Samenvatting

Asymmetric heterotic orbifolds are discussed from the worldsheet perspective. Starting from Buscher’s gauging of a theory of D compact bosons the duality covariant description of Tseytlin is obtained after a non–Lorentz invariant gauge fixing. A left–over of the gauge symmetry can be used to removed the doubled constant zero modes so that D physical target space coordinate remain. This can be thought of as the worldsheet realization of the strong constraint of double field theory. The extension of this description to the heterotic theory is straightforward as all results are written in terms of the invariant and the generalized metrics. An explicit method is outline how to obtain a generalized metric which is invariant under T–duality orbifold actions. It is explicitly shown how shift orbifolds lead to redefinitions of the Narain moduli. Finally, a number of higher dimensional T–folds are constructed including a novel asymmetric Z6 orbifold.