This review is devoted to open strings, and in particular to the often surprising features of
their spectra. It follows and summarizes developments that took place mainly at the …

In this review I discuss some basic aspects of non-perturbative string theory. The topics
include tests of duality symmetries based on the analysis of the low energy effective action …

A bstract We consider consequences of triviality of cobordism classes and anomaly
cancellation in supergravity theories in d> 6. We argue that this leads to the existence of …

By exploiting recent arguments about stable nonsupersymmetric D-brane states, we argue
that D-brane charge takes values in the K-theory of spacetime, as has been suspected …

Using “Tate's algorithm,” we identify loci in the moduli of F-theory compactifications
corresponding to enhanced gauge symmetry. We apply this to test the proposed F …

We show that configurations of multiple D-branes related by SU (N) rotations will preserve
unbroken supersymmetry. This includes cases in which two D-branes are related by a …

The primary purpose of these lecture notes is to explore the moduli space of type IIA, type
IIB, and heterotic string compactified on a K3 surface. The main tool which is invoked is that …

Many important ideas about string duality that appear in conventional T 2 compactification
have analogs for T2 compactification without vector structure. We analyze some of these …

Recent theoretical developments have shown that extra space-time dimensions can lower
the fundamental GUT, Planck, and string scales. However, recent evidence for neutrino …

We formulate an extension of Maldacena's AdS/CFT conjectures to the case of branes
located at singular points in the ambient transverse space. For singularities which occur at …