Generalized Holographic and Ricci Dark Energy Models
  In this paper, we consider generalized holographic and Ricci dark energy
models where the energy densities are given as
$\rho_{R}=3c^2M^{2}_{pl}Rf(H^2/R)$ and $\rho_{h}=3c^2M^{2}_{pl}H^2g(R/H^2)$
respectively, here $f(x),g(y)$ are positive defined functions of dimensionless
variables $H^2/R$ or $R/H^2$. It is interesting that holographic and Ricci dark
energy densities are recovered or recovered interchangeably when the function
$f(x)=g(y)\equiv 1$ or$f=g\equiv Id$ is taken respectively (for example
$f(x),g(x)=1-\epsilon(1-x)$, $\epsilon=0 \text{or} 1$ respectively). Also, when
$f(x)\equiv xg(1/x)$ is taken, the Ricci and holographic dark energy models are
equivalents to a generalized one. When the simple forms $f(x)=1-\epsilon(1-x)$
and $g(y)=1-\eta(1-y)$ are taken as examples, by using current cosmic
observational data, generalized dark energy models are researched. As expected,
in these cases, the results show that they are equivalent
($\epsilon=1-\eta=1.312$) and Ricci-like dark energy is more favored relative
to the holographic one where the Hubble horizon was taken as an IR cut-off.
And, the suggestive combination of holographic and Ricci dark energy components
would be $1.312 R-0.312H^2$ which is $2.312H^2+1.312\dot{H}$ in terms of $H^2$
and $\dot{H}$.
