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136
Fourdimensional String Compactifications with DBranes, Orientifolds and Fluxes
"... This review article provides a pedagogical introduction into various classes of chiral string compactifications to four dimensions with Dbranes and fluxes. The main concern is to provide all necessary technical tools to explicitly construct fourdimensional orientifold vacua, with the final aim to ..."
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Cited by 147 (18 self)
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This review article provides a pedagogical introduction into various classes of chiral string compactifications to four dimensions with Dbranes and fluxes. The main concern is to provide all necessary technical tools to explicitly construct fourdimensional orientifold vacua, with the final aim to come as close as possible to the supersymmetric Standard Model. Furthermore, we outline the available methods to derive the resulting fourdimensional effective action. Finally, we summarize recent attempts to address the
Moduli Stabilisation versus Chirality for MSSM like Type
 IIB Orientifolds,” JHEP 01 (2008) 058
"... We investigate the general question of implementing a chiral MSSM like Dbrane sector in Type IIB orientifold models with complete moduli stabilisation via Fterms induced by fluxes and spacetime instantons, respectively gaugino condensates. The prototype examples are the KKLT and the socalled lar ..."
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Cited by 62 (8 self)
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We investigate the general question of implementing a chiral MSSM like Dbrane sector in Type IIB orientifold models with complete moduli stabilisation via Fterms induced by fluxes and spacetime instantons, respectively gaugino condensates. The prototype examples are the KKLT and the socalled large volume compactifications. We show that the ansatz of first stabilising all moduli via Fterms and then introducing the Standard Model module is misleading, as a chiral sector notoriously influences the structure of nonperturbative effects and induces a Dterm potential. Focusing for concreteness on the large volume scenario, we work out the geometry of the swisscheese type CalabiYau manifold IP [1,3,3,3,5][15] (3,75) and analyse whether controllable and phenomenologically acceptable Kähler moduli stabilisation can occur by the combination of F and Dterms. Contents
Computation of Dbrane instanton induced superpotential couplings  Majorana masses from string theory
, 2007
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Nonperturbative and Flux superpotentials for Type
 I strings on the Z3 orbifold,” Nucl. Phys. B 782 (2007
"... Abstract: Nonperturbative effects are studied for Type I strings on the Z3 orbifold with ChanPaton symmetry broken by Wilson lines. Generalizing previous analyses that have focussed on (bi)fundamentals, it is argued that (anti)symmetric representations of the resulting gauge group play a decisive ..."
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Cited by 41 (11 self)
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Abstract: Nonperturbative effects are studied for Type I strings on the Z3 orbifold with ChanPaton symmetry broken by Wilson lines. Generalizing previous analyses that have focussed on (bi)fundamentals, it is argued that (anti)symmetric representations of the resulting gauge group play a decisive role in generating an ADSlike superpotential in this and related cases. Non perturbative corrections in the closed string moduli are only allowed if properly dressed with open string fields charged under the anomalous U(1) of the orbifold. A general discussion of instanton effects in SYM and string theories is given. Nonperturbative superpotentials induced by both ED5’s and ED1’s are analyzed. The superpotential generated by closed string fluxes, viz. ScherkSchwarz shifts (torsion), RR 3form flux as well as nongeometric fluxes is derived. Some preliminary comments on the compatibility of the two kinds of superpotentials and the issue of moduli stabilization are presented. Contents
Jumping Through Loops: On Soft Terms from Large Volume Compactifications
 JHEP
, 2007
"... We subject the phenomenologically successful large volume scenario of hepth/0502058 to a first consistency check in string theory. In particular, we consider whether the expansion of the string effective action is consistent in the presence of Dbranes and Oplanes. Due to the noscale structure at ..."
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Cited by 41 (0 self)
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We subject the phenomenologically successful large volume scenario of hepth/0502058 to a first consistency check in string theory. In particular, we consider whether the expansion of the string effective action is consistent in the presence of Dbranes and Oplanes. Due to the noscale structure at treelevel, the scenario is surprisingly robust. We compute the modification of soft supersymmetry breaking terms, and find only subleading corrections. We also comment that for largevolume limits of toroidal orientifolds and fibered CalabiYau manifolds the corrections can be more important,
Lifting DInstanton Zero Modes by Recombination and Background Fluxes
, 2007
"... We study the conditions under which Dbrane instantons in Type II orientifold compactifications generate a nonperturbative superpotential. If the instanton is noninvariant under the orientifold action, it carries four instead of the two Goldstone fermions required for superpotential contributions. ..."
