Description
We analyze GW production during preheating for an $\alpha$-attractor
potential terminating in the positive-curvature regime, with energy transfer via
$\phi\chi^{2}$. Linear Floquet analysis and nonlinear simulations show that $\phi$
fluctuations grow by parametric resonance, while $\chi$ undergoes tachyonic
bursts. The GW spectrum features two peaks: a dominant low-frequency peak
from the parametric channel and a subdominant high-frequency peak from the
tachyonic channel. Redshifted to today, the peak reaches $h^{2}\Omega_{\rm
GW}^{(0)} \sim 10^{-11}$ at $f_{p} \sim 10^{7}$ Hz. This multi-peak structure is a
characteristic imprint of trilinear preheating in $\alpha$-attractors.
