Semiclassical theory of the Coulomb anomaly

An effective action approach for the problem of Coulomb blocking of tunneling is discussed. The method is applied to the strong-coupling problem arising near zero bias, where perturbation theory diverges. We find an instanton for the electrodynamics in imaginary time, and express the anomaly in terms of the exact conductivity of the system σ(ω, q ) and the exact interaction.