2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/205577We show that Green function methods can be straightforwardly applied to nonlinear equations appearing as the leading order of a short time expansion. Higher order corrections can be then computed giving a satisfactory agreement with numerical results. The relevance of these results relies on the possibility of fully exploiting a gradient expansion in both classical and quantum field theory granting the existence of a strong coupling expansion. Having a Green function in this regime in quantum field theory amounts to obtain the corresponding spectrum of the theory.7 pages, 3 figures. Version accepted for publication in International Journal of Modern Physics AHigh Energy Physics - TheoryHigh Energy Physics - PhenomenologyMathematical Physicstext