Abstract
The Big Bang yield of 7Li is related not only to the baryonic density of the Universe but also to the width of the baryonic density distribution possibly resulting from the quark-hadron phase transition. For this transition, three physical parameters are considered: (a) the density contrast between the hadronic bubbles and the quark sea, (b) the volumes occupied respectively by these two phases, and (c) the neutron to proton ratio at the moment of primordial nucleosynthesis (after partial diffusion). These three parameters are displayed in an appropriate parameter space from which, after comparison with the cosmic abundances of the light nuclides D, 3He, 4He and 7Li, some conclusions about the physics of the quark-hadron phase transition can be extracted. In order to maintain an agreement between the calculations and the observations of primordial 7Li abundance, the width of the density distribution should be small (less than a factor of ten) (except in cases of extremely fast or extremely slow bubble nucleation and expansion rates). This suggests that the critical temperature Tc>200 MeV, in the higher part of the plausible range. The mean baryonic density is limited to the range 2 to 5*10-31 g cm-3, or h=(nb/ngamma )=3 to 7*10-10. Taking into account the uncertainties on the value of H0 the authors find Omega b=0.03 with a factor of three each side.