James Alvey tells us about the general state of BBN in 2021.

He gives a really nice pedagogical overview of the physics that goes into BBN calculations relevant for 2021 observations, talking through each of the relevant epochs (neutrino decoupling, the deuterium bottleneck, etc).

He gives particular emphasis to the recent LUNA measurements of the D + p →γ + 3He reaction (or deuterium + proton goes to photon and 3-Helium). This was previously the source of greatest uncertainty in predicting the final deuterium abundance of BBN.

Finally, he talks about the implications of the LUNA measurements on possible new physics beyond the standard model, in particular possible thermal relics.

The LUNA paper: https://www.nature.com/articles/s41586-020-2878-4 (no arXiv version, I think?)
James’ original paper on thermal relics: https://arxiv.org/abs/1910.01649
Addendum to James’ paper analysing implications of LUNA: https://arxiv.org/abs/2107.11232