Constraining primordial curvature perturbations with present and future GW detectors

TL;DR

This paper reviews how enhanced primordial scalar perturbations can generate detectable scalar-induced gravitational waves, and discusses the potential of current and future GW detectors to constrain early Universe models.

Contribution

It provides a review of the generation mechanisms of scalar-induced GWs and evaluates the prospects of detecting them with upcoming GW observatories.

Findings

Scalar-induced GWs can be significant for enhanced primordial scalar spectra.

Current GW detectors can place constraints on small-scale primordial perturbations.

Future GW observatories like LISA will improve sensitivity to these signals.

Abstract

Primordial scalar curvature perturbations ($\zeta$), typically probed on large cosmological scales via CMB and LSS observations, can be significantly enhanced on smaller scales by various early Universe mechanisms, for instance, non-minimal inflationary models. While decoupled at linear order, scalar and tensor perturbations, i.e., Gravitational Waves (GWs), interact at second order. As a consequence, an enhanced primordial scalar power spectrum $P_\zeta(k)$ can source a sizable stochastic GW background (SGWB). In these proceedings, we briefly review the generation mechanism of such signals, typically referred to as scalar-induced GWs (SIGWs), and discuss the prospects of measuring them with present and future Pulsar Timing Arrays datasets and future GW observatories like the Laser Interferometer Space Antenna LISA.