A Future Test of Gravitation Using Galaxy Cluster Velocities
  The accelerating expansion of the Universe at recent epochs has called into
question the validity of general relativity on cosmological scales. One probe
of gravity is a comparison of expansion history of the Universe with the
history of structure growth via gravitational instability: general relativity
predicts a specific relation between these two observables. Here we show that
the mean pairwise streaming velocity of galaxy clusters provides a useful
method of constraining this relation. Galaxy cluster velocities can be measured
via the kinetic Sunyaev-Zeldovich distortion of the cosmic microwave background
radiation; future surveys can provide large enough catalogs of cluster
velocities to discriminate between general relativity and other proposed
gravitational theories.
