Robust model comparison disfavors power law cosmology

TL;DR

This study compares power law and standard cosmologies using supernova and BAO data, finding that power law models are generally disfavored, especially when systematic errors are considered, challenging alternative cosmological theories.

Contribution

It provides a comprehensive model comparison showing that power law cosmology is less favored than LambdaCDM when systematic errors are included in the analysis.

Findings

Power law expansion is not strongly preferred over LambdaCDM with separate data sets.

Power law expansion is strongly disfavored when combining SN Ia and BAO data.

The Rh = ctC cosmology is conclusively disfavored by all data combinations including SN Ia.

Abstract

Late-time power law expansion has been proposed as an alternative to the standard cosmological model and shown to be consistent with some low-redshift data. We test power law expansion against the standard flat $\Lambda$CDM cosmology using goodness-of-fit and model comparison criteria. We consider Type Ia supernova (SN Ia) data from two current compilations (JLA and Union2.1) along with a current set of baryon acoustic oscillation (BAO) measurements that includes the high-redshift Lyman-$\alpha$ forest measurements from BOSS quasars. We find that neither power law expansion nor $\Lambda$CDM is strongly preferred over the other when the SN Ia and BAO data are analyzed separately but that power law expansion is strongly disfavored by the combination. We treat the $R_\text{h} = ct$ cosmology (a constant rate of expansion) separately and find that it is conclusively disfavored by all combinations of data that include SN Ia observations and a poor overall fit when systematic errors in the SN Ia measurements are ignored, despite a recent claim to the contrary. We discuss this claim and some concerns regarding hidden model dependence in the SN Ia data.