Contributions to Transport Theory from Multi-Particle Interactions and Production Processes

We use the Schwinger-Keldysh technique to study the collision term in the Boltzman equation for a system of quantum scalar fields. We study three three-loop diagrams in ϕ³ model and four-loop diagrams in ϕ⁴ model, and show how these diagrams correspond to multi-particle collisions and production processes.