Is dark energy really constant?

One well known problem of the standard cosmological constant model is the tension between the high level of clustering observed in the CMB and the one obtained from large-scale structures. This may be an indication that the way  dark energy affects clustering might differ from a simple cosmological constant. If dark energy actually couples to dark matter, then the way matter clusters will be altered. A model of coupled quintessence, where dark energy is modeled by a scalar field, is a specific example of how this can be achieved. Using redshift  distortion data, we can constrain the coupling between dark matter and dark energy, and show that when a coupling is present the tension with CMB is removed. The data also agrees with the weak lensing results from the KIDS-450 survey. Future missions like SKA and Euclid will be able to distinguish between these models and a simple cosmological constant.