Skewness as a test of dark energy perturbations
  We investigate the role played by dark energy perturbations in the skewness
$S_3$ of large-scale matter distribution. We consider a two-fluid universe
composed by matter and dark energy, with perturbations in both components, and
we estimate numerically the skewness of the matter density field as a function
of the dark energy parameters. We characterize today's $S_3$ value for
quintessence and phantom dark energy cosmologies as well as its dependence on
the matter density parameter $\Omega_{m0}$ and the dark energy sound speed
$c^2_s$ with accurate numerical fitting. These fits can be used to test
cosmology against future high quality data on large scale structure.
