Catalyzed 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 (BBN). 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 eight orders of magnitude more efficient than the standard channel. In particle physics models, where subsequent decay of X^- does not lead to large nonthermal BBN 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-/s ≲ 3 × 10^-17, which is one of the most stringent probes of electroweak scale remnants known to date. It is also argued that unstable charged particles with lifetime of order ∼2000 s may naturally lead to the depletion of ⁷Li by a factor of two, making it consistent with observationally determined abundances.