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Cited by 40 (15 self)
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We study the conditions under which Dbrane instantons in Type II orientifold compactifications generate a nonperturbative superpotential. If the instanton is noninvariant under the orientifold action, it carries four instead of the two Goldstone fermions required for superpotential contributions. Unless these are lifted, the instanton can at best generate higher fermionic Fterms of BeasleyWitten type. We analyse two strategies to lift the additional zero modes. First we discuss the process of instantonic brane recombination in Type IIA orientifolds. We show that in some cases charge invariance of the measure enforces the presence of further zero modes which, unlike the Goldstinos, cannot be absorbed. In other cases, the instanton exhibits reparameterisation zero modes after recombination and a superpotential is generated if these are lifted by suitable closed or open string couplings. In the second part of the paper we address lifting the extra Goldstinos of D3brane instantons by supersymmetric threeform background fluxes in Type IIB orientifolds. This requires nontrivial gauge flux on the instanton. Only if the part of the fermionic action linear in the gauge flux survives the orientifold projection can the extra Goldstinos be lifted.
An InstantonToolbox for FTheory Model Building
"... Several dimensionful parameters needed for model building can be engineered in a certain class of SU(5) Ftheory GUTs by adding extra singlet fields which are localized along pairwise intersections of D7branes. The values of these parameters, however, depend on dynamics external to the GUT which ca ..."
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Cited by 36 (6 self)
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Several dimensionful parameters needed for model building can be engineered in a certain class of SU(5) Ftheory GUTs by adding extra singlet fields which are localized along pairwise intersections of D7branes. The values of these parameters, however, depend on dynamics external to the GUT which causes the singlets to acquire suitable masses or expectation values. In this note, we demonstrate that D3instantons which wrap the same 4cycle as one of the intersecting D7’s can provide precisely the needed dynamics to generate several important scales, including the supersymmetrybreaking scale and the righthanded neutrino mass. Furthermore, these instantons seem unable to directly generate the µ term suggesting that, at least in this class of models, it should perhaps be tied to one of the other scales in the problem. More specifically, we study the simple system consisting of a pair of D7branes wrapping del Pezzo surfaces which intersect along a curve Σ of genus 0 or 1 and classify all instanton configurations which can potentially contribute to the superpotential. This allows one to formulate topological conditions which must be imposed on Σ for various modelbuilding applications. Along the way, we also observe that the construction of [7]
Local Models in FTheory and MTheory with Three Generations,” arXiv:0901.3785 [hepth
"... Abstract: We describe a general framework that can be used to geometrically engineer local, phenomenological models in Ftheory and Mtheory based on ALEfibrations, and we present several concrete examples of such models that feature three generations of matter with semirealistic phenomenology. We ..."
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Cited by 30 (0 self)
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Abstract: We describe a general framework that can be used to geometrically engineer local, phenomenological models in Ftheory and Mtheory based on ALEfibrations, and we present several concrete examples of such models that feature three generations of matter with semirealistic phenomenology. We show that the geometric structures required for generating interactions—tripleintersections of mattercurves in Ftheory and supersymmetric threecycles supporting multiple conical singularities in Mtheory—are generic in such ALEfibred manifolds, and that they can be understood in correspondence with one another. The models we can construct in this way are strictly limited in complexity by the maximality of the Ê8ALE space, but turn out to be just complex enough to accommodate some of the most realistic
Realistic Yukawa couplings through instantons in intersecting brane worlds
, 2007
"... The Yukawa couplings of the simpler models of Dbranes on toroidal orientifolds suffer from the socalled “rank one” problem – there is only a single nonzero mass and no mixing. We consider the oneloop contribution of E2instantons to Yukawa couplings on intersecting D6branes, and show that they c ..."
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Cited by 28 (1 self)
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The Yukawa couplings of the simpler models of Dbranes on toroidal orientifolds suffer from the socalled “rank one” problem – there is only a single nonzero mass and no mixing. We consider the oneloop contribution of E2instantons to Yukawa couplings on intersecting D6branes, and show that they can solve the rank one problem. In addition they have the potential to provide a geometric explanation for the hierarchies observed in the Yukawa coupling. In order to do this we provide
Realistic Yukawa structures from orientifold compactifications
, 2009
"... We perform a systematic analysis of globally consistent Dbrane quivers which realize the MSSM and analyze them with respect to their Yukawa couplings. Often, desired couplings are perturbatively forbidden due to the presence of global U(1) symmetries. We investigate the conditions under which Dbra ..."
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Cited by 25 (10 self)
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We perform a systematic analysis of globally consistent Dbrane quivers which realize the MSSM and analyze them with respect to their Yukawa couplings. Often, desired couplings are perturbatively forbidden due to the presence of global U(1) symmetries. We investigate the conditions under which Dbrane instantons will induce these missing couplings without generating other phenomenological drawbacks, such as Rparity violating couplings or a µterm which is too large. Furthermore, we systematically analyze which quivers allow for a mechanism that can account for the small neutrino masses and other experimentally observed hierarchies. We show that only a small fraction of the globally consistent Dbrane quivers