We study the stability of heterotic compactifications described by (0,2) gauged linear sigma models with respect to worldsheet instanton corrections to the space-time superpotential following the work of Beasley and Witten [1]. We show that generic models elude the vanishing theorem proved there, and may not determine supersymmetric heterotic vacua. We then construct a subclass of linear models...

The strong coupling dynamics of string theories in dimension d ≥ 4 are studied. It is argued, among other things, that eleven-dimensional supergravity arises as a low energy limit of the ten-dimensional Type IIA superstring, and that a recently conjectured duality between the heterotic string and Type IIA superstrings controls the strong coupling dynamics of the heterotic string in five, six, a...

Equilibria are determined for the two-locus model in a partially selfing population when one locus is neutral and the other locus is heterotic. At an equilibrium point, the frequency of heterozygotes at the neutral locus is greater than that expected from one-locus theory, even if the heterotic locus is on a different chromosome. Thus, the neutral locus also appears to be heterotic. The magnitu...

We study the constraints on five–dimensional N = 1 heterotic M–theory imposed by a consistent anomaly–free coupling of bulk and boundary theory. This requires analyzing the cancellation of triangle gauge anomalies on the four–dimensional orbifold planes due to anomaly inflow from the bulk. We find that the semi–simple part of the orbifold gauge groups and certain U(1) symmetries have to be free...

The heterotic string compacti ed on a Calabi{Yau three-fold X3 has been the phenomenologically most promising candidate amongst perturbatively de ned string theories for quite some time [1]. In particular, compacti cations with (0; 2) supersymmetry can easily lead to realistic gauge groups [2]. The de nition of the theory involves the understanding of a suitable stable vector bundle V on X3, wh...

We present several examples of T/P orbifolds with P ⊂ SU4. We compute their Hodge numbers and consider turning on discrete torsion. We then study supersymmetric compactifications of type II, heterotic, and type I strings on these orbifolds. Heterotic compactifications to D=2 have a B-field tadpole with coefficient given by that of the anomaly polynomial. In the SO32 heterotic with standard embe...

We present several examples of T/P orbifolds with P ⊂ SU4. We compute their Hodge numbers and consider turning on discrete torsion. We then study supersymmetric compactifications of type II, heterotic, and type I strings on these orbifolds. Heterotic compactifications to D=2 have a B-field tadpole with coefficient given by that of the anomaly polynomial. In the SO32 heterotic with standard embe...

In this paper we consider Type I string theory compactified on a Z7 orbifold. The model has N = 1 supersymmetry, a U(4) ⊗ U(4) ⊗ U(4) ⊗ SO(8) gauge group, and chiral matter. There are only D9-branes (for which we discuss tadpole cancellation conditions) in this model corresponding to a perturbative heterotic description in a certain region of the moduli space. We construct the heterotic dual, m...

A bstract We use a moduli space exploration algorithm to produce complete list of maximally enhanced gauge groups that are realized in the heterotic string 7d, encompassing usual Narain component, and five other components with rank reduction via nontrivial holonomy triples. Using lattice embedding techniques we find an explicit match mechanism singularity freezing M-theory on K3. The global da...

In this article we review four-dimensional string vacua with N = 2 space-time supersymmetry. In particular, we will discuss several aspects of the string-string duality between the heterotic string, compactified on K3 × T 2 , and the type II superstring compactified on a Calabi-Yau threefold. We investigate the massless supersymmetric spectra, showing agreement for a large class of dual heterot...