Magnetic monopole - domain wall collisions
  Interactions of different types of topological defects can play an important
role in the aftermath of a phase transition. We study interactions of
fundamental magnetic monopoles and stable domain walls in a Grand Unified
theory in which $SU(5) \times Z_2$ symmetry is spontaneously broken to
$SU(3)\times SU(2)\times U(1)/Z_6$. We find that there are only two distinct
outcomes depending on the relative orientation of the monopole and the wall in
internal space. In one case, the monopole passes through the wall, while in the
other it unwinds on hitting the wall.
