Although the MiniBooNE experiment has severely restricted the possible existence of light sterile neutrinos , a few anomalies persist in oscillation data , and the possibility of extra light species contributing as a subdominant hot ( or warm ) component is still interesting .
In many models , this species would be in thermal equilibrium in the early universe and share the same temperature as active neutrinos , but this is not necessarily the case .
In this work , we fit up-to-date cosmological data with an extended \Lambda CDM model , including light relics with a mass typically in the range 0.1–10 eV .
We provide , first , some nearly model-independent constraints on their current density and velocity dispersion , and second , some constraints on their mass , assuming that they consist either in early decoupled thermal relics , or in non-resonantly produced sterile neutrinos .
Our results can be used for constraining most particle-physics-motivated models with three active neutrinos and one extra light species .
For instance , we find that at the 3 \sigma confidence level , a sterile neutrino with mass m _ { s } = 2 eV can be accommodated with the data provided that it is thermally distributed with T _ { s } / T _ { \nu } ^ { id } \lesssim 0.8 , or non-resonantly produced with \Delta N _ { \text { eff } } \lesssim 0.5 .
The bounds become dramatically tighter when the mass increases .
For m _ { s } \lesssim 0.9 eV and at the same confidence level , the data is still compatible with a standard thermalized neutrino .