Self-similar Evaporation and Collapse in the Quantum Portrait of Black Holes

TL;DR

This paper models black hole evaporation as a quantum critical Bose condensate of gravitons, revealing scaling solutions and decay mechanisms that shed light on black hole collapse and information scrambling.

Contribution

It introduces a toy model capturing black hole evaporation via graviton condensate decay, highlighting critical scaling solutions and decay channels affecting black hole lifetimes.

Findings

Semiclassical evaporation laws are reproduced by two-body decay processes.

Three-body decay channels lead to very short condensate lifetimes.

Scaling solutions at criticality are found during collapse, indicating potential fast scrambling mechanisms.

Abstract

We investigate Hawking evaporation in a recently suggested picture in which black holes are Bose condensates of gravitons at a quantum critical point. There, evaporation of a black hole is due to two intertwined effects. Coherent excitation of a tachyonic breathing mode is responsible for the collapse of the condensate, while incoherent scattering of gravitons leads to Hawking radiation. To explore this, we consider a toy model of a single bosonic degree of freedom with derivative self-interactions. We consider the real-time evolution of a condensate and derive evaporation laws for two possible decay mechanisms in the Schwinger-Keldysh formalism. We show that semiclassical results can be reproduced if the decay is due to an effective two-body process, while the existence of a three-body channel would imply very short lifetimes for the condensate. In either case, we uncover the existence of scaling solutions in which the condensate is at a critical point throughout the collapse. In the case of a two-body decay we moreover discover solutions that exhibit the kind of instability that was recently conjectured to be responsible for fast scrambling.