2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/188397The closed time-path formalism is a powerful Green's function formulation to describe non-equilibrium phenomena in field theory and it leads to a complete non-equilibrium quantum kinetic theory. We make use of this formalism to write down the set of quantum Boltzmann equations relevant for leptogenesis. They manifest memory effects and off-shell corrections. In particular, memory effects lead to a time-dependent CP asymmetry whose value at a given instant of time depends upon the previous history of the system. This result is particularly relevant when the asymmetry is generated by the decays of nearly mass-degenerate heavy states, as in resonant or soft leptogenesis.21 pages, 5 figures. IOP LaTeX class used. Minor corrections and references added. Matches the version published in JCAPHigh Energy Physics - Phenomenologytext