Probing unification scenarios with Big Bang Nucleosynthesis

Big Bang Nucleosynthesis (BBN) is an observational cornerstone of the Hot Big Bang model and a sensitive probe of physics beyond it. Although some analytic approximations can be made, a fully consistent analysis must be done numerically, starting with the classic code by Kawano and leading to the recently developed PRyMordial, a publicly available Python code. An example of physics beyond the standard model to which BBN is sensitive are Grand Unified Theory (GUT) models.

A self-consistent perturbative analysis of the effects of variations in nature’s fundamental constants, unavoidable in a broad class of GUT models, has recently been developed, and describes the relevant variations with only three parameters: ∆ఈಶಾ ఈಶಾ , 𝑅 and 𝑆. The specific goal of this work is to implement this perturbative approach in the PRyMordial code and use the extended code to obtain constraints on the variations of the abovementioned fundamental constants using current observations.

Two different viable scenarios were found, and the three parameters were constrained independently for both cases. The variation of the gravitational coupling can be implemented by varying either particle masses, or Newton’s gravitational constant. With the variation of masses, we obtained a 1σ interval of [−4.89 × 10ିହ, 5.22 × 10ିହ] for ∆ఈಶಾ ఈಶಾ and a ratio 𝑆/𝑅 = 2.53 ± 0.06 correlating with the observational values of Helium-4 and Deuterium abundances. For the variation of 𝐺ே, we obtained one (𝑅, 𝑆) point (−1.52, −6.06) that works best for any ∆ఈಶಾ ఈಶಾ , constraining each of the three in a 1σ interval: [−2.00 × 10ିହ, 2.33 × 10ିହ] for ∆∆ఈಶಾ ఈಶಾ , [−15.7,16.2] for 𝑅, and [−127.3, 135.4] for 𝑆.