Constraints from Ly-\(\alpha\) forests on non-thermal dark matter including resonantly-produced sterile neutrinos

Abstract

We use the BOSS DR9 quasar spectra to constrain non-thermal dark matter models: cold-plus-warm dark matter and sterile neutrinos resonantly produced in the presence of a lepton asymmetry. We establish constraints on the warm thermal relic mass \(m_{x}\) and its relative abundance \(F_{wdm}=\Omega_{wdm}/\Omega_{dm}\) using a suite of cosmological hydrodynamical simulations in 28 C+WDM configurations. The 2D bounds in the \(m_{x} - F_{wdm}\) parameter space approximately follow \(F_{\rm{wdm}} \sim 0.243 (\rm{keV}/m_x)^{-1.31}\). At 95% C.L., our limits from BOSS data alone imply that \(m_{x}> 2.5\) keV if \(F_{\rm{wdm}}>80\%\), while masses as low as 0.7 keV are consistent with the data if \(F_{\rm{wdm}}<15\%\) of the total dark matter density. We also constrain sterile neutrino mass and mixing angle by further producing the non-linear flux power spectrum of 8 RPSN models, where the input linear power spectrum is computed directly from the particles distribution functions. We find values of lepton asymmetries for which sterile neutrinos as light as 6 keV (resp. 3.5 keV) are consistent with BOSS at \(2\sigma\) (resp. \(3\sigma\)). These limits tighten by close to a factor of 2 for values of lepton asymmetries departing from those yielding the coolest distribution functions. Our bounds can be strengthened if we include higher-resolution data (XQ-100, HIRES MIKE). At these scales, however, the flux power spectrum exhibits a suppression compatible with the one expected from WDM. We do not investigate the mechanism responsible for this suppression, but we show how much our bounds would strengthen under the assumption that it is caused by the evolution of the IGM temperature. A 7 keV neutrino produced in a lepton asymmetry \(\mathcal{L} = |n_{\nu_e} - n_{\bar{\nu}_e}|/s = 8 \times 10^{-6}\) is consistent at \(1.9\sigma\) with BOSS data, and not necessarily excluded by our higher-resolution bounds.