Cosmological Stasis Confronts BBN

Big Bang Nucleosynthesis (BBN) is a highly successful theory in describing the early Universe. Recent measurements of Helium-4 ($Y_p$) in extremely metal-poor galaxies from the Subaru Survey challenge the current understanding of the abundance of $Y_p$ predicted from the Particle Data Group (PDG). We investigate this tension by looking for indications of a cosmological epoch of Stasis during the BBN era, paying careful attention to the effects of Stasis on the baryon-to-photon ratio $\eta_b$ and the uncertainties in the nuclear reaction network. We consider both CMB and BBN observational data and perform a Bayesian analysis centered on the Subaru Helium-4 value. We find that the presence of a stasis epoch during the BBN era can explain the Subaru Helium-4 value while remaining in statistical significance for other, more constrained, BBN outputs such as $N_\text{eff}$ and Deuterium. We discuss the implications of this finding and the implications for Stasis as a part of cosmology beyond $\Lambda$CDM.