Fluctuation Statistics and Diffusive Properties of the 2D Triangular   Lorentz Gas in the Finite-Horizon Regime
  We study chaotic behavior and diffusion in the 2D periodic Lorentz gas in the finite-horizon regime. The dynamical observable which we consider is the length of single particle's trajectories, which moves in a triangular array of rigid disks. To analyze the chaoticity of this system, we construct a matrix of the length of trajectories and perform a level spacing analysis of the spectrum of this matrix. We find that a universal behavior occurs both in level spacing distribution and spectral rigidity. In order to examine diffusion in this classical system, we investigate the variance of the length of trajectories versus number of collisions to disks. In the case where there is a finite-horizon, such a variance scales linearly with number of bounces. This shows that a normal diffusion exists and a central limit theorem is maintained in this regime. 
A. Hosseinizadeh, J.F. Laprise, H. Kr\"oger, G. Melkonyan, R.   Zomorrodi
nlin.CD