This paper is concerned with the mean-field limit for the gradient flow evolution of particle systems with pairwise Riesz interactions, as the number of particles tends to infinity. Based on a modulated energy method, using regularity and stability properties of the limiting equation, as inspired by the work of Serfaty [28] in the context of the Ginzburg-Landau vortices, we prove a mean-field limit result in dimensions 1 and 2 in cases for which this problem was still open.
IntroductionWe consider the energy of a system of N particles in the Euclidean space R d (d ≥ 1) interacting via (repulsive) Riesz pairwise interactions:where the interaction kernel is given bywith c d,s > 0 some normalization constants. We note that the Coulomb case corresponds to the choice s = d − 2, d ≥ 2. Particle systems with more general Riesz interactions as considered here are extensively motivated in the physics literature (cf. for instance [2,20]), as well as in the context of approximation theory with the study of Fekete points (cf.[14] and the references therein). Recently, a detailed description of such systems beyond the mean-field limit in the static case was obtained in [21], and also in [17] for non-zero temperature. In the present contribution, we are rather interested in the dynamics of such systems, and more precisely in a rigorous justification of the mean-field limit of their gradient flow evolution as the number N of particles tends to infinity, which has indeed remained an open problem wheneverWe thus consider the trajectories x t i,N driven by the corresponding flow, i.e. the solutions to the following system of ODEs:where (xis a sequence of N distinct initial positions. Since energy can only decrease in time and since the interaction is repulsive, particles cannot collide, and moreover it is easily seen that a particle cannot escape to infinity in finite time; from these observations and from the Picard-Lindelöf theorem, we may conclude that the trajectories x t i,N are smooth and well-defined on the whole of R + := [0, ∞). As the number of particles gets large, we would naturally like to pass to a continuum description of the system, in terms of the particle density distribution. For that purpose, we define the empirical measure associated with the point-vortex dynamics:2) 1 and the question is then to understand the limit of µ t N as N ↑ ∞. More precisely, assuming convergence at initial time This equation in the weak sense just means the following:As far as existence issues as well as basic properties of the solutions of (1.3) are concerned, we refer to [9,8] . Schochet's original paper [27] was actually only concerned with the mean-field limit for a particle approximation of the 2D Euler equation, but the same argument directly applies to the present setting. However, due to a possible lack of uniqueness of L 1 weak solutions to equation (1.3), Schochet [27] could only prove that the empirical measure µ t N converges up to a subsequence to some solution of (1.3). The key idea, which only holds for logarithmic i...