Asymptotic expansion of European options with mean-reverting stochastic volatility dynamics

We develop methods for pricing European options under general mean-reverting stochastic volatility dynamics, which can be used with both affine and non-affine volatility models. In our methods, the option price under stochastic volatility is expanded as a power series of parameters or variables by transferring the original partial differential equation to a set of solvable inhomogeneous Black-Scholes equations. The analytic approximation is more generally applicable than the fast Fourier transform, because it does not rely on the existence of a characteristic function. Finally, we numerically demonstrate our approach with the Heston, 3/2, and continuous-time GARCH models.