Probing Time-Varying Dark Energy with DESI: The Crucial Role of Precision Matter Density (m0) Measurements
Abstract
Accurate measurements of fundamental cosmological parameters, especially the Hubble constant (H0) and present-day matter density (m0), are crucial for constraining dark energy (DE) evolution. We analyze the sensitivities of cosmological observables (H(z), DL(z), EG) to m0, w0, and wan under different parametrizations. Our results show observables are far more sensitive to m0 than to DE equation of state parameters (e.g., at z 0.5, H(z)'s m0 sensitivity is 0.7 vs. wa's 0.04). This hierarchy mandates high-precision m0 measurements to accurately constrain time-varying DE. We also find DE parameter sensitivity highly depends on parametrization; the standard CPL form shows low sensitivity to wa, but ω(z) = w0 + wa (1+z) significantly enhances it. Our analysis of DESI DR1/DR2 data confirms these theoretical limits: standalone DESI data primarily provides only upper limits for wa, underscoring insufficient constraining power for a definitive time-varying DE detection. While combined datasets offer tighter constraints, interpretation requires caution due to parametrization influence. We further confirm this point using simulated Supernovae MCMC data. In conclusion, improving m0 precision and adopting optimized parametrizations are imperative for future surveys like DESI to fully probe dark energy's nature.
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