Inelastically decoupling dark matter

We present a new dark matter candidate, the inelastically decoupling relic (iELDER), which is a cold thermal relic whose abundance is determined by the freeze out of its inelastic scattering off of bath particles in the presence of 3 → 2 self-annihilations. The dark matter is predicted to be light, in the O(MeV − GeV) range, with significant self-annihilations and very weak inelastic couplings to ordinary matter. We demonstrate iELDER dark matter using a Z₃-symmetric toy model as well as quantum chromodynamics (QCD)-like pion theories—the latter showing promising prospects for detection and providing a new benchmark for future searches.