On structure formation from a small-scales-interacting dark sector

Understand

We consider a cosmological model with an interaction between dark matter and dark energy which leaves the background cosmology unaffected and only affects the evolution of the perturbations.

• This is achieved by introducing a coupling given in terms of the relative velocities of dark matter and dark energy.
• This interaction has the distinctive feature of appearing predominantly on small scales, where peculiar velocities can become important.
• We confront the predictions of the model to cosmological observations and find a potential alleviation of the known tension in the amplitude of density perturbations as measured by low redshift galaxy surveys and the Planck data.