  We develop a general approach to nonequilibrium nanostructures formed by
one-dimensional channels coupled by tunnel junctions and/or by impurity
scattering. The formalism is based on nonequilibrium version of functional
bosonization. A central role in this approach is played by the Keldysh action
that has a form reminiscent of the theory of full counting statistics. To
proceed with evaluation of physical observables, we assume the weak-tunneling
regime and develop a real-time instanton method. A detailed exposition of the
formalism is supplemented by two important applications: (i) tunneling into a
biased Luttinger liquid with an impurity, and (ii) quantum-Hall Fabry-Perot
interferometry.
