Cosmic bubble and domain wall instabilities II: Fracturing of colliding
  walls
  We study collisions between nearly planar domain walls including the effects
of small initial nonplanar fluctuations. These perturbations represent the
small fluctuations that must exist in a quantum treatment of the problem. In a
previous paper, we demonstrated that at the linear level a subset of these
fluctuations experience parametric amplification as a result of their coupling
to the planar symmetric background. Here we study the full three-dimensional
nonlinear dynamics using lattice simulations, including both the early time
regime when the fluctuations are well described by linear perturbation theory
as well as the subsequent stage of fully nonlinear evolution. We find that the
nonplanar fluctuations have a dramatic effect on the overall evolution of the
system. Specifically, once these fluctuations begin to interact nonlinearly the
split into a planar symmetric part of the field and the nonplanar fluctuations
loses its utility. At this point the colliding domain walls dissolve, with the
endpoint of this being the creation of a population of oscillons in the
collision region. The original (nearly) planar symmetry has been completely
destroyed at this point and an accurate study of the system requires the full
three-dimensional simulation.
