Cosmic Chronometers in the R_h=ct Universe

TL;DR

This study compares the R_h=ct universe model with the standard LCDM model using cosmic chronometer data, finding that R_h=ct is statistically favored based on multiple model selection criteria.

Contribution

It demonstrates that the R_h=ct universe better fits cosmic chronometer measurements than LCDM, using statistical tools and model comparison metrics.

Findings

R_h=ct fits data with reduced chi^2=0.745

Likelihood of R_h=ct being correct is about 82-91%

LCDM model has more free parameters and lower probability of being correct

Abstract

The use of luminous red galaxies as cosmic chronometers provides us with an indispensable method of measuring the universal expansion rate H(z) in a model-independent way. Unlike many probes of the cosmological history, this approach does not rely on integrated quantities, such as the luminosity distance, and therefore does not require the pre-assumption of any particular model, which may bias subsequent interpretations of the data. We employ three statistical tools -- the Akaike, Kullback, and Bayes Information Criteria (AIC, KIC and BIC) -- to compare the LCDM model and the R_h=ct Universe with the currently available measurements of H(z), and show that the R_h=ct Universe is favored by these model selection criteria. The parameters in each model are individually optimized by maximum likelihood estimation. The R_h=ct Universe fits the data with a reduced chi^2_dof=0.745 for a Hubble constant H_0=63.2+/-2.5 km/s/Mpc, and H_0 is the sole parameter in this model. By comparison, the optimal LCDM model, which has three free parameters (including H_0=68.9+/-2.4 km/s/Mpc, Omega_m=0.32, and a dark-energy equation of state p_de=-rho_de), fits the H(z) data with a reduced chi^2_dof=0.777. With these chi^2_dof values, the AIC yields a likelihood of about 82 per cent that the distance--redshift relation of the R_h=ct Universe is closer to the correct cosmology, than is the case for LCDM. If the alternative BIC criterion is used, the respective Bayesian posterior probabilities are 91.2 per cent (R_h=ct) versus 8.8 per cent (LCDM). Using the concordance LCDM parameter values, rather than those obtained by fitting LCDM to the cosmic chronometer data, would further disfavor LCDM.