2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40607We investigate the time dependence of the quantum statistical model with $λϕ^4/4!$ self-interaction and consider the resulting induced particle number density. For a special example in which the classical approximation exhibits parametric resonance, the effects of the back reaction and especially of collisions, treated in a perturbative way, are analysed.LaTeX, 9 pages, 7 figuresHigh Energy Physics - Phenomenologytext