Search for dark matter using sub-PeV $\boldsymbol{\gamma}$-rays observed
  by Tibet AS$_{\boldsymbol{\gamma}}$
  The discovery of diffuse sub-PeV gamma-rays by the Tibet AS$_\gamma$
Collaboration promises to revolutionize our understanding of the high-energy
astrophysical universe. It has been shown that these data broadly agree with
prior theoretical expectations. We study the impact of this discovery on a
well-motivated new physics scenario: PeV-scale decaying dark matter (DM).
Considering a wide range of final states in DM decay, a number of DM density
profiles, and numerous astrophysical background models, we find that these data
provide the most stringent limit on DM lifetime for various Standard Model
final states. In particular, we find that the strongest constraints are derived
for DM masses in between a few PeV to a few tens of PeV. Near-future data of
these high-energy gamma-rays can be used to discover PeV-scale decaying DM.
