  We develop a consistent semiclassical description of field-theoretic
collision-induced tunneling at arbitrary high collision energies. As a
playground we consider a (1+1)-dimensional false vacuum decay initiated by a
collision of N particles at energy E, paying special attention to the realistic
case of N=2 particles. We demonstrate that the cross section of this process is
exponentially suppressed at all energies. Moreover, the respective
suppressesion exponent F_N(E) exhibits a specific behavior which is significant
for our semiclassical method and assumed to be general: it decreases with
energy, reaches absolute minimum F=F_min(N) at a certain threshold energy
E=E_rt(N), and stays constant at higher energies. We show that the minimal
suppression F_min(N) and threshold energy can be evaluated using a special
class of semiclassical solutions which describe exponentially suppressed
transitions but nevertheless evolve in real time. Importantly, we argue that
the cross section at energies above E_rt(N) is computed perturbatively in the
background of the latter solutions, and the terms of this perturbative
expansion stay bounded in the infinite-energy limit. Transitions in the
high-energy regime proceed via emission of many soft quanta with total energy
E_rt; the energy excess E-E_rt remains in the colliding particles till the end
of the process.

High Energy Physics - Phenomenology;High Energy Physics - Theory