Tail of the contact force distribution in static granular materials.

We numerically study the distribution P(f) of contact forces in frictionless bead packs, by averaging over the ensemble of all possible force network configurations. We resort to umbrella sampling to resolve the asymptotic decay of P(f) for large f , and determine P(f) down to values of order 10{-45} for ordered and disordered systems in two (2D) and three dimensions (3D). Our findings unambiguously show that, in the ensemble approach, the force distributions decay much faster than exponentially: P(f) approximately exp(-cf(alpha)}) , with alpha approximately 2.0 for 2D systems, and alpha approximately 1.7 for 3D systems.