Bounds from multimessenger astronomy on the superheavy dark matter

The purely gravitational evidence supporting the need for dark matter (DM) particles is compelling and based on Galactic to cosmological scale observations. Thus far, the promising weakly interacting massive particles scenarios have eluded detection, motivating alternative models for DM. We consider the scenarios involving the superheavy dark matter (SHDM) that potentially can be emitted by primordial black holes (PBHs) and can decay or annihilate into ultrahigh-energy (UHE) neutrinos and photons. The observation of a population of photons with energies E ≥1 0¹¹ G e V would imply the existence of completely new physical phenomena, or shed some light on DM models. Only the ultrahigh-energy cosmic-ray observatories have the capabilities to detect such UHE decay products via the measurements of UHE photon-induced extensive air showers. Using the upper bound on the flux of UHE cosmic rays beyond 10^11.3 GeV implying J (>10^11.3 GeV )<3.6 ×10^-5 km^-2 sr^-1 yr^-1 , at the 90% C.L. reported by the Pierre Auger Observatory, we obtain global limits on the lifetime of the DM particles with masses 10¹⁵≤M_X≤10¹⁷ GeV . The constraints derived here are new and cover a region of the parameter space not yet explored. We compare our results with the projected constraints from future POEMMA and JEM-EUSO experiments, in order to quantify the improvement that will be obtained by these missions. Moreover, assuming that an epoch of early PBHs domination introduces a unique spectral break, f_*, in the gravitational wave spectrum, the frequency of which is related to the SHDM mass, we map potential probes and limits of the DM particles masses on the f_*-M_X parameter space.