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Resolving conclusions about the early Universe requires accurate nuclear measurements

Nature Reviews Physics volume 3, pages 231–232 (2021)Cite this article

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Nuclear physics experiments give reaction rates that, via modelling and comparison with primordial abundances, constrain cosmological parameters. The error bars of a key reaction, D(p,γ)3He, were tightened in 2020, revealing discrepancies between different analyses and calling for more accurate measurements of other reactions.

One of the key parameters of the standard cosmological model is its density of baryons, a quantity that can be inferred by analysing1 the cosmic microwave background (CMB) or independently by studying Big Bang nucleosynthesis (BBN), the set of reactions that produced atomic nuclei from these baryons in the primordial Universe. The relevant measurements have dramatically improved in the past decades, and been complemented by new observational probes. As a consequence, the error bars on cosmological parameters have been reduced, leading to the era of precision cosmology. However, tensions between different observations remain. One of the key steps in BBN is the D(p,γ)3He reaction — that is, the fusion of deuterium with a proton resulting in a helium-3 nucleus and a photon, D + p → 3He + γ — which partially controls the abundance of deuterium in the first minutes after the Big Bang. The accuracy of the cross section of the D(p,γ)3He reaction was recently improved2, relaunching a debate on the baryon density and divergences between its estimation from BBN and the CMB. We wish to highlight the importance for cosmology of refined measurements and statistical analyses of three nuclear rates, D(p,γ)3He, D(d,n)3He and D(d,p)3He, and draw attention to the reasons of recent diverging conclusions by different teams.

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Authors and Affiliations

  1. Institut d’Astrophysique de Paris, CNRS, Paris, France

    Cyril Pitrou, Jean-Philippe Uzan & Elisabeth Vangioni

  2. Sorbonne Université, Institut Lagrange de Paris, Paris, France

    Cyril Pitrou, Jean-Philippe Uzan & Elisabeth Vangioni

  3. IJCLab, CNRS IN2P3, Université Paris-Saclay, Orsay, France

    Alain Coc

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  1. Cyril Pitrou
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  2. Alain Coc
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  4. Elisabeth Vangioni
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Correspondence to Cyril Pitrou.

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Pitrou, C., Coc, A., Uzan, JP. et al. Resolving conclusions about the early Universe requires accurate nuclear measurements. Nat Rev Phys 3, 231–232 (2021). https://doi.org/10.1038/s42254-021-00294-6

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