Using large scale structure data and a halo model to constrain
  Generalised Dark Matter
  Constraints on the properties of the cosmological dark matter have previously
been obtained in a model-independent fashion using the Generalised Dark Matter
(GDM) framework. Here we extend that work in several directions: We consider
the inclusion of WiggleZ matter power spectrum data, and show that this
improves the constraints on the two perturbative GDM parameters, $c^2_s$ and
$c^2_\text{vis}$, by a factor of 3, for a conservative choice of wavenumber
range. A less conservative choice can yield an improvement of up to an order of
magnitude compared to previous constraints. In order to examine the robustness
of this result we develop a GDM halo model to explore how non-linear structure
formation could proceed in this framework, since currently GDM has only been
defined perturbatively and only linear theory has been used when generating
constraints. We then examine how the halo model affects the constraints
obtained from the matter power spectrum data. The less-conservative wavenumber
range shows a significant difference between linear and non-linear modelling,
with the latter favouring GDM parameters inconsistent with $\Lambda$CDM,
underlining the importance of careful non-linear modelling when using this
data. We also use this halo model to establish the robustness of previously
obtained constraints, particularly those that involve weak gravitational
lensing of the cosmic microwave background. Additionally, we show how the
inclusion of neutrino mass as a free parameter affects previous constraints on
the GDM parameters.
