Can sterile neutrinos be the dark matter?

TL;DR

The Ly-alpha forest power spectrum measured by the Sloan Digital Sky Survey and high-resolution spectroscopy observations are used in combination with cosmic microwave background and galaxy clustering constraints to place limits on a sterile neutrino as a dark matter candidate in the warm dark matter scenario.

Abstract

We use the Ly-alpha forest power spectrum measured by the SDSS and high-resolution spectroscopy observations in combination with cosmic microwave background and galaxy clustering constraints to place limits on a sterile neutrino as a dark matter candidate in the warm dark matter (WDM) scenario. Such a neutrino would be created in the early universe through mixing with an active neutrino and would suppress structure on scales smaller than its free streaming scale. We ran a series of high-resolution hydrodynamic simulations with varying neutrino mass to describe the effect of a sterile neutrino on the Ly-alpha forest power spectrum. We find that the mass limit is m_s >14 keV at 95% c.l. (10keV at 99.9%), which is nearly an order of magnitude tighter constraint than previously published limits and is above the upper limit allowed by X-ray constraints, excluding this candidate as dark matter in this model. The corresponding limit for a neutrino that decoupled early while in thermal equilibrium is 2.5keV (95% c.l.).

Figures (2)

• Figure 1: Ratio of WDM power spectrum relative to CDM shown over the relevant observational range. From left to right the sterile neutrino masses are 6.5keV, 10keV, 14keV and 20keV. Top left corner shows 1d linear power spectrum, while the other 3 panels show the ratios from hydrodynamic simulations at redshifts 2, 3 and 4. We used concordance cosmology with $\Omega_{m}=0.28$ and $H_0=71{\rm km/s/Mpc}$. Dashed vertical line shows the upper limit on $k$ for SDSS data.
• Figure 2: To the left are the observed SDSS Ly$\alpha$ forest flux power spectra as a function of redshift from 2.2 (bottom) to 4.2 (top) in steps of 0.2. To the right are the power spectra from the high resolution data compiled at redshifts 2.4, 3.0 and 3.9. For each redshift the thick lines are from the best fitted CDM model, while the (generally lower at high k) thin lines are for the corresponding WDM model with 6.5keV sterile neutrino. The latter is discrepant with both SDSS and high resolution data, with most of the distinguishing power coming from higher redshifts.