-
[show abstract]
[hide abstract]
ABSTRACT: When locally engineering F-theory models some D7-branes for the gauge group factors are specified and matter is localized on the intersection curves of the compact parts of the world-volumes. In this note, we discuss to what extent one can draw conclusions about F-theory models by just restricting the attention locally to a particular seven-brane. Globally, the possible D7-branes are not independent from each other and the (compact part of the) D7-brane can have unavoidable intrinsic singularities. Many special intersecting loci which were not chosen by hand occur inevitably, notably codimension-three loci which are not intersections of matter curves. We describe these complications specifically in a global SU(5) model and also their impact on the tadpole cancellation condition.
Journal of Geometry and Physics. 02/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: We modify a recently proposed heterotic model hep-th/0703210, giving three net-generations of Standard Model fermions, to get rid of an additional U(1) factor in the gauge group. The method employs a stable SU(5) bundle on a Calabi–Yau threefold admitting a free involution. The bundle has to be built as a deformation of the direct sum of a stable SU(4) bundle and the trivial line bundle.
Physics Letters B. 07/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper we discuss two aspects of duality transformations on the Neveu-Schwarz (NS) 5-brane solutions in type II and
heterotic string theories. First we demonstrate that the non-extremal NS 5-brane background is U-dual to its CGHS limit, a
two-dimensional black hole times S
3×T
5; an intermediate step is provided by the near horizon geometry which is given by the three-dimensional BTZ
3 black hole (being closely related to AdS
3) times S
3×T
4. In the second part of the paper we discuss the T-duality between k NS 5-branes and the Taub-NUT spaces respectively ALE spaces, which are related to the resolution of the A
k−1 singularities of the non-compact orbifold C2/Zk. In particular in the framework of N=1 supersymmetric gauge theories related to brane box constructions we give the metric dual to two sets of intersecting NS
5-branes. In this way we get a picture of a dual orbifold background C3/Γ which is fibered together out of two N=2 models (Γ=Zk×Zk′). Finally we also discuss the intersection of NS 5-branes with D branes, which can serve as probes of the dual background
spaces.
05/2007: pages 127-145;
-
[show abstract]
[hide abstract]
ABSTRACT: After discussing some general problems for heterotic compactifications involving fivebranes we construct bundles, built as extensions, over an elliptically fibered Calabi–Yau threefold. For these we show that it is possible to satisfy the anomaly cancellation topologically without any fivebranes. The search for a specific Standard Model or GUT gauge group motivates the choice of an Enriques surface or certain other surfaces as base manifold. The burden of this construction is to show the stability of these bundles. Here we give an outline of the construction and its physical relevance. The mathematical details, in particular the proof that the bundles are stable in a specific region of the Kähler cone, are given in the mathematical companion paper math.AG/0611762.
Journal of Geometry and Physics. 12/2006;
-
[show abstract]
[hide abstract]
ABSTRACT: We construct two chains of four-dimensional F-theory/heterotic dual string pairs with N = 1 supersymmetry. On the F-theory side as well as on the heterotic side the geometry of the involved manifolds relies on del Pezzo surfaces. We match the massless spectra by using, for one chain of models, an index formula to count the heterotic bundle moduli and determine the dual F-theory spectra from the Hodge numbers of the four-folds X4 and of the type 1113 base spaces.
Nuclear Physics B. 05/1997;
-
[show abstract]
[hide abstract]
ABSTRACT: We construct stable bundle extensions on elliptically fibered Calabi–Yau threefolds. We show that these bundles can solve the topological anomaly constraint in heterotic string theory without the need for invoking background five-branes.
Journal of Geometry and Physics.
