Absorption of high-energy cosmic photons through double pair production in photon-photon collisions

Abstract

' yields 2e/sup +/ + 2e/sup -/ dominates that from the lower- order process gamma + gg yields e/sup +/ + e/sup -/ for high-energy photons traversing a 2.8 K blackbody photon gas. Existence of the 2e/sup +/, 2e/sup -/ process and the cosmic blackbody radiation thus guarantees that the universe is opaque for all photon energies above 10/sup 14/ eV. The question of single-pair production in collisions with cosmic radio-wave photons is discussed, and the uncertainty in the knowledge of the important low-frequency end of the radio spectrum is emphasized. Other processes ( gamma + gamma -- muons, hadrons, etc.) are discussed briefly, and it is concluded that they are of minor importance. (auth)