Overturning and apparent anisotropic pressure in Eddington-inspired Born-Infeld theory on compact stars

The advantage of mapping modified gravity theories with standard matter into general relativity (GR) with modified matter is that we can quickly implement the well-established analytical and numerical methods developed within GR to study modified gravity theories and compare the modified gravity theories with current observational data. In this paper, we explicitly show that overturning/cracking instability may occur in an isotropic Eddington-inspired Born-Infeld (EiBI) stellar structure. Analyses are done by reducing the Tolman-Oppenheimer-Volkoff-like equations of EiBI into the ones of GR with an additional anisotropiclike nonlinear term. We obtain the term by expanding the stellar structure equations with respect to