Precision Detection of the Cosmic Neutrino Background

In the standard big bang cosmology the canonical value for the ratio of relic neutrinos to cosmic microwave background (CMB) photons is 9/11. Within the framework of the standard model of particle physics there are small corrections, in sum about $1\%$, due to slight heating of neutrinos by electron-positron annihilations and finite-temperature QED effects. We show that this leads to changes in the predicted CMB anisotropies that will bias determination of the other cosmological parameters if not correctly taken into account. These changes might be detected by future satellite experiments.