Dibaryons cannot be the dark matter

TL;DR

This paper demonstrates that the hypothetical $SU(3)$ flavor-singlet dibaryon $S$ cannot account for dark matter due to its negligible relic abundance after early-universe thermalization and freeze-out.

Contribution

It provides a detailed analysis showing that the early-universe production and thermalization of the dibaryon $S$ prevent it from being a viable dark matter candidate.

Findings

Dibaryon $S$ accounts for at most $10^{-11}$ of baryon number.

Thermal reactions in the early universe suppressed $S$ relic abundance.

$S$ cannot explain the observed dark matter to baryon ratio.

Abstract

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.