Supersymmetry breaking in disordered systems and relation to functional renormalization and replica-symmetry breaking

In this article, we study an elastic manifold in quenched disorder in the limit of zero temperature. Naively it is equivalent to a free theory with elasticity in Fourier space proportional to k(4) instead of k(2), i.e. a model without disorder in two space dimensions less. This phenomenon, called dimensional reduction, is most elegantly obtained using supersymmetry. However, scaling arguments suggest, and functional renormalization shows, that dimensional reduction breaks down beyond the Larkin length. Thus one equivalently expects a breakdown of supersymmetry. Using methods of functional renormalization, we show how supersymmetry is broken. We also discuss the relation to replica-symmetry breaking, and how our formulation can be put into work to lift apparent ambiguities in standard functional renormalization group calculations.