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Challenging the ω0ωaCDM parametrization through rational expansions in view of the DESI DR2

Youri Carloni1,2,3,*, Orlando Luongo1,2,3,4,5,†, and Marek Biesiada6,‡

  • *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 113, 103525 – Published 14 May, 2026

DOI: https://doi.org/10.1103/m4c5-7vx1

Abstract

In view of the new Dark Energy Spectroscopic Instrument 2025 results, we analyze three types of Padé cosmology, based on rational series making use of Padé approximants over the equations of state, namely Padéω (0, 1) and Padé (1, 1), plus a Padéq (0, 1), i.e., a rational expansion on the dark energy deceleration parameter, in which the numerator and denominator orders are incorporated into the above brackets. These scenarios appear as alternative dark energy parametrizations with respect to the well-known ω0ωaCDM model. Accordingly, we perform Monte Carlo Markov chain analyses with the publicly available class Boltzmann code, including the three Padé parametrizations, along with the ω0ωaCDM and ΛCDM standard pictures. To this end, we combine independent probes from high to low redshifts to obtain reliable constraints on the cosmological parameters of these models and compare them using statistical selection criteria. Our results show that ω0ωaCDM parametrization is not significantly preferred over the Padé cosmology. On the contrary, the deviance information criterion identifies Padé (1, 1) as the best-fit model along with the ω0ωaCDM parametrization. Based on our bounds, we further investigate the evolution of the squared sound speed, revealing that the Padéq (0, 1) and Padéω (0, 1) parametrizations exhibit enhanced stability compared with the other cases here considered and, therefore, describe robust alternatives for the cosmological background.

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Phys. Rev. D 113, 103525– Published 14 May, 2026
  • Received 30 November 2025
  • Accepted 16 April 2026
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