Infinite horizon billiards: Transport at the border between Gauss and Lévy universality classes.

We consider transport in two billiard models, the infinite horizon Lorentz gas and the stadium channel, presenting analytical results for the spreading packet of particles. We first obtain the cumulative distribution function of traveling times between collisions, which exhibits nonanalytical behavior. Using a renewal assumption and the Lévy walk model, we obtain the particles' probability density.

Dispersion of particles in an infinite-horizon Lorentz gas.

We consider a two-dimensional Lorentz gas with infinite horizon. This paradigmatic model consists of pointlike particles undergoing elastic collisions with fixed scatterers arranged on a periodic lattice. It was rigorously shown that when t→∞, the distribution of particles is Gaussian.