Cryptons: a stringy form of decaying superheavy dark matter, as a source   of the ultra high energy cosmic rays
  Cryptons, metastable bound states of matter in the string hidden sector, with dynamically determined masses M_X on the order of 10^{12} GeV and lifetimes tau_X greater than or on the order of 10^{18} yr, may be generated, through inflation, with an abundance close to that required for a near-critical universe. Their decay debris may be responsible for the most energetic particles striking Earth's atmosphere. Recent developments of this astonishing hypothesis are reviewed, indicating that NESTOR or the PIERRE AUGER project may be able to confirm or refute the existence of cryptons. 
D.V. Nanopoulos