Scrutinizing Exotic Cosmological Models Using ESSENCE Supernova Data Combined with Other Cosmological Probes

TL;DR

The paper probes whether exotic cosmologies are required beyond flat $\Lambda$CDM by combining ESSENCE SN Ia data with high-z SNe, CMB, and BAO constraints. It adopts information-criterion model comparison (AIC and BIC) to balance fit quality against model complexity across a suite of dark-energy and gravity models, including constant and evolving $w$, DGP, Cardassian, and Chaplygin-gas scenarios. The results consistently favor the simple flat $\Lambda$ model, with many non-standard models either having worse information criteria scores or reducing to $\Lambda$ in their best-fit limits; some, like flat DGP and standard Chaplygin-gas variants, are strongly disfavored. The study highlights the current limits of distinguishing complex cosmologies with present data and emphasizes the role of future, higher-quality measurements to decisively test deviations from $\Lambda$CDM.

Abstract

The first cosmological results from the ESSENCE supernova survey (Wood-Vasey et al. 2007) are extended to a wider range of cosmological models including dynamical dark energy and non-standard cosmological models. We fold in a greater number of external data sets such as the recent Higher-z release of high-redshift supernovae (Riess et al. 2007) as well as several complementary cosmological probes. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to gauge the worth of models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, the preferred cosmological model is the flat cosmological constant model, where the expansion history of the universe can be adequately described with only one free parameter describing the energy content of the universe. Among the more exotic models that provide good fits to the data, we note a preference for models whose best-fit parameters reduce them to the cosmological constant model.

Figures (9)

• Figure 1: Flat dark-energy model: a flat universe with constant $w$ (Sect. \ref{['sect:flatde']}). The constraint from each of the observational probes is shown by shaded contours (according to the legend). These are all 95% confidence intervals for two parameters. The combined contours (95% and 99.9% confidence intervals) are overlayed in black. The complementarity of the different observational probes is clearly demonstrated in the differing angles of the overlapping contours. The combined data form a clear preference around the cosmological constant model ($w=-1$). Despite the extra freedom afforded by allowing the dark energy to have an equation-of-state parameter that differs from $-1$, the data do not show any indication that this freedom is required.
• Figure 2: Flat, variable $w(a)$ model (Sect. \ref{['sect:wa']}). The contours are the same as in Fig. \ref{['fig:smfcomb']}. The parameters of this model are very poorly constrained by the current data.
• Figure 3: General DGP model (Sect. \ref{['sect:generaldgp']}). The dashed line shows the flat model. Here the contours from the different observational constraints disagree and the model is thus strongly disfavored.
• Figure 4: Cardassian expansion (Sect. \ref{['sect:cardassian']}). The dotted line shows the parameters that would agree with the flat, constant-$w$ model (for a wide range of $w$-values). The cross marks the parameters that match the flat $\Lambda$ model. This is a model with three free parameters ($\Omega_m$ is not shown), and it is not very well constrained by the current data.
• Figure 5: Flat generalized Chaplygin gas (Sect. \ref{['sect:generalchaplygin']}). The cross at $\alpha=0$, $A=0.72$ marks the parameters that match the best-fit flat $\Lambda$ model, while the dotted line shows the parameters that match the $\Lambda$ model (with $\Omega_m=1-A$). Again, despite the flexibility of this model, the best fit is achieved for parameters that are consistent with the flat $\Lambda$ model.