Dynamical vacuum energy in the expanding Universe confronted with observations: a dedicated study

TL;DR

This study investigates models of vacuum energy that evolve with the universe's expansion, testing their compatibility with current observations and exploring their implications for cosmic structure formation.

Contribution

It evaluates various dynamical vacuum energy models against observational data, identifying which models remain viable and their potential to explain dark energy dynamics.

Findings

Some models are consistent with current data.

Certain models are ruled out by observations.

Implications for structure formation are discussed.

Abstract

Despite the many efforts, our theoretical understanding of the ultimate nature of the dark energy component of the universe still lags well behind the astounding experimental evidence achieved from the increasingly sophisticated observational tools at our disposal. While the canonical possibility is a strict cosmological constant, or rigid vacuum energy density $\rho_{\Lambda}=$const., the exceeding simplicity of this possibility lies also at the root of its unconvincing theoretical status, as there is no explanation for the existence of such constant for the entire cosmic history. Herein we explore general models of the vacuum energy density slowly evolving with the Hubble function $H$ and/or its time derivative, $\rho_{\Lambda}(H,\dot{H})$. Some of these models are actually well-motivated from the theoretical point of view and may provide a rich phenomenology that could be explored in future observations, whereas some others have more limitations. In this work, we put them to the test and elucidate which ones are still compatible with the present observations and which ones are already ruled out. We consider their implications on structure formation, in combination with data on type Ia supernovae, the Cosmic Microwave Background, the Baryonic Acoustic Oscillations, and the predicted redshift distribution of cluster-size collapsed structures. The relation of these vacuum models on possible evidence of dynamical dark energy recently pointed out in the literature is also briefly addressed.