New analysis of the primordial nucleosynthesis in light of the lithium problem

Abstract

We are lucky to live in what eventually may be viewed as the best time during which we could explore the mysteries of the universe. One mystery was that the mass fraction of helium was always observed higher than about 0.23 since this is not produced in stars at this level. Another question was where the deuterium has been produced since it is destroyed in stars. The standard big bang nucleosynthesis (SBBN), which is a well-established theory responsible for the production of light elements during the first few minutes after big bang, has answered many of these questions and some still to be answered. It is clear that all abundances agree with observations except for lithium (7Li) which is higher by a factor of 3 than observations of the atmospheres of low metal halo stars. This discrepancy constitutes now one of the most intriguing problems in cosmology. In addition, lithium was shown to have a constant behavior as a function of metallicity, the so-called Spite Plateau . Such behavior is now in conflict with recent observations at very low metallicity which makes the lithium problem more complicated. In the present thesis, we will argue that nuclear physics or astrophysical solutions do not seem to resolve the lithium problem so that non-standard big bang nucleosynthesis should be considered. Therefore, we will give a new analysis of the SBBN in order to see the possibilities to resolve the so-called cosmological lithium problem while taking into account constraints from cosmology, astrophysics and particle physics.