Stringy structure at the BPS bound

Abstract

We explore the stringy structure of 1/2-BPS bound states of NS fivebranes carrying momentum or fundamental string charge, in the decoupling limits leading to little string theory and to AdS3/CFT2 duality. We develop an exact worldsheet description of these states using null-gauged sigma models, and illustrate the construction by deriving the closed-form solution sourced by an elliptical NS5-F1 supertube. The Calabi-Yau/Landau-Ginsburg correspondence maps this geometrical worldsheet description to a non-compact LG model whose superpotential is determined by the fivebrane source configuration. Singular limits of the 1/2-BPS configuration space result when the fivebrane worldvolume self-intersects, as can be seen from both sides of the CY/LG duality — on the Landau-Ginsburg side from the degeneration of the superpotential(s), and on the geometrical side from an analysis of D-brane probes. These singular limits are a portal to black hole formation via the condensation of the branes that are becoming massless, and thus exhibit in the gravitational bulk description the central actors in the non-gravitational dual theory underlying black hole thermodynamics.

The harder they fall, the bigger they become: tidal trapping of strings by microstate geometries

“…One of the possible supertube shape profile deformations is to offload its angular momentum j L,R into angular excitations further up the throat, sending the parameter a → 0; then the cap recedes to infinite redshift and the supergravity JHEP04(2021)259 approximation loses control of the horizon-scale structure. Another possibility is that shape gyrations of the underlying onebrane-fivebrane supertube cause it to self-intersect, at which point D-brane excitations -the manifestation of little strings in this duality frame -become light and again cause the breakdown of both the supergravity approximation as well as string perturbation theory [49].…”

“…There are some features missing from the perturbative string dynamics in geometrical microstates, that one expects to be important in generic black hole microstates. The generic excitations of the cap are stringy, as one sees, for example, in the enumeration of perturbative string vertex operators (see [49,60] for a recent discussion in the context of microstate geometries); furthermore, even such perturbative string excitations seem to miss out on the additional fractionation of quanta by the underlying branes in the background -branes in isolation outside the horizon appear to fractionate into smaller constituents upon being absorbed by the black hole, and the generic such fractionation seems difficult to accommodate within the context of geometrical backgrounds [61]. These properties of generic black holes are reflective of the strongly coupled little string theory dynamics that accounts for the black hole entropy [8,62,63] of the onebrane-fivebrane system.…”

“…Such orbits have played a significant role in suggesting that there are potential gravitational instabilities in microstate geometries [25]. However, it seems more likely that these apparent instabilities will actually evolve into the stringy scrambling of probes [22,26,49,64]. It would be useful to use the methods we describe here to obtain an estimate of the rate of such stringy scrambling.…”

Black holes and the swampland: the deep throat revelations

“…As for Black Hole physics, both possibilities (2) and (3) entail at least some breakdown of Supergravity as the description of arbitrarily-deep-throat bubbling solutions. As one approaches the scaling limit from a bubbling solution, the resulting geometry enters into a new phase, whose precise description may require other tools, for instance perturbative String Theory -that one uses in the microstate solutions of [41][42][43][44][45]. However, the extent of the breakdown, depending on which one of possibility (2) or ( 3) is correct, is very different.…”

“…With possibility (2), the bubbling solution acquires a critical maximal throat length after which supergravity completely breaks down. Thus, the new phase can possess a throat that is not arbitrarily deep, like in the instances of [46][47][48][49] and [42][43][44][45].…”