LIMITS ON MODELS OF THE ULTRAHIGH-ENERGY COSMIC-RAYS BASED ON TOPOLOGICAL DEFECTS

Using the propagation of ultrahigh energy nucleons, photons, and elect rons in the universal radiation backgrounds, we obtain limits on the l uminosity of topological defect scenarios for the origin of the highes t energy cosmic rays. The limits are set as a function of the mass of the X particles emitted by the cosmic strings or other defects, the co smological evolution of the topological defects, and the strength of t he extragalactic magnetic fields. The existing data on the cosmic ray spectrum and on the isotropic 100 MeV gamma-ray background limit signi ficantly the parameter space in which topological defects can generate the flux of the highest energy cosmic rays, and rule out models with the standard X-particle mass of 10(16) GeV and higher.