On DESI's DR2 exclusion of $\Lambda$CDM

Understand

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 $\Lambda$CDM cosmology.

• This can also be interpreted as the significance of the detection of the $w_a$ parameter that measures variation of the dark energy equation of state.
• DESI's DR2 article quotes exclusion of $\Lambda$CDM 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.