On DESI's DR2 exclusion of
Abstract
The DESI collaboration, combining their Baryon Acoustic Oscillation (BAO) data with cosmic microwave background (CMB) anisotropy and supernovae data, have found significant indication against the cosmology. This can also be interpreted as the significance of the detection of the wa parameter that measures variation of the dark energy equation of state. DESI's DR2 article quotes exclusion of for combinations of BAO and CMB data with each of three different and overlapping supernovae compilations (at 2.8-sigma for Pantheon+, 3.8-sigma for Union3, and 4.2-sigma for DESY5). We show that one can neither choose amongst nor average over these three different significances. We demonstrate how a principled statistical combination yields a combined exclusion significance of 3.1-sigma. Further we argue that, faced with these competing significances, the most secure inference from the DESI DR2 results is the 3.1-sigma level exclusion of obtained from combining DESI+CMB alone, omitting supernovae.
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