A New Mechanism for Bubble Nucleation: Classical Transitions
  Given a scalar field with metastable minima, bubbles nucleate quantum
mechanically. When bubbles collide, energy stored in the bubble walls is
converted into kinetic energy of the field. This kinetic energy can facilitate
the classical nucleation of new bubbles in minima that lie below those of the
"parent" bubbles. This process is efficient and classical, and changes the
dynamics and statistics of bubble formation in models with multiple vacua,
relative to that derived from quantum tunneling.
