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

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 sim1600 likely Type Ia SNe from DES and sim200 low-redshift SNe from other surveys. With DES-Dovekie, we obtain Ω_{rm m} = 0.330 pm 0.015 in Flat ΛCDM 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_aCDM 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_aCDM model. Using generally accepted thresholds for model preference, our updated data exhibits only a weak preference for evolving dark energy.