Lithium in Very Metal-poor Dwarf Stars - Problems for Standard Big Bang Nucleosynthesis?

Abstract

The standard model of primordial nucleosynthesis by the Big Bang as selected by the WMAP-based estimate of the baryon density ($Ω_bh^2$) predicts an abundance of $^7$Li that is a factor of three greater than the generally reported abundance for stars on the Spite plateau, and an abundance of $^6$Li that is about a thousand times less than is found for some stars on the plateau. This review discusses and examines these two discrepancies. They can likely be resolved without major surgery on the standard model of the Big Bang. In particular, stars on the Spite plateau may have depleted their surface lithium abundance over their long lifetime from the WMAP-based predicted abundances down to presently observed abundances, and synthesis of $^6$Li (and $^7$Li) via $α+ α$ fusion reactions may have occurred in the early Galaxy. Yet, there remain fascinating ways in which to remove the two discrepancies involving aspects of a new cosmology, particularly through the introduction of exotic particles.