Linear Density Perturbations in Multifield Coupled Quintessence

TL;DR

This paper investigates linear density perturbations in multifield coupled quintessence models, providing a comprehensive numerical analysis and assessing the validity of common approximations against upcoming observational data.

Contribution

It introduces a full set of gauge-invariant equations for these models, implements a numerical code, and evaluates the small scale approximation's accuracy for future surveys.

Findings

Deviation of full equations from approximation exceeds future experimental uncertainties.

Numerical code PYESSENCE is developed and will be publicly available.

Comparison shows significant differences at large k modes for upcoming experiments.

Abstract

We study the behaviour of linear perturbations in multifield coupled quintessence models. Using gauge invariant linear cosmological perturbation theory we provide the full set of governing equations for this class of models, and solve the system numerically. We apply the numerical code to generate growth functions for various examples, and compare these both to the standard $\Lambda$CDM model and to current and future observational bounds. Finally, we examine the applicability of the "small scale approximation", often used to calculate growth functions in quintessence models, in light of upcoming experiments such as SKA and Euclid. We find the deviation of the full equation results for large k modes from the approximation exceeds the experimental uncertainty for these future surveys. The numerical code, PYESSENCE, written in Python will be publicly available.