Quantum mechanics with a time-dependent random unitary Hamiltonian: A perturbative study of the non-linear Keldysh sigma-model Original Research Article

We 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 spe