Two Dimensional Quantum Dilaton Gravity and the Positivity of Energy

TL;DR

This paper derives an expression for the ADM mass in 2D quantum dilaton gravity, showing that Liouville-like models have a positive energy bound without critical boundaries, and explores implications for black hole radiation and boundary conditions.

Contribution

It introduces a method to evaluate the ADM mass in 2D quantum dilaton gravity and demonstrates energy bounds in Liouville-like models with specific boundary conditions.

Findings

Liouville-like models have a lower energy bound without critical boundary.

Negative ADM mass values are possible with RST boundary conditions.

Bondi mass approaches zero at large times but can be negative temporarily.

Abstract

Using an argument due to Regge and Teitelboim, an expression for the ADM mass of 2d quantum dilaton gravity is obtained. By evaluating this expression we establish that the quantum theories which can be written as a Liouville-like theory, have a lower bound to energy, provided there is no critical boundary. This fact is then reconciled with the observation made earlier that the Hawking radiation does not appear to stop. The physical picture that emerges is that of a black hole in a bath of quantum radiation. We also evaluate the ADM mass for the models with RST boundary conditions and find that negative values are allowed. The Bondi mass of these models goes to zero for large retarded times, but becomes negative at intermediate times in a manner that is consistent with the thunderpop of RST.