The Sterile Neutrino: First Hint of 4th Generation Fermions?

In this letter, we introduce the ``flipped see-saw mechanism'', a new type of see-saw mechanism with 4th-generation neutrinos. This mechanism naturally explains the light sterile neutrino which is needed to account for all neutrino oscillation data. At the same time it predicts that another Majorona neutrino should exist with mass of the electro-weak scale. We comment on some implications of this scenario on the oblique parameters used to parameterize precision electroweak measurements as well as on future experiments.