The lithium problem, a phenomenologist's perspective

TL;DR

This paper reviews the longstanding lithium problem in cosmology, discussing observational evidence, astrophysical explanations, and potential new physics, from a phenomenological perspective.

Contribution

It provides a comprehensive phenomenological overview of the lithium problem, including observational challenges and possible explanations within and beyond standard models.

Findings

Existence of a lithium abundance plateau questioned

Astrophysical processes may not fully explain lithium observations

Potential need for new physics beyond standard cosmology and particle physics

Abstract

Thirty years after the first observation of the 7Li isotope in the atmosphere of metal-poor halo stars, the puzzle about its origin persists. Do current observations still support the existence of a "plateau": a single value of lithium abundance, constant over several orders of magnitude in the metallicity of the target star? If this plateau exists, is it universal in terms of observational loci of target stars? Is it possible to explain such observations with known astrophysical processes? Can yet poorly explored astrophysical mechanisms explain the observations or do we need to invoke physics beyond the standard model of Cosmology and/or the standard model of Particle Physics to explain them? Is there a 6Li problem, and is it connected to the 7Li one? These questions have been discussed at the Paris workshop Lithium in the Cosmos, and I summarize here its contents, providing an overview from the perspective of a phenomenologist.