Testing Dark Matter Clustering with Redshift Space Distortions
  The growth rate of large scale structure can probe whether dark matter
clusters at gravitational strength or deviates from this, e.g. due to self
interactions. Measurement of the growth rate through redshift space distortions
in galaxy redshift surveys constrains the clustering strength, and its redshift
dependence. We compare such effects on growth to those from high redshift
deviations (e.g. early dark energy) or modified gravity, and give a simple,
highly accurate analytic prescription. Current observations can constrain the
dark matter clustering strength to F_{cl}=0.99\pm0.02 of standard, if all other
parameters are held fixed, but substantial covariances exist. Future galaxy
redshift surveys may constrain an evolving clustering strength to 28%,
marginalizing over the other parameters, or 4% if the dark energy parameters
are held fixed while fitting for dark matter growth. Tighter constraints on the
nature of dark matter could be obtained by combining cosmological and
astrophysical probes.
