Constraints on the phase plane of the dark energy equation of state

Classification of dark energy models in the plane of w and w', where w is the dark energy equation of state and w' its time-derivative in units of the Hubble time, has been studied in the literature. We take the current SN Ia, CMB and BAO data, invoke a widely used parametrization of the dark energy equation of state, and obtain the constraints on the w-w' plane. We find that several dark energy models including the cosmological constant, phantom, non-phantom barotropic fluids, and monotonic up-rolling quintessence are ruled out at the 68.3% confidence level based on the current observational data. On the other hand, down-rolling quintessence, including the thawing and the freezing models, is consistent with the current observations. All the above-mentioned models are still consistent with the data at the 95.4% confidence level. (C) 2009 Elsevier B.V. All rights reserved.