We continue the study of moduli stabilization, now focusing on its interplay with SUSY breaking in string compactifications. We describe different mechanisms proposed for heterotic and type II orientifold compactifications, and elaborate on type IIB models, which allow for very explicit computations. Fluxes not only help in fixing moduli but generically induce SUSY breaking soft terms in the effective action. Some scenarios of SUSY breaking in string construction boil down to SUSY breaking in the dilaton or geometric moduli sector, and can be described in the 4d effective supergravity action in a quite model independent formalism. This setup allows the computation of soft terms and sparticle spectrum of string compactifications in terms of a few parameters, which may be tested at the LHC if low-energy SUSY is realized in Nature.

SUSY and SUSY breaking in string compactifications

In previous chapters we have described the construction of string compactifications, mainly focusing on 4d N = 1 supersymmetric models; indeed, these have been far more studied than directly non-supersymmetric compatifications, for several reasons. SUSY constitutes a theoretically most compelling ingredient proposed for particle physics at the TeV scale, providing a natural solution to the hierarchy problem, as mentioned in Sections 1.3.3 and 2.6. This requires mechanisms breaking supersymmetry in string compactifications, at scales parametrically smaller than the fundamental string scale Ms.