  Many new physics models include secluded sectors that interact little with
the Standard Model and whose internal interactions control the dark matter
abundance. If these same interactions are responsible for maintaining kinematic
equilibrium within the secluded sector, it is possible that the phase-space
distributions will differ considerably from their thermal values during
freeze-out. This can potentially result in deviations of the dark matter
abundance from that computed under the assumption of thermal distributions. In
this paper, we revisit dark matter abundance computations for a benchmark
secluded sector by numerically tracking the phase-space distributions. Namely,
we show that the dark matter abundance can deviate considerably from standard
results during the freeze-out process, but that a longer period of annihilation
ultimately leaves only a slight excess.
