Constraints on the lepton asymmetry and radiation energy density: Implications for PLANCK
By using most of the present CMB and LSS measurements and the BBN constraints on the primordial helium abundance, Y_p, we set bounds on the radiation content of the Universe and neutrino properties. We consider lepton asymmetric cosmological models parametrized by the neutrino degeneracy parameter ξ_ν and the variation of the relativistic degrees of freedom, ΔN_{oth}^{eff}, due to possible other physical processes that occurred between BBN and structure formation epoch. We found that present CMB and LSS data constraints the neutrino degeneracy parameter at ξ_ν \leq 0.722, implying a lepton asymmetry of the neutrino background {\cal L}_ν \leq 0.614 (2-σ). We also found ΔN^{eff}_{oth}=0.572^{+1.972}_{-1.780}, the contribution to the effective number of relativistic neutrino species N^{eff}=3.058^{+1.971}_{-1.178} and a primordial helium abundance Y_p=0.249^{+0.014}_{-0.016} (2-σerrors). These results bring an important improvement over the similar ones obtained by using WMAP~1-year and older LSS data or the WMAP~3-year data alone and the standard primordial helium abundance value Y_p=0.24, relaxing the stringent BBN constraint on the neutrino degeneracy parameter (ξ_ν \leq 0.07). We forecast that the CMB temperature and polarization maps observed with high angular resolutions and sensitivity by the future Planck Mission will constraint the primordial primordial helium abundance at Y_p=0.247 \pm 0.002 (2-σerrors) in agreement with the most stringent limits on Y_p given by the BBN and the neutrino degeneracy parameter at ξ_ν \leq 0.280 (2-σ), not excluding the possibility of larger lepton asymmetry. This work has been done on behalf of Planck-LFI activities.