Diagnosing holographic dark energy models with statefinder hierarchy
  We apply a series of null diagnostics based on the statefinder hierarchy to
diagnose different holographic dark energy models including the original
holographic dark energy, the new holographic dark energy, the new agegraphic
dark energy, and the Ricci dark energy models. We plot the curves of
statefinders $S^{(1)}_3$ and $S^{(1)}_4$ versus redshift $z$ and the
evolutionary trajectories of $\{S^{(1)}_3, \epsilon\}$ and $\{S^{(1)}_4,
\epsilon\}$ for these models, where $\epsilon$ is the fractional growth
parameter. Combining the evolution curves with the current values of
$S^{(1)}_3$, $S^{(1)}_4$, and $\epsilon$, we find that the statefinder
$S^{(1)}_4$ performs better than $S^{(1)}_3$ for diagnosing the holographic
dark energy models. In addition, the conjunction of the statefinder hierarchy
and the fractional growth parameter is proven to be a useful method to diagnose
the holographic dark energy models, especially for breaking the degeneracy of
the new agegraphic dark energy model with different parameter values.
