Cosmological perturbations in the interacting dark sector: Mapping fields and fluids

There is no unique way to describe the dark energy-dark matter interaction, as we have little information about the nature and dynamics of the dark sector. Hence, in many of the phenomenological dark matter fluid interaction models in the literature, the interaction strength Q(nu) in the dark sector is introduced by hand. Demanding that the interaction strength Q(nu) in the dark sector must have a field theory description, we obtain a unique form of the interaction strength. We show the equivalence between the fields and fluids for the f(R,chi) model where f is an arbitrary, smooth function of R and a classical scalar field chi, which represents dark matter. Up to first order in perturbations, we show that the one-to-one mapping between the classical field theory description and the phenomenological fluid description of interacting dark energy and dark matter exists only for this unique form of interaction. We then classify the interacting dark energy models considered in the literature into two categories based on the field-theoretic description. We introduce a novel autonomous system and its stability analysis for the general interacting dark sector. We show that the dark-energy-dominated epoch occurs earlier than the noninteracting systems for a specific scalar field potential and a range of coupling strengths.

Automated summary

The study explores the interaction between dark energy and dark matter, finding a unique form of interaction strength and showing equivalence between fields and fluids in certain models. It also categorizes interacting dark energy models in the literature and introduces a novel autonomous system for stability analysis. The research demonstrates that the dark-energy-dominated epoch occurs earlier than noninteracting systems for specific scalar field potentials and coupling strengths.