  We study the effects of anisotropic thermal conduction along magnetic field
lines on an accelerated contact discontinuity in a weakly collisional plasma.
We first perform a linear stability analysis similar to that used to derive the
Rayleigh-Taylor instability (RTI) dispersion relation. We find that anisotropic
conduction is only important for compressible modes, as incompressible modes
are isothermal. Modes grow faster in the presence of anisotropic conduction,
but growth rates do not change by more than a factor of order unity. We next
run fully non-linear numerical simulations of a contact discontinuity with
anisotropic conduction. The non-linear evolution can be thought of as a
superposition of three physical effects: temperature diffusion due to vertical
conduction, the RTI, and the heat flux driven buoyancy instability (HBI). In
simulations with RTI-stable contact discontinuities, the temperature
discontinuity spreads due to vertical heat conduction. This occurs even for
initially horizontal magnetic fields due to the initial vertical velocity
perturbation and numerical mixing across the interface. The HBI slows this
temperature diffusion by reorienting initially vertical magnetic field lines to
a more horizontal geometry. In simulations with RTI-unstable contact
discontinuities, the dynamics are initially governed by temperature diffusion,
but the RTI becomes increasingly important at late times. We discuss the
possible application of these results to supernova remnants, solar prominences,
and cold fronts in galaxy clusters.
