Sterile neutrinos: Cosmology versus short-baseline experiments

Abstract

Cosmology and short baseline neutrino oscillation data both hint at the existence of light sterile neutrinos with masses in the 1 eV range. Here we perform a detailed analysis of the sterile neutrino scenario using both cosmological and SBL data. We have additionally considered the possibility that the extra neutrino degrees of freedom are not fully thermalised in the early universe. Even when analyzing only cosmological data we find a preference for the existence of massive sterile neutrinos in both (3+1) and (3+2) scenarios, and with the inclusion of SBL data the evidence is formally at the 3.3σ level in the case of a (3+1) model. Interestingly, cosmological and SBL data both point to the same mass scale of approximately 1 eV. In the (3+1) framework WMAP9+SPT provide a value of the sterile mass eigenstate m4 = (1.72 ± 0.65) eV: this result is strenghtened by adding the prior from SBL posterior to m4 = (1.27 ± 0.12) eV (m4 = (1.23 ± 0.13) eV when SDSS is also considered in the cosmological analysis). In the (3+2) scheme, two additional, non-fully thermalized, neutrinos are compatible with the whole set of cosmological and SBL data, leading to mass values of m4 = (0.95 ± 0.30) eV and m5 = (1.59 ± 0.49) eV. The inclusion of Planck data does not change our considerations about the mass scale; concerning the extra neutrino degrees of freedom, invoking a partial thermalisation the 3+1 model is still consistent with the latest data.

Light sterile neutrinos

“…15 This behavior has been explained in Ref. [215]. It was found also in the analysis presented in Ref.…”

“…The authors of Refs. [188,215,291,328,329] performed combined fits of cosmological data and short-baseline (SBL) oscillation data in the framework of light sterile neutrino models. The general result is that the sterile neutrino mass is constrained at the scale of 1 eV by short-baseline oscillation data and the full thermalization of the sterile neutrinos in the early Universe is disfavored by cosmological data.…”

Light sterile neutrinos in cosmology and short-baseline oscillation experiments

“…Following Refs. [40][41][42], we use the posterior distribution of m s m 4 ∆m 2 41 obtained from the analysis of SBL data as a prior in the CosmoMC analysis of cosmological data. The range of m s allowed by the analysis of SBL data [30] is shown in Fig.…”

“…In this paper we adopt a phenomenological approach similar to that in Refs. [40][41][42]: we use the results of the fit of SBL neutrino oscillation data as a prior for the analysis of cosmological data. In this way, in Section III we derive the combined constraints on N eff and m eff s and the related constraints on H 0 and m s .…”

How Self-Interactions can Reconcile Sterile Neutrinos with Cosmology

“…[5]) because the suppression of structure formation is too strong (see [6][7][8] for a detailed discussion). The problem is that the masses and mixing angles preferred by terrestrial data inevitably leads to almost complete thermalization of sterile neutrinos.…”