Results 1  10
of
46
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 ..."
Abstract

Cited by 147 (18 self)
 Add to MetaCart
(Show Context)
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
Spacetime Instanton Corrections in 4D String Vacua (The Seesaw Mechanism for DBrane Models)
, 2006
"... We systematically investigate instanton corrections from wrapped Euclidean Dbranes to the matter field superpotential of various classes of N=1 supersymmetric Dbrane models in four dimensions. Both gauge invariance and counting fermionic zero modes provide strong constraints on the allowed nonper ..."
Abstract

Cited by 136 (28 self)
 Add to MetaCart
We systematically investigate instanton corrections from wrapped Euclidean Dbranes to the matter field superpotential of various classes of N=1 supersymmetric Dbrane models in four dimensions. Both gauge invariance and counting fermionic zero modes provide strong constraints on the allowed nonperturbative superpotential couplings. We outline how the complete instanton computation boils down to the computation of open string disc diagrams for boundary changing operators multiplied by a oneloop vacuum diagram. For concreteness we focus on E2instanton effects in Type IIA vacua with intersecting D6branes, however the same structure emerges for Type IIB and heterotic vacua. The instantons wrapping rigid cycles can potentially destabilise the vacuum or generate perturbatively absent matter couplings such as proton decay operators, µparameter or righthanded neutrino Majorana mass terms. The latter allow the realization of the seesaw mechanism for MSSM like intersecting Dbrane models.
Fixing all moduli in a simple Ftheory compactification,” [arXiv:hepth/0503124
"... We discuss a simple example of an Ftheory compactification on a CalabiYau fourfold where background fluxes, nonperturbative effects from Euclidean D3 instantons and gauge dynamics on D7 branes allow us to fix all closed and open string moduli. We explicitly check that the known higher order correc ..."
Abstract

Cited by 91 (8 self)
 Add to MetaCart
(Show Context)
We discuss a simple example of an Ftheory compactification on a CalabiYau fourfold where background fluxes, nonperturbative effects from Euclidean D3 instantons and gauge dynamics on D7 branes allow us to fix all closed and open string moduli. We explicitly check that the known higher order corrections to the potential, which we neglect in our leading approximation, only shift the results by a small amount. In our exploration of the model, we encounter interesting new phenomena, including examples of transitions where D7 branes absorb O3 planes, while changing topology to preserve the net D3 charge.
Fluxes, moduli fixing and MSSMlike vacua in a simple IIA orientifold
, 2005
"... We study the effects of adding RR, NS and metric fluxes on a T6 /(Ω(−1) FLI3) Type IIA orientifold. By using the effective fluxinduced superpotential we obtain Minkowski or AdS vacua with broken or unbroken supersymmetry. In the Minkowski case some combinations of real moduli remain undetermined, w ..."
Abstract

Cited by 82 (4 self)
 Add to MetaCart
We study the effects of adding RR, NS and metric fluxes on a T6 /(Ω(−1) FLI3) Type IIA orientifold. By using the effective fluxinduced superpotential we obtain Minkowski or AdS vacua with broken or unbroken supersymmetry. In the Minkowski case some combinations of real moduli remain undetermined, whereas all can be stabilized in the AdS solutions. Many flux parameters are available which are unconstrained by RR tadpole cancellation conditions allowing to locate the minima at large volume and small dilaton. We also find that in AdS supersymmetric vacua with metric fluxes, the overall flux contribution to RR tadpoles can vanish or have opposite sign to that of D6branes, allowing for new modelbuilding possibilities. In particular, we construct the first N=1 supersymmetric intersecting D6brane models with MSSMlike spectrum and with all closed string moduli stabilized. Some axionlike fields remain undetermined but they are precisely required to give Stückelberg masses to (potentially anomalous) U(1) brane fields. We show that the cancellation of the FreedWitten anomaly guarantees that the axions with fluxinduced masses are orthogonal to those giving masses to the U(1)’s. Cancellation of such anomalies also guarantees that the D6branes in our N=1 supersymmetric AdS vacua are calibrated so that they are forced to preserve one unbroken supersymmetry.
One in a billion: MSSMlike Dbrane statistics
, 2005
"... Continuing our recent work hepth/0411173, we study the statistics of fourdimensional, supersymmetric intersecting Dbrane models in a toroidal orientifold background. We have performed a vast computer survey of solutions to the stringy consistency conditions and present their statistical implicatio ..."
Abstract

Cited by 66 (18 self)
 Add to MetaCart
Continuing our recent work hepth/0411173, we study the statistics of fourdimensional, supersymmetric intersecting Dbrane models in a toroidal orientifold background. We have performed a vast computer survey of solutions to the stringy consistency conditions and present their statistical implications with special emphasis on the frequency of Standard Model features. Among the topics we discuss are the implications of the Ktheory constraints, statistical correlations among physical quantities and an investigation of the various statistical suppression factors arising once certain Standard Model features are required. We estimate the frequency of an MSSM like gauge group with three generations to be one in a billion.
An open string landscape
 JHEP
, 2005
"... Abstract: The effect of fluxes on open string moduli is studied by analyzing the constraints imposed by supersymmetry on Dbranes in type IIB flux backgrounds. We show that generically the conditions of supersymmetry cannot be maintained when moving along the geometrical moduli space of the brane, s ..."
Abstract

Cited by 56 (3 self)
 Add to MetaCart
(Show Context)
Abstract: The effect of fluxes on open string moduli is studied by analyzing the constraints imposed by supersymmetry on Dbranes in type IIB flux backgrounds. We show that generically the conditions of supersymmetry cannot be maintained when moving along the geometrical moduli space of the brane, so that open string moduli are lifted. In specific examples, we find that there is a disconnected and discrete set of supersymmetric solutions to the open string equations of motion, which extends the familiar closed string landscape to the open string sector. Permanent addressContents
Computation of Dbrane instanton induced superpotential couplings  Majorana masses from string theory
, 2007
"... ..."
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. ..."
Abstract

Cited by 40 (15 self)
 Add to MetaCart
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.
D6branes and torsion
"... Abstract: The D6brane spectrum of type IIA vacua based on twisted tori ˜T 6 and RR background fluxes is analyzed. In particular, we compute the torsion factors of Hn(˜T 6, Z) and describe the effect that they have on D6brane physics. For instance, the fact that H3(˜T 6, Z) contains ZN subgroups ex ..."
Abstract

Cited by 31 (3 self)
 Add to MetaCart
(Show Context)
Abstract: The D6brane spectrum of type IIA vacua based on twisted tori ˜T 6 and RR background fluxes is analyzed. In particular, we compute the torsion factors of Hn(˜T 6, Z) and describe the effect that they have on D6brane physics. For instance, the fact that H3(˜T 6, Z) contains ZN subgroups explains why RR tadpole conditions are affected by geometric fluxes. In addition, the presence of torsional (co)homology shows why some D6brane moduli are lifted, and it suggests how the Dbrane discretum appears in type IIA flux compactifications. Finally, we give a clear, geometrical understanding of the FreedWitten anomaly in the present type IIA setup, and discuss its consequences for the construction of semirealistic flux vacua. Contents 1. Motivation and Summary
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 ..."
Abstract

Cited by 28 (1 self)
 Add to MetaCart
(Show Context)
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