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

TL;DR

This paper introduces a new holographic dark energy model in a non-flat universe, constrains it with diverse observational data, and finds that an open universe is favored, with the model fitting well especially when considering a time-varying supernova parameter.

Contribution

It proposes a more natural IR cutoff for holographic dark energy in a non-flat universe and incorporates a time-varying supernova parameter into the analysis.

Findings

Time-varying supernova parameter improves fit significantly.

Open universe is mildly favored by current data.

Parameter c of dark energy is constrained around 0.65-0.72.

Abstract

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, SDSS-DR7, 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 $\beta$ of supernovae is likely to vary during the cosmic evolution, we also consider such a case that $\beta$ in SNLS3 is time-varying in our data fitting. Compared to the constant $\beta$ case, the time-varying $\beta$ case reduces the value of $\chi^2$ by about 35 and results in that $\beta$ deviates from a constant at about 5$\sigma$ level, well consistent with the previous studies. For the parameter $c$ of the holographic dark energy, the constant $\beta$ fit gives $c=0.65\pm 0.05$ and the time-varying $\beta$ fit yields $c=0.72\pm 0.06$. In addition, an open universe is favored (at about 2$\sigma$) for the model by the current data.