Abstract

One method of accounting for the observed acceleration of the universe is to modify general relativity to include a new degree of freedom, which plays the role of dark energy. General relativity has been tested to incredibly high precision over the last century and so there are tight constraints preventing any radical modifications. However, these constraints all come from local tests and there is nothing precluding modifications on large, extra-galactic scales. There is a class of theories that possess screening mechanisms where the strength of gravity depends on the local density. In these theories, gravity would be screened in our galaxy satisfying local constraints but would vary on cosmic scales. In this talk I will introduce some of these different screening mechanisms before introducing a new, model independent test of these theories. In unscreened regions of the universe, the properties of stars are dramatically altered: they are more luminous and ephemeral. We therefore expect unscreened galaxies to be more luminous and metal-enriched than their screened counterparts. These phenomena are an excellent probe of new physics and by searching for them we can increase the current bound on such theories by at least an order of magnitude.