Long lived superheavy dark matter with discrete gauge symmetries - art. no. 063507

The recently observed ultrahigh energy (UHE) cosmic rays beyond the Greisen -Zatsepin-Kuzmin bound can be explained by the decays of some superheavy X particles forming a part of dark matter in our universe. We consider variou s discrete gauge symmetries Z(N) to ensure the required long lifetime (tau( X)similar or equal to 10(10)-10(22) yr) of the X particle to explain the UH E cosmic rays in the minimal supersymmetric standard model (MSSM) with mass ive Majorana neutrinos. We show that there is no anomaly-free discrete gaug e symmetry to make the lifetime of the X particle sufficiently long in the MSSM with the X particle. We find, however, possible solutions to this prob lem especially by enlarging the particle contents in the MSSM. We show a nu mber of solutions introducing an extra pair of singlets Y and (Y) over bar which have fractional Z(N)(N = 2,3) charges. The present experimental const raints on the X particle are briefly discussed. [S0556-2821(99)02306-1].