Moduli stabilization from magnetic fluxes in type I string theory

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 validity away from the low-energy supergravity approximation. Moreover, it can be easily implemented in constructions of string models based on intersecting D-branes. (c) 2005 Elsevier B.V. All rights reserved.