New interactions in the dark sector mediated by dark energy

TL;DR

This paper explores the possibility of multiple dark matter species interacting via a dark energy field, analyzing their background and perturbation evolution, revealing complex behaviors beyond single-fluid models.

Contribution

It introduces models with multiple dark matter species and interactions mediated by dark energy, analyzing their effects on cosmological evolution at background and perturbation levels.

Findings

Background evolution mimics a single fluid with a time-varying coupling.

Perturbation evolution differs significantly from background predictions.

Attractive and repulsive forces influence structure formation.

Abstract

Cosmological observations have revealed the existence of a dark matter sector, which is commonly assumed to be made up of one particle species only. However, this sector might be more complicated than we currently believe: there might be more than one dark matter species (for example two components of cold dark matter or a mixture of hot and cold dark matter) and there may be new interactions between these particles. In this paper we study the possibility of multiple dark matter species and interactions mediated by a dark energy field. We study both the background and the perturbation evolution in these scenarios. We find that the background evolution of a system of multiple dark matter particles (with constant couplings) mimics a single fluid with a time-varying coupling parameter. However, this is no longer true on the perturbative level. We study the case of attractive and repulsive forces as well as a mixture of cold and hot dark matter particles.