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Cosmography with DESI DR2 and SN data

Gabriel Rodrigues, Rayff de Souza, Jailson Alcaniz

TL;DR

This study uses a model-independent cosmographic approach with a fourth-order $y$-redshift expansion to constrain the kinematic parameters $H_0$, $q_0$, $j_0$, and $s_0$ from DESI DR2 BAO measurements and Type Ia SN data. By performing an MCMC analysis on a combined dataset of DESI DR2 with SN catalogs (DESY5, Pantheon+, Union3) and fixing the appropriate priors, the authors test the ΛCDM benchmark $j_0=1$. They find that DESI DR2 alone yields $j_0$ consistent with unity at the $2σ$ level, but adding SN data shifts $j_0$ away from 1 with increasing significance, reaching $>5σ$ for DESI DR2+$DESY5$. These results provide a model-independent indication of dynamic dark energy and offer a complementary cross-check to parametric analyses by the DESI Collaboration.

Abstract

In this paper, we present a kinematic analysis of the Universe's expansion history using cosmography, with a particular emphasis on the jerk parameter $j_0$, which is equal to one in the standard $Λ$CDM scenario. We use distance measurements from DESI DR2, both independently and in combination with current Type Ia supernova (SN) samples, to constrain the cosmographic parameters up to the fourth order without relying on a specific cosmological model. Our results show that for the DESI DR2 data alone, the $Λ$CDM prediction ($j_0 = 1$) falls within the 2$σ$ confidence region. However, when DESI DR2 is combined with the Union3, Pantheon+, and DESY5 SN datasets, the result obtained is discrepant with the $Λ$CDM model at about 3.4$σ$, 4.1$σ$, and 5.4$σ$, respectively. These results are consistent with the conclusions based on dark energy parameterizations reported by the DESI Collaboration, which suggest the presence of a dynamic dark energy component in the universe.

Cosmography with DESI DR2 and SN data

TL;DR

This study uses a model-independent cosmographic approach with a fourth-order -redshift expansion to constrain the kinematic parameters , , , and from DESI DR2 BAO measurements and Type Ia SN data. By performing an MCMC analysis on a combined dataset of DESI DR2 with SN catalogs (DESY5, Pantheon+, Union3) and fixing the appropriate priors, the authors test the ΛCDM benchmark . They find that DESI DR2 alone yields consistent with unity at the level, but adding SN data shifts away from 1 with increasing significance, reaching for DESI DR2+. These results provide a model-independent indication of dynamic dark energy and offer a complementary cross-check to parametric analyses by the DESI Collaboration.

Abstract

In this paper, we present a kinematic analysis of the Universe's expansion history using cosmography, with a particular emphasis on the jerk parameter , which is equal to one in the standard CDM scenario. We use distance measurements from DESI DR2, both independently and in combination with current Type Ia supernova (SN) samples, to constrain the cosmographic parameters up to the fourth order without relying on a specific cosmological model. Our results show that for the DESI DR2 data alone, the CDM prediction () falls within the 2 confidence region. However, when DESI DR2 is combined with the Union3, Pantheon+, and DESY5 SN datasets, the result obtained is discrepant with the CDM model at about 3.4, 4.1, and 5.4, respectively. These results are consistent with the conclusions based on dark energy parameterizations reported by the DESI Collaboration, which suggest the presence of a dynamic dark energy component in the universe.

Paper Structure

This paper contains 6 sections, 13 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Cosmography
  3. Methodology and Results
  4. Cosmographic expressions
  5. $\Lambda$CDM Model
  6. Final Remarks

Figures (3)

  • Figure 1: Relative differences between the cosmographic expansion for different orders and the flat $\Lambda$CDM model distance measurements. The dashed gray line indicates the maximum redshift value of the data corresponding to each distance measurement.
  • Figure 2: Confidence contours for the kinematic parameters at 68% and 95% confidence levels obtained with DESI DR2 and current SN samples.
  • Figure 3: Constraints on the kinematic parameters at 68% and 95% confidence levels for DESI DR2, with and without the inclusion of different SN samples. The top panel shows the marginalized posterior distribution of $j_0$ for the datasets considered while the bottom panel presents the confidence contours in the $j_0$–$H_0$ plane.