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 for all of the Standard
Model final states we consider.Comment: 9 pages, 5 figure