Neutron diffusion and nucleosynthesis in an inhomogeneous big bang model

Abstract

This article presents an original code for big bang nucleosynthesis in a baryon inhomogeneous model of the Universe. In this code neutron diffusion between high and low baryon density regions is calculated simultaneously with the nuclear reactions and weak decays that compose the nucleosynthesis process. The size of the model determines the time when neutron diffusion becomes significant. This article describes in detail how the time of neutron diffusion relative to the time of nucleosynthesis affects the final abundances of $^{4}\mathrm{He}$, deuterium and $^{7}\mathrm{Li}$. These results will be compared with the most recent observational constraints of $^{4}\mathrm{He}$, deuterium and $^{7}\mathrm{Li}$. This inhomogeneous model has $^{4}\mathrm{He}$ and deuterium constraints in concordance for baryon-to-photon ratio $\ensuremath{\eta}=(4.3\ensuremath{-}12.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ $^{7}\mathrm{Li}$ constraints are brought into concordance with the other isotope constraints by including a depletion factor as high as 5.9. These ranges for the baryon-to-photon ratio and for the depletion factor are larger than the ranges from a standard big bang nucleosynthesis model.