EuCAIFCon 2025

Data–Driven Dark Energy: Probing w(a) with Flexknots

Not scheduled

20m

THotel, Cagliari, Sardinia, Italy

Poster + Flashtalk Inference & Uncertainty

Speaker

Adam Ormondroyd (University of Cambridge)

Description

Recent cosmological surveys have opened a new window onto the nature of dark energy. In our work we reconstruct the dark energy equation of state using a “flexknot” parameterisation that represents $w(a)$ as a linear spline with free–moving nodes. By combining the latest DESI Baryonic Acoustic Oscillation measurements with Pantheon+ supernovae data—and cross–checking our results with an independent Cobaya–based pipeline—we obtain posterior distributions for $w(a)$ that reveal an unexpected W–shaped structure. Although the Bayesian evidence does not ultimately favour dynamical dark energy over the standard $\mathrm{\Lambda }$CDM model, our analysis shows that even non–CMB datasets can indicate deviations from a constant $w=–1$.
We also generalise dataset tension statistics to marginalise over multiple models, ensuring our unexpected results are not driven by inter-dataset disagreement.
We finish with a brief discussion of the pedagogical advantages and computational benefits of developing an analysis pipeline in-house, which, in addition to increasing efficiency, allows us to analytically marginalise nuisance parameters and provides confidence that these features are genuinely driven by the data.