Coherent Freeze-Out of Dark Matter

We propose a novel coherent freeze-out mechanism where a weakly interacting massive particle (WIMP) is quadratically coupled to a light axionlike particle (ALP). Although the coupling is too feeble to thermalize the ALP, coherent forward scattering induces medium-dependent mass shifts that significantly modify both WIMP freeze-out and ALP misalignment dynamics. The symmetry of the ALP potential is broken at high temperatures and restored through either a first-order transition or a crossover. In the former, WIMPs alone compose dark matter with annihilation cross sections enhanced by up to 3 orders of magnitude relative to the standard scenario; in the latter, a Planck-suppressed coupling naturally yields an ALP abundance of the order of the observed dark matter density, largely independent of its initial displacement and mass.