Recent indications from both particle physics and cosmology suggest the existence of more than three neutrino species .
In cosmological analyses the effects of neutrino mass and number of species can in principle be disentangled for fixed cosmological parameters .
However , since we do not have perfect measurements of the standard \Lambda Cold Dark Matter model parameters some correlation remains between the neutrino mass and number of species , and both parameters should be included in the analysis .
Combining the newest observations of several cosmological probes ( cosmic microwave background , large scale structure , expansion rate ) we obtain N _ { \mathrm { eff } } = 3.58 ^ { +0.15 } _ { -0.16 } ( 68 \% \mathrm { CL } ) ^ { +0.55 } _ { -0.53 } ( 95 \%% \mathrm { CL } ) and \sum m _ { \nu } < 0.60 \textrm { eV } ( 95 \% \mathrm { CL } ) , which are currently the strongest constraints on N _ { \mathrm { eff } } and \sum m _ { \nu } from an analysis including both parameters .
The preference for N _ { \mathrm { eff } } > 3 is now at a 2 \sigma level .