The oscillating dark energy: future singularity and coincidence problem

We consider the oscillating dark energy with periodic equation of state in two equivalent formulations: ideal fluid or scalar-tensor theory. It is shown that such dark energy suggests the natural way for the unification of early-time inflation with late-time acceleration. We demonstrate how it describes the transition from deceleration to acceleration or from non-phantom to phantom era and how it solves the coincidence problem. The occurrence of finite-time future singularity for the oscillating (phantom) universe is also investigated. (c) 2006 Elsevier B.V. All rights reserved.