Black-Hole Bombs and Photon-Mass Bounds

TL;DR

This paper demonstrates that superradiant instabilities of massive vector fields around rotating black holes can set stringent upper bounds on the photon mass, with current observations constraining it to less than 4x10^{-20} eV.

Contribution

It introduces a new framework for analyzing perturbations of rotating Kerr black holes up to second order in rotation, enabling tighter bounds on ultralight bosonic particles.

Findings

Current black hole spin data constrains photon mass to <4x10^{-20} eV.

Future measurements could lower this bound to <10^{-22} eV.

Superradiance provides a natural probe for ultralight particles.

Abstract

Generic extensions of the standard model predict the existence of ultralight bosonic degrees of freedom. Several ongoing experiments are aimed at detecting these particles or constraining their mass range. Here we show that massive vector fields around rotating black holes can give rise to a strong superradiant instability which extracts angular momentum from the hole. The observation of supermassive spinning black holes imposes limits on this mechanism. We show that current supermassive black hole spin estimates provide the tightest upper limits on the mass of the photon (mv<4x10^{-20} eV according to our most conservative estimate), and that spin measurements for the largest known supermassive black holes could further lower this bound to mv<10^{-22} eV. Our analysis relies on a novel framework to study perturbations of rotating Kerr black holes in the slow-rotation regime, that we developed up to second order in rotation, and that can be extended to other spacetime metrics and other theories.