A direct measurement of the renormalized disorder correlator, and avalanche size distributions

Kay Wiese, ENS Paris

The central object of the field theory of disordered systems is the renormalized disorder correlator. Due to metastability in the system, it has a cusp at the origin. From a field-theory point of view, this cusp questions the method as such. It is therefore important to measure it directly, in a numerical simulation or experiment. However, only recently such a protocol has been devised. Here we present numerical simulations and the first experiment to implement this protocol: We measure the center-of-mass fluctuations of the height of a contact line at depinning, including the cusp. This cusp is also the key to obtain the avalanche-size distribution directly from the field theory. This is the first analytic method (apart from few exact results) to go beyond mean field, allowing to predict the whole scaling function: the critical behavior at small avalanche sizes, characterized by the exponent tau, the shoulder at intermediate sizes, and a compacted exponential tail. These results are confronted with large-scale numerical simulations.