Diffusion dynamics for an infinite system of two-type spheres and the associated depletion effect

We consider a random diffusion dynamics for an infinite system of hard spheres of two different sizes evolving in ${\mathbb{R}}^d$, its reversible probability measure, and its projection on the subset of the large spheres. The main feature is the occurrence of an attractive short-range dynamical interaction – known in the physics literature as a depletion interaction – between the large spheres, which is induced by the hidden presence of the small ones. By considering the asymptotic limit for such a system when the density of the particles is high, we also obtain a constructive dynamical approach to the famous discrete geometry problem of maximisation of the contact number of $n$ identical spheres in ${\mathbb{R}}^d$. As support material, we propose numerical simulations in the form of movies.