`Faster than light' photons and rotating black holes

TL;DR

This paper explores how quantum electrodynamics predicts possible superluminal photon travel near rotating black holes, challenging classical notions of causality in curved spacetime.

Contribution

It extends previous analyses to Kerr black holes, establishing theorems on photon polarization and horizon behavior, and discusses implications for the ergosphere boundary.

Findings

Photon propagation can be superluminal in Kerr spacetime.

Polarization sum rule and horizon theorem are supported.

Implications for the ergosphere's stationary limit surface are discussed.

Abstract

The effective action for QED in curved spacetime includes equivalence principle violating interactions between the electromagnetic field and the spacetime curvature. These interactions admit the possibility of superluminal yet causal photon propagation in gravitational fields. In this paper, we extend our analysis of photon propagation in gravitational backgrounds to the Kerr spacetime describing a rotating black hole. The results support two general theorems -- a polarisation sum rule and a `horizon theorem'. The implications for the stationary limit surface bounding the ergosphere are also discussed.