modes, the separations between Regions II and III, and between Regions III and IV are given by the times $-\Delta$ and $\Delta$, respectively, because the modes enter and exit the Hubble radius at these two times. The situation in the case of Model 2 is simpler. The evolution of small scale modes is the same as the case with a flat plateau, while the large scale modes have only four regions which we denote by Regions I, II, IV and V, respectively. The separation between Regions II and IV, in this case, is the time $\tau= 0$.

The Computation of the Power Spectrum {#sec3}
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We are interested in the power spectrum of the primordial curvature perturbation $\zeta$ (see, e.g., Ref. [@MFB] for a review of the theory of cosmological perturbations). We quantize the linear fluctuations and write them in terms of the more convenient Mukhanov-Sasaki variable $v$. In the case of a constant equation of state, the relation between $\zeta$ and $v$ is $$\begin{aligned}
v = C a \zeta \, ,\end{aligned}$$ where $C$ is a constant. Thus, the equation of motion for the mode function $v$, in momentum space, is given by $$\begin{aligned}
v'' + \bigg(k^2 - \frac{a''}{a} \bigg) 