Thermal Dark Matter from Freeze-Out of Inverse Decays

We propose a new thermal dark matter candidate whose abundance is determined by the freeze-out of inverse decays. The relic abundance depends parametrically only on a decay width, while matching the observed value requires that the coupling determining the width - and the width itself - should be exponentially small. The dark matter is therefore very weakly coupled to the standard model, evading conventional searches. This inverse decay dark matter can be discovered by searching for the long-lived particle that decays into the dark matter at future planned experiments.