Review of the semiclassical formalism for multiparticle production at high energies

These notes provide a comprehensive review of the semiclassical approach for calculating multiparticle production rates for initial states with few particles at very high energies. In this work we concentrate on a scalar field theory with a mass gap. Specifically, we look at a weakly-coupled theory in the high-energy limit, where the number of particles in the final state scales with energy, n similar to E -> infinity, and the coupling lambda -> 0 with n lambda held fixed. In this regime, the semiclassical approach allows us to calculate multiparticle rates non-perturbatively. (C) 2019 Elsevier B.V. All rights reserved.