J. Phys. Colloques
Volume 35, Numéro C2, Mars 1974Colloque international sur les collisions photon-photon dans les anneaux de stockage électron-positron / International colloquium on photon-photon collisions in electron-positron storage rings
|Page(s)||C2-124 - C2-124|
J. Phys. Colloques 35 (1974) C2-124-C2-124
Absorption of high-energy cosmic photons through double pair production in photon-photon collisionsR. W. BROWN1, K. O. MIKAELIAN1 and R. J. GOULD2
1 Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA
2 Department of Physics, University of California at San Diego, La Jolla, California 92037, USA
At photon energies above 7.2 x 1020 eV, absorption by γ + γ' → 2 e+ + 2 e- dominates that from the lower-order process γ + γ' → e+ + e- for high-energy photons traversing a 2.8 K blackbody photon gas. Existence of the 2 e+, 2 e- process and the cosmic blackbody radiation thus guarantees that the universe is opaque for all photon energies above 1014 eV. The question of single-pair production in collisions with cosmic radio-wave photons is discussed, and the uncertainty in our knowledge of the important low-frequency end of the radio spectrum is emphasized. Other processes (γ + γ' → muons, hadrons, etc.) are discussed briefly, and it is concluded that they are of minor importance.