Quantum induced superradiance

TL;DR

This paper demonstrates that quantum backreaction can induce superradiance in black holes where it is classically absent, leading to dynamical instability and the formation of quantum black hole bombs in a three-dimensional anti-de Sitter space.

Contribution

It shows that semi-classical backreaction can induce superradiance in quantum black holes, providing a new stability criterion and extending the Gubser-Mitra conjecture.

Findings

Quantum backreaction induces superradiance in black holes.

Quantum black holes with superradiance are dynamically unstable.

Thermally unstable black holes are also dynamically unstable.

Abstract

Superradiance, the phenomenon enabling energy extraction through radiation amplification, is not universal to all black holes. We show that semi-classical backreaction can induce superradiance, even when absent at the classical level. Specifically, we compute the quasinormal modes of a massless scalar field probing a family of rotating `quantum' black holes in three-dimensional anti-de Sitter space, accounting for all orders of backreaction due to quantum conformal matter. A subset of these modes is identified as superradiant, leading to the formation of quantum black hole `bombs'. All such quantum black holes have curvature singularities shrouded by horizons. Thus, while backreaction enforces cosmic censorship, it also renders the black holes dynamically unstable. Further, we find all thermally unstable black holes are dynamically unstable, though the converse does not hold generally. Our findings thus suggest a semiclassical version of the Gubser-Mitra conjecture on black hole stability. This motivates us to propose a stability criterion for quantum black holes.