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May 28, 2026Open Access

Phase Stability of the COCM Oscillatory Signal: A Comparison Between DR1+CC and DR2+CC Fits

Key Points

This research aims to examine the phase stability of the COCM oscillatory signal across two datasets, DR1+CC and DR2+CC.
Applied COCM semi-fixed parameterization to DR1+CC (n = 24) and DR2+CC (n = 14) datasets.
Analyzed phase shifts and their sensitivity to sampling noise and data spacing.
Used mock datasets under ΛCDM to assess statistical significance of observed phase shifts.
Best-fit phase shifts showed approximately Δφ = 1.85 rad between DR1+CC and DR2+CC.
Analysis indicates that the observed phase shift is likely due to sampling noise, consistent with expectations.
Current data do not stabilize phase φ; further data from DESI DR3 are required for clarification.

Abstract

The COCM semi-fixed parametrisation fits H(z) with amplitude A₀, phase φ, and background parameters, with frequency ωz = 11.1991 fixed. Applied to DR1+CC (n = 24) and DR2+CC (n = 14), the best-fit phase shifts by Δφ ≈ 1.85 rad. Among the fitted parameters, φ has the highest sensitivity to sampling, because the oscillation half-period Δz ≈ 0.28 is comparable to the typical spacing between data points. This paper examines whether the observed shift is statistically expected or indicates a systematic effect. Using mock datasets drawn under ΛCDM at the same sizes as DR1 and DR2, we argue that phase shifts of this magnitude are consistent with sampling noise. The phase φ remains undetermined with current data; its stabilisation requires DESI DR3. The propagation of phase uncertainty to the low-redshift crossing predictions of the COCM is quantified.

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