Big-Bang Nucleosynthesis After Planck

TL;DR

This paper evaluates big-bang nucleosynthesis using Planck data, confirming the lithium problem persists and exploring how new measurements and rates affect BBN predictions and consistency with CMB data.

Contribution

It provides updated BBN analyses incorporating Planck data, new neutron capture rates, and examines the impact on primordial element abundances and neutrino counts.

Findings

The lithium problem remains unresolved and is reinforced by new data.

The effective number of neutrino species is measured as 2.86 ± 0.15.

Future CMB measurements will improve constraints on BBN parameters.

Abstract

We assess the status of big-bang nucleosynthesis (BBN) in light of the final Planck data release and other recent developments, and in anticipation of future measurements. Planck data fix the cosmic baryon density to 0.9% precision, and determine the helium abundance and effective number of neutrinos with precision approaching that of astronomical and BBN determinations respectively. In addition, new high-redshift measurements give D/H to better precision than theoretical predictions, and new Li/H data reconfirm the lithium problem. We present new ${}^{7}{\rm Be}(n,p){}^{7}{\rm Li}$ rates using new neutron capture measurements; we have also examined the effect of proposed changes in the $d(p,\gamma){}^{3}{\rm He}$ rates. Using these results we perform a series of likelihood analyses. We assess BBN/CMB consistency, with attention to how our results depend on the choice of Planck data, as well as how the results depend on the choice of non-BBN, non-Planck data sets. Most importantly the lithium problem remains, and indeed is more acute given the very tight D/H observational constraints; new neutron capture data reveals systematics that somewhat increases uncertainty and thus slightly reduces but does not essentially change the problem. We confirm that $d(p,\gamma){}^{3}{\rm He}$ theoretical rates brings D/H out of agreement and slightly increases 7Li; new experimental data are needed at BBN energies. Setting the lithium problem aside, we find the effective number of neutrino species at BBN is $N_\nu = 2.86 \pm 0.15$. Future CMB Stage-4 measurements promise substantial improvements in BBN parameters: helium abundance determinations will be competitive with the best astronomical determinations, and $N_{\rm eff}$ will approach sensitivities capable of detecting the effects of Standard Model neutrino heating of the primordial plasma. (Abridged)