Microstate Geometries and Entropy Enhancement

Abstract

In string theory, black-hole backgrounds are far from unique and there are large families of completely smooth, horizonless geometries with the same structure as a black hole from infinity down to the neighborhood of the black-hole horizon. These microstate geometries cap off in foam of topological bubbles. I review some of the recent progress in constructing these smooth horizonless geometries and discuss some of the physical implications.

19 pages, 2 figures. Contribution to the proceedings of "30 Years of Mathematical Methods in High Energy Physics - In honor of Professor Tohru Eguchi's 60th Birthday."