  The infinite-U Anderson model is applied to transport through a quantum dot.
The current and density of states are obtained via the non-crossing
approximation for two spin-degenerate levels weakly coupled to two leads. At
low temperatures, the Kondo peak in the equilibrium density of states strongly
enhances the linear-response conductance. Application of a finite voltage bias
reduces the conductance and splits the peak in the density of states. The split
peaks, one at each chemical potential, are suppressed in amplitude by a finite
dissipative lifetime. We estimate this lifetime perturbatively as the time to
transfer an electron from the higher chemical potential lead to the lower
chemical potential one. At zero magnetic field, the clearest signatures of the
Kondo effect in transport through a quantum dot are the broadening, shift, and
enhancement of the linear-response conductance peaks at low temperatures, and a
peak in the nonlinear differential conductance around zero bias.
