Distinguishing constant and evolving Omega_m models

Determine whether DESI Full-Shape modelling constraints favor a constant matter-density parameter Omega_m over the redshift-dependent linear model Omega_m(z)=mz+c.

Background

The paper compares a constant-Omega_m model with a linear redshift-dependent parameterization, Omega_m(z)=mz+c, using DESI DR1 Full-Shape constraints supplemented by the DESI DR2 Lyman-alpha constraint. Current model-selection statistics, including the Akaike Information Criterion and Bayesian evidence, do not decisively distinguish the two descriptions.

The authors therefore leave unresolved whether the apparent increase in Omega_m with redshift reflects a genuine breakdown of the constant-parameter LambdaCDM description or is compatible with statistical fluctuations and observational systematics. Forecasts suggest that later DESI data releases may provide stronger evidence, but the present data do not settle the issue.

References

Focussing on DESI FS modelling constraints on the $\Lambda$CDM parameter $\Omega_m$ , which exhibit greater convergence towards constant $\Omega_m$ compared to DESI BAO (Fig. 5 of ), our analysis shows that it is no longer clear that a constant $\Omega_m$ model is preferred over an $\Omega_m(z)$ model (\ref{eq:line}) tracing a line.

— A Prediction for DESI Full-Shape: Increasing Tomographic $Ω_m(z)$ Trend  (2608.19883 - Colgáin et al., 20 Aug 2026) in Section 5, Conclusions