Red Giant evolution in Modified Gravity

Abstract

In this paper, we study the chameleon profile in inhomogeneous density distributions and find that the fifth force in thin shell near the surface is weaker from what expected in homogeneous density distributions. Also, we check the validity of quasi-static approximation for the chameleon scalar field in the astrophysical time scales. We have investigated the rolling down behaviour of the scalar field on its effective potential inside a one solar mass red giant star by using MESA code. We have found that the scalar field is fast enough to follow the minimum of the potential. This adiabatic behaviour reduces the fifth force and extends the screened regions to lower densities where the field has smaller mass and was expected to be unscreened. As a consequence, the star evolution is similar to what expected from standard general relativity. In addition, considering the stability of star, an approximate constraint on the coupling constant $\beta$ is found.