Constraints on metastable superheavy dark matter coupled to sterile neutrinos with the Pierre Auger Observatory

Dark matter particles could be superheavy, provided their lifetime is much longer than the age of the Universe. Using the sensitivity of the Pierre Auger Observatory to ultrahigh energy neutrinos and photons, we constrain a specific extension of the Standard Model of particle physics that meets the lifetime requirement for a superheavy particle by coupling it to a sector of ultralight sterile neutrinos. Our results show that, for a typical dark coupling constant of 0.1, the mixing angle 𝜃𝑚 between active and sterile neutrinos must satisfy, roughly, 𝜃𝑚≲1.5×10−6⁢(𝑀𝑋/109  GeV)−2 for a mass 𝑀𝑋 of the dark-matter particle between 108  GeV and 1011  GeV.