Confinement in 4D Yang-Mills Theories from Non-Critical Type 0 String Theory

We study five dimensional non critical type 0 string theory and its correspondence to non supersymmetric Yang Mills theory in four dimensions. We solve the equations of motion of the low energy effective action and identify a class of solutions that translates into a confining behavior in the IR region of the dual gauge theories. In particular we identify a setup which is dual to pure SU(N) Yang-Mills theory. Possible flows of the solutions to the UV region are discussed. The validity of the solutions and potential sub-leading string corrections are also discussed.Comment: 25 pages, Latex. 1 figure. v2: refs. added, minor corrections, note added in section

Permutation Orbifold of N=2 Supersymmetric Minimal Models

In this paper we apply the previously derived formalism of permutation orbifold conformal field theories to N=2 supersymmetric minimal models. By interchanging extensions and permutations of the factors we find a very interesting structure relating various conformal field theories that seems not to be known in literature. Moreover, unexpected exceptional simple currents arise in the extended permuted models, coming from off-diagonal fields. In a few situations they admit fixed points that must be resolved. We determine the complete CFT data with all fixed point resolution matrices for all simple currents of all Z_2-permutations orbifolds of all minimal N=2 models with k\neq 2 mod 4.Comment: 48 page

Transport and subgap states in superconducting heterostructures of effective Dirac systems

In recent years, effective Dirac systems recieved a lot of attention in solid state physics. These are systems whose dispersion can effectively be described by a Dirac cone, the most prominent examples beeing graphene and topological insulators (TIs). These systems exhibit intriguing phenomena—for example, TIs can host perfectly transmitted modes or, in conjunction with superconductors, Majorana zero modes. This thesis deals with superconducting heterostructures of both of the aforementioned materials and examines transport phenomena as well as the formation of subgap states in such systems: In the first chapter, superconducting bilayer graphene with a chemisorbed adatom is investigated and the existence of peculiar subgab states, so-called Yu-Shiba-Rusinov states, is shown. The second chapter deals with T junction devices make out of three-dimensional (3D) TI nanowires. Together with proximity induced superconductivity in one arm and external magnetic fields, this setup allows for the occurence of crossed Andreev reflection, including perfect crossed Andreev reflection, and negative nonlocal conductances. In the third chapter, Josephson junctions of 3D TI nanowires are investigated. The physical origin of unusual, experimentally observed supercurrent oscillations in dependence of a parallel magnetic field is examinated in a semiclassical analysis

Brikkernes stilling: - erfaringer med konkurrence og selskabsdannelser i den kollektive trafik 1990-2002

I perioden siden begyndelsen af 1990'erne er der sket en gennemgribende ændring af rollefordelingen i og den institutionelle organisering af den kollektive trafik i Danmark. Udviklingen har været et pro- dukt af en række forhold: Den europæiske politisk-økonomiske bevægelse henimod privatisering og selskabshenlæggelse af offentlige driftsaktiviteter igangsat ikke mindst fra Storbritannien, de stigende konkrete problemer med at drive en række kollektive transportaktiviteter i Danmark inden for de hid- tidige rammer, behovet for at skaffe midler fra privatiseringsprovenuerne til finansering af offentlige udgifter, mv. I dette oplæg drøftes en række af de problemstillinger, som de institutionelle ændringer har givet anledning til

Spin relaxation, Josephson effect and Yu-Shiba-Rusinov states in superconducting bilayer graphene

Bilayer graphene has two nonequivalent sublattices and, therefore, the same adatom impurity can manifest in spectrally distinct ways—sharp versus broad resonances near the charge neutrality—depending on the sublattice it adsorbs at. Employing Green's function analytical methods and the numerical kwant package, we investigate the spectral and transport interplay between the resonances and superconducting coherence induced in bilayer graphene by proximity to an s-wave superconductor. Analyzing doping and temperature dependencies of quasiparticle spin-relaxation rates, energies of Yu-Shiba-Rusinov states, Andreev spectra, and the supercurrent characteristics of Josephson junctions, we find unique superconducting signatures discriminating between resonant and off-resonant regimes. Our findings are in certain aspects going beyond the superconducting bilayer graphene and hold for generic s-wave superconductors functionalized by the resonant magnetic impurities

On meson resonances and chiral symmetry

We study meson resonances with quantum numbers J^P=1^+ in terms of the chiral SU(3) Lagrangian. At leading order a parameter-free prediction is obtained for the scattering of Goldstone bosons off vector mesons with J^P=1^- once we insist on approximate crossing symmetry of the unitarized scattering amplitude. A resonance spectrum arises that is remarkably close to the empirical pattern. In particular, we find that the strangeness-zero resonances h_1(1380), f_(1285) and b_1(1235) are formed due to strong K \bar K_\mu and \bar K K_\mu channels. This leads to large coupling constants of those resonances to the latter states.Comment: 29 pages, 6 figures, more detailed discussions are give