I'm currently working on a post on how the CP-violating term in the PMNS matrix is indirect evidence both for massive neutrinos and for a sterile neutrino.
In the mean time, I wanted to let readers of this blog know that you can read the following paper that was just recently published by Physical Review Letters, in which the author shows that a 7 keV sterile neutrino is an extremely plausible candidate for dark matter. The paper can also be found on the Arxiv website, where it was posted back on March 4th.
Their main results are summarized in Figure 1 of the paper. They suggest that recent observation of a 3.57 keV X-ray line can be explained by a 7.1 keV sterile neutrino with a mixing parameter of approximately 3*10^-11 (sin squared of two times the mixing angle to be precise.) This leads to predictions of the temperature at which the sterile neutrinos were produced.
I think that this is certainly interesting research, and the model works much better than ColdDarkMatter models. However, there are still a lot of assumptions in the model, and I would hesitant to make any firm statements about whether a sterile neutrinos have been discovered. There is clearly no discovery because the research is no where near "5sigma" certainty (like what has been required to claim discovery of new particles.)
The reason that I mentioned this article is that hopefully NSF, NASA and European equivalent agencies devote more time and effort to searching for WarmDarkMatter and Sterile Neutrinos.
(Sterile neutrinos can explain why ordinary neutrinos have mass and are intriguing candidates for dark matter. I'm still a little shocked that so much time/money/effort has gone into looking for GeV ColdDarkMatter. Unfortunately, this is likely all just a side-effect of the physics community irrational devotion to supersymmetry and superstring theory. It's good to see that the hype of supersymmetry, superstring theory, and ColdDarkMatter is finally being realized by the public at large.)