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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
- 2008

I determine the twisted K–theory of all compact simply connected simple Lie groups. The computation reduces via the Freed–Hopkins–Teleman theorem [1] to the CFT prescription, and thus explains why it gives the correct result. Finally I analyze the exceptions noted by Bouwknegt et al [2].

- Volker Braun
- 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)

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)

- Volker Braun
- 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)

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
- 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)