The ups and downs of inferred cosmological lithium

TL;DR

This paper reviews evidence suggesting that stellar processes, particularly atomic diffusion, are responsible for lowering surface lithium levels from primordial predictions, highlighting the need for improved models of stellar mixing.

Contribution

It emphasizes the role of atomic diffusion in stellar lithium depletion and discusses the limitations of current stellar models in predicting convective mixing effects.

Findings

Atomic diffusion likely causes surface lithium depletion in stars.

Stellar lithium-6 abundances are no longer supported by recent evidence.

Current models lack precise predictions of convective boundary mixing.

Abstract

I summarize the stellar side of the cosmological lithium problem(s). Evidence from independent studies is accumulating and indicates that stars may very well be fully responsible for lowering their surface lithium from the predicted primordial value to observed levels through internal element-transport mechanisms collectively referred to as atomic diffusion. While atomic diffusion can be modelled from first principles, stellar evolution uses a parametrized representation of convection making it impossible to predict convective-boundary mixing as a vital stellar process moderating atomic diffusion. More work is clearly needed here for a fully quantitative picture of lithium (and metallicity) evolution as stars age. Lastly, note that inferred stellar lithium-6 abundances have all but disappeared.