The open story of the magnetic fluxes

We discuss the effects of oblique internal magnetic fields on the spectrum of type I superstrings compactified on tori. In particular we derive general formulae for the magnetic shifts and multiplicities of open strings connecting D9-branes with arbitrary magnetic fluxes. We discuss the flux induced potential and offer an interpretation of the stabilization of R-R moduli associated to deformations of the complex structure of T^6 in terms of non-derivative mixing with NS-NS moduli. Finally we briefly comment on how to extract other low energy couplings and generalize our results to toroidal orbifolds and other configurations governed by rational conformal field theories on the worldsheet.Comment: 36 pages, LaTeX, References adde

Gauge thresholds in the presence of oblique magnetic fluxes

We compute the one-loop partition function and analyze the conditions for tadpole cancellation in type I theories compactified on tori in the presence of internal oblique magnetic fields. We check open - closed string channel duality and discuss the effect of T-duality. We address the issue of the quantum consistency of the toroidal model with stabilized moduli recently proposed by Antoniadis and Maillard (AM). We then pass to describe the computation of one-loop threshold corrections to the gauge couplings in models of this kind. Finally we briefly comment on coupling unification and dilaton stabilization in phenomenologically more viable modelsComment: 34 pages, 2 figures; references added, major changes to the discussion of the model proposed by Antoniadis and Maillar