Review on effects of long-lived negatively charged massive particles on Big Bang Nucleosynthesis

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 Li-7 abundances of metal-poor stars, and predicts a primordial Be-9 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 -> 2P transition for Li-7 and Be-7,Be-9. The Be-7 destruction occurs via a recombination with the X- followed by a proton capture, and the primordial Li-7 abundance is reduced. Also, the Be-9 production occurs via the recombination of Li-7 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 derived parameter region for the Li-7 reduction 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) similar to O(1) TeV, while the stau and KK tau cannot.