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.

• Received 22 January 2022
• Revised 26 December 2022
• Accepted 14 February 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.121001

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Published by the American Physical Society