Effects of Radiative Diffusion on the Dynamical Corotation Torque in Three-Dimensional Protoplanetary Disks

The dynamical corotation torque arising from the deformation of the horseshoe orbits, along with the vortensity gradient in the background disk, is important for determining orbital migration rate and direction of low-mass planets. Previous two-dimensional studies predicted that the dynamical corotation torque is positive, decelerating the inward planet migration. In contrast, recent three-dimensional studies have shown that buoyancy resonance makes the dynamical corotation torque negative, accelerating the inward migration. In this paper, we study the dependence of the dynamical corotation torque on the thermal transport using three-dimensional simulations. We first show that our results are consistent with previous three-dimensional studies when the disk is fully adiabatic. In more realistic radiative disks, however, radiative diffusion suppresses the buoyancy resonance significantly, especially at high-altitude regions, and yields a positive dynamical corotation torque. This alleviates the issue of a rapid migration caused by the negative dynamical corotation torque in the adiabatic disks. Our results suggest that radiative diffusion together with stellar irradiation and accretion heating is needed to accurately describe the migration of low-mass planets.