  The nonequilibrium time evolution of a quantum dot is studied by means of
dynamic equations for time-dependent Greens functions derived from a
two-particle-irreducible (2PI) effective action for the Anderson impurity
model. Coupling the dot between two leads at different voltages, the dynamics
of the current through the dot is investigated. We show that the 2PI approach
is capable to describe the dynamical build-up of the Kondo effect, which shows
up as a sharp resonance in the spectral function, with a width exponentially
suppressed in the electron self coupling on the dot. An external voltage
applied to the dot is found to deteriorate the Kondo effect at the
hybridization scale. The dynamic equations are evaluated within different
nonperturbative resummation schemes, within the direct, particle-particle, and
particle-hole channels, as well as their combination, and the results compared
with that from other methods.
