Revisiting cosmic distance duality with megamasers and DESI DR2 observations: Model-independent constraints on early-late calibration

Abstract

The cosmic distance duality relation (CDDR) connects the angular diameter distance (𝑑𝐴) and the luminosity distance (𝑑𝐿) at a given redshift. This fundamental relation holds in any metric theory of gravity, provided that photon number is conserved and light propagates along null geodesics. A deviation from this relation could indicate new physics beyond the standard cosmological model. In this work, we test the validity of the CDDR at very low redshifts (𝑧 <0.04) by combining 𝑑𝐴 from the Megamaser Cosmology Project with 𝑑𝐿 from the Pantheon + sample of type Ia supernovae (SNIa). We further incorporate high-redshift baryon acoustic oscillations- (BAO) based 𝑑𝐴 measurements from DESI DR2 in combination with SNIa data, highlighting the critical role of the 𝑟𝑑−𝑀𝑏 (early-late) calibration in testing the CDDR using these two probes. Assuming CDDR holds, we perform a Bayesian analysis to derive model-independent constraints on the calibration parameters. Using only BAO and SNIa data, we observe a strong degeneracy between 𝑟𝑑 and 𝑀𝑏. However, the inclusion of calibration-free megamaser measurements breaks this degeneracy, enabling independent constraints without relying on a specific cosmological model or distance-ladder techniques. Additionally, we present a forecast incorporating the expected precision from future megamaser and SNIa observations, demonstrating their potential to significantly tighten constraints on early-late calibration parameters, under the assumption of validity of CDDR.