The Cheshire Cap

TL;DR

This paper proposes a new model for black hole interiors where long string degrees of freedom resolve inner horizon singularities and facilitate information transfer, linking microstate geometries to black hole entropy.

Contribution

It introduces a novel conceptual framework connecting microstate geometries, long string states, and the structure of black hole horizons.

Findings

Singularities in microstate geometries resemble fivebrane dynamics.

Long string degrees of freedom emerge at the inner horizon.

Proposed interior model allows information communication across horizons.

Abstract

A key role in black hole dynamics is played by the inner horizon; most of the entropy of a slightly nonextremal charged or rotating black hole is carried there, and the covariant entropy bound suggests that the rest lies in the region between the inner and outer horizon. An attempt to match this onto results of the microstate geometries program suggests that a `Higgs branch' of underlying long string states of the configuration space realizes the degrees of freedom on the inner horizon, while the `Coulomb branch' describes the inter-horizon region and beyond. Support for this proposal comes from an analysis of the way singularities develop in microstate geometries, and their close analogy to corresponding structures in fivebrane dynamics. These singularities signal the opening up of the long string degrees of freedom of the theory, which are partly visible from the geometry side. A conjectural picture of the black hole interior is proposed, wherein the long string degrees of freedom resolve the geometrical singularity on the inner horizon, yet are sufficiently nonlocal to communicate information to the outer horizon and beyond.