# Empirical Measure and Small Noise Asymptotics under Large Deviation Scaling for Interacting Diffusions

## TL;DR

This paper analyzes the large deviation behavior of interacting diffusions with both individual and common noise, revealing how different noise intensities influence the empirical measure's asymptotics.

## Contribution

It provides a detailed characterization of large deviation regimes for systems with small common noise, extending understanding of mean field and Freidlin-Wentzell asymptotics.

## Key findings

- Different noise intensities lead to distinct large deviation behaviors.
- Precise regimes for large deviations under various scaling limits.
- Application to Feynman-Kac functionals in particle systems.

## Abstract

Consider a collection of particles whose state evolution is described through a system of interacting diffusions in which each particle is driven by an independent individual source of noise and also by a small amount of noise that is common to all particles. The interaction between the particles is due to the common noise and also through the drift and diffusion coefficients that depend on the state empirical measure. We study large deviation behavior of the empirical measure process which is governed by two types of scaling, one corresponding to mean field asymptotics and the other to the Freidlin-Wentzell small noise asymptotics. Different levels of intensity of the small common noise lead to different types of large deviation behavior, and we provide a precise characterization of the various regimes. We also study large deviation behavior of interacting particle systems approximating various types of Feynman-Kac functionals. Proofs are based on stochastic control representations for exponential functionals of Brownian motions and on uniqueness results for weak solutions of stochastic differential equations associated with controlled nonlinear Markov processes.