Orbifolds versus smooth heterotic compactifications

Following the recent exploration of smooth heterotic compactifications with unitary bundles, orbifold compactifications in six dimensions can be shown to correspond in the blow-up to compactifications with U(1) gauge backgrounds. A powerful tool is the comparison of anomaly polynomials. The presentation here focuses on heterotic SO(32) compactifications in six dimensions including five-branes. Four dimensional and E8 x E8 models are briefly commented on.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTe

Towards exact field theory results for the Standard Model on fractional D6-branes

Fractional D6-branes on toroidal orbifold backgrounds are known to be able to accommodate the particle spectrum and gauge group of the Standard Model, but up to now exact results for their low-energy effective action are missing. Here we discuss how the conceptual ansatz of matching the string theoretic gauge couplings at one-loop with the supergravity expressions is generalised from the six-torus to orbifold backgrounds on which the Standard Model spectrum can be realised on fractional D6-branes. The Kaehler metrics and perturbatively exact holomorphic gauge kinetic functions can be classified in terms of the vanishing of some intersection angle and the related beta function coefficients, which potentially opens the possibility to extrapolate to smooth Calabi-Yau backgrounds.Comment: 1+3 pages, 2 tables; proceedings of the EPS-HEP 2011 conference in Grenoble 21-27 July 2011; v2: introduction and conclusion extended, published versio

Mapping an Island in the Landscape

We provide a complete classification and statistical analysis of all type IIA orientifold compactifications with intersecting D6-branes on the orbifold T^6/Z'_6. The total number of four dimensional N=1 supersymmetric models is found to be O(10^23). After a statistical analysis of the gauge sector properties of all possible solutions, we study three subsets of configurations which contain the chiral matter sector of the standard model, a Pati-Salam or SU(5) GUT model, respectively. We find O(10^15) compactifications with an MSSM and O(10^11) models with a Pati-Salam sector. Along the way we derive an explicit algebraic formulation for the computation of the non-chiral matter spectrum for all Z_N orbifolds.Comment: 46 pages, 10 figures; v2: typos corrected, new examples and expanded study on chiral exotic

Discrete Abelian gauge symmetries and axions

We combine two popular extensions of beyond the Standard Model physics within the framework of intersecting D6-brane models: discrete Zn symmetries and Peccei-Quinn axions. The underlying natural connection between both extensions is formed by the presence of massive U(1) gauge symmetries in D-brane model building. Global intersecting D6-brane models on toroidal orbifolds of the type T6/Z2N and T6/Z2xZ2M with discrete torsion offer excellent playgrounds for realizing these extensions. A generation-dependent Z2 symmetry is identified in a global Pati-Salam model, while global left-right symmetric models give rise to supersymmetric realizations of the DFSZ axion model. In one class of the latter models, the axion as well as Standard Model particles carry a non-trivial Z3 charge.Comment: Contribution to the proceedings of DISCRETE2014; 13 page