Strong Scatterings Invalidate Proposed Models of Enhanced Tidal Disruption Event Rates in Post-starburst Galaxies

Stars wandering too close to supermassive black holes (SMBHs) can be ripped apart by the tidal forces of the black hole. Recent optical surveys have revealed that E+A galaxies are over-represented by a factor of ∼30, while green galaxies are over-represented in both optical and IR surveys. Different stellar models have been proposed to explain this tidal disruption event (TDE) preference: ultrasteep stellar densities in the nuclear cluster, radial velocity anisotropies, and a top-heavy initial mass function (IMF). Here, we explore these hypotheses in the framework of our revised loss cone theory that accounts for both weak and strong scattering, i.e., a scattering strong enough to eject a star from the nuclear cluster. We find that when accounting for weak and strong scatterings, both ultrasteep densities and radial velocity anisotropies fail to explain the post-starburst preference of TDEs, except when considering a high anisotropy factor together with a high SMBH mass and a shallow density profile of stellar-mass BHs γ_bh = 7/4. Our findings hold when combining either model with top-heavy IMFs. Hence, our work emphasizes both the importance of taking into account strong scatterings and the need for new hypotheses to explain the post-starburst preference of TDEs.