Universality in the mean spatial shape of avalanches

TL;DR

This paper introduces a new way to define and analyze the universal mean spatial shape of avalanches in elastic interfaces, revealing a cusp singularity and confirming predictions with simulations.

Contribution

It provides the first analytical prediction of the spatial shape of avalanches, including a new definition and universal scaling functions beyond mean-field theory.

Findings

Universal scaling functions with cusp singularity predicted

Good agreement between analytical results and numerical simulations

Enhanced understanding of avalanche spatial structure

Abstract

Quantifying the universality of avalanche observables beyond critical exponents is of current great interest in theory and experiments. Here, we improve the characterization of the spatio-temporal process inside avalanches in the universality class of the depinning of elastic interfaces in random media. Surprisingly, at variance with the temporal shape, the spatial shape of avalanches has not yet been predicted. In part this is due to a lack of an analytically tractable definition: how should the shapes be centered? Here we introduce such a definition, accessible in experiments, and study the mean spatial shape of avalanches at fixed size centered around their starting point (seed). We calculate the associated universal scaling functions, both in a mean-field model and beyond. Notably, they are predicted to exhibit a cusp singularity near the seed. The results are in good agreement with a numerical simulation of an elastic line.