Simplified Quartessence Cosmology
  We propose a new class of accelerating world models unifying the cosmological dark sector (dark matter and dark energy). All the models are described by a simplified version of the Chaplygin gas Quartessence cosmology. It is found that even for $\Omega_k \neq 0$, this Quartessence scenario depends only on a pair of parameters which can severely be constrained by the cosmological tests. As an example we perform a joint analysis involving the latest SNe type Ia data and the recent Sloan Digital Sky Survey measurement of baryon acoustic oscillations. In our analysis we have considered the SNe type Ia Union sample compiled by Kowalski et al. (2008). At 95.4% (c.l.), we find for BAO + Union sample, $\alpha=0.81^{+0.04}_{-0.04}$ and $\Omega_{\rm Q4}=1.15^{+0.16}_{-0.17}$. The best fit for this simplified Quartessence scenario is a spatially closed Universe and its reduced $\chi^2$ is exactly the same of the flat concordance model (LambdaCDM) 
J. A. S. Lima, J. V. Cunha, J. S. Alcaniz