Testing Gravity on Cosmological Scales using Strong Gravitational Lensing

Time delays of strongly lensed quasars have long been used to measure either the mass of the lensing galaxy or cluster, or the Hubble parameter, after assuming a value for one or the other from independent measurements. Given the growing number of precise time-delay measurements, we study the possibility of strong lensing unveiling finer information, namely serving as a test of Einstein gravity on cosmological scales. In this context, we present a phenomenological model of gravitational screening, where the classic solar system PPN curvature parameter gamma is promoted to a step function in space, dividing the galactic or cluster dark matter halo into an inner GR region, and an outer non-GR region extending to extra-galactic space. We confront our model with available data, and pave the way for upcoming observations and more sophisticated analyses.