A Bayesian Perspective on Evidence for Evolving Dark Energy

2025/11/13 by Ong, Dily Duan Yi, Yallup, David, Handley, Will · 5 citations
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Instrumentation and Methods for Astrophysics (astro-ph.IM)

paper · doi:10.48550/arxiv.2511.10631

Abstract

The DESI collaboration reports a significant preference for a dynamic dark energy model (w₀w_aCDM) over the cosmological constant (ΛCDM) when their data are combined with other frontier cosmological probes. We present a direct Bayesian model comparison using nested sampling to compute the Bayesian evidence, revealing a contrasting conclusion: for the key combination of the DESI DR2 BAO and the Planck CMB data, we find the Bayesian evidence modestly favours ΛCDM (log-Bayes factor ln B = -0.57\scriptstyle±0.26), in contrast to the collaboration's 3.1σ frequentist significance in favoring w₀w_aCDM. Extending this analysis to also combine with the DES-Y5 supernova catalogue, our Bayesian analysis reaches a significance of 3.07\scriptstyle±0.10 σ in favour of w₀w_aCDM. By performing a comprehensive tension analysis, employing five complementary metrics, we pinpoint the origin: a significant (≈ 2.95σ), low-dimensional tension between DESI DR2 and DES-Y5 that is present only within the ΛCDM framework. The w₀w_aCDM model is preferred precisely because its additional parameters act to resolve this specific dataset conflict. The convergence of our findings with independent geometric analyses suggests that the preference for dynamic dark energy is primarily driven by the resolution of inter-dataset tensions, warranting a cautious interpretation of its statistical significance.

Citations

• The Dark Energy Survey supernova program: a reanalysis of cosmology results and evidence for evolving dark energy with an updated Type Ia supernova calibration
• unimpeded: A Public Grid of Nested Sampling Chains for Cosmological Model Comparison and Tension Analysis
• Bayesian and frequentist perspectives agree on dynamical dark energy
• Exoplaneteers Keep Overestimating Sigma Significances
• Baryon Acoustic Oscillations from a Different Angle
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints
• Comparing the DES-SN5YR and Pantheon+ SN cosmology analyses: Investigation based on "Evolving Dark Energy or Supernovae systematics?"
• Evolving Dark Energy or Supernovae Systematics?
• Union Through UNITY: Cosmology with 2,000 SNe Using a Unified Bayesian Framework
• Discovering the Significance of 5 sigma
• Calibration ofρValues for Testing Precise Null Hypotheses

Cited by

• Controlled Tension Forecasting: Quantifying Cross-Probe Biases in ω₀ω_aCDM
• A model-independent assessment of the late-time dark energy density evolution
• Cosmological constraints from the DESI DR1 Bispectrum Full-Shape and DR2 BAO
• Background solutions to the Hubble tension in f(Q) gravity and consistency with BAO measurements
• Inflation, Open Universes, and Dark Energy
• A Sequentially-Valid Reanalysis of DESI's Dynamical Dark Energy Signal

Related

• The prior dependence of the DESI results
• Dynamic or Systematic? Bayesian model selection between dark energy and supernova biases
• Evidence for Dynamical Dark Energy using DESI DR2 Lyα Forest
• Extended Dark Energy analysis using DESI DR2 BAO measurements
• Bayesian and frequentist perspectives agree on dynamical dark energy