Probing the string axiverse by gravitational waves from Cygnus X-1

TL;DR

This paper explores how gravitational wave observations from Cygnus X-1 can constrain the properties of string axions in the axiverse scenario, providing limits on axion decay constants and masses.

Contribution

It introduces a method to use gravitational wave data to set bounds on string axion parameters around black holes, particularly from Cygnus X-1.

Findings

If no GW signal is detected, the axion decay constant must be below the GUT scale.

Constraints are established for axion masses between 1.1×10⁻¹² eV and 2.5×10⁻¹² eV.

Additional bounds are discussed for isolated black holes.

Abstract

In the axiverse scenario, a massive scalar field (string axion) forms a cloud around a rotating black hole (BH) by superradiant instability and emits continuous gravitational waves (GWs). We examine constraints on the string axion parameters that can be obtained from GW observations. If no signal is detected in a targeted search for GWs from Cygnus X-1 in the LIGO data, the decay constant $f_a$ must be smaller than the GUT scale in the mass range $1.1\times 10^{-12}\mathrm{eV}<\mu<2.5\times 10^{-12}\mathrm{eV}$. Constraints from invisible isolated BHs are also discussed.