Planck 2015 constraints on spatially-flat dynamical dark energy models

TL;DR

This paper uses Planck 2015 data to constrain flat dynamical dark energy models, finding they slightly improve fit over Lambda-CDM and help reduce tension between different cosmological measurements.

Contribution

It provides the first detailed constraints on tilted XCDM and $$CDM models using Planck 2015 data, showing they fit the data slightly better than Lambda-CDM.

Findings

Dynamical dark energy models slightly improve fit to CMB and BAO data.

These models reduce tension between Planck CMB and weak lensing measurements.

The improvement over Lambda-CDM is not statistically significant.

Abstract

We determine constraints on spatially-flat tilted dynamical dark energy XCDM and $\phi$CDM inflation models by analyzing Planck 2015 cosmic microwave background (CMB) anisotropy data and baryon acoustic oscillation (BAO) distance measurements. XCDM is a simple and widely used but physically inconsistent parameterization of dynamical dark energy, while the $\phi$CDM model is a physically consistent one in which a scalar field $\phi$ with an inverse power-law potential energy density powers the currently accelerating cosmological expansion. Both these models have one additional parameter compared to standard $\Lambda$CDM and both better fit the TT + lowP + lensing + BAO data than does the standard tilted flat-$\Lambda$CDM model, with $\Delta \chi^2 = -1.26\ (-1.60)$ for the XCDM ($\phi$CDM) model relative to the $\Lambda$CDM model. While this is a 1.1$\sigma$ (1.3$\sigma$) improvement over standard $\Lambda$CDM and so not significant, dynamical dark energy models cannot be ruled out. In addition, both dynamical dark energy models reduce the tension between the Planck 2015 CMB anisotropy and the weak lensing $\sigma_8$ constraints.