Putting flat ΛCDM in the (Redshift) bin

Flat ΛCDM cosmology is specified by two constant fitting parameters at the background level in the late Universe, the Hubble constant H₀ and matter density (today) Ω_m. Mathematically, H₀ and Ω_m are either integration constants arising from solving ordinary differential equations or are directly related to integration constants. Seen in this context, if fits of the ΛCDM model to cosmological probes at different redshifts lead to different (H₀,Ω_m) parameters, this is a mismatch between mathematics and observation. Here, in mock observational Hubble data (OHD) (geometric probes of expansion history) we demonstrate evolution in distributions of best fit parameters with effective redshift. As a result, considerably different (H₀,Ω_m) best fits from Planck-ΛCDM cannot be precluded in high redshift bins. We explore if OHD, Type Ia supernovae and standardisable quasar samples exhibit redshift evolution of best fit ΛCDM parameters. In all samples, we confirm a decreasing H₀ and increasing Ω_m trend with increasing bin redshift. Through comparison with mocks, we confirm that similar behaviour can arise randomly within the flat ΛCDM model with probabilities as low as p=0.0021 (3.1σ). We present complementary profile distribution analysis confirming the shifts in cosmological parameters in high redshift bins. In particular, we identify a redshift range where Planck (H₀,Ω_m) values are disfavoured at 99.6% (2.9σ) confidence level in a combination of OHD and supernovae data.