RDP 9204: The Term Structure of Interest Rates, Real Activity and inflation Equation (A22)

\begin{array}{l} \frac{δ (R - \bar{R})}{δ t} = 0 & \Rightarrow & t^{* *} = \frac{1}{θ+ψ} \ln [(\frac{θ-α}{ψ+α}) (\frac{θ}{ψ})] \end{array}