A Novel Approach to Peng's Maximum Principle for McKean-Vlasov Stochastic Differential Equations
Johan Benedikt Spille, Wilhelm Stannat
TL;DR
This work addresses Peng's maximum principle for McKean-Vlasov SDEs, where mean-field interactions via the law $\mu_t$ complicate second-order dualization. It introduces a third adjoint, a conditional MV-BSDE on an extended product space with two independent copies, to dualize the quadratic mixed Lions derivatives and to preserve a consistent proof framework. The main result yields a Peng-type necessary condition expressed with a second-level adjoint term, while clarifying the role of the third adjoint as a methodological device rather than a term in the final principle. The proposed approach facilitates potential extensions to common-noise and infinite-dimensional settings, and provides a robust variational scheme for mean-field control problems under nonconvex controls.
Abstract
We present a novel approach to the proof of Peng's maximum principle for McKean-Vlasov stochastic differential equations (SDE). The main step is the introduction of a third adjoint equation, a conditional McKean-Vlasov backward SDE, to accommodate the dualization of quadratic terms containing two independent copies of the first-order variational process. This is an intrinsic extension of the maximum principle from Peng for standard SDE and gives a conceptually consistent proof. Our approach will be useful in further extensions to the common noise setting and the infinite dimensional setting.
