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

Youri Carloni1,2,3,*, Orlando Luongo4,3,5,6,7,†, and Marek Biesiada8,‡

  • *Contact author: youri.carloni@unicam.it
  • †Contact author: orlando.luongo@unicam.it
  • ‡Contact author: marek.biesiada@ncbj.gov.pl
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Phys. Rev. D 114, 103515 – Published 10 November, 2026

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

Abstract

We introduce a density-level pivot construction for the Chevallier–Polarski–Linder parametrization by defining the normalized dark energy density fp≡f(ap) and the equation of state ωp≡ω(ap) at an optimized pivot scale factor ap. This reparametrization leaves the underlying 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 DESI DR2 results, we compare a newly proposed fafbCDM parametrization, 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 parametrizations using the compressed cosmic microwave background, DESI DR2 baryon acoustic oscillations, cosmic chronometers, 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 Chevallier–Polarski–Linder parametrization 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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Phys. Rev. D 114, 103515– Published 10 November, 2026
  • Received 8 August 2026
  • Accepted 25 September 2026
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