Multiple Transitions in Vacuum Dark Energy and H 0 Tension

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 the cosmic microwave background, baryonic acoustic oscillations, and supernovae. 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 toward its Harrison–Zel’dovich scale-invariant value.