Effects of the electromagnetic interaction upon particle creation in Robertson-Walker universes. I. A general framework for the calculation of particle creation

Abstract

The author presents an investigation of the effects of the electromagnetic interaction described by the Lagrangian Lint=ie psi gamma mu Amu psi upon particle creation in expanding Robertson-Walker universes with the line element ds2=C2( eta )(dx2-d eta 2). This interaction causes the simultaneous creation of photons and electron-positron pairs and thus proves to be a peculiar source of cosmological photons which cannot be created as free particles in the cosmological models considered. Since the electromagnetic interaction does not change the conformal-invariance properties of the theory, conformal symmetry is broken by the mass term of the Dirac equation alone even if this interaction is included. Consequently, there is no effect due to interaction and thus no particle creation at all if the particle mass can be considered as negligible. This type of interaction may significantly affect processes like particle production much later than the Planck time when the age of the universe is about the Compton time of the Dirac particles. The creation of electrons and positrons by the gravitational field, which is possible even in the absence of non-gravitational interactions, causes the electromagnetic interaction to produce additionally less than one electron-positron pair per photon.