Particle Physics Catalysis of Thermal Big Bang Nucleosynthesis

We point out that the existence of metastable, τ>10³ 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=10⁸ K, lead to the catalytic enhancement of ⁶Li 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 (τ>10⁵ s) relative to entropy of n_X^-/s3×10^-17, which is one of the most stringent probes of electroweak scale remnants known to date.