Tunneling Phenomena in Cosmology: Some Fundamental Problems
  The fundamental problem of how tunneling in thermal medium is completed is addressed, and a new time scale of order 1/friction for its termination, which is usually much shorter than the Hubble time, is pointed out. Enhanced non-linear resonance is responsible for this short time scale. This phenomenon occurs when the semiclassical periodic motion in a metastable potential well resonates with one of the environment harmonic oscillators coupled to its motion. 
M. Yoshimura