Big Bang Nucleosynthesis
Examensarbete för kandidatexamen
The fundamental physical processes that govern the Big Bang nucleosynthesis (BBN) have been studied. BBN refers to the production of predominantly light nuclei in the early Universe, which occurs on the time scale of a few minutes 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 from which observational support of BBN and key estimates of parameters could be understood, and in the case of the latter also reproduced. The emphasis has been placed on the time leading up to BBN, speciﬁcally the relation between 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 degrees of complexity, have been performed in order to verify the theoretical work and the estimates of key parameters. By mass the most important abundances were found to be 75.2 % 1 H and 24.8 % 4 He with help of the NUC123 software. These abundances were found to agree well with both observations and simulations referred to in literature. One important exception is 7 Li for which the calculated abundance diﬀers signiﬁcantly from the observational values. Even though the over all good agreement is a strong evidence for the standard models for both BBN and the Big Bang, this discrepancy points to shortcomings in the theory. Simply put, neither of these models can be completely wrong, though they do not paint the whole picture either.
Elementarpartikelfysik , Kärnfysik , Elementary particle physics , Nuclear physics