In light of recent findings which seem to disfavor a scenario with ( warm ) dark matter entirely constituted of sterile neutrinos produced via the Dodelson-Widrow ( DW ) mechanism , we investigate the constraints attainable for this mechanism by relaxing the usual hypothesis that the relic neutrino abundance must necessarily account for all of the dark matter .
We first study how to reinterpret the limits attainable from X-ray non-detection and Lyman- \alpha forest measurements in the case that sterile neutrinos constitute only a fraction f _ { s } of the total amount of dark matter .
Then , assuming that sterile neutrinos are generated in the early universe solely through the DW mechanism , we show how the X-ray and Lyman- \alpha results jointly constrain the mass-mixing parameters governing their production .
Furthermore , we show how the same data allow us to set a robust upper limit f _ { s } \lesssim 0.7 at the 2 \sigma level , rejecting the case of dominant dark matter ( f _ { s } = 1 ) at the \sim 3 \sigma level .