A New Consistency Test for the ΛCDM Model Using Radial and Transverse Baryon Acoustic Oscillation Measurements

Abstract

We present a calibration-free consistency test of spatially flat ΛCDM based on baryon acoustic oscillation (BAO) distance measurements. The method forms ratios of BAO distances including the Hubble distance, the comoving angular diameter distance, and the volume-averaged distance, so that the sound horizon scale cancels, and then maps each observed ratio to an effective flat-ΛCDM matter density parameter, ΩMΛ , defined as the value of ΩM that reproduces the measured ratio within ΛCDM. Flat ΛCDM predicts that ΩMΛ should be independent of redshift and of the particular ratio used. For ratios involving the integrated distances, we associate them with well-defined effective line-of-sight redshift intervals based on the integral mean value theorem. We apply the test to BAO measurements from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1) and Data Release 2 (DR2), propagating the full published BAO covariance matrices into all derived ratios and ΩMΛ constraints. We find no statistically significant deviation from flat ΛCDM in either DESI DR1 or DESI DR2. Within current uncertainties, the inferred ΩMΛ values are broadly consistent with a redshift-independent constant, providing an internal consistency check of flat ΛCDM that can be strengthened straightforwardly as BAO measurements improve.