How Well Do We Know the Scalar-Induced Gravitational Waves?

TL;DR

This paper examines the accuracy of current models predicting gravitational waves from scalar perturbations, emphasizing the importance of non-Gaussian effects which may significantly alter expected wave amplitudes.

Contribution

It highlights the limitations of Gaussian-based models and discusses the potential impact of non-Gaussianity on gravitational wave predictions.

Findings

Non-Gaussianity can significantly affect gravitational wave amplitude.

Standard quadratic models may underestimate or misrepresent the true signals.

Nonlinear effects require more accurate modeling beyond Gaussian approximations.

Abstract

Gravitational waves sourced by amplified scalar perturbations are a common prediction across a wide range of cosmological models. These scalar curvature fluctuations are inherently nonlinear and typically non-Gaussian. We argue that the effects of non-Gaussianity may not always be adequately captured by an expansion around a Gaussian field, expressed through nonlinear parameters such as $f_{\rm{NL}}$. As a consequence, the resulting amplitude of the stochastic gravitational wave background may differ significantly from predictions based on the standard quadratic source model routinely used in the literature.