Cogito, ergo - strings: Supersymmetric ergoregions and their stringy excitations

TL;DR

This paper investigates supersymmetric rotating bound states with ergoregions in supergravity, analyzing their string excitations and holographic duals using gauged WZW models, revealing novel BPS states with negative or zero energy.

Contribution

It introduces a worldsheet description of supersymmetric ergoregions using gauged WZW models and explores their holographic duals, including twisted sector states at orbifold singularities.

Findings

Identification of BPS excitations with negative or zero energy

Construction of vertex operators for twisted sector states

Holographic mapping of supergravity backgrounds to CFT transitions

Abstract

Supergravity solutions describing supersymmetric rotating bound states of NS fivebranes, fundamental strings and momentum can sometimes have an ergoregion but no horizon. In such supersymmetric ergoregions, there is an unusual feature that there exist BPS "excitations" that cost negative (or zero) energy as measured from asymptotic infinity. We study the spectrum of supergravity and string excitations of these backgrounds using their worldsheet description as gauged Wess-Zumino-Witten (WZW) models, and construct their holographic map to transitions in the dual spacetime CFT. The backgrounds generically contain orbifold singularities, and we exhibit vertex operators corresponding to twisted sector ground states localized at the orbifold fixed points. The gauged WZW model thus provides a valuable tool to explore the stringy structure of such heavy BPS states in $AdS_3/CFT_2$.