Increase in the primordial He-4 yield in the two-doublet four-neutrino mixing scheme - art. no. 093003

We assess the effects on big bang nucleosynthesis (BBN) of lepton number ge neration in the early universe resulting from the two-doublet four-neutrino mass-mixing scheme. It has been argued that this neutrino mass-mixing arra ngement gives the most viable fit to the existing data. We study full 4x4 m ixing matrices and show how possible symmetries in these can affect the BBN He-4 abundance yields. Though there is as yet no consensus on the reliabil ity of BBN calculations with neutrino flavor mixing, we show that, in the c ase where the sign of the lepton number asymmetry is unpredictable, BBN con siderations may pick out specific relationships between mixing angles. In p articular, reconciling the observed light element abundances with a <(<nu>) over bar>(mu)reversible arrow<(<nu>)over bar>(e) oscillation interpretation of LSND would allow unique new constraints on the neutrino mixing angles i n this model.