Constraining the cosmic radiation density due to lepton number with BBN

We discuss the bounds on the cosmological lepton number from Big Bang Nucleosynthesis (BBN), in light of recent evidences for a non-zero value of the neutrino mixing angle theta(13) (sin(2) theta(13) greater than or similar to 0.005 at 2 sigma). We compute the largest possible neutrino asymmetries per flavour compatible with He-4 and H-2 primordial yields versus the neutrino mass hierarchy and mixing angles, tracing completely the neutrino oscillation dynamics through decoupling and BBN. The interplay between flavour oscillations and scatterings, in general, leads to non-thermal distortions of the neutrino spectra, depending on theta(13), increasing the final value for the effective number of neutrinos N-eff. Values for N-eff from neutrino asymmetries which are large enough to be detectable with Planck data are found only for the range sin(2) theta(13) <= 0.01.