A dynamic Heston local–stochastic volatility model and Legendre transform dual-asymptotic solution for optimal investment strategy problems with CARA utility

In this paper, we consider a Heston local–stochastic volatility (HLSV) model to study an optimal investment strategy problem, and analyze the optimal strategy when the volatility component of the model obeys a slow varying process and a fast varying process, respectively. For the optimal investment objective with a constant absolute risk aversion (CARA) utility function, the analytical solution under the HLSV model cannot be obtained due to the complicated nonlinearity of the partial differential equation. In this paper we employ a dual method, Legendre transformation, and an asymptotic expansion technique to derive an asymptotic solution. We also apply a Monte Carlo method to compute the optimal strategy, which can be compared with the asymptotic solution. Finally, numerical examples are provided to support our theoretical results.