Lyman-alpha Forests cool Warm Dark Matter

TL;DR

This paper uses extensive Lyman-alpha forest data and advanced hydrodynamical simulations to set tight constraints on warm dark matter particle masses, significantly impacting sterile neutrino dark matter models.

Contribution

It provides the most stringent bounds to date on warm dark matter particle masses using Lyman-alpha forest data alone, refining previous limits and considering cosmological parameter variations.

Findings

Lower bounds on dark matter particle masses: >4.09 keV (thermal relics), >24.4 keV (sterile neutrinos).

Bounds are slightly relaxed when combined with Planck CMB data.

Results challenge non-resonant sterile neutrino dark matter models.

Abstract

The free-streaming of keV-scale particles impacts structure growth on scales that are probed by the Lyman-alpha forest of distant quasars. Using an unprecedentedly large sample of medium-resolution QSO spectra from the ninth data release of SDSS, along with a state-of-the-art set of hydrodynamical simulations to model the Lyman-alpha forest in the non-linear regime, we issue one of the tightest bounds to date, from Ly-$\alpha$ data alone, on pure dark matter particles : $m_X > 4.09 \: \rm{keV}$ (95% CL) for early decoupled thermal relics such as a hypothetical gravitino, and correspondingly $m_s > 24.4 \: \rm{keV}$ (95% CL) for a non-resonantly produced right-handed neutrino. This limit depends on the value on $n_s$, and Planck measures a higher value of $n_s$ than SDSS-III/BOSS. Our bounds thus change slightly when Ly-$\alpha$ data are combined with CMB data from Planck 2016. The limits shift to $m_X > 2.96 \: \rm{keV}$ (95% CL) and $m_s > 16.0 \: \rm{keV}$ (95% CL). Thanks to SDSS-III data featuring smaller uncertainties and covering a larger redshift range than SDSS-I data, our bounds confirm the most stringent results established by previous works and are further at odds with a purely non-resonantly produced sterile neutrino as dark matter.