Recently it has been reported that there may be a discrepancy between big bang nucleosynthesis theory and observations ( BBN crisis ) .
We show that BBN predictions agree with the primordial abundances of light elements , ^ { 4 } He , D , ^ { 3 } He and ^ { 7 } Li inferred from the observational data if the electron neutrino has a net chemical potential \xi _ { \nu _ { e } } due to lepton asymmetry .
We estimate that \xi _ { \nu _ { e } } = 0.043 ^ { +0.040 } _ { -0.040 } ( 95 \% C.L . )
and \Omega _ { b } h ^ { 2 } = 0.015 ^ { +0.006 } _ { -0.003 } ( 95 \% C.L .
) .