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Between non-criticality and non-linearity (Nunc est vacuum)
Start date: 01 Sep 2008, End date: 31 Aug 2010 PROJECT  FINISHED 

One of the central tasks of fundamental physics is to derive an effective description at low energy from a more fundamental theory. In particular, superstring theory includes a large number of aspects of particle physics and general relativity. In this context, one of the key points is the mechanism of supersymmetry breaking. Its effective description contains important conceptual and phenomenological difficulties. That’s why we propose to consider the effective action and vacuum structure of non-supersymmetric orientifold compactifications of Type IIB string theory. Two essential features appear when supersymmetry is broken on configurations of branes. A dilaton tadpole is generated and the broken supersymmetry is realized on the world-volume of the branes in a non-linear way. This non-linear supersymmetry provides a very powerful tool for computing the off-shell brane effective action. We propose in particular to use it in order to explore the Kahler potential of matter fields beyond its quadratic approximation. This will allow us to better understand the field redefinition and the mass spectrum of these chiral fields. A second essential step toward a better understanding of vacua with broken supersymmetry is the stabilization of the dilaton. Indeed, the presence of a dilaton tadpole on the disk indicates an instability. We analyze its resolution by considering non-critical backgrounds. Using exact boundary conformal field theory methods, we propose to compute in details the sphere and disk contributions to the scalar potential. They arise respectively from the effective central charge and from supersymmetry breaking terms. Evidences for the existence of non-supersymmetric vacua at a perturbative regime will then be studied. These two complementary approaches will then enable us to propose stable non-supersymmetric branes constructions reproducing the basic features of the standard model of particle physics.
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