Early nucleosynthesis, chemical evolution of galaxies and particle physics

Abstract

After a brief review of the most recent works dealing with the primordial abundances of the very light elements (D, ³He, ⁴He and ⁷Li) it is argued that the simple models of early nucleosynthesis predicting the existence of three neutrino flavors and a low baryonic density in the Universe imply specific galactic evolution schemes leading to a destruction of deuterium during the galactic history such that its present abundance is at most the tenth of its primordial one. Several models of chemical evolution of the Galaxy have been designed for that purpose. It has been found that models assuming a star formation rate (SFR) varying in time in two steps (the early epoch t <- 1Gyr where SFR is assumed to be constant and the rest of the galactic evolution when SFR is proportional to the gas density) are especially well suited to account for such a large deuterium destruction. By contrast, galactic evolution models assuming a bimodal SFR do not lead to such deuterium destruction effect.

Finally several very recent models attempting to account for the synthesis of the very light nuclear species in models such that OB = 1 (ξ_B being the baryonic cosmological parameter) are mentioned especially the recent scenario which proposes that the early nucleosynthesis is affected by the quark-hadron phase transition.