The role of center vortices in Gribov's confinement scenario

The connection of Gribov's confinement scenario in Coulomb gauge with the center vortex picture of confinement is investigated. For this purpose we assume a vacuum wave functional which models the infrared properties of the theory and in particular shows strict confinement, i.e. an area law of the Wilson loop. We isolate the center vortex content of this wave functional by standard lattice methods and investigate their contributions to various static propagators of the Hamilton approach to Yang-Mills theory in Coulomb gauge. We find that the infrared properties of these quantities, in particular the infrared divergence of the ghost form factor, are dominated by center vortices.Comment: 18 pages, 5 figure

Broad boron sheets and boron nanotubes: An ab initio study of structural, electronic, and mechanical properties

Based on a numerical ab initio study, we discuss a structure model for a broad boron sheet, which is the analog of a single graphite sheet, and the precursor of boron nanotubes. The sheet has linear chains of sp hybridized sigma bonds lying only along its armchair direction, a high stiffness, and anisotropic bonds properties. The puckering of the sheet is explained as a mechanism to stabilize the sp sigma bonds. The anisotropic bond properties of the boron sheet lead to a two-dimensional reference lattice structure, which is rectangular rather than triangular. As a consequence the chiral angles of related boron nanotubes range from 0 to 90 degrees. Given the electronic properties of the boron sheets, we demonstrate that all of the related boron nanotubes are metallic, irrespective of their radius and chiral angle, and we also postulate the existence of helical currents in ideal chiral nanotubes. Furthermore, we show that the strain energy of boron nanotubes will depend on their radii, as well as on their chiral angles. This is a rather unique property among nanotubular systems, and it could be the basis of a different type of structure control within nanotechnology.Comment: 16 pages, 17 figures, 2 tables, Versions: v1=preview, v2=first final, v3=minor corrections, v4=document slightly reworke

Dielectric function of the QCD vacuum

It is shown that the inverse of the ghost form factor in the Hamilton approach to Yang-Mills theory in Coulomb gauge can be interpreted as the color dielectric function of the QCD vacuum. Furthermore the horizon condition to the ghost form factor implies that in the infrared the QCD vacuum is a perfect color diaelectric medium and therefore a dual superconductor. The dielectric function is explicitly calculated within a previously developed variational approach, using a specific ansatz for the vacuum wave functional.Comment: 4 pages, 1 figure, revised version as published in Phys. Rev. Let

The Obama Factor: Change and Stability in Cultural and Political Anti-Americanism

Global public opinion toward the United States is an important factor in international politics. But to what degree are distinct dimensions of attitudes toward the United States associated with the person of the president and the consumption of U.S.-produced media content? Two surveys of German college students before and after the 2008 U.S. presidential election revealed that attitudes toward U.S. foreign policies improved from 2008 to 2009, and views on U.S. culture remained stable. Perceptions of Obama depended less on attitudes toward U.S. culture than perceptions of ordinary U.S. Americans, indicating a potential for the president to influence foreign political support, even in the face of cultural reservations. Consumption of some types of U.S. media was also associated with lower levels of anti-Americanism

Quantum Energies of Interfaces

We present a method for computing the one-loop, renormalized quantum energies of symmetrical interfaces of arbitrary dimension and codimension using elementary scattering data. Internal consistency requires finite-energy sum rules relating phase shifts to bound state energies.Comment: 8 pages, 1 figure, minor changes, Phys. Rev. Lett., in prin

Functionalizing graphene by embedded boron clusters

We present a model system that might serve as a blueprint for the controlled layout of graphene based nanodevices. The systems consists of chains of B7 clusters implanted in a graphene matrix, where the boron clusters are not directly connected. We show that the graphene matrix easily accepts these alternating boron chains, and that the implanted boron components may dramatically modify the electronic properties of graphene based nanomaterials. This suggests a functionalization of graphene nanomaterials, where the semiconducting properties might be supplemented by parts of the graphene matrix itself, but the basic wiring will be provided by alternating chains of implanted boron clusters that connect these areas.Comment: 10 pages, 2 figures, 1 tabl