Dibaryons cannot be the dark matter

The hypothetical S U (3 ) flavor-singlet dibaryon state S with strangeness -2 has been discussed as a dark-matter candidate capable of explaining the curious 5-to-1 ratio of the mass density of dark matter to that of baryons. We study the early-universe production of dibaryons and find that irrespective of the hadron abundances produced by the QCD quark/hadron transition, rapid particle reactions thermalized the S abundance, and it tracked equilibrium until it "froze out" at a tiny value. For the plausible range of dibaryon masses (1860-1890 MeV) and generous assumptions about its interaction cross sections, S 's account for at most 10^-11 of the baryon number and, thus, cannot be the dark matter. Although it is not the dark matter, if the S exists, it might be an interesting relic.