Warm Dark Matter from keVins

We propose a simple model for Warm Dark Matte (WDM) in which two femions are added to the Standard,Model: (quasi-) stable keVins (keV inert fermions) which account for WDM and their unstable brothers, the GeVins (GeV inert fermions), both of which carry zero electric charge and zero lepton number, and are (approximately) inert, in the sense that their only interactions are via suppressed couplings to the Z. We consider scenarios in which stable keVins are thermally produced and their abundance is subsequently diluted by entropy production from the decays of the heavier unstable GeVins. This mechanism could be implemented in a wide variety of models, including E-6 inspired supersymmetric models or models involving sterile neutrinos.