Revisiting ultrahigh-energy constraints on decaying superheavy dark matter

We revisit constraints on decaying very heavy dark matter (VHDM) using the latest ultrahigh-energy cosmic-ray (UHECR; E≳1018 eV) data and ultrahigh-energy (UHE) γ-ray flux upper limits, measured by the Pierre Auger Observatory. We present updated limits on the VHDM lifetime (τχ) for masses up to ∼1015 GeV, considering decay into quarks, leptons, and massive bosons. In particular, we consider not only the UHECR spectrum but their composition data that favors heavier nuclei. Such a combined analysis improves the limits at ≲1012 GeV because VHDM decay does not produce UHECR nuclei. We also show that the constraints from the UHE γ-ray upper limits are ∼10 more stringent than that obtained from cosmic rays, for all of the Standard Model final states we consider. The latter improves our limits to VHDM lifetime by a factor of two for dark matter mass ≳1012 GeV.