• Accepted Paper

Do we really need alternatives to the ω0ωaCDM parametrization after the DESI DR2?

Youri Carloni, Orlando Luongo, and Marek Biesiada

Phys. Rev. D - Accepted 25 September, 2026

DOI: https://doi.org/10.1103/vrgg-2b2t

Abstract

We introduce a density-level pivot construction for the Chevallier-Polarski-Linder (CPL) parameterization by defining the normalized dark energy density $f_p\equiv f_{\rm DE}(a_p)$ and the equation of state ωp≡ω(ap) at an optimized pivot scale factor ap. This reparameterization leaves the underlying CPL cosmology unchanged and allows the two models to be compared using parameters with a direct physical interpretation at the epoch where the data are most sensitive. Accordingly, following the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) results, we compare a newly proposed fafbCDM parameterization, based on a second-order Taylor expansion of the normalized dark energy density, with the standard ω0ωaCDM model. In particular, we constrain the original and pivoted parameterizations using compressed cosmic microwave background (CMB), DESI DR2 baryon acoustic oscillations (BAO), cosmic chronometers (CC), and Pantheon+ Type Ia supernovae data, with the SH0ES prior imposed on H0. We find that applying the same density-level pivot prescription to the ω0ωaCDM model substantially reduces the correlation between its dark energy parameters and provides less correlated constraints in the pivot variables. The statistical comparison shows that this model remains favored over the Taylor expansion of the dark energy density, even when both models are analyzed in the optimized parameter basis. Moreover, the pivoted CPL parameterization accurately reproduces the background evolution of quintessence models, providing a reliable phenomenological approximation to the underlying dark energy dynamics, better than the fafbCDM model. We conclude that changing the parameter basis improves the performance of the ω0ωaCDM model, which emerges as the most suitable framework to describe the dark energy sector within the class of models considered here.

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