Evolution of Oscillating Scalar Fields as Dark Energy

TL;DR

This paper analyzes oscillating scalar field models for dark energy, classifying their evolution based on when oscillations begin relative to cosmic epochs, and compares these models with supernova data.

Contribution

It provides a classification scheme for oscillating dark energy models based on the timing of oscillation onset and evaluates their consistency with observations.

Findings

Oscillation frequency relative to expansion rate always increases if dark energy declines slowly.

Models can be classified into early, late, and non-oscillating types based on oscillation onset.

Some models in all three classes fit supernova data well.

Abstract

Oscillating scalar fields, with an oscillation frequency much greater than the expansion rate, have been proposed as models for dark energy. We examine these models, with particular emphasis on the evolution of the ratio of the oscillation frequency to the expansion rate. We show that this ratio always increases with time if the dark energy density declines less rapidly than the background energy density. This allows us to classify oscillating dark energy models in terms of the epoch at which the oscillation frequency exceeds the expansion rate, which is effectively the time at which rapid oscillations begin. There are three basic types of behavior: early oscillation models, in which oscillations begin during the matter-dominated era, late oscillation models, in which oscillations begin after scalar-field domination, and non-oscillating models. We examine a representative set of models (those with power-law potentials) and determine the parameter range giving acceptable agreement with the supernova observations. We show that a subset of all three classes of models can be consistent with the observational data.