Mean Field Control with Poissonian Common Noise: A Pathwise Compactification Approach

Abstract: This paper contributes to the compactification approach to tackle mean-field control (MFC) problems with Poissonian common noise. To overcome the lack of compactness and continuity issues due to common noise, we exploit the point process representation of the Poisson random measure with finite intensity and propose a pathwise formulation by freezing a sample path of the common noise. We first study a pathwise relaxed control problem in an auxiliary setup without common noise but with finite deterministic jumping times over the finite horizon. By employing the compactification argument for the pathwise relaxed control problem with Skorokhod topology, we establish the existence of optimal controls in the pathwise formulation. To address the original problem, the main challenge is to close the gap between the problem in the original model with common noise and the pathwise formulation. With the help of concatenation techniques over the sequence of deterministic jumping times, we develop a new tool, also interpreted as the superposition principle in the pathwise formulation, to draw a relationship between the pathwise relaxed control problem and the pathwise measure-valued control problem associated to Fokker-Planck equation. As a result, we can bridge the desired equivalence among different problem formulations. We also extend the methodology to solve mean-field games with Poissonian common noise, confirming the existence of a strong mean field equilibrium.