Model-Independent Probe of Cosmic Distance Duality Relation

TL;DR

This study tests the cosmic distance duality relation without assuming a specific cosmological model, using gravitational lensing and supernova data to verify its validity in flat and non-flat universes.

Contribution

It provides a model-independent test of the CDDR using observational data, considering both flat and curved spacetime scenarios, which is a novel approach.

Findings

CDDR is consistent with observations in flat universe.

CDDR holds within 1σ in non-flat universe with mild curvature dependence.

No significant deviation from CDDR found with non-linear parametrization.

Abstract

In this paper, cosmic distance duality relation is probed without considering any background cosmological model. The only \textit{a priori} assumption is that the Universe is described by the Friedmann-Lema$\hat{i}$tre-Robertson-Walker (FLRW) metric The strong gravitational lensing (SGL) data is used to construct the dimensionless co-moving distance function $d(z)$ and latest type Ia supernovae (SNe Ia) Pantheon+ data is used to estimate luminosity distances at the corresponding redshifts $z$. Using the distance sum rule along null geodesics of the FLRW metric, the CDDR violation is probed in both flat and non-flat space-time by considering two parametrizations for $\eta(z)$, the function generally used to probe the possible deviations from CDDR. The results show that, CDDR is compatible with the observations at a very high level of confidence for linear parametrization in flat Universe. In non-flat Universe too, CDDR is valid within $1\sigma$ confidence interval with a mild dependence of $\eta$ on the curvature density parameter $\Omega_{K}$ . The results for non-linear parametrization also show no significant deviation from CDDR.