In this work we have discussed the effect of turning on constant electromagnetic fields on some direction of the compact manifold in type I models. From the beginning this subject has received much attention in the String comunity for both theoretical and phenomenological reasons. It suggested a new way of supersymmetry breaking, a notorius problem in String Theory, even in toroidal compactifications. This is a consequence of the different coupling of particles of different helicities to magnetic fields. The breaking occurs at string scale, which can be fixed at TeV scale in D-branes models avoiding the hierarchy problem. Over the last years, many efforts were addressed in the construction of String Theory vacua using internal \parallel" magnetic uxes on \factorizable" tori Td = T2 :::T2 or, in the T-dual framework, with branes intersecting at angle. The results presented here should have clarified several features of the dynamics of open strings coupled to \oblique" magnetic fields; a magnetic configuration more general than \parallel" uxes. The effect of a general constant abelian gauge field is the inclusion of a boundary action, quadratic in the string coordinates. The importance of this perturbative deformation is that it is simple to treat and may be solved exactly and at the same time it is rich enough to construct models with SM-like spectrum and gauge group. Its effect is a Lorentz rotation of the left-moving modes relative to the right-moving ines. This was shown in the transverse closed string channel, where turning on magnetic fields corresponds to changing the phase and to rescale some boundary reection coefficients by the BI factor. In the direct open string channel this is responsible for \twisted" terms, we called them charged sector throughout this thesis, whose modes are shifted by a ux dependent amount. The attractive feature is the appearence of chiral matter families due to a non vanishing index of the Dirac operator coupled to magnetized D-branes. This is the counterpart of the Landau levels of a particle interacting with an external magnetic field and moving in a compact space in quantum mechanics. In the T-dual picture they appear as low energy excitations of open strings stretched between two stacks of rotated branes and the number of intersections is in correspondence with the number of chiral families; the Landau levels degeneracy in the magnetic ux picture. Another important motivation of this work is the (partial) stabilization of closed string moduli of type I vacua via open strings (non) abelian uxes. K ahler and complex structure moduli may be frozen at local supersymmetric minima of the ux induced scalar potential. In the present work we derive general formulae for the magnetic shifts and multiplicities of open strings connecting D9-branes with arbitrary magnetic uxes. We discuss the ux induced potential and offer an interpretation of the stabilization of R-R moduli associated to deformations of the complex structure of T6 in terms of non-derivative mixings with NS-NS moduli. Finally we brie y comment on how to extract other low energy couplings. In particular, pushing the analysis to one loop order in perturbation theory we have derived explicit formulae for the one loop partition functions of type I supertrings on tori with arbitrary abelian uxes. The check of quantum consistency via open-closed string duality allowed to identify the correct tadpole conditions. These conditions guarantee the absence of non Abelian gauge anomalies, while mixed and cubic U(1) gauge anomalies are cancelled by the generalized GS mechanism, mediated by closed string fields. The main consequence is that some or all the U(1) abelian vectors acquire a mass. As in the case of \ parallel" magnetic fields, the coexistence of N = 1 oblique uxes and the cancellation of all RR charges seems hard to be achieved in toroidal compactifications, where all the closed string moduli are stabilized.
Trevigne, E. (2009). Magnetic fluxes and moduli stabilization in Type I superstrings.
|Titolo:||Magnetic fluxes and moduli stabilization in Type I superstrings|
|Data di pubblicazione:||30-lug-2009|
|Anno Accademico:||A.A. 2006/2007|
|Settore Scientifico Disciplinare:||Settore FIS/01 - Fisica Sperimentale|
|Tipologia:||Tesi di dottorato|
|Citazione:||Trevigne, E. (2009). Magnetic fluxes and moduli stabilization in Type I superstrings.|
|Appare nelle tipologie:||07 - Tesi di dottorato|