Holographic Ricci dark energy: Interacting model and cosmological
  constraints
  We extend the holographic Ricci dark energy model to include some direct,
non-gravitational interaction between dark energy and dark matter. We consider
three phenomenological forms for the interaction term $Q$ in the model, namely,
$Q$ is taken proportional to the Hubble expansion rate and the energy densities
of dark sectors (taken to be $\rho_{\rm de}$, $\rho_{\rm m}$, and $\rho_{\rm
de}+\rho_{\rm m}$, respectively). We obtain a uniform analytical solution to
the three interacting models. Furthermore, we constrain the models by using the
latest observational data, including the 557 Union2 type Ia supernovae data,
the cosmic microwave background anisotropy data from the 7-yr WMAP, and the
baryon acoustic oscillation data from the SDSS. We show that in the interacting
models of the holographic Ricci dark energy, a more reasonable value of
$\Omega_{\rm m0}$ will be obtained, and the observations favor a rather strong
coupling between dark energy and dark matter.
