  A wide range of models describing modifications to General Relativity have
been proposed, but no fundamental parameter set exists to describe them.
Similarly, no fundamental theory exists for dark energy to parameterize its
potential deviation from a cosmological constant. This motivates a
model-independent search for deviations from the concordance GR+LambdaCDM
cosmological model in large galaxy redshift surveys. We describe two
model-independent tests of the growth of cosmological structure, in the form of
quantities that must equal one if GR+LambdaCDM is correct. The first, epsilon,
was introduced previously as a scale-independent consistency check between the
expansion history and structure growth. The second, upsilon, is introduced here
as a test of scale-dependence in the linear evolution of matter density
perturbations. We show that the ongoing and near-future galaxy redshift surveys
WiggleZ, BOSS, and HETDEX will constrain these quantities at the 5-10% level,
representing a stringent test of concordance cosmology at different redshifts.
When redshift space distortions are used to probe the growth of cosmological
structure, galaxies at higher redshift with lower bias are found to be most
powerful in detecting deviations from the GR+LambdaCDM model.
