Perturbative Understanding of Non-Perturbative Processes and Quantumization versus Classicalization

Understand

In some instances of study of quantum evolution of classical backgrounds it is considered inevitable to resort to non-perturbative methods at the price of treating the system semiclassically.

• We show that a fully quantum perturbative treatment, in which the background is resolved as a multi-particle state, recovers the semiclassical non-perturbative results and allows going beyond.
• We reproduce particle-creation by a classical field in a theory of two scalars as well as in scalar QED in terms of scattering processes of high multiplicity.
• The multi-particle treatment also gives a transparent picture of why a single-process transition from a classical to a quantum state, which we call quantumization, is exponentially suppressed, whereas the opposite process, classicalization, can take place swiftly if the microstate degeneracy of the classical state is high.