keV scale νR dark matter and its detection in β decay experiments

We study dark matter (DM) in the model with one keV scale right-handed neutrino nu(R1) and two GeV scale right-handed neutrinos nu(R2,3), the nu SM. We find that one of the GeV scale right-handed neutrinos can have a much longer lifetime than the other when two GeV scale right-handed neutrinos are degenerate. We show that the mass and mixing of light neutrinos can be explained in this case. Significant entropy release can be generated in a reheating produced by the decay of one of the GeV scale nu(R). The density of nu(R1) DM can be diluted by 2 orders of magnitude, and the mixing of nu(R1) with active neutrinos is allowed to be much larger, reaching the bound from x-ray observation. This mixing can lead to a sizable rate of nu(R1) capture by radioactive nuclei. The nu(R1) capture events are mono-energetic electrons with keV scale energy away from the beta decay spectrum. This is a new way to detect DM in the Universe.