  Low-mass planets migrating inwards in laminar protoplanetary disks (PPDs)
experience a dynamical corotation torque, which is expected to slow down
migration to a stall. However, baroclinic effects can reduce or even reverse
this effect, leading to rapid inward migration. In the radiatively inefficient
inner disk, one such mechanism is the buoyancy response of the disk to an
embedded planet. Recent work has suggested that radiative cooling can quench
this response, but for parameters that are not necessarily representative of
the inner regions of PPDs. We perform global three dimensional inviscid
radiation hydrodynamics simulations of planet-disk interaction to investigate
the effect of radiative cooling on the buoyancy-driven torque in a more
realistic disk model. We find that the buoyancy response exerts a negative
dynamical corotation torque -- albeit partially damped due to radiative cooling
-- resulting in sustained, rapid inward migration. Models that adopt a local
cooling prescription significantly overestimate the impact of the buoyancy
response, highlighting the importance of a realistic treatment of radiation
transport that includes radiative diffusion. Our results suggest that low-mass
planets should migrate inwards faster than has been previously expected in
radiative disks, with implications for the formation and orbital distribution
of super-Earths and sub-Neptunes at intermediate distances from their host
stars, unless additional physical processes that can slow down migration are
considered.
