EXTENDING COSMOLOGICAL TESTS OF GENERAL RELATIVITY WITH THE SQUARE KILOMETRE ARRAY

Tests of general relativity (GR) are still in their infancy on cosmological scales, but forthcoming experiments promise to greatly improve their precision over a wide range of distance scales and redshifts. One such experiment, the Square Kilometre Array (SKA), will carry out several wide and deep surveys of resolved and unresolved neutral hydrogen (HI) 21 cm line-emitting galaxies, mapping a significant fraction of the sky from 0 <= z <= 6. I present forecasts for the ability of a suite of possible SKA H I surveys to detect deviations from GR by reconstructing the cosmic expansion and growth history. SKA Phase 1 intensity mapping surveys can achieve sub1% measurements of f sigma(8) out to z approximate to 1, with an SKA1-MID Band 2 survey out to z less than or similar to 0.6 able to surpass contemporary spectroscopic galaxy surveys such as DESI and Euclid in terms of constraints on modified gravity parameters if challenges such as foreground contamination can be tackled effectively. A more futuristic Phase 2 H I survey of similar to 109 spectroscopic galaxy redshifts would be capable of detecting a similar to 2% modification of the Poisson equation out to z approximate to 2.