where Yt is an Ornstein-Uhlenbeck (OU) process with large rate of mean-reversion
1/ε, that is ε is a small positive parameter, and which admits the Gaussian invariant
distribution N(m, ν2). The function f is positive increasing, which can be assumed
smooth bounded and bounded away from zero for technical simplicity. The Brownian
motions Wt and Wy t are correlated according to dW,Wy t = ρ dt where ρ is constant
with |ρ| < 1. The equation for the asset price St is unchanged, and the Brownian
motion Zt is independent of Wt and Wy t . As before, the function β(M) is given by (5).