Light-Element Nucleosynthesis: Big Bang and Later on

Abstract

We present a model for big bang nucleosynthesis which combines baryon inhomogeneities with the effects of the decays of massive particles (masses higher than a few GeV). Those particles, with half-lives longer than the standard nucleosynthesis epoch, give rise to both electromagnetic and hadron cascades which modify the abundances of the light nuclides resulting from the previous, inhomogeneous thermonuclear nucleosynthesis stage. We find a region in the parameter space of this composite model where there is agreement with currently inferred primordial abundances for values of $Ω_{b}h^{2}_{50}$ as high as 0.35 ($Ω_{b}$ being the baryon fraction of the closure density and $h_{50}$ the Hubble constant in units of 50 km/s/Mpc). Possible improvements of the model are pointed out.