Semiclassical multiparticle production in scalar theories

A semiclassical approach to calculate multiparticle cross sections in scalar theories is proposed. The formalism is based on singular solutions to the field equation, which satisfy certain boundary and extremizing conditions. At low multiplicities and small kinetic energies per final particle the main perturbative results are reproduced in the framework of this formalism. A lower bound on the three-level cross section in the ultra-relativistic regime is also obtained. (author)