Disk dispersal-driven instabilities: application to hot Neptunes

A population of short-period sub-Neptunes have mildly eccentric and large stellar obliquity orbits. This population is puzzling as dynamical instabilities and secular perturbations due to distant companions are generally unable to account for these observations. We propose that these planets have acquired their orbits due to a novel secular instability, in which the inclination grows due to a disk-dispersal driven secular resonance that forces the system into an unstable regime. We show how the predicted stellar obliquities and eccentricities of these sub-Neptunes depend on the relative strength of the general relativistic precession and the rotationally-induced stellar oblateness as well as the disk dispersal history of their natal disk.