Where are the black hole entropy degrees of freedom ?

TL;DR

This paper investigates the origin of black hole entropy, showing that ground state entanglement near the horizon accounts for the area law, while excited states involve degrees of freedom farther away, causing deviations.

Contribution

It demonstrates that horizon degrees of freedom are primarily responsible for the black hole area law, with excited states involving more distant degrees of freedom.

Findings

Ground state entanglement near the horizon obeys the area law.

Excited states involve degrees of freedom farther from the horizon.

Deviations from the area law occur in excited states.

Abstract

Understanding the area-proportionality of black hole entropy (the `Area Law') from an underlying fundamental theory has been one of the goals of all models of quantum gravity. A key question that one asks is: where are the degrees of freedom giving rise to black hole entropy located? Taking the point of view that entanglement between field degrees of freedom inside and outside the horizon can be a source of this entropy, we show that when the field is in its ground state, the degrees of freedom near the horizon contribute most to the entropy, and the area law is obeyed. However, when it is in an excited state, degrees of freedom far from the horizon contribute more significantly, and deviations from the area law are observed. In other words, we demonstrate that horizon degrees of freedom are responsible for the area law.