A short review on clustering dark energy

TL;DR

This paper reviews models of dark energy that can cluster on small scales, discussing their linear and nonlinear evolution, theoretical frameworks, and observational implications.

Contribution

It provides a comprehensive review of clustering dark energy models, including linear theory, nonlinear modeling, and recent numerical simulations, highlighting current challenges and prospects.

Findings

Dark energy perturbations influence structure formation on small scales.

Nonlinear models like generalized Spherical Collapse are explored with limitations.

Recent simulations offer new insights into dark energy fluctuations.

Abstract

We review dark energy models which can present non-negligible fluctuations on scales smaller than Hubble radius. Both linear and nonlinear evolutions of dark energy fluctuations are discussed. The linear evolution has a well-established framework, based on linear perturbation theory in General Relativity, and is well studied and implemented in numerical codes. We highlight the main results from linear theory to explain how dark energy perturbations become important on the scales of interest for structure formation. Next, we review some attempts to understand the impact of clustering dark energy models in the nonlinear regime, usually based on generalizations of the Spherical Collapse Model. We critically discuss the proposed generalizations of the Spherical Collapse Model that can treat clustering dark energy models and their shortcomings. Proposed implementations of clustering dark energy models in halo mass functions are reviewed. We also discuss some recent numerical simulations capable of treating dark energy fluctuations. Finally, we make an overview of the observational predictions based on these models.