Probing the dynamics of dark energy with divergence-free
  parametrizations: A global fit study
  The CPL parametrization is very important for investigating the property of
dark energy with observational data. However, the CPL parametrization only
respects the past evolution of dark energy but does not care about the future
evolution of dark energy, since $w(z)$ diverges in the distant future. In a
recent paper [J.Z. Ma and X. Zhang, Phys.\ Lett.\ B {\bf 699}, 233 (2011)], a
robust, novel parametrization for dark energy, $w(z)=w_0+w_1({\ln (2+z)\over
1+z}-\ln2)$, has been proposed, successfully avoiding the future divergence
problem in the CPL parametrization. On the other hand, an oscillating
parametrization (motivated by an oscillating quintom model) can also avoid the
future divergence problem. In this Letter, we use the two divergence-free
parametrizations to probe the dynamics of dark energy in the whole evolutionary
history. In light of the data from 7-year WMAP temperature and polarization
power spectra, matter power spectrum of SDSS DR7, and SN Ia Union2 sample, we
perform a full Markov Chain Monte Carlo exploration for the two dynamical dark
energy models. We find that the best-fit dark energy model is a quintom model
with the EOS across -1 during the evolution. However, though the quintom model
is more favored, we find that the cosmological constant still cannot be
excluded.
