X-Rays and Gamma-Rays at Cosmological Distances
Our recent work on absorption and reprocessing of γ-rays at cosmological redshifts as well as the current status of this field of research axe discussed. We consider Compton scattering and pair production by γ-rays on cosmic baryonic matter, and photon-photon scattering and photon-photon pair production by γ-rays and Compton scattering of relativistic pairs on the cosmic blackbody background. We point out the cosmological importance of photon-photon scattering. The region where the universe is transparent to γ-rays and the regions of dominance of the elementary processes in the photon-energy-redshift plane are determined. The problem of cosmological γ-ray reprocessing is relevant, e.g., for observational γ-ray astronomy, for which the signatures of the cosmological origin of discrete and background sources need to be determined, and for studies of the effects that pair cascades, caused by the decay of unstable particles from a hot Big Bang, have on the primordial nucleosynthesis and on the shape of the cosmic microwave background spectrum.
KeywordsPair Production Optical Depth Baryonic Matter Thomson Scattering Cosmological Redshift
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