The impact of Ωm0 prior bias on cosmological parameter estimation: reconciling DESI DR2 BAO and Pantheon + SNe Data

ABSTRACT Recent cosmological parameter analyses combining DESI DR2 Baryon Acoustic Oscillation (BAO) data with external probes, such as Pantheon + Supernovae (SNe) observations, have reported deviations of the dark energy equation-of-state parameters (₀, ₐ) from the standard Lambda Cold Dark Matter (CDM) model predictions (₀=-1, ₐ=0). A notable aspect of these results is the role of ₌₀ prior information from SNe, which is known to exhibit tension with BAO-only constraints. In this study, we rigorously investigate this effect through a statistical analysis using 1000 mock DESI DR2 BAO data realizations. We demonstrate that the strong degeneracy between ₀, ₐ, and ₌₀ causes significant biases in the estimated dark energy parameters when the ₌₀ prior mean deviates from its true underlying value. Specifically, applying an ₌₀ prior mean of 0. 33 (consistent with some SNe-only constraints) to mock data, assuming a true CDM universe (₌₀=0. 30, ₀=-1, ₐ=0), yields biased estimates such as ₀ -0. 82 0. 06 and ₐ -0. 82 0. 4. This systematic shift, driven by the ₌₀ prior, moves the estimated parameters towards the non-CDM region, offering a qualitative resemblance to outcomes reported in current combined DESI DR2 BAO + Pantheon + SNe analyses (e. g. ₀ = -0. 888^+0. 055-₀. ₀₆₄, ₐ = -0. 17 0. 46). Our findings suggest that these observed non-CDM parameters may largely arise from statistical biases due to ₌₀ prior tensions between data sets. This study proposes a potential resolution to current cosmological tensions without necessarily invoking new physics.