A Note on the Symmetry Reduction of SU(2) on Horizons of Various Topologies

TL;DR

This paper explores how the symmetry reduction from SU(2) to U(1) degrees of freedom applies to black holes with various horizon topologies in loop quantum gravity, impacting entropy calculations.

Contribution

It generalizes the symmetry reduction analysis to black holes with planar, toroidal, and higher genus horizons, extending previous SU(2) to U(1) reduction results.

Findings

Symmetry reduction to U(1) applies across different horizon topologies.

Explicit calculations of horizon quantities for various topologies.

Implications for black hole entropy in loop quantum gravity.

Abstract

It is known that the SU(2) degrees of freedom manifest in the description of the gravitational field in loop quantum gravity are generally reduced to U(1) degrees of freedom on an $S^2$ isolated horizon. General relativity also allows black holes with planar, toroidal, or higher genus topology for their horizons. These solutions also meet the criteria for an isolated horizon, save for the topological criterion, which is not crucial. We discuss the relevant corresponding symmetry reduction for black holes of various topologies (genus 0 and $\geq 2$) here and discuss its ramifications to black hole entropy within the loop quantum gravity paradigm. Quantities relevant to the horizon theory are calculated explicitly using a generalized ansatz for the connection and densitized triad, as well as utilizing a general metric admitting hyperbolic sub-spaces. In all scenarios, the internal symmetry may be reduced to combinations of U(1).