Ultra high energy cosmic ray, superheavy dark matter and extra dimension

We propose a new mechanism for explaining the very long lifetime of superheavy dark matter X, which is proposed as a source of the ultra high-energy cosmic rays above the GZK cutoff (5×1019 eV). The singlet X particle couples to the MSSM particles only through a bulk singlet field which develops the v.e.v. in the “hidden” brane. The distance between this hidden brane and the “visible” brane naturally leads to the exponential suppression of the coupling. The X particle decays predominantly into the higgsino and Higgs boson of the MSSM, and its decay spectrum is completely determined once their properties are known.