Entropic-force dark energy reconsidered
  We reconsider the entropic-force model in which both kind of Hubble terms
${\dot H}$ and $H^{2}$ appear in the effective dark energy (DE) density
affecting the evolution of the main cosmological functions, namely the scale
factor, deceleration parameter, matter density and growth of linear matter
perturbations. However, we find that the entropic-force model is not viable at
the background and perturbation levels due to the fact that the entropic
formulation does not add a constant term in the Friedmann equations. On the
other hand, if on mere phenomenological grounds we replace the ${\dot H}$
dependence of the effective DE density with a linear term $H$ without including
a constant additive term, we find that the transition from deceleration to
acceleration becomes possible but the recent structure formation data strongly
disfavors this cosmological scenario. Finally, we briefly compare the
entropic-force models with some related DE models (based on dynamical vacuum
energy) which overcome these difficulties and are compatible with the present
observations.
