Can Sterile Neutrinos Be Ruled Out as Warm Dark Matter Candidates?

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 Lyman-$\alpha$ flux power spectrum at $2.2<z<4.2$, cosmic microwave background data, and the galaxy power spectrum. We obtain a lower limit of $m_{\mathrm{WDM}}\gtrsim 10\mathrm{keV}$ ($2\sigma$) if the WDM consists of sterile neutrinos and $m_{\mathrm{WDM}}\gtrsim 2\mathrm{keV}$ ($2\sigma$) for early decoupled thermal relics. If we combine this bound with the constraint derived from x-ray flux observations of the Coma cluster, we find that the allowed sterile neutrino mass is $\sim 10\mathrm{keV}$ (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 a large entropy release.

Figure 1

Two-dimensional marginalized likelihoods (68% and 95% confidence limits) for $n_s$, ${\sigma }_8$, ${\Omega }_m$, and the effective optical depth at $z=3$, using the SDSS data at $z\le 4.2$ (left, green), $z\le 3.6$ (middle, white), and $z\le 3.2$ (right, blue).

Figure 2

One-dimensional marginalized likelihoods for the parameter $(1\mathrm{keV})/m_s$ for the SDSS Lyman-$\alpha$ data for the redshift ranges $z\le 3.2$, 3.6, 3.8, and 4.2 and the Viel-Haehnelt-Springel (VHS) [26] data.

Figure 3

This plot summarizes some of the parameter space constraints (at the 95% C.L.) for the sterile neutrino models, assuming that they constitute the dark matter. Limits are explained in the text.