Orateur
Description
I present new cosmological fits to the Hubble diagram built from supernovae and a homogeneous quasar sample spanning a redshift interval z = 0.7--3.5. The quasar distances are derived from the non-linear relation between X-ray and UV luminosities, and the sample is selected to minimize dust reddening, gas obscuration, host-galaxy contamination, and selection biases. This provides high-quality constraints in a redshift range otherwise poorly covered by Type~Ia supernovae. The main results are: (1) the combined Hubble diagram shows strong (> 4 σ) tension with the standard flat ΛCDM model at z ≥ 1.5; (2) in the overlap region, the quasar and supernova Hubble diagrams are fully consistent, supporting a common distance scale; (3) allowing for an evolving dark-energy equation of state yields a significantly better fit, with w_0 and w_a values compatible with those favored by recent DESI results; (4) our quasar Hubble diagram and cosmological constraints agree closely with an independent analysis based on ~6,000 quasars standardized via variability distances (Dutra et al.~2026). The convergence of two independent quasar methods strengthens the case that the deviation from flat \lcdm at high redshift is not driven by sample-specific systematics.