Optimal \(C^{\frac{1}{2}}\) Regularity of the Boltzmann Equation in Non-Convex Domains
摘要
Regularity of the Boltzmann equation, particularly in the presence of physical boundary conditions, heavily relies on the geometry of the boundaries. In the case of non-convex domains with specular reflection boundary conditions, the problem remained outstanding until recently due to the severe singularity of billiard trajectories near the grazing set, where the trajectory map is not differentiable. This challenge was addressed in Kim and Lee (Commun Pure Appl Math 77(4):2331–2386, 2024), where