2-Group Representations for Spin Foams

Just as 3d state sum models, including 3d quantum gravity, can be built using categories of group representations, "2-categories of 2-group representations" may provide interesting state sum models for 4d quantum topology, if not quantum gravity. Here we focus on the "Euclidean 2-group", built from the rotation group SO(4) and its action on the group of translations of 4d Euclidean space. We explain its infinite-dimensional unitary representations, and construct a model based on the resulting representation 2-category. This model, with clear geometric content and explicit "metric data" on triangulation edges, shows up naturally in an attempt to write the amplitudes of ordinary quantum field theory in a background independent way.Comment: 8 pages; to appear in proceedings of the XXV Max Born Symposium: "The Planck Scale", Wroclaw, Polan

Towards a dual spin network basis for (3+1)d lattice gauge theories and topological phases

Using a recent strategy to encode the space of flat connections on a three-manifold with string-like defects into the space of flat connections on a so-called 2d Heegaard surface, we propose a novel way to define gauge invariant bases for (3+1)d lattice gauge theories and gauge models of topological phases. In particular, this method reconstructs the spin network basis and yields a novel dual spin network basis. While the spin network basis allows to interpret states in terms of electric excitations, on top of a vacuum sharply peaked on a vanishing electric field, the dual spin network basis describes magnetic (or curvature) excitations, on top of a vacuum sharply peaked on a vanishing magnetic field (or flat connection). This technique is also applicable for manifolds with boundaries. We distinguish in particular a dual pair of boundary conditions, namely of electric type and of magnetic type. This can be used to consider a generalization of Ocneanu's tube algebra in order to reveal the algebraic structure of the excitations associated with certain 3d manifolds.Comment: 45 page

Supersymmetric holography on AdS3

The proposed duality between Vasiliev's supersymmetric higher spin theory on AdS3 and the 't Hooft limit of the 2d superconformal Kazama-Suzuki models is analysed in detail. In particular, we show that the partition functions of the two theories agree in the large N limit.Comment: 25 pages, 3 figures, improved fig.

Strong charge-transfer excitonic effects and Bose-Einstein exciton-condensate in graphane

Using first principles many-body theory methods (GW+BSE) we demonstrate that optical properties of graphane are dominated by localized charge-transfer excitations governed by enhanced electron correlations in a two-dimensional dielectric medium. Strong electron-hole interaction leads to the appearance of small radius bound excitons with spatially separated electron and hole, which are localized out-of-plane and in-plane, respectively. The presence of such bound excitons opens the path on excitonic Bose-Einstein condensate in graphane that can be observed experimentally.Comment: 8 pages, 6 figure

Monopole Bubbling via String Theory

In this paper, we propose a string theory description of generic 't Hooft defects in $\mathcal{N}=2$ $SU(N)$ supersymmetric gauge theories. We show that the space of supersymmetric ground states is given by the moduli space of singular monopoles and that in this setting, Kronheimer's correspondence is realized as T-duality. We conjecture that this brane configuration can be used to study the full dynamics of monopole bubbling.Comment: 46 pages plus Appendi

Nuclei with Tetrahedral Symmetry

We discuss a point-group-theory based method of searching for new regions of nuclear stability. We illustrate the related strategy with realistic calculations employing the tetrahedral and the octahedral point groups. In particular, several nuclei in the Rare Earth region appear as excellent candidates to study the new mechanism.Comment: 18 pages, 4 figures, submitted to International Journal of Modern Physics