Sahni, VarunWang, Limin2012-03-122012-03-122000-01-14http://hdl.handle.net/11007/1281We propose a new class of quintessence models in which late times oscillations of a scalar field give rise to an effective equation of state which can be negative and hence drive the observed acceleration of the universe. Our ansatz provides a unified picture of quintessence and a new form of dark matter we call Frustrated Cold Dark Matter (FCDM). FCDM inhibits gravitational clustering on small scales and could provide a natural resolution to the core density problem for disc galaxy halos. Since the quintessence field rolls towards a small value, constraints on slow-roll quintessence models are safely circumvented in our model.enNew cosmological modelQuintessenceDark matterGalaxyPreprint