Do we need soft cosmology?
  We examine the possibility of "soft cosmology", namely small deviations from
the usual framework due to the effective appearance of soft-matter properties
in the Universe sectors. One effect of such a case would be the dark energy to
exhibit a different equation-of-state parameter at large scales (which
determine the universe expansion) and at intermediate scales (which determine
the sub-horizon clustering and the large scale structure formation). Concerning
soft dark matter, we show that it can effectively arise due to the dark-energy
clustering, even if dark energy is not soft. We propose a novel parametrization
introducing the "softness parameters" of the dark sectors. As we see, although
the background evolution remains unaffected, due to the extreme sensitivity and
significant effects on the global properties even a slightly non-trivial
softness parameter can improve the clustering behavior and alleviate e.g. the
$f\sigma_8$ tension. Lastly, an extension of the cosmological perturbation
theory and a detailed statistical mechanical analysis, in order to incorporate
complexity and estimate the scale-dependent behavior from first principles, is
necessary and would provide a robust argumentation in favour of soft cosmology.
