A comparison of the R_h=ct and LCDM cosmologies using the Cosmic Distance Duality Relation

TL;DR

This study tests the cosmic distance duality relation without assuming a specific cosmology and finds strong support for it, then compares two cosmological models, favoring R_h=ct over LCDM based on the data.

Contribution

It introduces a model-independent test of the CDD and applies it to compare R_h=ct and LCDM cosmologies, favoring R_h=ct.

Findings

CDD is confirmed with high confidence in a model-independent way.

R_h=ct universe is favored over LCDM based on CDD data.

Likelihood of R_h=ct being correct is approximately 82.3%.

Abstract

The cosmic distance duality (CDD) relation (based on the Etherington reciprocity theorem) plays a crucial role in a wide assortment of cosmological measurements. Attempts at confirming it observationally have met with mixed results, though the general consensus appears to be that the data do support its existence in nature. A common limitation with past approaches has been their reliance on a specific cosmological model, or on measurements of the luminosity distance to Type Ia SNe, which introduces a dependence on the presumed cosmology in spite of beliefs to the contrary. Confirming that the CDD is actually realized in nature is crucial because its violation would require exotic new physics. In this paper, we study the CDD using the observed angular size of compact quasar cores and a Gaussian Process reconstruction of the HII galaxy Hubble diagram---without pre-assuming any particular background cosmology. In so doing, we confirm at a very high level of confidence that the angular-diameter and luminosity distances do indeed satisfy the CDD. We then demonstrate the potential power of this result by utilizing it in a comparative test of two competing cosmological models---the R_h=ct universe and LCDM---and show that R_h=ct is favoured by the CDD data with a likelihood ~82.3% compared with ~17.7% for the standard model.