LHAASO Galactic Plane $γ$-rays Strongly Constrain Heavy Dark Matter

Abstract: LHAASO, a ground-based observatory, is unveiling new frontiers in our understanding of high-energy $\gamma-$rays and cosmic rays. It has recently observed high energy diffuse $\gamma-$rays from the Galactic plane in the TeV-PeV range. For the first time, we analyze this data to search for signatures of heavy decaying and annihilating dark matter in the mass range $10^{5}-10^{11}$ GeV. We compute the expected photon flux from both Galactic and extragalactic dark matter, incorporating attenuation due to photon pair production. For the Galactic contribution, we include both prompt photons and secondary photons produced via inverse Compton scattering, accounting for electron/positron propagation. For the extragalactic component, in addition to the prompt and inverse Compton contributions, we also include cascade photons arising from inverse Compton scattering of pair-produced electrons and positrons. By combining all these contributions, we derive constraints on the dark matter parameter space. Our bounds for various two body Standard Model final states are strongest to date. This underscore LHAASO's capability to discover the nature of heavy dark matter.