Cosmic Chronometers, Pantheon+ Supernovae, and Quasars Favor Coasting Cosmologies over the Flat ΛCDM Model

Abstract

We test and compare coasting cosmological models with curvature parameters $k=\left\{-1,0,+1\right\}$ in ${H}_{0}^{2}{c}^{-2}$ units and the flat ΛCDM model by fitting them to cosmic chronometers (CCs), the Pantheon+ sample of Type Ia supernovae (SNe), and standardized quasars (QSOs). We used the emcee code for fitting CC data, a custom Markov Chain Monte Carlo implementation for SNe and QSOs, and Anderson–Darling tests for normality on normalized residuals for model comparison. Best-fit parameters are presented, constrained by data within redshift ranges z ≤ 2 for CCs, z ≤ 2.3 for SNe, and z ≤ 7.54 for QSOs. Coasting models, particularly the flat coasting model, are generally favored over the flat ΛCDM model. The overfitting of the flat ΛCDM model to Pantheon+ SNe and the large intrinsic scatter in QSO data suggest a need to refine error estimates in these data sets. We also highlight the seemingly fine-tuned nature of either the CC data or Ω _m _,0 in the flat ΛCDM model to an H _1 = H _0 coincidence when fitting H ( z ) = H _1 z + H _0 , a natural feature of coasting models.

Keywords

• Cosmology
• Cosmological models
• Observational cosmology
• Cosmological parameters