[2509.09585] Causal PDE-Control Models: A Structural Framework for Dynamic Portfolio Optimization

Classical portfolio models collapse under structural breaks, while modern machine-learning allocators adapt flexibly but often at the cost of transparency and interpretability. This paper introduces Causal PDE-Control Models (CPCMs), a unifying framework that integrates causal inference, nonlinear filtering, and forward-backward partial differential equations for dynamic portfolio optimization. The framework delivers three theoretical advances: (i) the existence of conditional risk-neutral measures under evolving information sets; (ii) a projection-divergence duality that quantifies the stability cost of departing from the causal driver manifold; and (iii) causal completeness, establishing that a finite driver span can capture all systematic premia. Classical methods such as Markowitz, CAPM, and Black-Litterman appear as degenerate cases, while reinforcement learning and deep-hedging policies emerge as unconstrained, symmetry-breaking approximations. Empirically, CPCM solvers implemented with physics-informed neural networks achieve higher Sharpe ratios, lower turnover, and more persistent premia than both econometric and machine-learning benchmarks, using a global equity panel with more than 300 candidate drivers. By reframing portfolio optimization around structural causality and PDE control, CPCMs provide a rigorous, interpretable, and computationally tractable foundation for robust asset allocation under nonstationary conditions.