Forward BSDEs and backward SPDEs for utility maximization under endogenous pricing

We study the expected utility maximization problem of a large investor who is allowed to make transactions on a tradable asset in a financial market with endogenous permanent market impacts as suggested in [24] building on [6, 7]. The asset price is assumed to follow a nonlinear price curve quoted in the market as the utility indifference curve of a representative liquidity supplier. We show that optimality can be fully characterized via a system of coupled forward-backward stochastic differential equations (FBSDEs) which is equivalent to a highly non-linear backward stochastic partial differential equation (BSPDE). Existence results can be achieved in the case where the driver function of the representative market maker is quadratic or the utility function of the large investor is exponential. Explicit examples are provided when the market is complete or the driver function is positively homogeneous.