The $S_8$ Tension in Light of Updated Redshift-Space Distortion Data and PAge Approximation

TL;DR

This study updates the measurement of the structure growth parameter S_8 using recent redshift-space distortion data combined with supernovae and BAO data, finding results consistent with CMB constraints and showing insensitivity to the cosmological model when using PAge approximation.

Contribution

It provides an updated, less model-dependent constraint on S_8 by combining RSD, SN, and BAO data, and demonstrates the robustness of these constraints with the PAge approximation.

Findings

Updated S_8 measurement consistent with CMB

RSD data prefers lower S_8, but results depend on the model

PAge approximation shows model-insensitive S_8 constraints

Abstract

One of the most prominent challenges to the standard Lambda cold dark matter ($\Lambda$CDM) cosmology is the tension between the structure growth parameter $S_8$ constrained by the cosmic microwave background (CMB) data and the smaller one suggested by the cosmic shear data. Recent studies show that, for $\Lambda$CDM cosmology, redshift-space distortion (RSD) data also prefers a smaller $S_8$ that is $\sim 2$-$3\sigma$ lower than the CMB value, but the result is sensitive to the cosmological model. In the present work we update the RSD constraint on $S_8$ with the most up-to-date RSD data set where the correlation between data points are properly taken into account. To reduce the model dependence, we add in our Monte Carlo Markov Chain calculation the most up-to-date data sets of Type Ia supernovae (SN) and baryon acoustic oscillations (BAO), whose correlation with RSD is also taken into account, to constrain the background geometry. For $\Lambda$CDM cosmology we find $S_8= 0.812 \pm 0.026$, which is $\sim 2\sigma$ larger than previous studies, and hence is consistent with the CMB constraint. By replacing $\Lambda$CDM with the Parameterization based on cosmic Age (PAge), an almost model-independent description of the late universe, we find that the RSD + SN + BAO constraint on $S_8$ is insensitive to the cosmological model.