Model-Independent Analysis of Type Ia Supernova Datasets and Implications for Dark Energy

Recent analyses combining DESI DR2 BAO with CMB and SNe Ia data have reported $2.8$–$4.2\sigma$ evidence for dynamical dark energy, but the significance depends strongly on the supernova sample, raising the question of whether this signal reflects new physics, dataset-specific systematics, or the choice of dark energy parameterization. We investigate this question by analyzing four SNe Ia compilations (Pantheon, Pantheon+, DES-Dovekie, and Union3) with DESI DR2 BAO and Planck CMB distance priors, using flux averaging, model-independent expansion rate extraction, parametric ($w_0{w}_a$CDM) fits, and a non-parametric reconstruction of the dark energy density ratio $X(z)\equiv {\rho }_{\mathrm{D}\mathrm{E}}(z)\mathrm{/}{\rho }_{\mathrm{D}\mathrm{E}}(0)$. Flux averaging reduces the ${\mathrm{\Omega }}_m$ difference between SNe and DESI from $\sim 2\sigma$ to $\sim 1\sigma$ for Pantheon+ and DES-Dovekie. The reconstructed $X(z)$ for DESI DR2 + CMB + SNe is consistent with $\mathrm{\Lambda }$CDM for Pantheon, Pantheon+, and DES-Dovekie except at $0.5<z<1$, consistent with Wang & Freese (2026). The largest deviation occurs at $z=2\mathrm{/}3$, reaching $\sim 2.7\sigma$ for Pantheon+ but only $1.6$–$1.7\sigma$ for Pantheon and DES-Dovekie. The $X(z)$ for DESI DR2 + CMB + Union3 is consistent with these within $1\sigma$, but shows an additional $2.4\sigma$ deviation at $z=1\mathrm{/}3$ besides the $\sim 2.7\sigma$ deviation at $z=2\mathrm{/}3$. Across all analyses, the departure from $\mathrm{\Lambda }$CDM correlates with each dataset’s ${\mathrm{\Omega }}_m$ preference. We demonstrate that a pure $\mathrm{\Lambda }$CDM universe with the measured ${\mathrm{\Omega }}_m$ differences can reproduce the observed $X(z)$ pattern, providing a viable alternative interpretation of the observed $X(z)\mathrm{\ne }1$ pattern. Future surveys by Euclid and Roman with sub-percent ${\mathrm{\Omega }}_m$ constraints will be essential to determine whether the signal reflects genuine dark energy evolution or residual inter-probe ${\mathrm{\Omega }}_m$ inconsistencies.