Hidden from view: Coupled Dark Sector Physics and Small Scales
  We study cluster mass dark matter haloes, their progenitors and surroundings
in an coupled Dark Matter-Dark Energy model and compare it to quintessence and
$\Lambda$CDM models with adiabatic zoom simulations. When comparing cosmologies
with different expansions histories, growth functions & power spectra, care
must be taken to identify unambiguous signatures of alternative cosmologies.
Shared cosmological parameters, such as $\sigma_8$, need not be the same for
optimal fits to observational data. We choose to set our parameters to
$\Lambda$CDM $z=0$ values. We find that in coupled models, where DM decays into
DE, haloes appear remarkably similar to $\Lambda$CDM haloes despite DM
experiencing an additional frictional force. Density profiles are not
systematically different and the subhalo populations have similar mass, spin,
and spatial distributions, although (sub)haloes are less concentrated on
average in coupled cosmologies. However, given the scatter in related
observables ($V_{\rm max},R_{V_{\rm max}}$), this difference is unlikely to
distinguish between coupled and uncoupled DM. Observations of satellites of MW
and M31 indicate a significant subpopulation reside in a plane. Coupled models
do produce planar arrangements of satellites of higher statistical significance
than $\Lambda$CDM models, however, in all models these planes are dynamically
unstable. In general, the nonlinear dynamics within and near large haloes masks
the effects of a coupled dark sector. The sole environmental signature we find
is that small haloes residing in the outskirts are more deficient in baryons
than their $\Lambda$CDM counterparts. The lack of a pronounced signal for a
coupled dark sector strongly suggests that such a phenomena would be
effectively hidden from view.
