Multiple transitions in vacuum dark energy and $H_0$ tension

TL;DR

This paper investigates how multiple vacuum energy transitions in the universe's history can influence the Hubble constant, potentially easing the tension between different measurements of its value.

Contribution

It introduces a phenomenological model with multiple vacuum energy transitions and analyzes its impact on the H_0 tension using combined cosmological data sets.

Findings

Late-time AdS-like vacuum energy increases H_0 values.

The model can alleviate the H_0 tension.

Spectral index n_s approaches 1 in the model.

Abstract

We study the effects of multiple transitions in the vacuum dark energy density on the $H_0$ tension problem. We consider a phenomenological model in which the vacuum energy density undergoes multiple transitions in the early as well as the late universe and compare the model's predictions using the three sets of data from CMB+BAO+SN. The transient dark energy can be either positive (dS-like) or negative (AdS-like). We conclude that a transient late-time AdS-type vacuum energy typically yields the higher value of $H_0$ which can alleviate the $H_0$ tension. In addition, to obtain a value of $H_0$ comparable to the value obtained from the local cosmological measurements the spectral index $n_s$ moves towards its Harrison-Zel'dovich scale invariant value