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 …

The possible tensor constructions of open string theories are analyzed from first principles.
To this end the algebraic framework of open string field theory is clarified, including the role …

A bstract We study systems with an Adler-Bell-Jackiw anomaly in terms of non-invertible
symmetry. We present a new kind of non-invertible charge defect where a key role is played …

A bstract The three tachyon-free non-supersymmetric string theories in ten dimensions
provide a handle on quantum gravity away from the supersymmetric lamppost. However …

We study superstrings with orientifold projections and with generalized open string
boundary conditions (D branes). We find two types of consistency condition, one related to …

This is a series of remedial lectures on open and unoriented strings for the heterotic string
generation. The particular focus is on the interesting features that arise under T-duality---D …

We show how to construct chiral tachyon-free perturbative orientifold models, where
supersymmetry is broken at the string scale on a collection of branes while, to lowest order …

We discuss string spectra in the low-tension limit using the BRST formalism, with emphasis
on the role of triplets of totally symmetric tensors and spinor-tensors and their …

We study topological properties of the D-brane resolution of three-dimensional orbifold
singularities, C 3/Λ, for finite abelian groups Λ. The D-brane vacuum moduli space is shown …

A bstract We construct rigid non-supersymmetric heterotic vacua with reduced rank and no
tachyons in six and four dimensions. These configurations are based on asymmetric orbifold …