Stable Non-BPS States and Their Holographic Duals

Stable non-BPS states can be constructed and studied in a variety of contexts in string theory. Here we review some interesting constructions that arise from suspended and wrapped branes. We also exhibit some stable non-BPS states that have holographic duals.Comment: 10 pages, LaTeX, 10 .eps figures (included); based on a talk given at Strings 2000, Michiga

Two dimensional black-hole as a topological coset model of c=1 string theory

We show that a special superconformal coset (with $\hat c =3$) is equivalent to $c=1$ matter coupled to two dimensional gravity. This identification allows a direct computation of the correlation functions of the $c=1$ non-critical string to all genus, and at nonzero cosmological constant, directly from the continuum approach. The results agree with those of the matrix model. Moreover we connect our coset with a twisted version of a Euclidean two dimensional black hole, in which the ghost and matter systems are mixed.Comment: 51 pages. Appendix by E. Frenke

Open-String Actions and Noncommutativity Beyond the Large-B Limit

In the limit of large, constant B-field (the ``Seiberg-Witten limit''), the derivative expansion for open-superstring effective actions is naturally expressed in terms of the symmetric products *n. Here, we investigate corrections around the large-B limit, for Chern-Simons couplings on the brane and to quadratic order in gauge fields. We perform a boundary-state computation in the commutative theory, and compare it with the corresponding computation on the noncommutative side. These results are then used to examine the possible role of Wilson lines beyond the Seiberg-Witten limit. To quadratic order in fields, the entire tree-level amplitude is described by a metric-dependent deformation of the *2 product, which can be interpreted in terms of a deformed (non-associative) version of the Moyal * product.Comment: 30 pages, harvma

Dualities and the SL(2,Z)SL(2,Z) Anomaly

The SL(2,Z) anomaly recently derived for type IIB supergravity in 10 dimensions is shown to be a consequence of T-duality with the type IIA string, after compactification to 2 dimensions on an 8-fold. This explains the identity of the gravitational 8-forms appearing in different contexts in the effective actions of type IIA and IIB string theories. In this framework, constraints on the compactification manifold arise from modular invariance of the 2d theory. Related issues in 6 dimensions are examined, and it is argued that similar anomalies are present on the worldvolumes of M-theory 5-branes and orientifold 5-planes

Dualities in theories with 32 supersymmetries: a beginner's guide

This is an introductory review of dualities in theories with 32 supersymmetries. I describe the maximally supersymmetric theories in 11 and 10 dimensional space-time, their spectrum, symmetries and inter-relationships, and their toroidal com-pactifications. The emphasis is on presenting a few simple ideas explicitly and with clarity

Branes as Stable Holomorphic Line Bundles On the Non-Commutative Torus

It was recently suggested by A. Kapustin that turning on a $B$-field, and allowing some discrepancy between the left and and right-moving complex structures, must induce an identification of B-branes with holomorphic line bundles on a non-commutative complex torus. We translate the stability condition for the branes into this language and identify the stable topological branes with previously proposed non-commutative instanton equations. This involves certain topological identities whose derivation has become familiar in non-commutative field theory. It is crucial for these identities that the instantons are localized. We therefore explore the case of non-constant field strength, whose non-linearities are dealt with thanks to the rank-one Seiberg--Witten map.Comment: 12 pages, LaTe

Closed string exchanges on C2/Z2C^2/Z_2 in a background B-field

In an earlier work it was shown that the IR singularities arising in the nonplanar one loop two point function of a noncommutative ${\cal N}=2$ gauge theory can be reproduced exactly from the massless closed string exchanges. The noncommutative gauge theory is realised on a fractional $D_3$ brane localised at the fixed point of the $C^2/Z_2$ orbifold. In this paper we identify the contributions from each of the closed string modes. The sum of these adds upto the nonplanar two-point function.Comment: 27 page

A Stable Non-BPS Configuration From Intersecting Branes and Antibranes

We describe a tachyon-free stable non-BPS brane configuration in type IIA string theory. The configuration is an elliptic model involving rotated NS5 branes, D4 branes and anti-D4 branes, and is dual to a fractional brane-antibrane pair placed at a conifold singularity. This configuration exhibits an interesting behaviour as we vary the radius of the compact direction. Below a critical radius the D4 and anti-D4 branes are aligned, but as the radius increases above the critical value the potential between them develops a minimum away from zero. This signals a phase transition to a configuration with finitely separated branes