paper

Constraints on Dynamical Dark Energy from Multiple Probes in the Full Dark Energy Survey

arXiv:2605.27221

Abstract

We present results on dark energy evolution, assuming a time-dependent equation of state $w (a) = w_{0} + w_{a} (1 - a)$ , from growth and geometric probes using the full six-year Dark Energy Survey dataset: type Ia supernovae, baryon acoustic oscillations, and weak gravitational lensing and galaxy clustering (3 $\times$ 2pt). The combination yields $w_{0} = - 0.8 4_{- 0.10}^{+ 0.10}$ and $w_{a} = - 0.4 4_{- 0.55}^{+ 0.60}$ , the tightest constraints ever obtained from a single survey, with $2.2 I ¨ $ deviation from a cosmological constant. Adding the DESI DR2 BAO data yields $w_{0} = - 0.8 4_{- 0.07}^{+ 0.06}$ and $w_{a} = - 0.5 3_{- 0.28}^{+ 0.33}$ , representing the most stringent low-redshift-only test of dynamical dark energy to date, with a $2.3 I ¨ $ deviation. In this combination, adding 3 $\times$ 2pt doubles the constraining power. Finally, when combined with primary CMB information, we obtain $w_{0} = - 0.8 2_{- 0.05}^{+ 0.05}$ , $w_{a} = - 0.6 3_{- 0.18}^{+ 0.21}$ , with a $3.0 I ¨ $ deviation. We find that including 3 $\times$ 2pt in the previously studied SN + DESI BAO + CMB combination leaves the significance essentially unchanged ( $3.2 I ¨ $ to $3.0 I ¨ $ ) while improving the figure of merit by $\sim$ 10\%. We systematically investigate the impact of leaving out each one of the probes and find that the significance of the deviation from a cosmological constant ranges from 2.3 to 3.2 $I ¨ $ , with best-fit parameters consistently in the region $w_{0} > - 1$ and $w_{a} < 0$ . Excluding SN from the all data combination yields a $2.6 I ¨ $ departure from $I^$ CDM, providing a cross-check independent of supernova photometric calibration. These results support the weak preference for evolving dark energy reported by several recent cosmological analyses. By combining growth and geometric probes from a single survey, this work realizes the multi-probe dark energy program envisioned at the inception of DES.

10 pages, 3 figures, 2 tables, including Supplemental Material. v2: version submitted to PRL