Measuring the ringdown scalar polarization of gravitational waves in Einstein scalar Gauss-Bonnet gravity

TL;DR

This paper models scalar gravitational wave polarization during black hole ringdowns in Einstein scalar Gauss-Bonnet gravity, assessing detectability with current and future gravitational wave observatories.

Contribution

It introduces a numerical relativity framework for scalar ringdown modes in EsGB gravity and evaluates their observability with next-generation detectors.

Findings

Scalar ringdown signals are below current detection thresholds.

Next-generation detectors could potentially observe scalar polarization.

The scalar wave amplitude depends on the theory's coupling parameters.

Abstract

We model the scalar waves produced during the ringdown stage of binary black hole coalescence in Einstein scalar Gauss-Bonnet (EsGB) gravity, using numerical relativity simulations of the theory in the decoupling limit. Through a conformal coupling of the scalar field to the metric in the matter-field action, we show that the gravitational waves in this theory can have a scalar polarization. We model the scalar quasi-normal modes of the ringdown signal in EsGB gravity, and quantify the extent to which current and future gravitational wave detectors could observe the spectrum of scalar radiation emitted during the ringdown phase of binary black hole coalescence. We find that within the limits of the theory's coupling parameters set by current theoretical and observational constraints, the scalar ringdown signal from black hole remnants in the $10^1 - 10^3 \, M_{\odot}$ mass range is expected to be well below the detectability threshold with the current network of gravitational-wave detectors (LIGO-Virgo-KAGRA), but is potentially measurable with next-generation detectors such as the Einstein Telescope.