The open story of the magnetic fluxes

TL;DR

The paper develops a comprehensive framework for open strings on type I toroidal compactifications with oblique abelian magnetic fluxes on D9-branes. It derives general magnetic shifts, multiplicities via index theorems, and KK-momentum rescalings across T^2 through T^6, and analyzes supersymmetry conditions, stability, and moduli stabilization arising from the Born-Infeld and WZ sectors. It further elucidates open-closed string mixing that lifts RR moduli and shows how holomorphy and stability constraints can fix complex structure and Kähler moduli in SUSY configurations, with explicit six-torus treatments and model examples. The results enable controlled model-building with chiral spectra and stabilized moduli in toroidal compactifications and offer pathways to generalizations to orbifolds and rational conformal field theories, with implications for gauge couplings and phenomenology. Overall, the work provides exact tools to analyze spectrum, stability, and low-energy couplings in magnetized-brane setups, expanding the landscape of viable Type I vacua.

Abstract

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.