On the Origin of the Light Elements (D, 3He, 4He and 7Li)

Abstract

The abundances of the very light elements (D, 3He, 4He and 7Li) constitute indeed one of the most powerful constraints in cosmology: they are known to fix very interesting limits on the baryonic density of the Universe and on the maximum number of neutrino (lepton) families in the frame of the simplest canonical models. Given the importance of these predictions, these models should be analysed very cautiously at the light of recent developments in the observations of these elements. In order to make the simplest models consistent with the observations, it is argued that a thorough destruction of D should occur during the galactic evolution. Moreover this review deals also with some models invoking the possible existence of massive unstable neutrinos, gravitinos or photinos which would decay into high energy photons or of quark nuggets which could be created during the quark-hadron phase transitions. Such models have been designed in an attempt to overcome the limitation on the Universe density coming from these abundance determinations. Although the simple canonical models are especially attractive such models cannot be disregarded.