Particle physics catalysis of thermal Big Bang Nucleosynthesis

TL;DR

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 relative to entropy of nX-/s less, which is one of the most stringent probes of electroweak scale remnants known to date.

Abstract

We point out that the existence of metastable, tau > 10^3 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 BBN. In particular, we show that the bound states of X^- with helium, formed at temperatures of about T=10^8K, lead to the catalytic enhancement of Li6 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 non-thermal BBN effects, this directly translates to the level of sensitivity to the number density of long-lived X^-, particles (τ>10^5 s) relative to entropy of n_{X^-}/s < 3\times 10^{-17}, which is one of the most stringent probes of electroweak scale remnants known to date.

Figures (4)

• Figure 1: Fraction of $X^-$ locked in the bound state with $^4$He: A. Realistic result based on Boltzmann equation, B. Saha-type prediction with a rapid switch from 0 to 1 at $T\simeq 8.3$ KeV
• Figure 2: SBBN and CBBN mechanisms for producing $^6$Li.
• Figure 3: Log$_{10}(^6{\rm Li})$ plotted as a function of $T$ in KeV for different choices of $\tau$ and $Y_X$: A. $\tau=\infty$ and $Y_X=10^{-2}$, B. $\tau=4\times 10^3$ s and $Y_X=10^{-2}$, C. $\tau=\infty$ and $Y_X=10^{-5}$, D. $\tau=4\times 10^3$ s and $Y_X=10^{-5}$.
• Figure 4: Constraint on initial abundance of $X^-$. $\log_{10}(Y_X)$ is plotted against $\tau$ in units of $10^3$ s. The thick horizontal line is the asymptotic exclusion boundary (\ref{['constraint']}).