Primordial Nucleosynthesis, Cosmic Microwave Background and Neutrinos

In this contribution we report on a combined analysis of the dependence of CMBR anisotropies and BBN on the energy fractions ΩBh 2 and Ωνh 2 = NνΩ 0 νh 2 for massless neutrinos (Nν standing for the effective neutrino number and Ωνh 2 for the energy contribution of a single ν− ν specie). This is aimed to test the standard and degenerate BBN scenario, using the recent results of the BOOMERanG [1] and MAXIMA-1 [2] CMBR experiments and the measurements of He, D and Li primordial abundances. The theoretical tools necessary to achieve this goal are nowadays rather robust. A new generation of BBN codes have been developed [3– 5], which give the He mass fraction Yp with a theoretical error of few per mille, this effort being justified in view of the small statistical error which is now quoted in the Yp measurements. On the other hand, the theoretical predictions on the CMBR anisotropies angular power spectrum have also recently reached a 1% level accuracy. An important new insight is represented by the recent results obtained by the BOOMERanG Collaboration [1]. For the first time, in fact, multifrequency maps of the microwave background anisotropies were realized over a significant part of the sky, with ∼ 10 resolution and high signal to noise ratio. In the last few years many results have been obtained on light element primordial abundances as well [6]. The He mass fraction Yp, has been measured with a 0.1% precision in two independent surveys, from regression to zero metallicity in Blue Compact Galaxies, giving a low value Y (l) p = 0.234±0.003, and a high one Y (h) p = 0.244±0.002, which are compatible at 2σ level only, may be due to large systematic errors. In our analysis [7] we adopted the more conservative value Yp = 0.238±0.005. A similar controversy holds in D measurements, where observations in different Quasars Absorption line Systems (QAS) lead to the incompatible results Y (l) D = (3.4±0.3) 10 , and Y (h) D = (2.0±0.5) 10. We performed our analysis for both low and high D data. Finally, the most recent estimate for Li primordial abundance, from the Spite plateau observed in the halo of POP II stars, gives Y7Li = (1.73±0.21)10 . The light nuclide yields strongly depend on the baryonmatter content of the universe, ΩBh . In particular, assuming a standard BBN scenario, i.e. vanishing neutrino chemical potentials, the likelihood analysis gives, at 95% C.L. [4],