One-dimensional inelastic collapse of four particles: asymmetric collision sequences and spherical billiard reduction

We consider a one-dimensional system of four inelastic hard spheres, colliding with a fixed restitution coefficient \(r\), and we study the inelastic collapse phenomenon for such a particle system. We study a periodic, asymmetric collision pattern, proving that it can be realized, despite its instability. We prove that we can associate to the four-particle dynamical system another dynamical system of smaller dimension, acting on \(\{1,2,3\} \times \mathbb{S}^2\), and that encodes the collision orders of each trajectory. We provide different representations of this new dynamical system, and study numerically its \(\omega\)-limit sets. In particular, the numerical simulations suggest that the orbits of such a system might be quasi-periodic.