Results 1  10
of
76
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
(Show Context)
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.
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.
Moduli stabilization in chiral type IIB orientifold models with fluxes
, 2003
"... We consider Type IIB orientifold models on CalabiYau spaces with threeform Gflux turned on. These fluxes freeze some of the complex structure moduli and the complex dilaton via an Fterm scalar potential. By introducing pairs of D9D9 branes with abelian magnetic fluxes it is possible to freeze a ..."
Abstract

Cited by 70 (11 self)
 Add to MetaCart
We consider Type IIB orientifold models on CalabiYau spaces with threeform Gflux turned on. These fluxes freeze some of the complex structure moduli and the complex dilaton via an Fterm scalar potential. By introducing pairs of D9D9 branes with abelian magnetic fluxes it is possible to freeze also some of the Kähler moduli via a Dterm potential. Moreover, such magnetic fluxes in general lead to chiral fermions, which make them interesting for string modelbuilding. These issues are demonstrated in a simple toy model based on a Z2 × Z ′ 2 orbifold.
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.
Computation of Dbrane instanton induced superpotential couplings  Majorana masses from string theory
, 2007
"... ..."
Getting just the supersymmetric standard model at intersecting branes on the Z6orientifold
 INTERSECTING BRANES ON THE Z6ORIENTIFOLD, PHYS. REV. D70 (2004) 126010, HEPTH/0404055
, 2004
"... In this paper, globally N = 1 supersymmetric configurations of intersecting D6branes on the Z6 orientifold are discussed, involving also fractional branes. It turns out rather miraculously that one is led almost automatically to just one particular class of 5 stack models containing the SM gauge gr ..."
Abstract

Cited by 56 (12 self)
 Add to MetaCart
In this paper, globally N = 1 supersymmetric configurations of intersecting D6branes on the Z6 orientifold are discussed, involving also fractional branes. It turns out rather miraculously that one is led almost automatically to just one particular class of 5 stack models containing the SM gauge group, which all have the same chiral spectrum. The further discussion shows that these models can be understood as exactly the supersymmetric standard model without any exotic chiral symmetric/antisymmetric matter. The superpartner of the Higgs finds a natural explanation and the hypercharge remains massless. However, the nonchiral spectrum within the model class is very different and does not in all cases allow for a N = 2 low energy field theoretical understanding of the necessary breaking U(1) × U(1) → U(1) along the Higgs branch, which is needed in order to get the standard Yukawa couplings. Also the leftright symmetric models belong to exactly one class of chiral spectra, where the two kinds of exotic chiral fields can have the interpretation of forming a composite Higgs. The aesthetical beauty of these models, involving only nonvanishing intersection numbers of
The Statistics of Supersymmetric Dbrane Models
, 2004
"... We investigate the statistics of the phenomenologically important Dbrane sector of string compactifications. In particular for the class of intersecting Dbrane models, we generalise methods known from number theory to determine the asymptotic statistical distribution of solutions to the tadpole ca ..."
Abstract

Cited by 53 (21 self)
 Add to MetaCart
We investigate the statistics of the phenomenologically important Dbrane sector of string compactifications. In particular for the class of intersecting Dbrane models, we generalise methods known from number theory to determine the asymptotic statistical distribution of solutions to the tadpole cancellation conditions. Our approach allows us to compute the statistical distribution of gauge theoretic observables like the rank of the gauge group, the number of chiral generations or the probability of an SU(N) gauge factor. Concretely, we study the statistics of intersecting branes on T 2 and T 4 / Z2 and T 6 / Z2 × Z2 orientifolds. Intriguingly, we find a statistical correlation between the rank of the gauge group and the number of chiral generations. Finally, we combine the statistics of the gauge theory sector with the statistics of the flux sector and study how distributions of gauge theoretic quantities are affected.
Chiral Dbrane models with frozen open string moduli
, 2005
"... Most intersecting Dbrane vacua in the literature contain additional massless adjoint fields in their low energy spectrum. The existence of these additional fields make it difficult to obtain negative beta functions and, eventually, asymptotic freedom. We address this important issue for N = 1 inter ..."
Abstract

Cited by 46 (14 self)
 Add to MetaCart
(Show Context)
Most intersecting Dbrane vacua in the literature contain additional massless adjoint fields in their low energy spectrum. The existence of these additional fields make it difficult to obtain negative beta functions and, eventually, asymptotic freedom. We address this important issue for N = 1 intersecting Dbrane models, rephrasing the problems in terms of (open string) moduli stabilization. In particular, we consider a Z2 × Z2 orientifold construction where D6branes wrap rigid 3cycles and such extra adjoint fields do not arise. We derive the model building rules and consistency conditions for intersecting branes in this background, and provide N = 1 chiral vacua free of adjoint fields. More precisely, we construct a PatiSalamlike model whose SU(4) gauge group is asymptotically free. We also comment on the application of these results for obtaining gaugino condensation in chiral Dbrane models. Finally, we embed our constructions in the framework of flux compactification, and construct new classes of N = 1 and N = 0 chiral flux vacua.
Four Dimensional Black Hole Microstates: From Dbranes to Spacetime Foam,” arXiv:hepth/0606118
"... We propose that every supersymmetric four dimensional black hole of finite area can be split up into microstates made up of primitive halfBPS “atoms”. The mutual nonlocality of the charges of these “atoms ” binds the state together. In support of this proposal, we display a class of smooth, horizo ..."
Abstract

Cited by 44 (6 self)
 Add to MetaCart
(Show Context)
We propose that every supersymmetric four dimensional black hole of finite area can be split up into microstates made up of primitive halfBPS “atoms”. The mutual nonlocality of the charges of these “atoms ” binds the state together. In support of this proposal, we display a class of smooth, horizonfree, four dimensional supergravity solutions carrying the charges of black holes, with multiple centers each carrying the charge of a halfBPS state. At vanishing string coupling the solutions collapse to a bound system of intersecting Dbranes. At weak coupling the system expands into the noncompact directions forming a topologically complex geometry. At strong coupling, a new dimension opens up, and the solutions form a “foam ” of spheres threaded by flux in Mtheory. We propose that this transverse growth of the underlying bound state of constitutent branes is responsible for the emergence of black hole horizons for coarsegrained observables. As such, it suggests the link between the Dbrane and “spacetime foam ” approaches to black hole entropy.