Standard and non-standard primordial neutrinos

The standard cosmological model predicts the existence of a cosmic neutrino background (CνB) with a present density of about per flavour, which affects big-bang nucleosynthesis (BBN), cosmic microwave background (CMB) anisotropies, and the evolution of large scale structures (LSS). We report on a precision calculation of the CνB properties including the modification introduced by neutrino oscillations. The role of a possible neutrino–antineutrino asymmetry and the impact of non-standard neutrino–electron interactions on the CνB are also briefly discussed.