  Using the Schwinger-Keldysh approach and the drone (Majorana) fermion
representation, we evaluate current distribution in a single-electron
transistor in a regime where a total tunnel resistance is small. Nonequilibrium
quantum fluctuations of charge induce a lifetime broadening of charge-state
level, as well as renormalization of system parameters. We find that the
lifetime broadening effect may suppress the probability of relatively large
current.
