On the tension between DESI DR2 BAO and CMB

TL;DR

Recent DESI DR2 BAO measurements show a consistent ~2σ tension with CMB data under ΛCDM, suggesting potential need for new physics such as dynamical dark energy with phantom crossing.

Contribution

This study quantifies the tension between DESI BAO and CMB data using Bayesian metrics and explores the implications for ΛCDM assumptions and possible new physics.

Findings

DESI BAO and CMB data are in ~2σ tension.

Phantom crossing in dark energy may reconcile the tension.

Key ΛCDM assumptions underlie the observed discrepancy.

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.