Physics-to-gauge conversion at black hole horizons

TL;DR

This paper demonstrates that imposing horizon constraints in 2D dilaton gravity reduces physical degrees of freedom and increases gauge symmetries, supporting the idea that horizons convert physical into gauge degrees of freedom.

Contribution

It provides a detailed analysis of phase space and gauge symmetries in 2D dilaton gravity with horizons, confirming a conjecture about degrees of freedom conversion.

Findings

Horizon constraints reduce the physical phase space.

Gauge symmetries increase in the presence of horizons.

Supports 't Hooft's conjecture on degrees of freedom conversion.

Abstract

Requiring the presence of a horizon imposes constraints on the physical phase space. After a careful analysis of dilaton gravity in 2D with boundaries (including the Schwarzschild and Witten black holes as prominent examples), it is shown that the classical physical phase space is smaller as compared to the generic case if horizon constraints are imposed. Conversely, the number of gauge symmetries is larger for the horizon scenario. In agreement with a recent conjecture by 't Hooft, we thus find that physical degrees of freedom are converted into gauge degrees of freedom at a horizon.