Probing the H0 Tension with Holographic Dark Energy in Unimodular Gravity: Insights from DESI DR2

TL;DR

This work tests a non-conservative Unimodular Gravity model in which holographic dark energy exchanges energy with matter via a diffusion term $Q$, extending the framework to include radiation and separate baryonic and cold dark matter components. Using a comprehensive dataset—Cosmic Chronometers, Pantheon Plus with and without SH0ES, DESI DR2 BAO, quasar X-ray/UV fluxes, and Planck 2018 CMB—the authors perform MCMC analyses to compare against $Λ$CDM, evaluating the ability to alleviate the $H_0$ tension. They find that $H_0$ tension remains unresolved in this UG setup and that Bayesian model selection yields no decisive preference for UG over $Λ$CDM; results are dataset dependent and sometimes indicate mild overfitting in AGN data. Nevertheless, the UG holographic DE framework remains well-motivated and capable of accommodating both early- and late-time observations, making it a valuable avenue for further theoretical and observational exploration, including potential links to inflation and quantum gravity effects.

Abstract

Motivated by the recent baryon acoustic oscillation measurements of DESI DR2 collaboration, this works presents an extended analysis of a cosmological model based on holographic dark energy within the framework of Unimodular Gravity. We probe the model with an extensive set of observations: cosmic chronometers, Pantheon Plus$+$SH0ES Type Ia supernovae, DESI DR2 BAO distances, quasar X-ray/UV fluxes (two independent calibrations), and Planck 2018 CMB data. The results are analyzed to assess the modelś ability to alleviate the Hubble tension and, in comparison with the standard $Λ$CDM framework, to determine which of the two scenarios is preferred according to Bayesian evidence. We conclude that the present implementation of holographic dark energy in Unimodular Gravity, while theoretically appealing, does not alleviate the Hubble tension and is not statistically preferred by Bayesian criteria when compared with the standard $Λ$CDM model. Nevertheless, in neither case does the preference become very strong or conclusive against it.

Figures (4)

• Figure 1: Comparison of parameter estimation between the two QSO/AGN models, labeled AGNI and AGNII, within the $\Lambda$CDM cosmological framework. The posterior probability distributions for each parameter are shown, along with the 68% and 95% confidence level contours. No significant differences are observed between the two AGN models.
• Figure 2: Comparison of parameter estimation between the two QSO/AGN models, labeled AGNI and AGNII, within the cosmological model based on UG. The posterior probability distributions for each parameter are shown, along with the 68% and 95% confidence level contours. As in the previous case, no significant differences are observed between the two AGN models.
• Figure 3: Posterior probability distributions and the 68% and 95% confidence regions for the six standard cosmological parameters within the $\Lambda$CDM model. We employ both early- (red plots) and late-time (blue plots) Universe datasets. The $H_0$ tension is evident.
• Figure 4: Posterior probability distributions and the 68% and 95% confidence regions for the $\beta$ parameter and the standard 6 cosmological parameters within the UG cosmological model. We employ both early- (red plots) and late-time (blue plots) Universe datasets. The $H_0$ tension is not alleviated in this model.