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—In this paper, we provide an overview on backhaul requirements in mobile networks featuring inter-site cooperation. We consider a heterogeneous deployment, where small cells are embedded into macro-cells. For reducing inter-cell interference , we consider intra-and inter-site joint transmission (JT)-coordinated multi-point (CoMP) in fully flexible… (More)

- Volker Braun, Sakura Schäfer-Nameki
- 2004

We present an encompassing treatment of D–brane charges in supersymmetric SO(3) WZW models. There are two distinct supersymmetric CFTs at each even level: the standard bosonic SO(3) modular invariant tensored with free fermions, as well as a novel twisted model. We calculate the relevant twisted K–theories and find complete agreement with the CFT analysis… (More)

- Volker Braun, Yang-Hui He, Burt A Ovrut, Tony Pantev
- 2005

Stable, holomorphic vector bundles are constructed on an torus fibered, non-simply connected Calabi-Yau threefold using the method of bundle extensions. Since the manifold is multiply connected, we work with equiv-ariant bundles on the elliptically fibered covering space. The cohomology groups of the vector bundle, which yield the low energy spectrum, are… (More)

We present the construction of exactly solvable superconformal field theories describing Type II string models compactified on compact G 2 manifolds. These models are defined by anti-holomorphic quotients of the form (CY×S 1)/Z Z 2 , where we realize the Calabi-Yau as a Gepner model. In the superconformal field theory the Z Z 2 acts as charge conjugation… (More)

- Volker Braun, Burt A Ovrut
- 2006

It is shown that strongly coupled heterotic M-theory with anti-five-branes in the S 1 /Z 2 bulk space can have meta-stable vacua which break N = 1 supersymmetry and have a small, positive cosmological constant. This is demonstrated for the " minimal " heterotic standard model. This vacuum has the exact MSSM matter spectrum in the observable sector, a… (More)

- Volker Braun, Yang-Hui He, Burt A Ovrut, Tony Pantev
- 2008

In previous papers, we introduced a heterotic standard model and discussed its basic properties. The Calabi-Yau threefold has, generically, three Kähler and three complex structure moduli. The observable sector of this vacuum has the spectrum of the MSSM with one additional pair of Higgs-Higgs conjugate fields. The hidden sector has no charged matter in the… (More)

- Ralph Blumenhagen, Volker Braun, Boris Körs, Dieter Lüst
- 2002

We investigate orientifolds of type II string theory on K3 and Calabi-Yau 3-folds with intersecting D-branes wrapping special Lagrangian cycles. We determine quite generically the chiral massless spectrum in terms of topological invariants and discuss both orbifold examples and algebraic realizations in detail. Intriguingly, the developed techniques provide… (More)

- Volker Braun, Yang-Hui He, Burt A Ovrut, Tony Pantev
- 2005

Within the context of the E 8 × E 8 heterotic superstring compactified on a smooth Calabi-Yau threefold with an SU (4) gauge instanton, we show the existence of simple, realistic N = 1 supersymmetric vacua that are compatible with low energy particle physics. The observable sector of these vacua has gauge group SU (3) C × SU (2) L × U (1) Y × U (1) B−L ,… (More)