  We present a hierarchical quantum master equation (HQME) approach, which
allows the numerically exact evaluation of higher-order current cumulants in
the framework of full counting statistics for nonequilibrium charge transport
in nanosystems. The novel methodology is exemplarily applied to a model of
vibrationally coupled electron transport in a molecular nanojunction. We
investigate the influence of cotunneling on avalanche-like transport, in
particular in the nonresonant transport regime, where we find that inelastic
cotunneling acts as trigger process for resonant avalanches. In this regime, we
also demonstrate that the correction to the elastic noise upon opening of the
inelastic transport channel is strongly affected by the nonequilibrium
excitation of the vibration as well as the polaron shift.
