KeVins and GeVins
One possible WDM candidate particle with a mass of a few keV comes from introducing two new, zero charge, zero lepton number fermions to the Standard Model of Particle Physics: "keV-mass inert particles" (keVins) and "GeV-mass inert particles" (GeVins). keVins are thermally overproduced, though the entropy production from the decays of unstable GeVins suppresses their abundance to the correct value. These particles are considered "inert" because they only have suppressed interactions with the Z boson. Sterile neutrinos with masses of a few keV are possible candidates for keVins. The sterility of such neutrinos would allow them to have masses of about 1 keV.
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