Model-independent test of the cosmic distance duality relation

Cheng Zong Ruan, Fulvio Melia, Tong Jie Zhang

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A validation of the cosmic distance duality (CDD) relation, η(z)≡ (1+z)2dA(z)/dL(z) = 1, 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 HII galaxy Hubble diagram using Gaussian Processes, to confirm the validity of the CDD at a very high level of confidence. Using parameterizations η(z) = 1 + η0z and η(z) = 1 + η1z+ η2z2, our best-fit results are η0= 0.0147+0.056-0.066, and η1= 0.1091+0.1680-0.1568and η2= -0.0603+0.0999-0.0988, 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.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Aug 28 2018


  • Cosmology: cosmological parameters, distance scale, observations
  • Galaxies: active
  • Gravitational lensing: strong

ASJC Scopus subject areas

  • General

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