Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area of the event horizon of the Universe. However, such a model would have a causality problem. In this paper, we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We show that this model does not only avoid the causality problem and is phenomenologically viable, but also naturally solves the coincidence problem of dark energy. Our analysis of the evolution of density perturbations show that the matter power spectra and CMB temperature anisotropy is only slightly affected by such modification.

In this paper, we use the type Ia supernovae data to constrain the holographic dark energy model proposed by Li. We also apply a cosmic age test to this analysis. We consider in this paper a spatially flat Friedmann-RobertsonWalker Universe with matter component and holographic dark energy component. The fit result shows that the case c < 1 (c = 0.21) is favored, which implies that the holographic dark energy behaves as a quintom-type dark energy. Furthermore, we also perform a joint analysis of SNe+CMB+LSS to this model; the result is well improved, and still upholds the quintom dark energy conclusion. The best fit results in our analysis are c = 0.81, Ω 0 m = 0.28, and h = 0.65, which lead to the present equation of state of dark energy w 0 = −1.03 and the deceleration/acceleration transition redshift z T = 0.63. Finally, an expected SNAP simulation using ΛCDM as a fiducial model is performed on this model, and the result shows that the holographic dark energy model takes on c < 1 (c = 0.92) even though the dark energy is indeed a cosmological constant.