2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/103137We analyze the perturbative series of the Keldysh-type sigma-model proposed recently for describing the quantum mechanics with time-dependent Hamiltonians from the unitary Wigner-Dyson random-matrix ensemble. We observe that vertices of orders higher than four cancel, which allows us to reduce the calculation of the energy-diffusion constant to that in a special kind of the matrix ϕ^4 model. We further verify that the perturbative four-loop correction to the energy-diffusion constant in the high-velocity limit cancels, in agreement with the conjecture of one of the authors.27 pages, 15 figures; typos corrected, one reference addedMesoscale and Nanoscale PhysicsDisordered Systems and Neural Networkstext