WMAP 5-year constraints on lepton asymmetry and radiation energy density: Implications for Planck

In this paper we set bounds on the radiation content of the Universe and neutrino properties by using the WMAP-5 year CMB measurements complemented with most of the existing CMB and LSS data (WMAP5+All), imposing also self-consistent BBN constraints on the primordial helium abundance. We consider lepton asymmetric cosmological models parametrized by the neutrino degeneracy parameter ξν and the variation of the relativistic degrees of freedom, ∆N eff , due to possible other physical processes occurred between BBN and structure formation epochs. We get a mean value of the effective number of relativistic neutrino species of Neff = 3.256 +0.103 −0.323 (68% CL), bringing an important improvement over the similar result obtained from WMAP5+BAO+SN+HST data [56]. We also find a strong correlation between Ωmh 2 and zeq, showing that we observe Neff mainly via the effect of zeq, rather than via neutrino anisotropic stress as claimed by the WMAP team [56]. WMAP5+All data provides also strong bounds on helium mass fraction and neutrino degeneracy parameter that rivals the similar bounds obtained from the conservative analysis of the present data on helium abundance. The inclusion in the analysis of LSS data reduces significantly the upper limit of the neutrino mass to mν < 0.453 eV (95% CL) with respect to the values obtained from the analysis from WMAP5-only data [55] and WMAP5+BAO+SN+HST data [56]. We forecast that the CMB temperature and polarization measurements observed with high angular resolutions and sensitivities by the future Planck satellite will reduces the errors on ξν and Yp down to σ(ξν ) ≃ 0.04 (68% CL) and σ(Yp) = 0.0112 (68% CL) respectively, values fully consistent with the BBN bounds on these parameters. This work has been done on behalf of Planck-LFI activities. PACS numbers: CMBR theory, dark matter, cosmological neutrinos, big bang nucleosynthesis WMAP 5-year constraints on lepton asymmetry and radiation energy density: Implications for Planck2