Our understanding of the Universe is known to be incomplete and new gaugeforces beyond those of the Standard Model might be crucial to describing itsobserved properties. A minimal and well-motivated possibility is a pureYang-Mills non-Abelian dark gauge force with no direct connection to theStandard Model. We determine here the relic abundances of the glueball boundstates that arise in such theories and investigate their cosmological effects.Glueballs are first formed in a confining phase transition, and their relicdensities are set by a network of annihilation and transfer reactions. Thelightest glueball has no lighter states to annihilate into, and its yield isset mainly by 3 to 2 number-changing processes which persistently releaseenergy into the glueball gas during freeze-out. The abundances of the heavierglueballs are dominated by 2 to 2 transfer reactions, and tend to be muchsmaller than the lightest state. We also investigate potential connectorsbetween the dark force and the Standard Model that allow some or all of thedark glueballs to decay. If the connection is weak, the lightest glueball canbe very long-lived or stable and is a viable dark matter candidate. Forstronger connections, the lightest glueball will decay quickly but otherheavier glueball states can remain stable and contribute to the dark matterdensity.
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