Static and dynamic phase transition in pinned charge density waves

We study the analytical properties of charge density waves, in presence of quenched random impurities, at the depinning transition. We deduce the equation for the threshold field, as a function of the coupling constant, in the strong pinning regime, by means of a mean field approah. The results are in excellent agreement with previous calculations and numerical simulations. The concept of critically examined, showing the presence of different critical lines, corresponding to the static and dynamic definition of the phase transition.