Axial Vector Duality as a Gauge Symmetry and Topology Change in String Theory

Lines generated by marginal deformations of WZW models are considered. The Weyl symmetry at the WZW point implies the existence of a duality symmetry on such lines. The duality is interpreted as a broken gauge symmetry in string theory. It is shown that at the two end points the axial and vector cosets are obtained. This shows that the axial and vector cosets are equivalent CFTs both in the compact and the non-compact cases. Moreover, it is shown that there are \s-model deformations that interpolate smoothly between manifolds with different topologies.Comment: LAteX file, CERN-TH.6816/93, RI-149-93. (previous file was corrupted by mailers

Dynamical Vacuum Selection in String Theory

We study a system of D-branes localized near an intersection of Neveu-Schwarz fivebranes, that is known to exhibit a landscape of supersymmetric and (metastable) supersymmetry breaking vacua. We show that early universe cosmology drives it to a particular long-lived supersymmetry breaking ground state.Comment: 42 pages, 7 figures; references and acknowledgement adde

Mirror Symmetry as a Gauge Symmetry

It is shown that in string theory mirror duality is a gauge symmetry (a Weyl transformation) in the moduli space of $N=2$ backgrounds on group manifolds, and we conjecture on the possible generalization to other backgrounds, such as Calabi-Yau manifolds.Comment: 11 page

Complex Structures, Duality, and WZW-Models in Extended Superspace

We find the complex structure on the dual of a complex target space. For $N=(2,2)$ systems, we prove that the space orthogonal to the kernel of the commutator of the left and right complex structures is {\em always} integrable, and hence the kernel is parametrized by chiral and twisted chiral superfield coordinates. We then analyze the particular case of $SU(2)\times SU(2)$, and are led to a new $N=2$ superspace formulation of the $SU(2)\times U(1)$ WZW-model.Comment: Latex, 16 pages. In this revised manuscript, we add a section and an author, and alter one of the conclusions of the pape

On Non-Perturbative Results in Supersymmetric Gauge Theories - A Lecture

Some notions in non-perturbative dynamics of supersymmetric gauge theories are being reviewed. This is done by touring through a few examples.Comment: 34 pages, Late

On Conformal Properties of the Dualized Sigma-Models

We have calculated the first-order beta-functions for a sigma-model ( with dilaton) dualized with respect to an arbitrary Lie group that acts without isotropy. We find that non-abelian duality preserves conformal invariance for semi-simple groups, but in general there is an extra contribution to the beta-function proportional to the trace of the structure constants, which cannot be absorbed into an additional dilaton shift. Two particular examples, a Bianchi V cosmological background and the G \otimes G WZW model, are discussed.Comment: 12 pages, LaTeX 2e with fleqn.sty (removed the Stony Brook emblem which was causing problems

Generalized Duality in Curved String-Backgrounds

The elements of $O(d,d,\Z)$ are shown to be discrete symmetries of the space of curved string backgrounds that are independent of $d$ coordinates. The explicit action of the symmetries on the backgrounds is described. Particular attention is paid to the dilaton transformation. Such symmetries identify different cosmological solutions and other (possibly) singular backgrounds; for example, it is shown that a compact black string is dual to a charged black hole. The extension to the heterotic string is discussed.Comment: 23 page

Target Space Duality I: General Theory

We develop a systematic framework for studying target space duality at the classical level. We show that target space duality between manifolds M and Mtilde arises because of the existence of a very special symplectic manifold. This manifold locally looks like M x Mtilde and admits a double fibration. We analyze the local geometric requirements necessary for target space duality and prove that both manifolds must admit flat orthogonal connections. We show how abelian duality, nonabelian duality and Poisson-Lie duality are all special cases of a more general framework. As an example we exhibit new (nonlinear) dualities in the case M = Mtilde = R^n.Comment: LaTeX, 29 pages, 1 eps figure. Added a couple of references and corrected a couple of typos. An FAQ that discusses some subtle points may be found at <http://www.physics.miami.edu/~alvarez/papers/duality/

Unitarity of supersymmetric SL(2,R)/U(1) and no-ghost theorem for fermionic strings in AdS(3) x N

The unitarity of the NS supersymmetric coset SL(2,R)/U(1) is studied for the discrete representations. The results are applied to the proof of the no-ghost theorem for fermionic strings in AdS(3) x N in the NS sector. A no-ghost theorem is proved for states in flowed discrete representations.Comment: LaTeX in JHEP style, 16 pages, typos correcte