Hunting WIMPzilla with the highest-energy cosmic rays

Abstract

In 15 years of data taking the Pierre Auger Observatory has observed no events beyond \(10^{11.3}\) GeV. This null result translates into an upper bound on the flux of ultrahigh-energy cosmic rays implying \(J (> 10^{11.3}\) GeV) \(< 3.6 \times 10^{-5}\) km\(^{-2}\) sr\(^{-1}\) yr\(^{-1}\), at the 90\%C.L. We interpret this bound as a constraint on extreme-energy photons originating in the decay super-heavy dark matter (SHDM) particles clustered in the Galactic halo. Armed with this constraint we derive the strongest lower limit on the lifetime of hadronically decaying SHDM particles. For masses in the range, \(10^{14} < M_X/ \) GeV \(< 10^{15}\), the limit derived in this work, \(\tau_X > 10^{24}\) yr, is orders of magnitude more restrictive than previous bounds. We also explore the capability of future NASA's POEMMA mission to search for SHDM signals.