Effects of quantum fields on singularities and particle horizons in the early universe. III. The conformally coupled massive scalar field

The behaviors of solutions to the semiclassical backreaction equations are investigated for conformally invariant free quantum fields and a conformally coupled massive scalar field in spatially flat homogeneous and isotropic spacetimes containing classical radiation. With one exception, only solutions that begin with the scale factor equal to zero are considered. It is found that in the limit that the scale factor vanishes the presence of the massive scalar field does not result in any new types of solutions, nor does it eliminate any. Thus the results of the first paper of this series on the existence of particle horizons are also valid for solutions beginning with zero scale factor if a conformally coupled massive scalar field is present. For intermediate values of the scale factor the massive scalar field can significantly affect the behaviors of specific solutions. Nevertheless, no new types of behaviors are observed and no old ones are eliminated. For large values of the scale factor it is uncertain what the behaviors of all solutions are, but asymptotically de Sitter solutions and asymptotically classical solutions continue to exist. Particle production causes the latter to expand like classical-matter-dominated universes at late times.