On the tension between DESI DR2 BAO and CMB

Abstract: Recent DESI DR2 baryon acoustic oscillation (BAO) measurement shows inconsistency with the cosmic microwave background (CMB) observation in $\Lambda$CDM. We used the Bayesian suspiciousness and goodness-of-fit tension metrics to quantify the significance of the tension. Both tension metrics consistently confirm a $\sim2\sigma$ tension between DESI BAO and CMB. We identified the key assumptions of $\Lambda$CDM underlying the tension between BAO and CMB. If the tension is physical, one or multiple of the assumptions might need to be broken by the potential new physics addressing the tension. In particular, the analysis shows that if dynamical dark energy is the only new physics behind the tension, phantom crossing is required to restore concordance between CMB and BAO.