On the Pipeline Dependence of DESI Dynamical Dark Energy

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 flat $\Lambda$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 flat $\Lambda$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 analyses highlight the fact that trustable scientific results should be independent of the analysis pipeline.