How to falsify the GR plus ΛCDM model with galaxy redshift surveys

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 parametrize its potential deviation from a cosmological constant. This motivates a model-independent search for deviations from the concordance GR + Lambda CDM 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 + Lambda CDM is correct. The first, epsilon, was introduced previously as a scale-independent consistency check between the expansion history and structure growth. The second, nu, 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 the presence of deviations from the GR + Lambda CDM model. However, because many dark energy or modified gravity models predict consistency with GR + Lambda CDM at high redshift, it is desirable to apply this approach to surveys covering a wide range of redshifts and spatial scales.