Lithium and Big-Bang Nucleosynthesis

Abstract

Since the discovery of the “Spite plateau” in 1982, lithium observations in halo stars have been used to deduce the primordial $^{7}Li$ abundance. Compared with the results of Big Bang nucleosynthesis (BBN) it provided an estimate of the baryonic density of the Universe, together with the other cosmological isotopes. However, recently, the observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, by the WMAP satellite, has provided a determination of this baryonic density ($\Omega_bh^2$) with an unprecedented precision. There is a very good agreement with deuterium observed in cosmological clouds, but we note a discrepancy between the deduced $^{7}Li$ abundance and the one observed in halo stars. The origin of this discrepancy, observational, stellar, nuclear or more fundamental remains to be clarified. A recent nuclear physics experiment provided new results on the $^{7}{\rm Be}({\rm d,p})2\alpha$, an up to now neglected reaction in BBN. Unfortunately, this cannot solve the $^{7}Li$ discrepancy.