Real-Time Instantons and Suppression of Collision-Induced Tunneling
  We consider tunneling processes in QFT induced by collisions of elementary particles. We propose a semiclassical method for estimating the probability of these processes in the limit of very high collision energy. As an illustration, we evaluate the maximum probability of induced tunneling between different vacua in a (1+1)-dimensional scalar model with boundary interaction. 
D. Levkov, S. Sibiryakov