Constraining new fundamental physics with multiwavelength astrometry

While the deflection of light is achromatic in General Relativity, it is not always so in several new-physics models (e.g. certain quantum-gravity and string-inspired models, models with nonminimal photon-gravity coupling or with massive photon etc.). We discuss how parameters of these models may be constrained by precise astrometry at different wavelenghts. From published observations of the gravitational lens MG J2016+112, we obtain world-best limits on chromatic gravitational deflection of light (and the unique limit on the photon mass relevant for distance scales >Mpc). We also outline prospects for further improvement of these limits.