Abstract :
If right-handed neutrinos are not singlets under the electroweak gauge group as it was proposed in a recent model, they can acquire electroweak scale masses and are thus accessible experimentally in the near future. When this idea is combined with quark–lepton unification à la Pati–Salam, one is forced to introduce new neutral particles which are singlets under the Standard Model (SM). These “sterile neutrinos” which exist in both helicities and which are different in nature from the popular particles with the same name can have their own seesaw with masses in the keV range for the lighter of the two eigenstates. The keV sterile neutrinos have been discussed in the literature as warm dark matter candidates with wide ranging astrophysical consequences such as structure formation, supernova asymmetries, pulsar kicks, etc. In addition, the model contains W-like and Z-like heavy gauge bosons which might be accessible at the LHC or the ILC. An argument is presented on why, in this model, it is natural to have four families which can obey existing constraints.
