Constraints from Ly-α forests on non-thermal dark matter including resonantly-produced sterile neutrinos

Abstract

We use BOSS DR9 quasars to constrain 2 cases of dark matter models:\ncold-plus-warm (C+WDM) where the warm component is a thermal relic, and sterile\nneutrinos resonantly produced in the presence of a lepton asymmetry (RPSN). We\nestablish constraints on the relic mass m_x and its relative abundance\n$F=\\Omega_{wdm}/\\Omega_{dm}$ using a suite of hydrodynamical simulations in 28\nC+WDM configurations. We find that the 3 sigma bounds approximately follow F ~\n$0.35 (keV/m_x)^{-1.37}$ from BOSS alone. We also establish constraints on\nsterile neutrino mass and mixing angle by producing the non-linear flux power\nspectrum of 8 RPSN models, where the input linear power spectrum is computed\ndirectly from the particles distribution functions. We find values of lepton\nasymmetries for which sterile neutrinos as light as 6.5 keV (resp. 3.5 keV) are\nconsistent with BOSS at the 2 sigma (resp. 3sigma) level. These limits tighten\nby close to a factor of 2 for lepton asymmetries departing from those yielding\nthe coolest distribution functions.\n Our Ly-a forest bounds can be strengthened if we include higher-resolution\ndata from XQ-100, HIRES and MIKE. At these smaller scales, the flux power\nspectrum exhibits a suppression that can be due to Doppler broadening, IGM\npressure smoothing or free-streaming of WDM particles. In the current work, we\nshow that if one extrapolates temperatures from lower redshifts via broken\npower laws in T_0 and gamma, then our 3 sigma C+WDM bounds strengthen to F~\n$0.20 (keV/m_x)^{-1.37}$, and the lightest RPSN consistent with our extended\ndata set have masses of 7.0 keV at the 3 sigma level. Using dedicated\nhydrodynamical simulations, we show that a 7 keV sterile neutrino produced in a\nlepton asymmetry $L = 8 \\times 10^{-6}$ is consistent at 1.9 sigma (resp. 3.1\nsigma) with BOSS (resp. BOSS + higher-resolution), for the thermal history\nmodels tested in this work.\n