment, seems to be to postulate a sterile neutrino. We present a realistic grand unified model based on the gauge group $SO(10)\times SO(10)^\prime$ that leads to the desired masses and mixings for the sterile and the known neutrinos needed to understand the above observations while fitting those of the known charged fermions. The model is a grand unified realization of the recently proposed idea that the sterile neutrino is the lightest neutrino of a mirror sector of the universe which has identical matter and gauge content as the standard model. The two SO(10)'s operate on the two sectors in a mirror symmetric way and are connected by a mixed Higgs representations whose net effect is to connect the superheavy right handed neutrinos of the two sectors.