Paper
A calibration-free null test from anisotropic BAO
Authors
Domenico Sapone, Savvas Nesseris
Abstract
Baryon acoustic oscillation (BAO) analyses usually report the anisotropic shift parameters $α_\perp(z)$ and $α_\parallel(z)$ 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-Lemaître-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.
Metadata
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Raw Data (Debug)
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"raw_xml": "<entry>\n <id>http://arxiv.org/abs/2603.18986v1</id>\n <title>A calibration-free null test from anisotropic BAO</title>\n <updated>2026-03-19T14:54:56Z</updated>\n <link href='https://arxiv.org/abs/2603.18986v1' rel='alternate' type='text/html'/>\n <link href='https://arxiv.org/pdf/2603.18986v1' rel='related' title='pdf' type='application/pdf'/>\n <summary>Baryon acoustic oscillation (BAO) analyses usually report the anisotropic shift parameters $α_\\perp(z)$ and $α_\\parallel(z)$ 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-Lemaître-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.</summary>\n <category scheme='http://arxiv.org/schemas/atom' term='astro-ph.CO'/>\n <published>2026-03-19T14:54:56Z</published>\n <arxiv:comment>6 pages, 4 figures</arxiv:comment>\n <arxiv:primary_category term='astro-ph.CO'/>\n <author>\n <name>Domenico Sapone</name>\n </author>\n <author>\n <name>Savvas Nesseris</name>\n </author>\n </entry>"
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