The variation of fundamental constants and the role of A=5 and A=8 nuclei on primordial nucleosynthesis

TL;DR

This study examines how changes in fundamental constants could influence primordial nucleosynthesis, focusing on nuclear reactions involving unstable nuclei and the potential impact of a stable Be-8 nucleus during the early universe.

Contribution

It provides a consistent microscopic model to evaluate how variations in fundamental constants affect key nuclear reaction rates in BBN, especially involving A=5 and A=8 nuclei.

Findings

Variation in constants has minimal impact on He3(d,p)He4 and H3(d,n)He4 reaction rates.

No significant production of carbon via the triple-alpha process during BBN.

Be-8 remains unstable, so its stability does not alter standard BBN outcomes.

Abstract

We investigate the effect of a variation of fundamental constants on primordial element production in big bang nucleosynthesis (BBN). We focus on the effect of a possible change in the nucleon-nucleon interaction on nuclear reaction rates involving the A=5 (Li-5 and He-5) and A=8 (Be-8) unstable nuclei and complement earlier work on its effect on the binding energy of deuterium. The reaction rates for He3(d,p)He4 and H3(d,n)He4 are dominated by the properties of broad analog resonances in He-5 and Li-5 compound nuclei respectively. While the triple alpha process is normally not effective in BBN, its rate is very sensitive to the position of the "Hoyle state" and could in principle be drastically affected if Be-8 were stable during BBN. The nuclear properties (resonance energies in He-5 and Li-5 nuclei, and the binding energies of Be-8 and D) are all computed in a consistent way using a microscopic cluster model. The n(p,gamma)d, He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates are subsequently calculated as a function of the nucleon-nucleon interaction that can be related to the fundamental constants. We found that the effect of the variation of constants on the He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates is not sufficient to induce a significant effect on BBN, even if Be-8 was stable. In particular, no significant production of carbon by the triple alpha reaction is found when compared to standard BBN. We also update our previous analysis on the effect of a variation of constants on the n(p,gamma)d reaction rate.