Black Hole Physics from Two Dimensional Dilaton Gravity based on $SL(2,R)/U(1)$ Coset Model

TL;DR

This paper studies quantum two-dimensional dilaton gravity models based on the $SL(2,R)/U(1)$ coset, revealing conditions under which curvature singularities are avoided, wormholes form from matter shock waves, and black hole evaporation occurs with positive Hawking radiation.

Contribution

It introduces a quantum dilaton gravity model based on $SL(2,R)/U(1)$, analyzing singularity avoidance, wormhole formation, and black hole mass evolution in a novel setting.

Findings

Curvature singularities are absent for $22<c_{matter}<24$.

Matter shock waves can create wormholes connecting causally disconnected regions.

Black holes evaporate completely with positive Hawking radiation even when $N<24$.

Abstract

We analyze quantum two dimensional dilaton gravity model, which is described by $SL(2,R)/U(1)$ gauged Wess-Zumino-Witten model deformed by $(1,1)$ operator. We show that the curvature singularity does not appear when the central charge $c_{\rm matter}$ of the matter fields is given by $22<c_{\rm matter}<24$. When $22<c_{\rm matter}<24$, the matter shock waves, whose energy momentum tensors are given by $T_{\rm matter} \propto \delta(x^+ - x^+_0)$, create a kind of wormholes, {\it i.e.,} causally disconnected regions. Most of the quantum informations in past null infinity are lost in future null infinity but the lost informations would be carried by the wormholes. We also discuss about the problem of defining the mass of quantum black holes. On the basis of the argument by Regge and Teitelboim, we show that the ADM mass measured by the observer who lives in one of asymptotically flat regions is finite and does not vanish in general. On the other hand, the Bondi mass is ill-defined in this model. Instead of the Bondi mass, we consider the mass measured by observers who live in an asymptotically flat region at first. A class of the observers finds the mass of the black hole created by a shock wave changes as the observers' proper time goes by, i.e. they observe the Hawking radiation. The measured mass vanishes after the infinite proper time and the black hole evaporates completely. Therefore the total Hawking radiation is positive even when $N<24$.