Both the supersymmetric SO(32) and E8 × E8 heterotic strings in ten dimensions have known strong-coupling duals. However, it has not been known whether there also exist strong-coupling duals for the non-supersymmetric heterotic strings in ten dimensions. In this paper, we construct explicit open-string duals for the circle-compactifications of several of these non-supersymmetric theories, among...

We investigate the non-perturbative equivalence of some heterotic/type IIA dual pairs with N = 2 supersymmetry. We compute R-like corrections, both on the type IIA and on the heterotic side. The coincidence of their perturbative part provides a test of duality. The type IIA result is then used to predict the full, non-perturbative correction to the heterotic effective action. We determine the i...

A Z2 orbifold compactification of the heterotic string is considered. The resulting 6D GUT groups can be SO(16) or E7 × SU(2) plus some hidden sector groups. The N = 4 supersymmetry is reduced to N = 2. In particular, the SO(16) 6D model with one spinor representation 128 can reduce to the previous 5D SO(16) or SO(14) family unification models after compactifying the sixth dimension. To obtain ...

We analyse the dipole solution of heterotic string theory in four dimensions. It has the structure of monopole and anti-monopole connected by flux line (string). Due to growing coupling near the poles, the length of the string diverges. However, exploiting the self-duality of heterotic string theory in four dimension, we argue that this string is correctly described in terms of dual variables.

In this paper we analyze discrete torsion in perturbative heterotic string theory. In previous work we have given a purely mathematical explanation of discrete torsion as the choice of orbifold group action on a B field, in the case that dH = 0; in this paper we perform the analogous calculations in heterotic strings where dH = 0.