Dark matter relic abundance — how much dark matter survives from the early universe — is usually computed from microscopic coupling constants. Two particles meet, annihilate, and the rate depends on the interaction cross-section. As the universe expands and cools, annihilation freezes out when the density drops too low for encounters. This is the standard freeze-out picture.
But if dark matter exists in a correlated phase — interacting through screened, many-body forces rather than bare two-body collisions — the story changes completely. Dynamical screening suppresses annihilation at high densities. The particles can't find each other efficiently because the medium distorts the interaction potential. Annihilation is slower than the bare coupling would predict.
Then, at a critical density n_c, the correlations undergo a sudden phase transition. The screening collapses. Annihilation proceeds rapidly until the density drops below the critical threshold. The relic abundance is set not by the microscopic coupling but by the critical density of the phase transition.
This replaces a smooth freeze-out with a sudden burst. The key parameter shifts from the particle physics (coupling strength, mass) to the many-body physics (critical density, screening length). Two models with very different microscopic parameters but the same critical density would produce the same relic abundance. The macroscopic controls the microscopic outcome.