Feng, B (reprint author), Chinese Acad Sci, Inst High Energy Phys, POB 918-4, Beijing 100039, Peoples R China.
Current observations seem to mildly favor an evolving dark energy with the equation of state getting across -1. This form of dark energy, dubbed quintom, is studied phenomenologically in this Letter with an oscillating equation of state. We find oscillating quintom can unify the early inflation and current acceleration of the universe, leading to the oscillations of the Hubble constant and a recurring universe. Our oscillating quintom would not lead to a big crunch nor big rip. The scale factor keeps increasing from one period to another and leads naturally to a highly flat universe. The universe in this model recurs itself and we are only staying among one of the epochs, in which sense the coincidence problem is reconciled. (c) 2006 Elsevier B.V. All rights reserved.