Dilaton gravity with a boundary: from unitarity to black hole evaporation

Abstract

We point out that two-dimensional Russo-Susskind-Thorlacius (RST) model for evaporating black holes is locally equivalent-at the full quantum level-to flat-space Jackiw-Teitelboim (JT) gravity that was recently shown to be unitary. Globally, the two models differ by a reflective spacetime boundary added in the RST model. Treating the boundary as a local and covariant deformation of quantum JT theory, we develop sensible semiclassical description of evaporating RST black holes. Nevertheless, our semiclassical solutions fail to resolve the information recovery problem, and they do not indicate formation of remnants. This means that either the standard semiclassical method incorrectly describes the evaporation process or the RST boundary makes the flat-space JT model fundamentally inconsistent.

Semiclassical $$ \mathcal{S} $$-matrix and black hole entropy in dilaton gravity

“…The approach of section 4.1 misses an important property of our model, namely, the presence of the boundary at φ = φ 0 . This boundary is necessary because it shields the singularities of the CGHS fields in the original Lorentzian path integral [27,35,42,[48][49][50]. Our complex scattering solutions satisfy this property, whereas the Euclidean instanton in figure 7a does not.…”

“…All fields in the path integral are then restricted to the submanifold φ < φ 0 (the rightmost region in figure 1). This model was shown to be equivalent to the flat limit of the Jackiw-Teitelboim gravity [32,33] with a boundary both at the classical [34] and quantum level [35].…”

“…Several appendices contain details of the calculations. We consider non-perturbative scattering in two-dimensional dilaton gravity with a boundary [31], see also [25,[27][28][29][30]35]. The gravitational action 1…”

“…Besides, it includes the timelike boundary at φ = φ 0 which cuts off the region of strong coupling. Importantly, a regulating boundary should be present in all configurations in the path integral (1.1), otherwise the CGHS fields would become singular at the quantum level [35,42]. In eq.…”

Failure of mean-field approximation in weakly coupled dilaton gravity

“…This report is based on the forthcoming publications [5], [6]. In Section 2 we propose a modified model describing evaporating black holes and consider semiclassical solutions.…”