Black hole superradiance and polarization-dependent bending of light

TL;DR

This paper investigates how axion clouds around Kerr black holes can cause polarization-dependent bending of light, revealing potential observable effects of axion-like particles in astrophysical settings.

Contribution

It introduces the concept that axion clouds act as optically active media, leading to polarization-dependent light bending near black holes, a novel effect in astrophysics.

Findings

Polarization-dependent light bending can occur near axion clouds.

The effect's magnitude depends on the axion type and cloud properties.

Potential for observational detection of axion-like particles.

Abstract

An inhomogeneous pseudo-scalar field configuration behaves like an optically active medium. Consequently, if a light ray passes through an axion cloud surrounding a Kerr black hole, it may experience a polarization-dependent bending. We explore the size and relevance of such effect considering both the QCD axion and a generic axion-like particle.