A short review on clustering dark energy

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.

Horndeski Helping Hubble: Towards a possible solution to the Hubble tension with Horndeski gravity

“…Hence, even though Model II is very different from the minimal quintessence setup, it gives the same observational results for gravitational wave distance measurements as the latter. The clustering of dark energy can thus be used as a novel probe to differentiate this scenario from the other models [89].…”

Constraints on the speed of sound in the k-essence model of dark energy

“…On the other hand, the inhomogeneous dark energy participates in the clustering. Hence the evolution of perturbations is different in inhomogeneous dark energy compared to the homogeneous one [47,48]. Thus, it is required to check whether a dark energy is homogeneous or not.…”