Further support for $S_8$ increasing with effective redshift

TL;DR

This study provides statistical evidence supporting an increasing trend of $S_8$ with redshift, combining recent datasets and previous findings to suggest potential deviations from the standard cosmological model.

Contribution

It quantifies the significance of the $S_8$ increasing trend across multiple datasets and combines results to strengthen evidence for potential new physics.

Findings

Combined significance of $3$ to $3.7\sigma$ for increasing $S_8$ trend.

Probabilities of $p=0.0163$ and $p=0.01893$ for individual datasets.

Supports previous studies indicating redshift-dependent $S_8$ behavior.

Abstract

In Adil et al. 2023, we reported an increasing trend in $S_8$ with effective redshift $z_{\textrm{eff}}$ based on $f \sigma_8(z)$ constraints over the redshift range $0 \lesssim z \lesssim 2$, and predicted that this trend would be observable in independent datasets. Recently, the studies by Artis et al. and the ACT+DESI collaboration appeared, presenting data that aligns with the expected trends. In this letter, we quantify the statistical significance of the increasing $S_8$ trends in recent studies by fitting a linear model to estimate the slope $\Delta\,S_8/\Delta\, z_{\textrm{eff}}$, and comparing the results to mock simulations. We find probabilities of $p = 0.0163$ and $p = 0.01893$, corresponding to approximately $2.1\sigma$ for each dataset. Using Fisher's method to combine the independent probabilities, we obtained $p=0.0027$ ($2.8 \sigma$). When we incorporate our earlier findings, the combined statistical significance reaches between $3\sigma$ and $3.7\sigma$. Finally, we discuss how ``scatter" in $\sigma_8$/$S_8$ constraints from recent DESI full-shape galaxy clustering fits this picture at low statistical significance. This letter continues a series of studies initiated in 2020 that explore redshift-dependent $\Lambda$CDM parameters as an indication of a breakdown in the standard cosmological model.