Four Dimensional Black Hole Microstates: From D-branes to Spacetime Foam

TL;DR

This paper proposes a microstate model for four-dimensional supersymmetric black holes, linking D-brane configurations to spacetime foam structures, and suggests this connection explains black hole entropy.

Contribution

It introduces a new perspective on black hole microstates as bound states of half-BPS atoms forming complex geometries and spacetime foam, bridging D-brane and spacetime foam approaches.

Findings

Smooth supergravity solutions with multiple centers

Collapse to intersecting D-branes at zero coupling

Formation of a foam of spheres at strong coupling

Abstract

We propose that every supersymmetric four dimensional black hole of finite area can be split up into microstates made up of primitive half-BPS "atoms''. The mutual non-locality of the charges of these "atoms'' binds the state together. In support of this proposal, we display a class of smooth, horizon-free, four dimensional supergravity solutions carrying the charges of black holes, with multiple centers each carrying the charge of a half-BPS state. At vanishing string coupling the solutions collapse to a bound system of intersecting D-branes. At weak coupling the system expands into the non-compact directions forming a topologically complex geometry. At strong coupling, a new dimension opens up, and the solutions form a "foam'' of spheres threaded by flux in M-theory. We propose that this transverse growth of the underlying bound state of constitutent branes is responsible for the emergence of black hole horizons for coarse-grained observables. As such, it suggests the link between the D-brane and "spacetime foam'' approaches to black hole entropy.