Cosmology with Ricci-type dark energy
  We consider the dynamics of a cosmological substratum of pressureless matter
and holographic dark energy with a cutoff length proportional to the Ricci
scale. Stability requirements for the matter perturbations are shown to single
out a model with a fixed relation between the present matter fraction
$\Omega_{m0}$ and the present value $\omega_{0}$ of the equation-of-state
parameter of the dark energy. This model has the same number of free parameters
as the $\Lambda$CDM model but it has no $\Lambda$CDM limit. We discuss the
consistency between background observations and the mentioned
stability-guaranteeing parameter combination.
