WIMPs Without Weakness: Generalized Mass Window with Entropy Injection
  We study general freeze-out scenarios where an arbitrary number of initial
and final dark matter particles participate in the number-changing freeze-out
interaction. We consider a simple sector with two particle species undergoing
such a thermal freeze-out; one of the relics is stable and gives rise to the
dark matter today, while the other one decays to the Standard Model, injecting
significant entropy into the thermal bath that dilutes the dark matter
abundance. We show that this setup can lead to a stable relic population that
reproduces the observed dark matter abundance without requiring weak scale
masses or couplings. The final dark matter abundance is estimated analytically.
We carry out this calculation for arbitrary temperature dependence in the
freeze-out process and identify the viable dark matter mass and cross section
ranges that explain the observed dark matter abundance. This setup can be used
to open parameter space for both heavy (above the unitarity bound) or light
(sub-GeV) dark matter candidates. We point out that the best strategy for
probing most parts of our parameter space is to look for signatures of an early
matter-dominant epoch.
