SPEAKER: Ryo Saito (APC, Paris)
ABSTRACT: Any infrared modification of gravity, which explains the current cosmic acceleration, has to preserve the successes of general relativity in the solar-system observations. In many theories of modified gravity, it is ensured by the Vainshtein mechanism that works near dense sources. Recently, it has been found that the Vainshtein mechanism can be partially broken inside a dense source, although not outside, in a general class of scalar-tensor theories. In this talk, we study the impact of this new type of deviation from standard gravity on the density profile of a star, modelling simply it as a polytropic sphere. We also show the existence of a universal upper bound on the amplitude of this type of modification, independently of the details of the equation of state.