We carry out a detailed study of the confinement phase transition in a dark sector with an SU(N) gauge group and a single generation of a dark heavy quark. We focus on heavy enough quarks such that their abundance freezes out before the phase transition, and the phase transition is of first order. We find that during this phase transition, the quarks are trapped inside contracting pockets of the deconfined phase and are compressed enough to interact at a significant rate, giving rise to a second stage of annihilation that can dramatically change the resulting dark matter abundance. As a result, the dark matter can be heavier than the often-quoted unitarity bound of ∼100 TeV. Our findings are almost completely independent of the details of the portal between the dark sector and the Standard Model. We comment briefly on possible signals of such a sector. Our main findings are summarized in a companion paper, while here we provide further details on different parts of the calculation.
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© 2021 authors. Published by the American Physical Society.