Physics with nonperturbative quantum gravity: radiation from a quantum black hole

TL;DR

This paper investigates quantum gravitational effects on black hole radiation using loop quantum gravity, finding that realistic eigenstates yield a thermal spectrum rather than the non-thermal spectrum previously suggested by simplified models.

Contribution

The study replaces a naive ansatz with actual eigenstates in loop quantum gravity to analyze black hole radiation spectra, challenging prior non-thermal predictions.

Findings

Realistic eigenstates produce a thermal Hawking spectrum.

The non-thermal spectrum result is likely an artifact of simplified models.

Application demonstrates concrete use of nonperturbative quantum gravity.

Abstract

We study quantum gravitational effects on black hole radiation, using loop quantum gravity. Bekenstein and Mukhanov have recently considered the modifications caused by quantum gravity on Hawking's thermal black-hole radiation. Using a simple ansatz for the eigenstates the area, they have obtained the intriguing result that the quantum properties of geometry affect the radiation considerably, yielding a definitely non-thermal spectrum. Here, we replace the simple ansatz employed by Bekenstein and Mukhanov with the actual eigenstates of the area, computed using the loop representation of quantum gravity. We derive the emission spectra, using a classic result in number theory by Hardy and Ramanujan. Disappointingly, we do not recover the Bekenstein-Mukhanov spectrum, but --effectively-- a Hawking's thermal spectrum. The Bekenstein-Mukhanov result is therefore likely to be an artefact of the naive ansatz, rather than a robust result. The result is an example of concrete (although somewhat disappointing) application of nonperturbative quantum gravity.