DESI and SNe: dynamical dark energy, Ω<i>m</i> tension or systematics?
Eoin Ó Colgáin, M. M. Sheikh-Jabbari
Abstract
ABSTRACT Dark Energy Spectroscopic Instrument (DESI) observations have led to statistically significant dynamical dark energy (DDE) claims. Noting that there is a mild DDE signal in DESI BAO alone, but no DDE signal in DESI FS galaxy clustering alone, in this letter we reconstruct the (flat) $\Lambda$CDM parameter $\Omega _m$ from the $w_0 w_a$CDM cosmologies advocated by the DESI collaboration. Our reconstruction drops correlations between $w_0 w_a$CDM parameters, which leads to inflated errors, yet still allows the identification of $\Lambda$CDM deviations. We identify (i) a mild increasing $\Omega _m$ trend at high redshift and (ii) a sharp departure from $\Lambda$CDM at low redshift. The latter is driven by SNe that are $1.9 \sigma - 2.5 \sigma$ discrepant with DESI FS modelling in overlapping redshift ranges. We identify a low redshift subsample of the Dark Energy Survey (DES) SNe sample that is discrepant with DESI at $3.4 \sigma$ despite both observables probing the same effective redshift. If SNe and DESI disagree on $\Omega _m$ at the same effective redshift, this implies a discrepancy in distances assuming the $\Lambda$CDM model is a good approximation to the physical Universe at similar redshifts. This ‘$\Omega _m$ tension’ most likely points to unexplored systematics.