Cosmography and flat $\Lambda$CDM tensions at high redshift

TL;DR

This paper critically examines high-redshift cosmography using supernovae, quasars, and gamma-ray bursts, revealing that previous claims of tension with the flat Lambda Cold Dark Matter model are due to model failure and data issues.

Contribution

It demonstrates that the log polynomial cosmographic expansion fails beyond redshift 2, and confirms the flat Lambda CDM model is preferred over previous tension claims.

Findings

Log polynomial expansion fails beyond z~2

Flat Lambda CDM is statistically preferred

QSO data causes the apparent tension

Abstract

Risaliti, Lusso \& collaborators have constructed a high-redshift Hubble diagram of supernovae (SNe); quasars (QSO) and gamma-ray bursts (GRB) that shows a "$\sim 4 \, \sigma$ tension with the $\Lambda$CDM model" based on a log polynomial cosmographic expansion (Risaliti et.al 2018, Lusso et.al 2019). In this work, we demonstrate that the log polynomial expansion generically fails to recover flat $\Lambda$CDM beyond $z \sim 2$, thus undermining the $\sim 4 \, \sigma$ tension claim. Moreover, through direct fits of both the flat $\Lambda$CDM and the log polynomial model to the SNe+QSO+GRB dataset, we confirm that the flat $\Lambda$CDM model is preferred. Ultimately, we trace the tension to the QSO data and show that a best-fit of the flat $\Lambda$CDM model to the QSO data leads to a flat $\Lambda$CDM Universe with no dark energy within $1 \, \sigma$. This marks an irreconcilable tension between the Risaliti-Lusso QSOs and flat $\Lambda$CDM.