Cosmic Distance Duality Relation with DESI DR2 and Transparency

Abstract: The Cosmic Distance Duality Relation (CDDR), a fundamental assumption in modern cosmology, posits a direct link between angular diameter distance and luminosity distance. This study presents a comprehensive, model-independent, and data-driven test of the CDDR using a combination of cosmological observations, including Supernovae (SN), Baryon Acoustic Oscillations (BAO), and Hubble parameter ($H(z)$) measurements. We employ both Gaussian Process Regression (GPR) and a novel Compressed Point (CPI) method for reconstructing the CDDR, alongside four distinct parameterizations for potential deviations. Nuisance parameters, such as the supernova absolute magnitude and BAO scale, are rigorously handled via both joint numerical fitting (Method I) and analytic marginalization (Method II). Our findings reveal that while direct reconstruction of the CDDR exhibits no significant deviation (less than 1-$\sigma$) under specific prior assumptions, a notable departure emerges when the SH0ES prior is incorporated, suggesting a systematic influence from the Hubble constant tension. Independently, our parameterized analysis corroborates the consistency of CDDR and confirms the equivalence of the two constraint methodologies. We also find no significant evidence for cosmic opacity. A comparative assessment of reconstruction techniques indicates that GPR generally yields higher precision. These results emphasize the critical role of prior choices and statistical methods in CDDR analyses, providing valuable insights into fundamental cosmological principles and the ongoing Hubble tension.