phase, the effective masses of the inflaton and waterfall fields change periodically through their mutual couplings, which leads to the rapid amplification of the field fluctuations ${{\delta}{\sigma}}$ and ${{\delta}{\psi}}$ called the parametric resonance [@Landau; @Shtanov:1994ce; @Kofman:1997yn]. In the present model, the most amplified fluctuations have wavenumber $ k_{\mathrm{peak}}$ [@Kawasaki:2006zv] given by $$\label{eq:2:kpeak}
 k_{\mathrm{peak}} \simeq 0.35 m_{ \sigma}.$$ We expect that these enhanced fluctuations produce gravitational waves at the scale $ k_{\mathrm{peak}}$.

Next, we consider the initial condition for the new inflation. Here, interactions between the two inflation sectors become important. During the smooth hybrid inflation, the relevant part of the potential is given by $${ V_{\mathrm{int}} = \frac{1}{2}{ \mu}^{4}{ \phi}^{2}} + 
{ \mu}^{ 2}{ v}^{ 2}{ \sigma}{ \phi}.$$ Thus, at the end of the smooth hybrid inflation, the value of the inflaton of the new inflation is given by $${{\phi}_{\mathrm{min}}=-}\frac{{ v}^{2}}{{\mu}^{2}}{\sigma}_{ c}.$$ During the oscillatory phase, the potential energy of the scalar fields averaged over one oscillation time is the half of the total energy density of the universe, which leads to the effective mass of $\phi$, $$\label{eq:nmass}
 m_{ \phi}^2 
 \simeq \frac{3H^2}{2}.$$ Taking into account $ \dot{H} =-\frac{3}{2}H^{2}$, and using eq. (\[eq:nmass\]), one can find that the amplitude of $ 