  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.
