Probing the existence of ultralight bosons with a single gravitational-wave measurement

TL;DR

This paper demonstrates that a single gravitational wave observation can confirm the existence of ultralight bosons, determine their mass, and distinguish them from other phenomena using data from LISA on extreme mass-ratio inspirals.

Contribution

It introduces a method to verify ultralight bosons and measure their mass from a single gravitational wave signal, leveraging the over-determined nature of black hole/cloud systems.

Findings

Single GW measurement can confirm light bosons.

Method applicable to bosons in $[10^{-16.5},10^{-14}]$ eV range.

LISA observations of extreme mass-ratio inspirals are suitable for this analysis.

Abstract

Light bosons, proposed as a possible solution to various problems in fundamental physics and cosmology, include a broad class of candidates for beyond the Standard Model physics, such as dilatons and moduli, wave dark matter and axion-like particles. If light bosons exist in nature, they will spontaneously form "clouds" by extracting rotational energy from rotating massive black holes through superradiance, a classical wave amplification process that has been studied for decades. The superradiant growth of the cloud sets the geometry of the final black hole, and the black hole geometry determines the shape of the cloud. Hence, both the black hole geometry and the cloud encode information about the light boson. For this reason, measurements of the gravitational field of the black hole/cloud system (as encoded in gravitational waves) are over-determined. We show that a single gravitational wave measurement can be used to verify the existence of light bosons by model selection, rule out alternative explanations for the signal, and measure the boson mass. Such measurements can be done generically for bosons in the mass range $[10^{-16.5},10^{-14}]$ eV using LISA observations of extreme mass-ratio inspirals.