Dynamical signatures of black holes in massive Chern-Simons gravity: Quasibound modes and time evolution

Abstract: Dynamical Chern-Simons (dCS) gravity is a promising extension of general relativity (GR), arising naturally from the low-energy limit of some string motivated theories. Even though dCS possesses an additional scalar degree of freedom, interestingly, the Schwarzschild black hole is an exact solution of it. Concerning dynamical phenomena, however, gravitational and scalar perturbations couple with each other, generating possible scenarios to understand the differences between dCS and GR. We study dynamical signatures of dCS considering that the scalar field potential has a mass term. We analyze the influence of the theory's parameter into the quasibound states and in the time evolution of purely gravitational initial profiles. We find that the coupling can make the dipolar modes \textit{less stable} and that at late times initial gravitational perturbations become contaminated with the scalar sector, presenting an oscillation that depends on the quasibound state frequencies. These results may be interesting in the light of superradiant instabilities in rotating systems and to find signatures of alternative theories in gravitational wave detections.