Robust evidence for dynamical dark energy in light of DESI DR2 and joint ACT, SPT, and Planck data

Abstract

Recent baryon acoustic oscillation (BAO) measurements released by DESI, when combined with cosmic microwave background (CMB) data and type Ia supernova (SN) data, suggest a significant preference for dynamical dark energy (DDE) that exhibits the phantom-like behavior in the past and has transitioned into quintessence-like behavior today. In this work, we conduct a comprehensive analysis of six representative DDE parametrization models by utilizing the latest and most precise CMB data jointly from ACT, SPT, and Planck, in conjunction with BAO data from DESI DR2 and SN data from DESY5, PantheonPlus, and Union3. Our overall analysis indicates that the preference for DDE in the Quintom-B regime remains robust, regardless of the DDE parameterization model and the data combination employed. The trend of this preference is significantly strengthened with the support of DESY5 SN data. Specifically, when using the CMB+DESI+DESY5 data, for the Barboza-Alcaniz (BA) model, we obtain $w_0 = -0.785 \pm 0.047$ and $w_a = -0.43^{+0.10}_{-0.09}$, which significantly deviate from the $\Lambda$CDM values and provide evidence for DDE at the $4.2\sigma$ level. By the reconstruction of the dark energy equation of state $w(z)$, normalized dark energy density $f_{\mathrm{DE}}(z)$, and the deceleration parameter $q(z)$, we also observe clear departures from $\Lambda$CDM, further reinforcing the case for DDE. Furthermore, the Bayesian evidence analysis indicates that the Chevallier-Polarski-Linder, BA and Exponential models are moderately favored relative to $\Lambda$CDM based on the CMB+DESI+DESY5 data.