Moduli stabilization from magnetic fluxes in type I string theory

TL;DR

The paper introduces a moduli-stabilization mechanism for Type I string theory based on constant internal magnetic fluxes on magnetized D9-branes, achieving N=1 vacua where all Kahler and complex-structure moduli are fixed with an exact string description. By exploiting the nonlinearity of the DBI action and carefully balancing flux-induced tadpoles, the authors show that both Kahler and complex-structure moduli can be set by flux data on T^6, and demonstrate this explicitly with a nine-stack toroidal construction that fixes all geometric moduli while allowing arbitrarily large extra dimensions. They also explain how RR moduli are stabilized via Chern-Simons couplings that absorb RR axions into massive U(1)s, and discuss generalizations to Calabi-Yau/orbifold compactifications and potential combinations with closed-string fluxes for dilaton stabilization. The approach provides an exact-string-description alternative to purely closed-flux stabilizations and can be integrated with intersecting D-brane model-building frameworks. Overall, it offers a concrete, tunable path to fully stabilize geometric moduli in supersymmetric Type I settings, with implications for realistic string phenomenology and moduli-scale control.

Abstract

We show that type I string theory compactified in four dimensions in the presence of constant internal magnetic fields possesses N=1 supersymmetric vacua, in which all Kahler class and complex structure closed string moduli are fixed. Furthermore, their values can be made arbitrarily large by a suitable tuning of the quantized magnetic fluxes. We present an explicit example for the toroidal compactification on T^6 and discuss Calabi-Yau generalizations. This mechanism can be complementary to other stabilization methods using closed string fluxes but has the advantage of having an exact string description and thus a validity away from the low-energy supergravity approximation. Moreover, it can be easily implemented in constructions of string models based on intersecting D-branes.