I. M. Dreyer, C. J. A. P. Martins
Abstract
We extend a recently developed big bang nucleosynthesis (BBN) code, PRyMordial, to constrain a broad class of grand unified theories to which BBN is sensitive, since these lead to varying fundamental couplings. A previously developed self-consistent perturbative analysis of the effects of these variations has been implemented in PRyMordial, leading to robust constraints of the value of the fine-structure constant, α, at the BBN epoch using current observations of helium-4 and deuterium abundances. We explored two different viable scenarios, relying on alternative assumptions on the gravitational sector: the variation of the gravitational coupling can be implemented by varying either particle masses, or Newton's gravitational constant. For the variation of masses, we obtained at 68% confidence level a constraint on the relative variation of α, between the BBN epoch and the present-day laboratory value, of ∆α/α=2±51 ppm (parts per million), while for the variation of Newton's constant the analogous constraint is ∆α/α=2±22 ppm. We also show that, given these constraints, these models do not provide a solution to the cosmological lithium problem.
Keywords
Cosmology
Physical Review D
Volume 113, Issue 103501, Page 12
2026 May
