Kac's Program for the Landau Equation

Abstract: We study the derivation of the spatially homogeneous Landau equation from the mean-field limit of some conservative $N$-particle system, which is formulated by passing to the grazing limit on Kac's walk in his program for the Boltzmann equation. It is the first time that propagation of chaos is resolved for some many-particle system approximating the Landau equation with Coulomb interactions, and that Kac's program is extended to the Landau equation in the regime of soft potentials. The convergence result is established in the weak sense, in the Wasserstein sense, and in the entropic sense, along with strong convergence in $L^1$. Motivated by the recent work of Bresch, Duerinckx and Jabin \cite{bresch2024duality}, we develop the duality approach to treat the singular Landau collision operator and adapt to Kac's program in kinetic theory. To overcome the difficulty generated by the Coulomb singularity, we prove some key functional estimates concerning the weighted Fisher information and the second-order Fisher information.