CONSTRAINING MODIFIED GRAVITY MODELS USING DESI BARYON ACOUSTIC OSCILLATIONS AND PLANCK CMB OBSERVATIONS: A COMPARATIVE COSMOLOGICAL ANALYSIS

Abstract

Baryon acoustic oscillations (BAO) and cosmic microwave background (CMB) observations provide complementary tests of the expansion history and gravitational dynamics of the Universe. This article develops a comparative framework for assessing phenomenological and theory-based modified-gravity models against the standard flat ΛCDM reference using DESI BAO measurements and Planck CMB information. The manuscript synthesizes published observational constraints, identifies the distinct roles of geometric and growth-sensitive probes, and outlines a reproducible inference strategy for model comparison. Particular attention is given to parameter degeneracies, the distinction between background expansion and perturbation growth, and the importance of theoretical stability. Published DESI analyses show that BAO measurements tightly constrain cosmological distances and that joint combinations with CMB information improve parameter determination; however, these results do not by themselves establish a preference for modified gravity. No new MCMC chain or modified-gravity likelihood fit is claimed here. The tables and figures are therefore comparative and methodological, with quantitative values explicitly identified as published benchmarks rather than original estimates. The framework is intended to support a subsequent reproducible analysis using public likelihoods and chains.