Cosmological probes of gravity

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While we know that General Relativity is an excellent description of gravitational interactions on solar system scales, at much larger (high energy physics) and much smaller (cosmology) energy scales this is far from certain. This opens up fascinating discovery windows to learn more about gravity and the dark components of the universe linked to its accelerated expansion. In exploring several of these windows, this project will span a wide range of physical systems and methods, from deriving observational bounds from the current and upcoming wealth of observational large scale structure data (with a focus on the DES and LSST surveys) to exploring theoretical high energy physicsconstraints on the behaviour of gravity. As part of this project, we will therefore explore cosmological constraints on dark energy and modified gravity on very large scales, where the physics is sufficiently linear to be analytically tractable. This will e.g. involve understanding, computing and combining novel constraints from the lensing and clustering of galaxies with those from the cosmic microwave background. We will use current data from DES (Dark Energy Survey) and a host of complementary extragalactic host catalogues to derive state-of-the-art bounds on gravitational physics and to forecast analogous constraints for the next generation of surveys, especially for LSST (Legacy Survey of Space and Time). Furthermore, we will complement these data-driven constraints with theoretical insights and constraints derived using techniques traditionally at home in particle physics, e.g. novel bounds on gravitational physics from considering the scattering of fundamental particles (such as gravitons). In combining them with bounds obtained directly from cosmology, we will be able to gain qualitatively new insights and thereby zero in on the nature of cosmological gravity.