Gianpiero Mangano, Gennaro Miele, Sergio Pastor, Ofelia Pisanti, Srdjan Sarikas
We discuss the bounds on the cosmological lepton number from Big Bang
Nucleosynthesis (BBN), in light of recent evidences for a large value of the
neutrino mixing angle theta13. The largest asymmetries for electron and muon or
tau neutrinos compatible with 4He and 2H primordial yields are computed versus
the neutrino mass hierarchy and mixing angles. The flavour oscillation dynamics
is traced till the beginning of BBN and neutrino distributions after decoupling
are numerically computed. The latter contains in general, non thermal
distortion due to the onset of flavour oscillations driven by solar squared
mass difference in the temperature range where neutrino scatterings become
inefficient to enforce thermodynamical equilibrium. Depending on the value of
theta13, this translates into a larger value for the effective number of
neutrinos, N_eff. Upper bounds on this parameter are discussed for both
neutrino mass hierarchies. Values for N_eff which are large enough to be
detectable by the Planck experiment are found only for the (presently
disfavoured) range sin^2(theta13)<0.01.
View original:
http://arxiv.org/abs/1110.4335
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