Electron-positron pairs creation by a photon in the radiation-dominated Robertson-Walker universe

Abstract

Creation of an arbitrary number of electron-positron pairs by a photon in the expanding spatially flat Robertson-Walker universe with the expansion law is considered. In Minkowski spacetime this process is forbidden by the conservation laws (if ). The total probability of the process and the mean number of the Dirac particles created as a result of photon decay have been calculated using the S-matrix approach. The process under consideration is characterized by the decay time of a photon. The pairs creation by the soft photon comes to an end near the Compton time and the decay time of the hard photon is proportional to its energy squared. The dependence of the total decay probability and the mean number of outgoing particles on the initial photon energy have been investigated. The hard photon decay probability increases with an increase of the photon energy as . The estimates having been made show that in the early universe the Dirac particles creation in the processes of photon decays dominates over their production from the vacuum of the free spinor field by the gravitational background.