Fundamental physics from galaxies

The project aims to devise and develop probes of new gravitational degrees of freedom at the galaxy scale. The particular emphasis will be on searches for the fifth forces typically generated by these degrees of freedom, and the screening mechanisms that effectively give them varying coupling to the different mass components of galaxies: stars, gas, dark matter and black holes. Although a number of theoretical tests have already been identified (e.g. equivalence principle violations between black holes and stars for Vainshtein-screened theories, or between stars and gas under thin-shell mechanisms), observational searches have so far been primitive. The student will compile archival datasets with constraining power for fifth forces, derive theoretical predictions for the observables from theories beyond LCDM, develop statistical methods for inferring model parameters, and establish the requirements for next-generation galaxy surveys to be maximally useful in this regard. There is also scope for theoretical development of screened modified gravity as it applies to galaxies. These tests are important not only in their own right, to establish the fundamental degrees of freedom of the gravitational sector, but also in the search for a dynamical explanation of dark energy, perhaps the greatest mystery in cosmology today.