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Putting Flat $\Lambda$CDM In The (Redshift) Bin

by Eoin Ó Colgáin, M.M. Sheikh-Jabbari, Rance Solomon, Maria G. Dainotti, Dejan Stojkovic

Submission summary

Authors (as registered SciPost users):

Eoin O Colgain

Abstract

Flat $\Lambda$CDM cosmology is specified by two constant fitting parameters in the late Universe, the Hubble constant $H_0$ and matter density (today) $\Omega_m$. In the cosmology literature, one typically \textit{assumes} that there is no redshift evolution of cosmological parameters when one fits data sets. Here, in mock observational Hubble data we demonstrate evolution in distributions of best fit parameters with effective redshift. As a result, considerably different $(H_0, \Omega_m)$ best fits from Planck-$\Lambda$CDM cannot be precluded in high redshift bins. We explore if observational Hubble data, Type Ia supernovae and standardisable quasar samples exhibit redshift evolution of best fit $\Lambda$CDM parameters. In all samples, we confirm an increasing $\Omega_m$ (decreasing $H_0$) trend with increasing bin redshift. Through comparison with mocks, we confirm that similar behaviour can arise randomly within the flat $\Lambda$CDM model with probabilities as low as $p = 0.0021$ ($3.1 \, \sigma$).