Corrective effect of many-body interactions in dynamical friction
  Dynamical friction is a fundamental and important phenomenon in astrophysics.
The Chandrasekhar formula is a well-known analytical estimation of the effect.
However, current astrophysicists have realized that the formula is not correct
in some cases because of several approximations dared in the formulation and/or
complex non-linearities in the real universe. For example, it has been
indicated that the dynamical friction doesn't work in cored density profiles
(constant density in the central region) despite that the Chandrasekhar formula
predicts drag force even in the constant densities. In the former half of this
paper, I discuss by N-body simulations that many-body interactions are also
important in actual dynamical friction though derivation of the Chandrasekhar
formula is based on the assumption of two-body interaction. In the simulation,
the many-body interactions are caused by a very small number of field particles
co-rotating with a perturber. However, the contribution from the many-body
interactions accounts for a non-negligible fraction of the actual dynamical
friction. In the latter half, I discuss why the cored profiles suppress the
dynamical friction. One possible explanation is that corrective effect of the
many-body interactions drive orbital motion of the perturber. The cessation of
dynamical friction by this corrective effect would be feasible even in shallow
cusp density profiles although the shallow cusp may evolve into a constant
density.
