  At any epoch, particle physics must be open to completely unexpected
discoveries, and that is reason enough to extend the reach of searches for
ultra-high energy (UHE) photons. The observation of a population of photons
with energies $E \gtrsim 100$ EeV would for example imply the existence of
either a completely new physical phenomena, or particle acceleration mechanisms
heretofore never seen or imagined. But as we outline in this Letter of
Interest, there are also good arguments for super-heavy dark matter (SHDM) in a
parameter range such that it could be discovered via its decays to, in
particular, UHE photons. Only ultra-high energy cosmic ray observatories have
capabilities to detect UHE photons. We first investigate how current and future
observations can probe and constrain SHDM models in important directions, and
then outline some of the scenarios that motivate such searches. We also discuss
connections between constraints on SHDM and on the parameter values of
cosmological models.
