S 8 increases with effective redshift in ΛCDM cosmology

Abstract Hubble constant H0 and weighted amplitude of matter fluctuations S8 determinations are biased to higher and lower values, respectively, in the late Universe with respect to early Universe values inferred by the Planck collaboration within flat ΛCDM cosmology. If these anomalies are physical, i.e. not due to systematics, they naively suggest that H0 decreases and S8 increases with effective redshift. Here, subjecting matter density today Ωm to a prior, corresponding to a combination of Planck CMB and BAO data, we perform a consistency test of the Planck-ΛCDM cosmology and show that S8 determinations from fσ8(z) constraints increase with effective redshift. Due to the redshift evolution, a ∼3σ tension in the S8 parameter with Planck at lower redshifts remarkably becomes consistent with Planck within 1σ at high redshifts. This provides corroborating support for an S8 discrepancy that is physical in origin. We further confirm that the flat ΛCDM model is preferred over a theoretically ad hoc model with a jump in S8 at a given redshift. In the absence of the CMB+BAO Ωm prior, we find that >3σ tensions with Planck in low redshift data are ameliorated by shifts in the parameters in high redshift data. Results here and elsewhere suggest that the ΛCDM cosmological parameters are redshift dependent. Fitting parameters that evolve with redshift is a recognisable hallmark of model breakdown.