Standard and non-standard primordial neutrinos

The standard cosmological model predicts the existence of a cosmic neutrino background (C nu B) with a present density of about n(nu) + n((nu) over right arrow) similar or equal to 110 cm(-3) 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 C nu B 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 C nu B are also briefly discussed.