Realistic sterile neutrino dark matter with keV mass does not contradict cosmological bounds

TL;DR

This work presents a realistic extension of the standard model with three sterile neutrinos, consistent with neutrino oscillation data and baryogenesis, and shows that for each mass >or= 2 keV there exists at least one model accounting for 100% of DM.

Abstract

Previous fits of sterile neutrino dark matter models to cosmological data assumed a peculiar production mechanism, which is not representative of the best-motivated particle physics models given current data on neutrino oscillations. These analyses ruled out sterile neutrino masses smaller than 8-10 keV. Here we focus on sterile neutrinos produced resonantly. We show that their cosmological signature can be approximated by that of mixed Cold plus Warm Dark Matter (CWDM). We use recent results on LambdaCWDM models to show that for each mass greater than or equal to 2 keV, there exists at least one model of sterile neutrino accounting for the totality of dark matter, and consistent with Lyman-alpha and other cosmological data. Resonant production occurs in the framework of the nuMSM (the extension of the Standard Model with three right-handed neutrinos). The models we checked to be allowed correspond to parameter values consistent with neutrino oscillation data, baryogenesis and all other dark matter bounds.

Figures (4)

• Figure 1: Characteristic form of the RP sterile neutrino distribution function for $m_s^\textsc{rp} =3\:\mathrm{keV}$ and various values of the lepton asymmetry parameter $L_6$. The spectrum for $L_6=16$ (red solid line) is shown together with its resonant (dashed) and non-resonant (dashed-dotted) components. All these spectra have the same shape for $q\gtrsim 3$.
• Figure 2: TFs for the models M4L12 (top) and M3L16 (bottom), together with CWDM spectra for the same mass and $F_{\textsc{wdm}\xspace} \simeq 0.15$ or 0.2.
• Figure 3: 1 and 2-$\sigma$ bounds from WMAP5 and SDSS Ly-$\alpha$ data on $\Lambda$CWDM parameters. Red points correspond to approximations for the models M4L12, M3L16, M2L25. Results to the left of black vertical lines were already reported in Boyarsky:08c.
• Figure 4: Region of masses and mixing angles for RP sterile neutrinos consistent with existing constraints.