WMAP five-year constraints on lepton asymmetry and radiation energy density: implications for Planck
- ISS Institute for Space Sciences Bucharest-Magurele, Ro-077125 (Romania)
In this paper we set bounds on the radiation content of the Universe and neutrino properties by using the WMAP (Wilkinson microwave anisotropy probe) five-year CMB (cosmic microwave background) measurements complemented with most of the existing CMB and LSS (large scale structure) data (WMAP5+All), imposing also self-consistent BBN (big bang nucleosynthesis) constraints on the primordial helium abundance. We consider lepton asymmetric cosmological models parametrized by the neutrino degeneracy parameter {xi}{sub {nu}} and the variation of the relativistic degrees of freedom, {Delta}N{sub eff}{sup oth}, due to possible other physical processes occurring between BBN and structure formation epochs. We get a mean value of the effective number of relativistic neutrino species of N{sub eff} = 2.98 {sub 2.27}{sup 3.60} {sub 1.65}{sup 4.37}, providing an important improvement over the similar result obtained from WMAP5+BAO+SN+HST (BAO: baryonic acoustic oscillations; SN: supernovae; HST: Hubble Space Telescope) data (Komatsu et al (WMAP Collaboration), 2008 Astrophys. J. Suppl. submitted [0803.0547]). We also find a strong correlation between {Omega}{sub m}h{sup 2} and z{sub eq}, showing that we observe N{sub eff} mainly via the effect of z{sub eq}, rather than via neutrino anisotropic stress as claimed by the WMAP team (Komatsu et al (WMAP Collaboration), 2008 Astrophys. J. Suppl. submitted [0803.0547]). WMAP5+All data provide a strong bound on the helium mass fraction of Y{sub p} = 0.2486 {+-} 0.0085 (68% CL), that rivals the bound on Y{sub p} obtained from the conservative analysis of the present data on helium abundance. For the neutrino degeneracy parameter we find a bound of -0.216{<=}{xi}{sub {nu}}{<=}0.226 (68% CL), which represents an important improvement over the similar result obtained by using the WMAP three-year data. The inclusion in the analysis of LSS data reduces the upper limit of the neutrino mass to m{sub {nu}}<0.46 eV (95% CL) with respect to the values obtained from the analysis from WMAP5-only data (Dunkley et al (WMAP Collaboration), 2008 Astrophys. J. Suppl. submitted [0803.0586]) and WMAP5+BAO+SN+HST data (Komatsu et al (WMAP Collaboration), 2008 Astrophys. J. Suppl. submitted [0803.0547]). We forecast that the CMB temperature and polarization measurements observed with high angular resolutions and sensitivities by the future Planck satellite will reduce the errors on {xi}{sub {nu}} and Y{sub p} down to {sigma}({xi}{sub {nu}}){approx_equal}0.089 (68% CL) and {sigma}(Y{sub p}) = 0.013 (68% CL) respectively, values fully consistent with the BBN bounds on these parameters. This work has been done on behalf of Planck-LFI (low frequency instrument) activities.
- OSTI ID:
- 22156665
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2008, Issue 06; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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