First order equation on random measures as superposition of weak solutions to the McKean-Vlasov equation

Abstract: The goal of this paper is to define an evolution equation for a curve of random probability measures $(M_t){t\in[0,T]}\subset \mathcal{P}(\mathcal{P}(\mathbb{R}^d))$ associated to a non-local drift $b:[0,T]\times\mathbb{R}^d \times \mathcal{P}(\mathbb{R}^d) \to \mathbb{R}^d$ and a non-local diffusion term $a:[0,T]\times \mathbb{R}^d \times \mathcal{P}(\mathbb{R}^d) \to \operatorname{Sym}+(\mathbb{R}^{d\times d})$. Then, we show that any solution to that equation can be lifted to a superposition of solutions to a non-linear Kolmogorov-Fokker-Planck equation and also to a superposition of weak solutions to the McKean-Vlasov equations. Finally, we use this superposition result to show how existence and uniqueness can be transferred from the equation on random measures to the associated non-linear Kolmogorov-Fokker-Planck equation and to the McKean-Vlasov equation, assuming uniqueness of the linearized KFP.