Scalar-induced gravitational waves with non-Gaussianity up to all orders

TL;DR

This paper introduces a lattice simulation approach to accurately compute scalar-induced gravitational waves with non-Gaussianity up to all orders, revealing significant impacts on the spectra.

Contribution

It proposes a novel lattice simulation method for full-order non-Gaussianity in SIGWs, verified against existing results and applied to various early-Universe models.

Findings

Non-Gaussianity can significantly alter SIGW ultraviolet spectra.

Lattice simulations match semi-analytical results for non-Gaussian SIGWs.

High-order non-Gaussianities impact primordial black hole constraints.

Abstract

Scalar-induced gravitational waves (SIGWs) are ubiquitous in many early-Universe processes accompanied by non-Gaussianity; while Gaussian perturbation can generate significant SIGWs, computations of SIGWs can be significantly affected and enhanced if the scalar perturbations have some degree of non-Gaussianity; hence, precise calculations of these kinds of SIGWs involve a full understanding of non-Gaussianity. In this Letter, we propose to use the lattice simulations to directly calculate the energy density spectra of SIGWs with non-Gaussianity up to all orders. Our proposal has been first verified to match the existing semi-analytical results with non-Gaussianity, and then applied to more general cases, including high-order primordial non-Gaussianities, the logarithmic dependence in curvature perturbations, the curvaton model, and the ultra slow-roll model. We find that even a modest non-Gaussianity can significantly alter ultraviolet behaviors in SIGW spectra, necessitating special cautions in future detections as well as mutual constraints on/from primordial black holes.