Cosmological variation of the deuteron binding energy, strong interaction, and quark masses from big bang nucleosynthesis

We use big bang nucleosynthesis calculations and light element abundance data to constrain the relative variation of the deuteron binding energy since the Universe was a few minutes old, δQ=Q(BBN)-Q(present). Two approaches are used, first treating the baryon to photon ratio η as a free parameter, but with the additional freedom of varying δQ, and second using the WMAP value of η and solving only for δQ. Including varying Q yields a better fit to the observational data than imposing the present day value, rectifying the discrepancy between the ⁴He abundance and the deuterium and ⁷Li abundances, and yields good agreement with the independently determined ηWMAP. Using ηWMAP, the minimal deviation consistent with the data is significant at about the 4σ level; δQ/Q=-0.019±0.005. If the primordial ⁴He abundance lies towards the low end of values in the literature, this deviation is even larger and more statistically significant. Taking the light element abundance data at face value, our result may be interpreted as variation of the dimensionless ratio X=mₛ/ΛQCD of the strange quark mass and strong scale: δX/X=(1.1±0.3)×10^-3. These results provide a strong motivation for a more thorough exploration of the potential systematic errors in the light element abundance data.