Exploring the Evidence for Evolving Dark Energy with the Jeffreys prior
Abstract
We investigate the impact of applying the uninformative Jeffreys prior in a re-analysis of DESI DR2 BAO, Planck 2018 CMB, and Type Ia Supernovae (DES-SN5YR, DES-Dovekie, Pantheon+, Union3). We incorporate this prior into new posterior inference and evidence calculations. We introduce novel techniques for interpreting the Jeffreys prior physically. To overcome the computational expense of the Jeffreys prior, we develop a fully JAX-based pipeline consisting of CosmoPower−JAX emulators, gradient-based posterior inference using the No-U-Turn Sampler (NUTS), and evidence calculations using JAX-accelerated nested sampling. We demonstrate that while the parameter constraints on w0 and wa remain robust to prior choice (exhibiting only minor shifts of the marginalised posterior towards the Maximum A Posteriori in less constraining dataset combinations), the Bayesian evidence is highly sensitive to the use of the Jeffreys prior; replacing uniform priors with the Jeffreys prior reverses the model-selection preference in dataset combinations that favour dynamical dark energy under the uniform prior, while strengthening existing preferences for ΛCDM. This is driven primarily by the significantly larger Occam penalty applied by the Jeffreys prior which penalises the overfitting of the data by a w0waCDM model.
Related
- How theory-informed priors affect DESI evidence for evolving dark energy
- Evidence for evolving dark energy from DESI DR2 BAO and Pantheon+, DES-Dovekie, and Union3
- Rolling Galileons: Evolving Braiding Strength for Viable Dark Energy
- Constraining quantum-gravity predictions for evolving dark energy
- Evolving dark energy and a younger Universe from cosmic inhomogeneity
BibTeX
@misc{layton2026exploring,
title = {{Exploring the Evidence for Evolving Dark Energy with the Jeffreys prior}},
author = {Joshua Layton and Alex Hall and Naomi Clare Robertson},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.26493},
eprint = {2610.26493},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.26493},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Exploring the Evidence for Evolving Dark Energy with the Jeffreys prior
AU - Joshua Layton
AU - Alex Hall
AU - Naomi Clare Robertson
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.26493
UR - https://arxiv.org/abs/2610.26493
AB - We investigate the impact of applying the uninformative Jeffreys prior in a re-analysis of DESI DR2 BAO, Planck 2018 CMB, and Type Ia Supernovae (DES-SN5YR, DES-Dovekie, Pantheon+, Union3). We incorporate this prior into new posterior inference and evidence calculations. We introduce novel techniques for interpreting the Jeffreys prior physically. To overcome the computational expense of the Jeffreys prior, we develop a fully JAX-based pipeline consisting of CosmoPower−JAX emulators, gradient-based posterior inference using the No-U-Turn Sampler (NUTS), and evidence calculations using JAX-accelerated nested sampling. We demonstrate that while the parameter constraints on w_0 and w_a remain robust to prior choice (exhibiting only minor shifts of the marginalised posterior towards the Maximum A Posteriori in less constraining dataset combinations), the Bayesian evidence is highly sensitive to the use of the Jeffreys prior; replacing uniform priors with the Jeffreys prior reverses the model-selection preference in dataset combinations that favour dynamical dark energy under the uniform prior, while strengthening existing preferences for ΛCDM. This is driven primarily by the significantly larger Occam penalty applied by the Jeffreys prior which penalises the overfitting of the data by a w_0w_aCDM model.
ER -