Planet-disk interaction in highly inclined systems
  We study the interaction of a proto-planetary disk and a planet on a highly
inclined orbit in the linear regime. The evolution of the planet is dominated
by dynamical friction for planet masses above several Earth-masses. Smaller
planets are dominated by aerodynamic drag, especially for very high
inclinations and retrograde orbits.
  The time-scales associated with migration and inclination damping are
calculated. For certain values of the inclination, the inclination damping
time-scale is longer than the migration time-scale and the disk lifetime. This
result shows that highly inclined planets can not (re-)align with the
proto-planetary disk.
  We discuss the dependence of numerical simulations on the gravitational
softening parameter. We find only a logarithmic dependence, making global three
dimensional simulations of this process computationally feasible.
  A large fraction of Hot Jupiters is on highly inclined orbits with respect to
the rotation axis of the star. On the other hand small-mass planetary systems
discovered by the Kepler mission have low mutual inclinations. This shows that
there are two distinct formation mechanisms at work. The process that creates
inclined Hot Jupiters does not operate on small mass planets because the
damping timescales are so long that these systems would still be inclined
today.
