New constraints on neutrino physics from BOOMERANG data

We have performed a likelihood analysis of the recent data on the cosmic microwave background radiation anisotropy from the BOOMERANG experiment. These data place a strong upper bound on the radiation density present at recombination. Expressed in terms of the equivalent number of neutrino species the 2 sigma bound is N-nu less than or equal to 13. This bound is not flavor sensitive. It also applies to the Universe at a much later epoch, and as such places severe limits on scenarios with decaying neutrinos. The bound also yields a firm upper limit on the lepton asymmetry in the Universe.