Scalar field–perfect fluid correspondence and non-linear perturbation equations

Abstract

The properties of dynamical dark energy (DE) and, in particular, the possibility that itcan form or contribute to stable inhomogeneities have been widely debated inrecent literature, and also in association with a possible coupling betweenDE and dark matter (DM). In order to clarify this issue, in this paper wepresent a general framework for the study of the non-linear phases of structureformation, showing the equivalence of two possible descriptions of DE: a scalar fieldϕ self-interactingthrough a potential V (ϕ) and a perfect fluid with an assigned negative equation of statew(a). This enables us to show that, in the presence of coupling, the mass of DE quanta mayincrease where large DM condensations are present, with the result that also DE may beinvolved in the clustering process.