Reconciling sterile neutrinos with big bang nucleosynthesis

TL;DR

The big bang nucleosynthesis bounds on the mixing of neutrinos with sterile species are reexamine and it is shown that for for {ital L}{sub {nu}} large enough (greater than about 10{sup {endash}5}) the standard BBN bounds do not apply.

Abstract

We re-examine 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 $L_ν > 7 \times 10^{-5}$ it is consistent with BBN. The BBN bounds on sterile neutrinos mixing with electron neutrinos can also be weakened considerably.