Probing departures from $Λ$CDM by late-time datasets

TL;DR

Problem: Determine whether late-time data reveal departures from $\Lambda$CDM. Approach: Bayesian MCMC analysis of multiple dynamical dark energy parameterizations against CC, DESI DR2 BAO, Pantheon$^+$, DES-SN5Y, Union3; compute Bayesian evidence differences $\Delta \ln \mathcal{Z}$ to compare with $\Lambda$CDM. Findings: CC+DESI DR2 show mild deviations; including SN data amplifies deviations for several models (e.g., BA, JBP, Logarithmic), with a persistent preference for $\omega_0>-1$ and $\omega_a<0$ (Quintom-B); but $\Lambda$CDM remains the overall preferred model across most dataset combinations. Significance: late-time datasets hint at dynamical dark energy and motivate Stage IV surveys and cross-survey analyses to decisively test beyond-$\Lambda$CDM physics in the dark sector.

Abstract

Observational data play a pivotal role in identifying cosmological models that are both theoretically consistent and empirically viable. In this work, we investigate whether the standard $Λ$CDM model exhibits significant departure with current late time datasets, including Cosmic Chronometers, Baryon Acoustic Oscillations from DESI DR2, and various Type Ia supernova compilations (Pantheon$^+$, DES-SN5Y, Union3). We analyze several dynamical dark energy models, including $ω$CDM, o$ω$CDM, $ω_0ω_a$CDM, Logarithmic, Exponential, JBP, BA, and GEDE. While CC + DESI DR2 data show mild deviations from $Λ$CDM ($\lesssim 2σ$), adding supernova samples (DES-SN5Y or Union3) increases deviations, with BA, JBP, and Logarithmic models reaching $3-3.5σ$, and CC + DESI DR2 + DES-SN5Y producing the largest deviations. We find consistent evidence for $ω_0 > -1$ and $ω_a < 0$ in all dark energy models, indicating that the cosmological constant faces a potential crisis and that dynamical dark energy models could provide a possible solution, characterized by a Quintom-B type scenario. The $Λ$CDM model has long served as the cornerstone of modern cosmology, successfully shaping our understanding of the Universe from its earliest epochs to the present day. However, in light of DESI DR2 and other recent measurements, emerging cracks in this paradigm suggest that a complete understanding of the cosmos may require moving beyond the cosmological constant and exploring new physics governing the dark sector.

Figures (6)

• Figure 1: The figure shows the corner plot of the o$\Lambda$CDM, $\omega$CDM, o$\omega$CDM, $\omega_a \omega_0$CDM, Logarithmic, Exponential, JBP, BA, and GEDE models using DESI DR2 measurements in combination with the CMB and SNe Ia measurements, at the 68% (1$\sigma$) and 95% (2$\sigma$) confidence intervals.
• Figure 2: The figure shows the posterior distributions of different planes of the o$\Lambda$CDM , $\omega$CDM, o$\omega$CDM, $\omega_a \omega_0$CDM, Logarithmic, Exponential, JBP, BA, and GEDE models using DESI DR2 measurements in combination with the CMB and SNe Ia measurements, at the 68% (1$\sigma$) and 95% (2$\sigma$) confidence intervals.
• Figure 3: The figure shows the $\sigma$ deviation of each model from the $\Lambda$CDM model using different combinations of datasets with the DESI DR2 data.
• Figure 4: The figure shows a comparison of various models relative to $\Lambda$CDM across different cosmological datasets, using the Bayesian evidence differences ($|\Delta \ln \mathcal{Z}|$).
• Figure 5: This figure shows the evolution of $\omega(z)$ as a function of redshift, using DESI DR2 measurements with different combinations of SNe Ia compilations (Pantheon$^+$, DESY5, Union3) and CMB, providing compelling evidence for dynamical DE.