Particle Physics Catalysis of Thermal Big Bang Nucleosynthesis

We point out that the existence of metastable, $\tau >{10}^3\mathrm{s}$, negatively charged electroweak-scale particles ($X^{-}$) alters the predictions for lithium and other primordial elemental abundances for $A>4$ via the formation of bound states with nuclei during big bang nucleosynthesis. In particular, we show that the bound states of $X^{-}$ with helium, formed at temperatures of about $T={10}^8\mathrm{K}$, lead to the catalytic enhancement of ${}^6\mathrm{Li}$ production, which is 8 orders of magnitude more efficient than the standard channel. In particle physics models where subsequent decay of $X^{-}$ does not lead to large nonthermal big bang nucleosynthesis effects, this directly translates to the level of sensitivity to the number density of long-lived $X^{-}$ particles ($\tau >{10}^5\mathrm{s}$) relative to entropy of $n_{X^{-}}/s\lesssim 3\times {10}^{-17}$, which is one of the most stringent probes of electroweak scale remnants known to date.