Dibaryons cannot be the dark matter
  The hypothetical $SU(3)$ 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.
