The H0 and BAO tensions, the wXCDM model, and dynamical dark energy in the late universe

Abstract: In the first part of my talk, I will review the phenomenology required to alleviate the Hubble tension with late-time new physics in view of the so-called angular (2D) and anisotropic (3D) BAO data, which are in tension. Then, I will present a recent model, the wXCDM, which combines quintessence and an exotic component called “phantom matter” that satisfies the strong energy condition, but has negative energy density and positive pressure. This model is able to outperform its competitors and solve the H0 tension when confronted with a very rich data set, including 2D BAO. When angular BAO is replaced with 3D BAO, as expected, the model is unable to produce large values of H0. However, it still leads to low values of chi2, similar to those found with the CPL parametrization. Finally, I will describe the Weighted Function Regression method and use it to reconstruct in a Bayesian and model-agnostic way the effective dark energy properties and the late cosmic expansion history, assessing the impact of the supernovae data on the quantification of the statistical evidence for dynamical dark energy in the late universe.