paper

Supersymmetry and Positive Energy in Classical and Quantum Two-Dimensional Dilaton Gravity

arXiv:hep-th/9210017 · doi:10.1103/PhysRevD.47.1569

Abstract

An supersymmetric version of two dimensional dilaton gravity coupled to matter is considered. It is shown that the linear dilaton vacuum spontaneously breaks half the supersymmetries, leaving broken a linear combination of left and right supersymmetries which squares to time translations. Supersymmetry suggests a spinorial expression for the ADM energy , as found by Witten in four-dimensional general relativity. Using this expression it is proven that is non-negative for smooth initial data asymptotic (in both directions) to the linear dilaton vacuum, provided that the (not necessarily supersymmetric) matter stress tensor obeys the dominant energy condition. A {\it quantum} positive energy theorem is also proven for the semiclassical large- equations, despite the indefiniteness of the quantum stress tensor. For black hole spacetimes, it is shown that is bounded from below by , where is the value of the dilaton at the apparent horizon, provided only that the stress tensor is positive outside the apparent horizon. This is the two-dimensional analogue of an unproven conjecture due to Penrose. Finally, supersymmetry is used to prove positive energy theorems for a large class of generalizations of dilaton gravity which arise in consideration of the quantum theory.

21 pages

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