2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/15187The square of the four momentum of a photon in vacuum is zero. However, in an unmagnetized plasma it is equal to the square of the plasma frequency. Further, the electron-photon coupling vertex is modified in a plasma to include the effect of the plasma medium. I calculate the cross sections of the three processes - the Compton scattering, electron-positron pair annihilation and production in a plasma. At high plasma densities, the cross sections are found to change significantly. Such high plasma densities exist in several astrophysical sources.8 pages tex files including figuresAstrophysicstext