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arXiv · 2603.18986

A calibration-free null test from anisotropic BAO

Domenico Sapone·Savvas Nesseris
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Abstract

Baryon acoustic oscillation (BAO) analyses usually report the anisotropic shift parameters $\alpha_\perp(z)$ and $\alpha_\parallel(z)$ relative to a fiducial cosmology, and these quantities are primarily used for cosmological parameter inference. Here we show that they can also be used to construct a direct internal consistency test of the background geometry. In particular, we derive a new null test of flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) geometry written entirely in terms of the reported BAO shift parameters. The test is calibration free: the sound-horizon ratio $r_{\rm d}/r^{\rm fid}_{\rm d}$ cancels identically, so the relation is independent of the absolute BAO scale. We also derive a calibration-free reconstruction of the deceleration parameter $q(z)$ from the radial BAO sector. Applying these results to anisotropic DESI DR2 BAO measurements, we find no evidence for a breakdown of the flat-FLRW distance relation within current uncertainties. Our results show that anisotropic BAO measurements already provide a nontrivial internal geometric consistency test before performing any model fit.

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Domenico Sapone, Savvas Nesseris. 2026-03-19. A calibration-free null test from anisotropic BAO. https://arxiv.org/abs/2603.18986

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