PROPAGATION OF ULTRA-HIGH ENERGY PROTONS AND GAMMA-RAYS OVER COSMOLOGICAL DISTANCES AND IMPLICATIONS FOR TOPOLOGICAL DEFECT MODELS

We describe the results of a hybrid matrix-Monte Carlo calculation of cascading of UHE cosmic rays and gamma-rays through the cosmic backgro und radiation fields over cosmological distances. We calculate the gam ma-ray and neutrino emission that results from the cascade, as well as the effect of cascading on the primary spectrum. We discuss the resul ts for various cosmic ray injection spectra and primary species. Certa in models for the production of the highest energy cosmic rays are rul ed out.