Model-independent Test of the Cosmic Distance Duality Relation

Abstract

A validation of the cosmic distance duality (CDD) relation, h() ( ) () () z zdz dz º+ = 1 A L 1 2 , coupling the luminosity (dL) and angular-diameter (dA) distances, is crucial because its violation would require exotic new physics. We present a model-independent test of the CDD, based on strong lensing and a reconstruction of the H II galaxy Hubble diagram using Gaussian processes, to confirm the validity of the CDD at a very high level of confidence. Using parameterizations h( )z z = +1 h0 and h( )z zz =+ + 1 h h 1 2 2, our best-fit results are h = - + 0.0147 0 0.066 0.056, and h = - + 0.1091 1 0.1568 0.1680 and h = - - + 0.0603 2 0.0988 0.0999, respectively. In spite of these strong constraints, however, we also point out that the analysis of strong lensing using a simplified single isothermal sphere (SIS) model for the lens produces some irreducible scatter in the inferred CDD data. The use of an extended SIS approximation, with a power-law density structure, yields very similar results, but does not lessen the scatter due to its larger number of free parameters, which weakens the best-fit constraints. Future work with these strong lenses should therefore be based on more detailed ray-tracing calculations to determine the mass distribution more precisely