Revealing Intrinsic Flat $\mathrm{\Lambda }$CDM Biases with Standardizable Candles

Emerging high redshift cosmological probes, in particular quasars (QSOs), show a preference for larger matter densities, ${\mathrm{\Omega }}_m\approx 1$, within the flat $\mathrm{\Lambda }$CDM framework. Here, using the Risaliti-Lusso relation for standardizable QSOs, we demonstrate that the QSOs recover the $\mathit{\text{same}}$ Planck-$\mathrm{\Lambda }$CDM Universe as Type Ia supernovae (SN), ${\mathrm{\Omega }}_m\approx 0.3$ at lower redshifts $0<z\lesssim 0.7$, before transitioning to an Einstein-de Sitter Universe (${\mathrm{\Omega }}_m=1$) at higher redshifts $z\gtrsim 1$. We illustrate the same trend, namely increasing ${\mathrm{\Omega }}_m$ and decreasing $H_0$ with redshift, in SN but poor statistics prevent a definitive statement. We explain physically why the trend is expected in the flat $\mathrm{\Lambda }$CDM cosmology, illustrate the intrinsic bias and non-Gaussian tails with mock Pantheon data, and identify a similar trend in BAO below $z=1$. Our results highlight an intrinsic bias in the flat $\mathrm{\Lambda }$CDM Universe, whereby ${\mathrm{\Omega }}_m$ increases, $H_0$ decreases and $S_8$ increases with effective redshift, thus providing a new perspective on $\mathrm{\Lambda }$CDM tensions; even in a Planck-$\mathrm{\Lambda }$CDM Universe the current tensions might have been expected.