Constraining neutrino physics with big bang nucleosynthesis and cosmic microwave background radiation

We perform a likelihood analysis of the recent results on the anisotropy of cosmic microwave background radiation from the BOOMERanG and DASI experiments to show that they single out an effective number of neutrinos in good agreement with standard big bang nucleosynthesis. We also consider degenerate big bang nucleosynthesis to provide new bounds on effective relativistic degrees of freedom N_ and, in particular, on the neutrino chemical potential _. When including supernova type Ia data we find, at 2, N_<~7 and -0. 01<~₄<~0. 22, |, |<~2. 6.