Is the $w_0w_a$CDM cosmological parameterization evidence for dark energy dynamics partially caused by the excess smoothing of Planck PR4 CMB anisotropy data?

TL;DR

This study evaluates flat $\Lambda$CDM and dynamical dark energy models using Planck PR4 data, finding mild evidence for evolving dark energy potentially influenced by residual smoothing effects in the data.

Contribution

It compares PR3 and PR4 Planck data constraints on dark energy models, highlighting the impact of residual smoothing on the evidence for dark energy dynamics.

Findings

PR4 data reduces the CMB lensing anomaly compared to PR3.

Current data mildly favor dynamical dark energy over a cosmological constant.

Part of the preference for evolving dark energy may be due to residual smoothing in PR4 spectra.

Abstract

We study the performance of the flat $\Lambda$CDM model and the dynamical dark energy parameterizations $w_0$CDM and $w_0w_a$CDM, in which the dark energy (DE) equation of state is either constant ($w=w_0$) or redshift-dependent [$w(z)=w_0+w_a z/(1+z)$], without and with a varying CMB lensing consistency parameter $A_L$, using combinations of Planck PR4 CMB data (PR4 and lensing), and a compilation of non-CMB data composed of baryon acoustic oscillation (BAO) data that do not include DESI BAO data, Pantheon+ type Ia supernova observations, Hubble parameter measurements $H(z)$, and growth rate $f\sigma_8$ data. We also compare results from earlier Planck PR3 data with those obtained using PR4 data in order to assess the stability of cosmological constraints. For the largest data combinations, PR3/PR4+lensing+non-CMB, the cosmological parameters inferred from PR3 and PR4 data are consistent, almost all differing by $1\sigma$ or less. For the $\Lambda$CDM$+A_L$ model, we have $A_L=1.087 \pm 0.035$ for PR3 and $A_L=1.053 \pm 0.034$ ($1.6\sigma$ above unity) for PR4, which indicates that the CMB lensing anomaly is reduced when PR4 data are used. For the $w_0 w_a$CDM parameterization, we find $w_0 = -0.863\pm0.060$ (quintessence-like) and $w_0+w_a=-1.37^{+0.19}_{-0.17}$ (phantom-like), suggesting that the current observations favor dynamical DE over a cosmological constant at about $1.8\sigma$. For the $w_0w_a$CDM$+A_L$ parameterization, we find $w_0=-0.877\pm 0.060$ and $w_0 + w_a =-1.29_{-0.17}^{+0.20}$, corresponding to a preference for dynamical DE over a cosmological constant of about $1.5\sigma$ and with $A_L = 1.042 \pm 0.037$ exceeding unity at $1.1\sigma$. These results indicate that while the PR4 data mildly favor a time-evolving DE, part of this preference may be associated with possible residual excess smoothing present in the Planck PR4 CMB anisotropy spectra (abridged).