Quantum fermion superradiance and vacuum ambiguities on charged black holes

TL;DR

This paper explores quantum fermion superradiance around charged black holes, revealing nonthermal particle fluxes and vacuum ambiguities that influence black hole discharge and energy loss interpretations.

Contribution

It demonstrates the existence of quantum fermion superradiance and analyzes how vacuum ambiguities affect its physical interpretation.

Findings

Quantum fermion fields exhibit superradiant fluxes.

Vacuum ambiguities impact the understanding of black hole discharge.

Nonthermal particle fluxes are observed at future null infinity.

Abstract

Unlike a classical charged bosonic field, a classical charged fermion field on a static charged black hole does not exhibit superradiant scattering. We demonstrate that the quantum analogue of this classical process is however present. We construct a vacuum state for the fermion field which has no incoming particles from past null infinity, but which contains, at future null infinity, a nonthermal flux of particles. This state describes both the discharge and energy loss of the black hole, and we analyze how the interpretation of this phenomenon depends on the ambiguities inherent in defining the quantum vacuum.