Cosmic chronometers in the Rh = ct Universe

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 Lambda cold dark matter (Lambda CDM) model and the R-h = ct Universe with the currently available measurements of H(z), and show that the R-h = ct Universe is favoured 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 +/- 1.6 km s(-1) Mpc(-1), and H-0 is the sole parameter in this model. By comparison, the optimal Lambda CDM model, which has three free parameters (including H-0 = 68.9 +/- 3.3 km s(-1) Mpc(-1), (m) = 0.32, and a dark-energy equation of state p(de) = -(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 approximate to 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 Lambda CDM. 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 (Lambda CDM). Using the concordance Lambda CDM parameter values, rather than those obtained by fitting Lambda CDM to the cosmic chronometer data, would further disfavour Lambda CDM.