  We study the imprint of Dark Energy on the density profile of Dark Matter
halos using a set of high-resolution large volume cosmological N-body
simulations from the Dark Energy Universe Simulation Series (DEUSS). We first
focus on the analysis of the goodness-of-fit of the Navarro-Frenk-White (NFW)
profile which we find to vary with halo mass and redshift. We also find that
the fraction of halos ill-fitted by NFW varies with cosmology, thus indicating
that the mass assembly of halos with perturbed density profiles carries a
characteristic signature of Dark Energy. To access this information
independently of any parametric profile, we introduce a new observable
quantity: the halo sparsity $s_\Delta$. This is defined as the mass ratio
$M_{200}/M_\Delta$, i.e. the ratio of mass inside a sphere of radius $r_{200}$
to that contained within a radius $r_\Delta$, enclosing 200 and $\Delta$ times
the mean matter density respectively. We find the average sparsity to be nearly
independent of the total halo mass, while its value can be inferred to better
than a few percent from the ratio of the integrated halo mass functions at
overdensities $\Delta$ and 200 respectively. This provides a consistency
relation that can validate observational measurements of the halo sparsity.
Most importantly, the sparsity significantly varies with the underlying Dark
Energy model, thus providing an alternative cosmological probe.
