Does stability in Einstein frame guarantee stability in Jordan frame? (2002.02767v2)

Abstract: Scalar tensor theories of gravity can be formulated in the Einstein or in the Jordan frame, which are related by the conformal transformations. Although the two frames are describe the same physics, and are equivalent, the stability of the field equations in two frames are not the same. Here we implement dynamical system and phase space approach as a robustness tool to investigate this issue. We concentrate on the Brans Dicke theory, but the results can easily be generalized. Our analysis show that while there is one-to-one correspondence between critical points in two frames and each critical point in one frame is mapped to its corresponds in other frame , however stability of a critical points in one frame does not grantee the stability in other frame. Hence an unstable point in one frame may be mapped to a stable point in other frame. All trajectories between two critical points in phase space in one frame are different from their corresponds in other ones. This indicates that the dynamical behavior of variables and cosmological parameters are different in two frames. Hence for those features of the study which focus on observational measurements we must use the (JF) where experimental data have their usual interpretation