Big Bang Nucleosynthesis

Abstract: The fundamental physical processes that govern the Big Bang nucleosynthesis(BBN) have been studied. BBN refers to the production of predominantlylight nuclei in the early Universe, which occurs on the time scale of a fewminutes after the bang. An initial intensive literature study was carried out,followed by computer simulations with the scientific code NUC123.The aim of the literature study was to build a theoretical basis fromwhich observational support of BBN and key estimates of parameters couldbe understood, and in the case of the latter also reproduced. The emphasishas been placed on the time leading up to BBN, specifically the relationbetween time and temperature, the universal expansion and the baryon-to-photon ratio, in order to determine the onset of BBN.Additionally, different simulations, based on models with varying degreesof complexity, have been performed in order to verify the theoretical work andthe estimates of key parameters. By mass the most important abundanceswere found to be 75.2 % 1H and 24.8 % 4He with help of the NUC123 software.These abundances were found to agree well with both observations andsimulations referred to in literature. One important exception is 7Li forwhich the calculated abundance differs significantly from the observationalvalues. Even though the over all good agreement is a strong evidence for thestandard models for both BBN and the Big Bang, this discrepancy pointsto shortcomings in the theory. Simply put, neither of these models can becompletely wrong, though they do not paint the whole picture either.