Reconciling Sterile Neutrinos with Big Bang Nucleosynthesis

We reexamine the big bang nucleosynthesis (BBN) bounds on the mixing of neutrinos with sterile species. These bounds depend on the assumption that the relic neutrino asymmetry L_ν is very small. We show that for L_ν large enough (greater than about 10^-5) the standard BBN bounds do not apply. We apply this result to the sterile neutrino solution to the atmospheric neutrino anomaly and show that for L_ν>7×10^-5 it is consistent with BBN. The BBN bounds on sterile neutrinos mixing with electron neutrinos can also be weakened considerably.