Black hole superradiance and polarization-dependent bending of light

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.

Comments: Bulk of 29 pages + 11 figures. v2: minor changes, version accepted for publication in JCAP