The electromagnetic fine-structure constant in primordial nucleosynthesis revisited

Abstract

AbstractWe study the dependence of the primordial nuclear abundances as a function of the electromagnetic fine-structure constant $$\alpha $$ α , keeping all other fundamental constants fixed. We update the leading nuclear reaction rates, in particular the electromagnetic contribution to the neutron-proton mass difference pertinent to $$\beta $$ β -decays, and go beyond certain approximations made in the literature. In particular, we include the temperature-dependence of the leading nuclear reactions rates and assess the systematic uncertainties by using four different publicly available codes for Big Bang nucleosynthesis. Disregarding the unsolved so-called lithium-problem, we find that the current values for the observationally based $${}^{2}\text {H}$$ 2 H and $${}^{4}\text {He}$$ 4 He abundances restrict the fractional change in the fine-structure constant to less than $$2\%$$ 2 %  , which is a tighter bound than found in earlier works on the subject.