Constraining the window on sterile neutrinos as warm dark matter

Sterile neutrinos may be one of the best warm dark matter candidates we have today. Both lower and upper bounds on the mass of the sterile neutrino come from astronomical observations. We show that the proper inclusion of the neutrino momentum distribution reduces the allowed region to be 2.6 keV<5 keV for the simplest models. A search for a spectral line with E = m/2 is thus more interesting than ever before.