Multidimensional indefinite stochastic Riccati equations and zero-sum linear-quadratic stochastic differential games with non-markovian regime switching

This paper is concerned with two-player zero-sum linear-quadratic stochastic differential games in a regime switching model. The controlled inhomogeneous system coefficients depend on the underlying noises, so it is a non-Markovian regime switching model. Based on a new kind of multidimensional indefinite stochastic Riccati equation (SRE) and a multidimensional linear backward stochastic differential equation (BSDE) with unbounded coefficients, we can provide optimal feedback control-strategy pairs for the two players in a closed-loop form. The main contribution of this paper, which is important in its own right from the BSDE theory point of view, is to prove the existence and uniqueness of the new kind of multidimensional indefinite SRE. Interestingly, the components of the solution can take positive, zero and negative values simultaneously. We also obtain the corresponding optimal feedback control-strategy pairs for homogeneous systems under closed convex cone control constraints. Finally, these results are applied to portfolio selection problems with different short-selling prohibition constraints in a regime switching market with random coefficients.