Standard-like models from Intersecting D5-branes

We construct intersecting D5-brane orbifold models that yield the (non-supersymmetric) standard model up to vector-like matter and charged-singlet scalars. The models are constrained by the requirement that twisted tadpoles cancel, and that the gauge boson coupled to the weak hypercharge $U(1)_Y$ does not get a string-scale mass via a generalised Green-Schwarz mechanism. Gauge coupling constant ratios close to those measured are easily obtained for reasonable values of the parameters, consistently with having the string scale close to the electroweak scale, as required to avoid the hierarchy problem.Comment: 13 pages, LaTeX file, version to appear in Physics Letters

Chiral D-brane Models with Frozen Open String Moduli

Most intersecting D-brane 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 D-brane models, rephrasing the problems in terms of (open string) moduli stabilization. In particular, we consider a Z2 x Z2 orientifold construction where D6-branes wrap rigid 3-cycles 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 Pati-Salam-like model whose SU(4) gauge group is asymptotically free. We also comment on the application of these results for obtaining gaugino condensation in chiral D-brane 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.Comment: 55 pages, 4 figures. Bibtex forma

Identifying and remeshing contact interfaces in a polyhedral assembly for digital mock-up applications

Polyhedral models are widely used for applications such as manufacturing, digital simulation or visualization. They are discrete models; easy to store, to manipulate, allowing levels of resolution for visualization. They can be easily exchanged between CAD systems without loss of data. Previous works (Comput Aided Des 29(4):287–298, 1997, Comput Graphics 22(5):565–585, 1998) have focused on simplification process applied to polyhedral part models. The goal of the proposed approach is to extend these processes to polyhedral assembly models, describing the digital mock-up of a future manufacturing product. To apply simplification techniques or other processes on polyhedral assemblies, contact surfaces between interacting objects have to be identified and specific constraints must be applied for processing. The approach proposed allows checking and maintaining a global consistency of the assembly model to ensure the reliability of the future processes. Thus, contacts between objects are detected using an approach that works for a static configuration of the assembly. Finally, a precise detection of the faces involved in each contact area is made and the resulting input domains identified are processed using a local Frontal Delaunay re-meshing technique to produce an identical tessellation on both objects involved in the processed contact. The quality of the triangulation produced is also checked

One in a Billion: MSSM-like D-Brane Statistics

Continuing our recent work hep-th/0411173, we study the statistics of four-dimensional, supersymmetric intersecting D-brane 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 K-theory 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.Comment: 36 pages, 12 figures; v2: typos corrected, one ref. added; v3: minor changes, version to appear in JHE