Probing the independence within the dark sector in the fluid
  approximation
  The standard model of cosmology is based on two unknown dark components that
are uncoupled from each other. In this paper we investigate whether there is
evidence for an interaction between these components of cold dark matter (CDM)
and dark energy (DE). In particular, we focus on a minimal extension and
reconstruct the interaction history at low-redshifts non-parametrically using a
variation of the commonly used principal component analysis. Although we focus
on the interaction in the dark sector, any significant deviation from the
standard model that changes the expansion history of the Universe, should leave
imprints detectable by our analysis. Thus, detecting signatures of interaction
could also be indicative of other non-standard phenomena even if they are not
the results of the interaction. It is thus interesting to note that the results
presented in this paper do not provide support for the interaction in the dark
sector, although the uncertainty is still quite large. In so far as interaction
is present but undetectable using current data, we show from a Fisher forecast
that forthcoming LSST and DESI surveys will be able to constrain a DM-DE
coupling at $20\%$ precision --- enough to falsify the non-interacting
scenario, assuming the presence of a modest amount of interaction.
