Enhancing gravitational wave anisotropies with peaked scalar sources

TL;DR

This paper investigates how peaked scalar sources influence anisotropies in cosmological gravitational wave backgrounds, highlighting their unique frequency dependence and implications for detection with space-based GW detectors and CMB experiments.

Contribution

It clarifies the relation between two methods of calculating GW anisotropies and analyzes the observational prospects of detecting peaked scalar-induced GW backgrounds.

Findings

GW anisotropies have a distinct frequency dependence due to peaked scalar spectra.

Enhanced GW backgrounds in space-based detector bands improve detection prospects.

Cross-correlation methods can effectively identify scalar-induced GW anisotropies.

Abstract

Gravitational wave (GW) backgrounds of cosmological origin are expected to be nearly isotropic, with small anisotropies resembling those of the cosmic microwave background. We analyse the case of a scalar-induced GW background and clarify in the process the relation between two different approaches to calculating GW anisotropies. We focus on GW scenarios sourced by a significantly peaked scalar spectrum, which are frequently considered in the context of primordial black holes production. We show that the resulting GW anisotropies are characterised by a distinct frequency dependence. We explore the observational consequences concentrating on a GW background enhanced in the frequency band of space-based GW detectors. We study the detectability of the signal through both cross-correlations among different space-based GW detectors, and among GW and CMB experiments.