Scalar field-perfect fluid correspondence and nonlinear perturbation equations

TL;DR

This paper establishes a framework linking scalar field and perfect fluid descriptions of dark energy, analyzing their nonlinear structure formation and clustering behavior, especially when coupled with dark matter.

Contribution

It introduces a general equivalence between scalar field and perfect fluid models of dark energy, facilitating the study of nonlinear perturbations and clustering in coupled dark energy-dark matter scenarios.

Findings

DE mass can increase in regions with large DM condensations

Scalar field and perfect fluid descriptions are equivalent for nonlinear analysis

Coupled DE can participate in structure formation processes

Abstract

The properties of dynamical Dark Energy (DE) and, in particular, the possibility that it can form or contribute to stable inhomogeneities, have been widely debated in recent literature, also in association to a possible coupling between DE and Dark Matter (DM). In order to clarify this issue, in this paper we present a general framework for the study of the nonlinear phases of structure formation, showing the equivalence between two possible descriptions of DE: a scalar field \phi self-interacting through a potential V(\phi) and a perfect fluid with an assigned negative equation of state w(a). This enables us to show that, in the presence of coupling, the mass of DE quanta may increase where large DM condensations are present, so that also DE may partake to the clustering process.