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.