QUANTUM-ELECTRODYNAMIC PROCESSES IN A RADIATION-DOMINATED ROBERTSON-WALKER UNIVERSE
Quantum electrodynamics in an expanding Robertson-Walker universe with the line element ds2=dt2 – a2(t)(dx2+dy2+dz2) (radiation-dominated universe) is considered. The differential probability of bremsstrahlung of an electron in the external gravitational field and the differential probability of an electron-positron pair and photon creation from the vacuum are calculated by using the perturbative S-matrix formalism. The behavior of these probabilities in different kinematic regions is investigated. The total probabilities are shown to be finite. In conclusion, the total probability of a pair and photon creation from vacuum We is compared with the total probability of pair production due to an expansion of the universe W0. The comparison shows that We=1.9·10−2W0 at about the Compton time of an electron.