Production of Gravitational Waves from Preheating and Tachyonic Instabilities

TL;DR

This paper investigates gravitational wave production during preheating in $ ext{alpha}$-attractor models, revealing a distinctive multi-peak spectrum resulting from parametric resonance and tachyonic instabilities.

Contribution

It introduces a detailed analysis of GW spectra from $ ext{alpha}$-attractor preheating, highlighting the characteristic multi-peak structure caused by different instability channels.

Findings

GW spectrum has two peaks: low-frequency from parametric resonance, high-frequency from tachyonic bursts.

Peak amplitude today is approximately $10^{-11}$ at around $10^{7}$ Hz.

Multi-peak structure is a unique signature of trilinear preheating in $ ext{alpha}$-attractors.

Abstract

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 $f^{(0)}_{p} \sim 10^{7}$ Hz. This multi-peak structure is a characteristic imprint of trilinear preheating in $\alpha$-attractors.