Abstract.We consider the approximation of a mean field stochastic process by a large interacting particle system. We derive non-asymptotic large deviation bounds measuring the concentration of the empirical measure of the paths of the particles around the law of the process. The method is based on a coupling argument, strong integrability estimates on the paths in Hölder norm, and a general concentration result for the empirical measure of identically distributed independent paths.
Mathematics Subject Classification. 82C22, 35K55, 90C08.Received April 3, 2008. Revised September 29, 2008 This paper is devoted to the study of the particle approximation of a mean field stochastic process. In the models to be considered, the evolution is governed by a random diffusive term, an exterior force field and a mean field interaction depending on the law of the process itself.Quantitative estimates on the approximation have been obtained at the level of the time marginals. Let indeed μ t be the law of the considered process at time t, and (X i t ) 1≤i≤N be the position of the N particles in the phase space R d ; let alsoμ N t denote their empirical measure. First, [16] adapted concentration of measure ideas to obtain non-asymptotic bounds on the deviation of observables 1where ϕ is a given Lipschitz function on R d . Then, transposing Sanov's large deviation argument to their setting, [6] got non-asymptotic bounds on the deviation ofμ N t around μ t at the very level of the measures, namely for a distance which induces a topology stronger that the narrow topology.In this work we go one step further again by considering the law μ [0,T ] of the paths of the process on a given time interval [0, T ]. A natural object to consider in the particle approximation is now the empirical measurê μ N [0,T ] of the N trajectories (X i t ) 0≤t≤T . We shall give a precise meaning and estimates on the convergence ofμ N [0,T ] to μ [0,T ] ; we shall see that they imply previously mentioned results by projection at time t, but above all they give concentration estimates at the level of the paths.In the first section we state our main results and give an insight of the proofs, which will be given in more detail in the following sections.