Revisiting the holographic dark energy in a non-flat universe: alternative model and cosmological parameter constraints

We propose an alternative model for the holographic dark energy in a non-flat universe. This new model differs from the previous one in that the IR length cutoff L is taken to be exactly the event horizon size in a non-flat universe, which is more natural and theoretically/conceptually concordant with the model of holographic dark energy in a flat universe. We constrain the model using the recent observational data including the type Ia supernova data from SNLS3, the baryon acoustic oscillation data from 6dF, SDSSDR7, BOSS-DR11, and WiggleZ, the cosmic microwave background data from Planck, and the Hubble constant measurement from HST. In particular, since some previous studies have shown that the color-luminosity parameter β of supernovae is likely to vary during the cosmic evolution, we also consider such a case that β in SNLS3 is timevarying in our data fitting. Compared to the constant β case, the time-varying β case reduces the value of χ2 by about 35 and results in that β deviates from a constant at about 5σ level, well consistent with the previous studies. For the parameter c of the holographic dark energy, the constant β fit gives c = 0.65 ± 0.05 and the time-varying β fit yields c = 0.72 ± 0.06. In addition, an open universe is favored (at about 2σ) for the model by the current data. (orig.)