Implications of DES 5YR SNe Dataset for $\Lambda$CDM

TL;DR

This study analyzes five-year DES supernova data combined with Planck and DESI data, revealing a redshift-dependent increase in matter density and potential deviations from the standard $ ext{Lambda}$CDM model, including negative dark energy densities.

Contribution

It shifts focus to the matter density parameter $ ext{Omega}_m$ in $ ext{Lambda}$CDM, demonstrating its redshift evolution and tension with Planck data using both frequentist and Bayesian methods.

Findings

$ ext{Omega}_m$ increases with redshift in DES data.

Discrepancy of $2.5 \sigma$ in $ ext{Omega}_m$ with Planck.

Evidence for non-flat universe at high redshift.

Abstract

Dark Energy Survey five-year supernovae data (DES 5YR SNe) in conjunction with Planck CMB and Dark Energy Spectroscopic Instrument (DESI) BAO data has detected a strong dynamical dark energy (DE) deviation from the $\Lambda$CDM model.Here we shift the focus of DES data to the pressureless matter sector in the $\Lambda$CDM model by studying the matter density parameter $\Omega_m$. Employing primarily frequentist profile likelihoods, supported by complementary Bayesian methods, we demonstrate that $\Omega_m$ increases with effective redshift in the DES data up to a point that there is a $2.5 \sigma$ discrepancy with Planck. We relax the traditional $\Omega_m \leq 1$ prior to demonstrate negative DE densities $\Omega_m > 1$ at the highest effective redshift probed. Nevertheless, the largest discrepancy with Planck occurs for profile likelihoods and posteriors peaked at $\Omega_m < 1$ in the traditional $\Lambda$CDM regime. Our findings corroborate earlier observations in Pantheon and Pantheon+ datasets with an independent SNe dataset with a higher effective redshift. In an appendix, we confirm that curvature $\Omega_k$ decreases with effective redshift disfavouring a flat Universe in higher redshift DES SNe at $> 3 \sigma$. Our choice of $\Omega_k$ prior leads to an underestimation of the tension with a flat Universe.