Breaking Dark: Hunting Heavy Decaying Dark Matter with Tibet AS_γ and LHAASO-KM2A

Recent measurements of diffuse sub-PeV gamma-rays by the Tibet AS_γ and LHAASO collaborations have reshaped our understanding of the gamma-ray sky. Besides uncovering the nature of `PeVatrons', these measurements can also be used to probe the non-gravitational nature of dark matter. PeV-scale decaying dark matter can produce high-energy gamma rays in the final state and contribute to the measurements made by extensive air-shower detectors like Tibet AS_γ and LHAASO. Using the latest Tibet AS_γ upper limits on diffuse gamma rays away from the Galactic plane and the LHAASO-KM2A measurements of diffuse gamma rays from the Galactic plane, we put stringent constraints on lifetimes of decaying DM for masses ~ 10⁶ - 10⁹ GeV. Future observations of high-energy diffuse gamma-ray emission can thus provide stronger limits or potentially discover heavy decaying dark matter.