PHOTON-EMISSION FROM THE VACUUM IN A RADIATION-DOMINATED UNIVERSE

A study is made of photon emission from the vacuum accompanied by production of an arbitrary number of electron-positron pairs in a Robertson-Walker space with the expansion law a(t) = a0 square-root t. In Minkowski space, this process is forbidden by the conservation laws. The total probability of the process and the mean number of Dirac particles produced in the process of interaction of the quantized fields are calculated. Approximate expressions for the probability of emission of soft and hard photons are found. Numerical estimates are obtained for the mean number N-gamma of emitted photons and the number N(D) of produced particles, and they are compared with the number N0 of Dirac particles produced from the vacuum in the absence of radiative interaction. The comparison shows that N(D) = 0.90N-gamma and N-gamma = 1.25 X 10(-3) N0.