Linear Density Perturbations in Multifield Coupled Quintessence
  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.
