On the Analysis Dependence of DESI Dynamical Dark Energy

TL;DR

This paper demonstrates that claims of dynamical dark energy from DESI data depend heavily on the analysis pipeline, showing no significant evidence for dynamical DE when using certain modeling approaches, and emphasizing the importance of pipeline independence.

Contribution

The study explicitly shows the dependence of DESI dynamical dark energy results on the analysis pipeline and confirms the absence of a dynamical DE signal in certain models.

Findings

No significant dynamical DE signal in FS modeling with DESI data.

Late-time accelerated expansion confirmed at >3.4 sigma in FS + BAO.

Results depend on the analysis pipeline used.

Abstract

We continue scientific scrutiny of the DESI dynamical dark energy (DE) claim by explicitly demonstrating that the result depends on the analysis pipeline. Concretely, we define a likelihood that converts the $w_0 w_a$CDM model back into the (flat) $\Lambda$CDM model, which we fit to DESI constraints on the $\Lambda$CDM model from DR1 Full-Shape (FS) modelling and BAO. We further incorporate CMB constraints. Throughout, we find that $w_0$ and $w_a$ are within $1 \sigma$ of the $\Lambda$CDM model. Our work makes it explicit that, in contrast to DR1 and DR2 BAO, there is no dynamical DE signal in FS modelling, even when combined with BAO and CMB. Moreover, one confirms late-time accelerated expansion today $(q_0 < 0)$ at $ \gtrsim 3.4 \sigma$ in FS modelling + BAO. On the contrary, DR1 and DR2 BAO fail to confirm $q_0 < 0$ under similar assumptions. Our analysis highlights the fact that trustable scientific results should be independent of the analysis pipeline.