String Dualities in the Presence of Anomalous U(1) Symmetries

Anomalous U(1) gauge symmetries in type II orientifold theories show some unexpected properties. In contrast to the heterotic case, the masses of the gauge bosons are in general of order of the string scale even in the absence of large Fayet-Iliopoulos terms. Despite this fact, the notion of heterotic-type II orientifold duality remains a useful concept, although this symmetry does not seem to hold in all cases considered. We analyse the status of this duality symmetry, clarify the properties of anomalous U(1) gauge symmetry in the orientifold picture and comment on the consequences for phenomenological applications of such anomalous gauge symmetries.