Nguyen Van Hieu, Nguyen Bich Ha, Nguyen Van Hop

The infinite system of differential equations for the nonequilibrium Green functions
of electrons in a single-level quantum dot connected with two conducting leads is truncated by
applying the mean-field approximation to the mean values of the products of four operators. As
the result the system of Dyson equations for the two-point real-time nonequilibrium Green functions
in the Keldysh formalism as well as that of the two-point imaginary-time Green functions
are derived.