Big-Bang Nucleosynthesis After Planck (1912.01132v1)

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)

• The paper re-evaluates Big-Bang Nucleosynthesis using precise Planck cosmic baryon density measurements to refine key nuclear reaction rates.
• It demonstrates excellent concordance for deuterium predictions while highlighting a persistent discrepancy in lithium production.
• The study employs detailed likelihood analyses and updated experimental data to urge further investigation into BBN reaction rates and early Universe physics.

Big-Bang Nucleosynthesis After Planck: A Computational Analysis

The paper "Big-Bang Nucleosynthesis After Planck" by Fields et al. conducts a thorough re-examination of Big-Bang Nucleosynthesis (BBN) in the context of the most recent data from the Planck satellite and other contemporary measurements. This investigation assesses the precision and consistency of BBN predictions in light of the independenly derived cosmic baryon density, the helium abundance, and the effective number of neutrinos as determined by Planck data.

The authors underline the relation among these parameters, all of which are intertwined through BBN, showcasing that BBN remains a robust and insightful tool for understanding the early Universe. The Planck data enable an unprecedented precision in determining the cosmic baryon density, which translates into a more reliable mediation of primordial nuclear processes. One key utility of the paper is a comprehensive likelihood analysis, examining a range of reactions contributing to light element synthesis and addressing both cross-sectional data and theoretical predictions.

Major Findings and Numerical Results

1. Baryon Density and Nuclear Reaction Rates:
   • The cosmic baryon density inferred from Planck shows a precision of 0.9%, revealing key insights into primordial reaction rates, especially with respect to light elements like deuterium (D) and helium-4 ($^4He$).
   • Updated reaction rates, such as for $^7Be(n,p)^7Li$, are considered using newer neutron capture measurements, impacting the predictions of $^7Li$ production and addressing the enduring lithium problem.
2. Concordance and Discrepancies:
   • While the deuterium-to-hydrogen ratio (D/H) is in excellent agreement with observational data, tensions remain regarding the lithium prediction, which remains at odds with observed low-metallicity halo star abundances—a persisting lithium problem.
   • The number of light neutrino species at BBN, deduced to be $N_\nu = 2.86 \pm 0.15$, indicates a marginal tension with the Standard Model expectation.
3. Revised Nuclear Rates:
   • New experimental data on reactions such as $^2H(p,\gamma)^3He$ reveal discrepancies between theory-based predictions and experimental measurements at BBN energies, necessitating further investigation to align these with observationally consistent results.

Theoretical and Practical Implications

• The precise determination of these key cosmological parameters underscores the consistency between BBN and the Cosmic Microwave Background (CMB) data and frames a more cohesive picture of early Universe physics.
• In light of the ongoing lithium problem, the authors emphasize the need for further experimental work, particularly at BBN energies, to refine nuclear reaction rate models, which have significant implications for both nuclear physics and cosmology.
• The paper posits that CMB Stage-4 observations could bring substantial improvements, potentially allowing for resolutions that can afford precision tests of early Universe conditions and fundamental physics, such as neutrino thermal history.

Future Prospects in Cosmology and Astrophysics

• The results anticipated from future CMB observatories may bolster the sensitivity of cosmic parameter measurements to a point where potential slight deviations from the Standard Model predictions can be unambiguously tested.
• Advances in high-resolution deuterium measurements and continued observations of low-metallicity star lithium abundances are deemed essential to further reconcile the discrepancies noted.

In conclusion, Fields et al.'s work richly contributes to the field by updating the state of BBN with respect to cutting-edge data, elucidating significant cosmological parameters, and drawing generous attention towards unresolved tensions warranting further astrotechnological innovation.