A unification of RDE model and XCDM model

In this Letter, we propose a new generalized Ricci dark energy (NGR) model to unify Ricci dark energy (RDE) and XCDM. Our model can distinguish between RDE and XCDM by introducing a parameter beta called weight factor. When beta = 1, NGR model becomes the usual RDE model. The XCDM model is corresponding to beta = 0. Moreover, NGR model permits the situation where neither beta = 1 nor beta = 0. We then perform a statefinder analysis on NGR model to see how beta effects the trajectory on the r-s plane. In order to know the value of beta, we constrain NGR model with latest observations including type la supernovae (SNe la) from Union2 set (557 data), baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. With Markov Chain Monte Carlo (MCMC) method, the constraint result is beta = 0.08(-0.21)(+0.30) (1 sigma)(-0.28)(+0.43)(2 sigma), which manifests the observations prefer a XCDM universe rather than RDE model. It seems RDE model is ruled out in NCR scenario within 2 sigma regions. Furthermore, we compare it with some of successful cosmological models using AIC information criterion. NCR model seems to be a good choice for describing the universe. (C) 2012 Elsevier B.V. All rights reserved.