We present constraints on the mass of warm dark matter (WDM) particles from a
combined analysis of the matter power spectrum inferred from the Sloan Digital
Sky Survey \lya flux power spectrum at 2.2<z<4.2, cosmic microwave background
data, and the galaxy power spectrum. We obtain a lower limit of m~10 keV (2
sigma) if the WDM consists of sterile neutrinos and m~2 keV (2 sigma) for early
decoupled thermal relics. If we combine this bound with the constraint derived
from x-ray flux observations in the Coma cluster, we find that the allowed
sterile neutrino mass is ~10 keV (in the standard production scenario). Adding
constraints based on x-ray fluxes from the Andromeda galaxy, we find that dark
matter particles cannot be sterile neutrinos, unless they are produced by a
nonstandard mechanism (resonant oscillations, coupling with the inflaton) or
get diluted by some large entropy release.Comment: 4 pages, 3 figures, matches published versio