Coherent scalar-field oscillations in an expanding universe

This is the authors' abstract. We don't add key points for this paper.

Motivated by the cosmological importance of coherent (classical), scalar-field oscillations in the context of the invisible axion and the new inflationary-universe scenario, we analyze, in general, the classical evolution of a scalar field in an isotropic and homogeneous cosmology. For a scalar potential of the form V(φ)=aφⁿ, the energy density of the scalar-field oscillations decreases as R^-6n/(n+2) when the oscillations are rapid compared to the expansion rate (R=cosmicscalefactor). We also investigate the effect of higher-order terms in the potential perturbatively, and analyze the decay of the coherent field oscillations due to quantum particle creation.