Gamma rays from superheavy relic particles in the halo

Superheavy (SH) quasistable particles generated in the early universe could be responsable for ultrahigh energy cosmic rays (UHECRs) and be a component of cold dark matter in the universe. These particles are likely to cluster in the galactic halo, so that the main part of UHECRs are gamma rays produced in the decay of neutral pions. Charged pions are also produced in the same process and result in high energy electrons. We consider here the production of gamma rays by synchrotron emission of these electrons in the galactic magnetic field. The gamma ray fluxes are in the region of interest for some current and proposed experiments (e.g. EGRET, GLAST, MILAGRO) in the energy range 0.1-10(4) GeV. A comparison with the existing upper limits at 10(5)-10(8) GeV is also carried out. The detection of this flux of gamma rays would be an important signature of SH relic particles as sources of UHECRs and would give a clue to the physics of the early universe. [S0556-2821(99)03114-8].