Neutrinos produced by ultrahigh-energy photons at high redshift

Some of the proposed explanations for the origin of ultrahigh-energy cosmic rays invoke new sources of energetic photons (e.g., topological defects, r elic particles, etc.). At high redshift, when the cosmic microwave backgrou nd has a higher temperature hut the radio background is low, the ultrahigh- energy photons can generate neutrinos through pair production of muons and pions. The resulting diffuse background of 10(17) eV neutrinos can be detec ted by future experiments.