Clarifying spherical collapse in coupled dark energy cosmologies

TL;DR

This paper refines the spherical collapse model for coupled dark energy cosmologies, incorporating the effects of a fifth force mediated by the scalar field, and clarifies the treatment of inhomogeneous scalar fields.

Contribution

It derives a consistent spherical collapse framework from hydrodynamical equations, accounting for fifth forces in coupled dark energy models, and applies it to various cosmological scenarios.

Findings

Correct formulation of spherical collapse with fifth force

Application to coupled quintessence and neutrino models

Clarification of inhomogeneous scalar field treatment

Abstract

The spherical collapse model is often used to follow the evolution of overdensities into the nonlinear regime. We describe the correct approach to be used in coupled dark energy cosmologies, where a fifth force, different from gravity and mediated by the dark energy scalar field, influences the collapse. We reformulate the spherical collapse description by deriving it directly from the set of nonlinear hydrodynamical Navier Stokes equations. By comparing with the corresponding relativistic equations, we show how the fifth force should be taken into account within the spherical collapse picture and clarify the problems arising when an inhomogeneous scalar field is considered within a spherical collapse picture. We then apply our method to the case of coupled quintessence, where the fifth force acts among cold dark matter particles, and to growing neutrino quintessence, where the fifth force acts between neutrinos. Furthermore, we review this method when applied to standard cosmologies and apply our analysis to minimally coupled quintessence and check past results for early dark energy parametrizations.