2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/197165We study nonlinear response in weakly coupled nonequilibrium $ϕ^4$ theory in the context of both classical transport theory and real time quantum field theory, based on a generalized Kubo formula which we derive. A novel connection between these two approaches is established which provides a diagrammatic interpretation of the Boltzmann equation.5 pages in RevTex with 4 Postscript figuresHigh Energy Physics - Phenomenologytext