Superstrata on Orbifolded Backgrounds

Some microstates of the Strominger-Vafa black hole are represented by smooth horizonless geometries called superstrata. The standard superstrata are deformations of ${\rm AdS}_3\times S^3$, but there are also generalizations of superstrata on the orbifold $({\rm AdS}_3\times S^3)/\mathbb{Z}_p$. In this paper, we discuss aspects of such orbifolded superstrata. We present a CFT perspective on the structure of orbifolded superstrata, showing that they can be constructed in a $p$-covering space of the orbifold CFT just as the standard superstrata. We also explicitly write down and study the geometry of the orbifolded superstrata, focusing on the difference from the non-orbifold case, $p=1$. We discuss further generalization of superstrata to the ones on a fractional spectral flow of $({\rm AdS}_3\times S^3)/\mathbb{Z}_p$. This generalization involves new fractional mode excitations of the CFT side. We estimate the number of those generalized superstrata, and show that their entropy is too small to account for the Strominger-Vafa entropy. We will discuss some implications of this result, related to the typical microstates of the black hole and the relevant supersymmetry index.Comment: 27 pages + Appendi

Exotic branes and non-geometric backgrounds

When string/M-theory is compactified to lower dimensions, the U-duality symmetry predicts so-called exotic branes whose higher dimensional origin cannot be explained by the standard string/M-theory branes. We argue that exotic branes can be understood in higher dimensions as non-geometric backgrounds or U-folds, and that they are important for the physics of systems which originally contain no exotic charges, since the supertube effect generically produces such exotic charges. We discuss the implications of exotic backgrounds for black hole microstate (non-)geometries.Comment: 4 pages. v2: journal version. The discussion on "double puff-up" revise

Nonsupersymmetric Flux Vacua and Perturbed N=2 Systems

We geometrically engineer N=2 theories perturbed by a superpotential by adding 3-form flux with support at infinity to local Calabi-Yau geometries in type IIB. This allows us to apply the formalism of Ooguri, Ookouchi, and Park [arXiv:0704.3613] to demonstrate that, by tuning the flux at infinity, we can stabilize the dynamical complex structure moduli in a metastable, supersymmetry-breaking configuration. Moreover, we argue that this setup can arise naturally as a limit of a larger Calabi-Yau which separates into two weakly interacting regions; the flux in one region leaks into the other, where it appears to be supported at infinity and induces the desired superpotential. In our endeavor to confirm this picture in cases with many 3-cycles, we also compute the CIV-DV prepotential for arbitrary number of cuts up to fifth order in the glueball fields.Comment: 70 pages (47 pages + 4 appendices), 10 figure

Precision Microstate Counting of Small Black Rings

We examine certain two-charge supersymmetric states with spin in five-dimensional string theories which can be viewed as small black rings when the gravitational coupling is large. Using the 4D-5D connection, these small black rings correspond to four-dimensional non-spinning small black holes. Using this correspondence, we compute the degeneracy of the microstates of the small black rings exactly and show that it is in precise agreement with the macroscopic degeneracy to all orders in an asymptotic expansion. Furthermore, we analyze the five-dimensional small black ring geometry and show qualitatively that the Regge bound arises from the requirement that closed time-like curves be absent.Comment: 4 pages, LaTeX, references adde