Effect of quark-mass variation on big bang nucleosynthesis

TL;DR

This paper investigates how variations in the light quark mass during big bang nucleosynthesis affect nuclear reaction rates and primordial element abundances, finding a specific quark mass change improves agreement with observations but also complicates the lithium problem.

Contribution

It introduces a quantitative analysis of quark mass variation effects on BBN and highlights the impact on lithium abundance discrepancies.

Findings

A relative quark mass variation of 0.016 improves primordial abundance predictions.

Quark mass changes can shift nuclear resonance positions, affecting lithium production.

Variation in quark mass could worsen the lithium abundance discrepancy.

Abstract

We calculate the effect of variation in the light-current quark mass, $m_q$, on standard big bang nucleosynthesis. A change in $m_q$ at during the era of nucleosynthesis affects nuclear reaction rates, and hence primordial abundances, via changes the binding energies of light nuclei. It is found that a relative variation of $\delta m_q/m_q = 0.016 \pm 0.005$ provides better agreement between observed primordial abundances and those predicted by theory. This is largely due to resolution of the existing discrepancies for 7Li. However this method ignores possible changes in the position of resonances in nuclear reactions. The predicted 7Li abundance has a strong dependence on the cross-section of the resonant reactions 3He(d,p)4He and t(d,n)4He. We show that changes in $m_q$ at the time of BBN could shift the position of these resonances away from the Gamow window and lead to an increased production of 7Li, exacerbating the lithium problem.