DESI DR1 tracers and CPL parameters
Individual run · T-6799b1ee63f8
Public summary of an internal test, not yet independently validated or published.
Question investigated
In DESI DR1, do quasars at effective z = 1.491 favor the point w₀ = −0.667 and wₐ = −1.09 over the cosmological constant?
Test conditions
Use the official DESI DR1 full-shape analysis for quasars at effective z = 1.491. Compare the reference w₀ = −1, wₐ = 0 with the alternative w₀ = −0.667, wₐ = −1.09, fitting nuisance bias parameters and retaining the Planck angular constraint. Define Δχ² = reference χ² − alternative χ².
Result
Δχ² = −210.46: the alternative point has a higher χ² than the reference and fails the prespecified fit-improvement criteria. This conclusion applies to the two points and redshift bin compared; it does not rule out the full family of dynamical dark-energy models.
Key figure
Reference χ² − alternative χ²
-210.46
w₀ = -0.667, wₐ = -1.09
Source: Tower public snapshot
Specific limitations
- The comparison involves two fixed points in parameter space. It does not explore the full parameter distribution or measure the global significance of an alternative to the cosmological constant.
- Δχ² = reference χ² − alternative χ². A positive value indicates a lower-χ² fit for the alternative. The comparison involves fixed cosmological points: Δχ² alone does not provide a significance in σ or a probability. The conclusion depends on the data and criteria used.