Signatures of Primordial Gravitational Waves on the Large-Scale Structure of the Universe

TL;DR

This paper investigates how primordial gravitational waves can generate scalar perturbations that influence the large-scale structure of the universe, offering a new way to detect or constrain these waves through galaxy surveys.

Contribution

It introduces a novel mechanism where tensor-induced scalar modes from primordial gravitational waves affect the matter power spectrum, enabling new observational constraints.

Findings

Tensor-induced scalar modes evolve similarly to standard matter perturbations.

Primordial models with high-frequency gravitational waves leave detectable signatures in the matter power spectrum.

Potential to probe primordial gravitational waves on previously unexplored scales.

Abstract

We study the generation and evolution of second-order energy-density perturbations arising from primordial gravitational waves. Such "tensor-induced scalar modes" approximately evolve as standard linear matter perturbations and may leave observable signatures in the Large-Scale Structure of the Universe. We study the imprint on the matter power-spectrum of some primordial models which predict a large gravitational-wave signal at high frequencies. This novel mechanism in principle allows us to constrain or detect primordial gravitational waves by looking at specific features in the matter or galaxy power-spectrum, thereby allowing to probe them on a range of scales unexplored so far.