The Dark Energy Survey Supernova Program: A Reanalysis Of Cosmology Results And Evidence For Evolving Dark Energy With An Updated Type Ia Supernova Calibration

TL;DR

This work reanalyzes the DES-SN5YR supernova sample with an updated calibration (DES-Dovekie), retrained SALT3 model, and corrected colour-law implementation, achieving tighter cosmological constraints. By combining DES-Dovekie SN data with Planck/ACT/SPT CMB and DESI DR2 BAO, the study finds $\\Omega_m = 0.3045 \\pm 0.0032$ (SN+CMB+BAO) and $w_0 = -0.803 \\pm 0.054$, $w_a = -0.72 \\pm 0.21$ in a Flat $w_0w_a$CDM framework, with a frequentist $3.2\\sigma$ and Bayesian $\\Delta \log \mathcal{Z} = -1.7$ indicating only weak evidence for evolving dark energy. The analysis shows reduced tension with external probes and finds no robust evidence for nonzero spatial curvature, while the Hubble constant remains incongruent with local distance-ladder measurements. The improvements over DES-SN5YR demonstrate that cross-survey calibration, updated colour laws, and refined systematics modeling are critical for robust SN-based cosmology and for interpreting late-time dark energy evolution. Overall, the results suggest a mild preference for evolving dark energy but are not statistically decisive given current data combinations.

Abstract

We present improved cosmological constraints from a re-analysis of the Dark Energy Survey (DES) 5-year sample of Type Ia supernovae (DES-SN5YR). This re-analysis includes an improved photometric cross-calibration, recent white dwarf observations to cross-calibrate between DES and low redshift surveys, retraining the SALT3 light curve model and fixing a numerical approximation in the host galaxy colour law. Our fully recalibrated sample, which we call DES-Dovekie, comprises $\sim$1600 likely Type Ia SNe from DES and $\sim$200 low-redshift SNe from other surveys. With DES-Dovekie, we obtain $Ω_{\rm m} = 0.330 \pm 0.015$ in Flat $Λ$CDM which changes $Ω_{\rm m}$ by $-0.022$ compared to DES-SN5YR. Combining DES-Dovekie with CMB data from Planck, ACT and SPT and the DESI DR2 measurements in a Flat $w_0 w_a$CDM cosmology, we find $w_0 = -0.803 \pm 0.054$, $w_a = -0.72 \pm 0.21$. Our results hold a significance of $3.2σ$, reduced from $4.2σ$ for DES-SN5YR, to reject the null hypothesis that the data are compatible with the cosmological constant. This significance is equivalent to a Bayesian model preference odds of approximately 5:1 in favour of the Flat $w_0 w_a$CDM model. Using generally accepted thresholds for model preference, our updated data exhibits only a weak preference for evolving dark energy.

Figures (15)

• Figure 5: Systematic and statistical error budget on $\Omega_{\rm m}$ for a Flat $\Lambda$CDM cosmology with SNIa only. Systematics are colour coded as in Figure \ref{['fig:ERR_BUDGET']}, and only significant ($\sigma_{\rm sys} > 0.005$) systematics are labelled. The statistical error is presented in grey.
• Figure 6: Systematic and statistical uncertainty budget on $w$, both with (right) and without (left) a CMB prior. Those systematic uncertainties that are not labelled with text represent a negligible (<0.005) systematic contribution.
• Figure 7: The median binned differences between the nominal distances and the 9 calibration systematics (colour coded for each systematic surface) for DES-Dovekie. Comparable to Figure 10 in Dovekie, though we observe no obvious redshift-dependence.
• Figure 8: Effects of different Survey modelling systematics on the inferred SN Ia distances. Left: Choosing a shallower galaxy catalogue (DES 'SVA Gold’). Right: Varying the efficiency of obtaining a spectroscopic redshift. Green points are individual realisations, black points are binned means.
• Figure 9: Constraints on the matter density for Flat $\Lambda$CDM for DES-Dovekie (blue), Planck CMB (grey), DESI DR2 BAO (black), and the combination SN+CMB+BAO (dark blue).