DESI DR2 meets cosmography: a comparative study of Pad Chebyshev, and Taylor expansions
cosmological parameters; observations; theory
We perform a comprehensive cosmographic analysis of the late-time Universe using the latest Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) baryon acoustic oscillation (BAO) measurements, comparing Taylor, Pad and Chebyshev expansions as model-independent reconstructions of the background expansion. We consider Padapproximants of order (2,1) and (2,2), a Chebyshev expansion, and a third-order Taylor series. Due to its limited radius of convergence, the Taylor expansion is constrained using only the low-redshift DESI sub-set (z < 1), while the rational Padforms and the Chebyshev expansion are applied over the full DESI DR2 redshift range. Cosmographic parameters are inferred through a Bayesian Markov chain Monte Carlo (MCMC) analysis, and the resulting best-fitting reconstructions of H(z), dL(z), and BAO distance indicators are compared with the predictions of the Lambda cold dark matter (CDM) model. All methods are consistent with CDM at low redshift, but the Chebyshev expansion exhibits noticeable deviations at higher redshifts, while the Pad2,1) and Pad2,2) reconstructions remain closely aligned with CDM across the DESI DR2 range. A model-selection analysis based on Akaike Information Criterion and Bayesian Information Criterion shows a clear statistical preference for the Taylor expansion over low-zCDM, and a strong preference for Padcosmography over CDM when the full DESI DR2 data set is used. These results demonstrate the constraining power of DESI DR2 for cosmographic studies and highlight the utility of rational approximants, especially Padforms, in extending cosmography reliably to higher redshifts beyond the domain of traditional Taylor series. The Author(s) 2026. Published by Oxford University Press on behalf of Royal Astronomical Society.
Mishra, Sai Swagat; Kavya, N.S.; Sahoo, P.K.; Bamba, Kazuharu
Monthly Notices of the Royal Astronomical Society;Volume;546;Issue;4;Article No.;stag197;
https://doi.org/10.1093/mnras/stag197 https://www.scopus.com/pages/publications/105030931293?origin=resultslist
Mishra S.S., Department of Mathematics, School of Computer Science and Artificial Intelligence, SR University, Telangana, Warangal, 506371, India, Department of Mathematics, Birla Institute of Technology and Science, Hyderabad Campus, Jawahar Nagar, Kapra Mandal, Medchal District, Telangana, Pilani, 500078, India; Kavya N.S., Centre for Mathematical Needs, Department of Mathematics, CHRIST (Deemed to be University), Bengaluru, 560029, India; Sahoo P.K., Department of Mathematics, Birla Institute of Technology and Science, Hyderabad Campus, Jawahar Nagar, Kapra Mandal, Medchal District, Telangana, Pilani, 500078, India; Bamba K., Faculty of Symbiotic Systems Science, Fukushima University, Fukushima, 960-1296, Japan