# Review on Effects of Long-lived Negatively Charged Massive Particles on Big Bang Nucleosynthesis

## TL;DR

This review discusses how long-lived negatively charged massive particles could influence Big Bang Nucleosynthesis, potentially resolving lithium abundance discrepancies and predicting increased beryllium production, with implications for supersymmetric and extra-dimensional models.

## Contribution

It provides a comprehensive analysis of the reactions involving $X^-$ particles in BBN and constrains their properties, highlighting their role in addressing the lithium problem and predicting primordial beryllium.

## Key findings

- $^7$Li abundance can be reduced via $X^-$ interactions.
- Primordial $^9$Be abundance is increased beyond standard BBN predictions.
- Candidates for $X^-$ include selectron, smuon, KK electron, and KK muon.

## Abstract

We review important reactions in the big bang nucleosynthesis (BBN) model involving a long-lived negatively charged massive particle, $X^-$, which is much heavier than nucleons. This model can explain the observed $^7$Li abundances of metal-poor stars, and predicts a primordial $^9$Be abundance that is larger than the standard BBN prediction. In the BBN epoch, nuclei recombine with the $X^-$ particle. Because of the heavy $X^-$ mass, the atomic size of bound states $A_X$ is as small as the nuclear size. The nonresonant recombination rates are then dominated by the $d$-wave $\rightarrow$ 2P transition for $^7$Li and $^{7,9}$Be. The $^7$Be destruction occurs via a recombination with the $X^-$ followed by a proton capture, and the primordial $^7$Li abundance is reduced. Also, the $^9$Be production occurs via the recombination of $^7$Li and $X^-$ followed by deuteron capture. The initial abundance and the lifetime of the $X^-$ particles are constrained from a BBN reaction network calculation. We estimate that the derived parameter region for the $^7$Li reduction is allowed in supersymmetric or Kaluza-Klein (KK) models. We find that either the selectron, smuon, KK electron or KK muon could be candidates for the $X^-$ with $m_X\sim {\mathcal O}(1)$ TeV, while the stau and KK tau cannot.