Nucleosynthesis in the Early Universe

Abstract

One of the reasons why the standard Big Bang model is taken so seriously is its remarkable success in accounting for the observed abundances of the light elements by primordial nucleosynthesis, meaning the nuclear processes which took place during the first ten minutes of the cosmic expansion. The results of this analysis are crucial for a number of aspects of galaxy formation. In particular, primordial nucleosynthesis provides one of the most important constraints upon the density parameter in the form of baryonsΩ_B. In developing these results, we need to study in some detail the rôle of neutrinos in the early Universe, howthey change the dynamics of the expansion and how they decouple from the electrons and positrons. The neutrinos provide an example of the type of decoupling process which is important for other unknown types of weakly interacting particle.