Revealing Intrinsic Flat $\Lambda$CDM Biases with Standardizable Candles

TL;DR

This paper reveals an intrinsic bias in flat $ ext{Lambda}$CDM cosmology, showing that matter density estimates increase and Hubble constant estimates decrease with redshift, which may explain existing cosmological tensions.

Contribution

The study demonstrates that standardizable quasars recover the same cosmology as supernovae at low redshift but show increasing matter density at higher redshift, revealing an intrinsic bias in flat $ ext{Lambda}$CDM.

Findings

QSOs recover Planck-$ ext{Lambda}$CDM at low z

Matter density $ ext{Omega}_m$ increases with redshift

Bias explains $ ext{Lambda}$CDM tensions

Abstract

Emerging high redshift cosmological probes, in particular quasars (QSOs), show a preference for larger matter densities, $\Omega_{m} \approx 1$, within the flat $\Lambda$CDM framework. Here, using the Risaliti-Lusso relation for standardizable QSOs, we demonstrate that the QSOs recover the \textit{same} Planck-$\Lambda$CDM Universe as Type Ia supernovae (SN), $\Omega_m \approx 0.3$ at lower redshifts $ 0 < z \lesssim 0.7$, before transitioning to an Einstein-de Sitter Universe ($\Omega_m =1$) at higher redshifts $z \gtrsim 1$. We illustrate the same trend, namely increasing $\Omega_{m}$ 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 $\Lambda$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 $\Lambda$CDM Universe, whereby $\Omega_m$ increases, $H_0$ decreases and $S_8$ increases with effective redshift, thus providing a new perspective on $\Lambda$CDM tensions; even in a Planck-$\Lambda$CDM Universe the current tensions might have been expected.