Scattering Theory for Quantum Hall Anyons in a Saddle Point Potential

We study the theory of scattering of two anyons in the presence of a quadratic saddle-point potential and a perpendicular magnetic field. The scattering problem decouples in the centre-of-mass and the relative coordinates. The scattering theory for the relative coordinate encodes the effects of anyon statistics in the two-particle scattering. This is fully characterized by two energy-dependent scattering phase shifts. We develop a method to solve this scattering problem numerically, using a generalized lowest Landau level approximation.Comment: 5 pages. Published version, with clarified presentatio

On the Observability of "Invisible" / "Nearly Invisible" Charginos

It is shown that if the charginos decay into very soft leptons or hadrons + $\not{E}$ due to degeneracy/ near- degeneracy with the LSP or the sneutrino, the observability of the recently proposed signal via the single photon (+ soft particles) + $\not{E}$ channel crucially depends on the magnitude of the \SNU mass due to destructive interferences in the matrix element squared. If the \SNU's and, consequently, left-sleptons are relatively light, the size of the signal, previously computed in the limit \MSNU \to \infty only, is drastically reduced. We present the formula for the signal cross section in a model independent way and discuss the observability of the signal at LEP 192 and NLC energies.Comment: 27 pages, Late

Strong flavour changing effective operator contributions to single top quark production

We study the effects of dimension six effective operators on the production of single top quarks at the LHC. The operator set considered includes terms with effective gluon interactions and four-fermion terms. Analytic expressions for the several partonic cross sections of single top production will be presented, as well as the results of their integration on the parton density functions.Comment: 20 pages, 7 fig

Electrical Conductance of Molecular Wires

Molecular wires (MW) are the fundamental building blocks for molecular electronic devices. They consist of a molecular unit connected to two continuum reservoirs of electrons (usually metallic leads). We rely on Landauer theory as the basis for studying the conductance properties of MW systems. This relates the lead to lead current to the transmission probability for an electron to scatter through the molecule. Two different methods have been developed for the study of this scattering. One is based on a solution of the Lippmann-Schwinger equation and the other solves for the {\bf t} matrix using Schroedinger's equation. We use our methodology to study two problems of current interest. The first MW system consists of 1,4 benzene-dithiolate (BDT) bonded to two gold nanocontacts. Our calculations show that the conductance is sensitive to the chemical bonding between the molecule and the leads. The second system we study highlights the interesting phenomenon of antiresonances in MW. We derive an analytic formula predicting at what energies antiresonances should occur in the transmission spectra of MW. A numerical calculation for a MW consisting of filter molecules attached to an active molecule shows the existence of an antiresonance at the energy predicted by our formula.Comment: 14 pages, 5 figure

Efficient atomic self-interaction correction scheme for non-equilibrium quantum transport

Density functional theory calculations of electronic transport based on local exchange and correlation functionals contain self-interaction errors. These originate from the interaction of an electron with the potential generated by itself and may be significant in metal-molecule-metal junctions due to the localized nature of the molecular orbitals. As a consequence, insulating molecules in weak contact with metallic electrodes erroneously form highly conducting junctions, a failure similar to the inability of local functionals of describing Mott-Hubbard insulators. Here we present a fully self-consistent and still computationally undemanding self-interaction correction scheme that overcomes these limitations. The method is implemented in the Green's function non-equilibrium transport code Smeagol and applied to the prototypical cases of benzene molecules sandwiched between gold electrodes. The self-interaction corrected Kohn-Sham highest occupied molecular orbital now reproduces closely the negative of the molecular ionization potential and is moved away from the gold Fermi energy. This leads to a drastic reduction of the low bias current in much better agreement with experiments.Comment: 4 pages, 5 figure

The effect of vacancy-induced magnetism on electronic transport in armchair carbon nanotubes

The influence of local magnetic moment formation around three kinds of vacancies on the electron conduction through metallic single-wall carbon nanotubes is studied by use of the Landauer formalism within the coherent regime. The method is based on the single-band tight-binding Hamiltonian, a surface Green's function calculation, and the mean-field Hubbard model. The numerical results show that the electronic transport is spin-polarized due to the localized magnetic moments and it is strongly dependent on the geometry of the vacancies. For all kinds of vacancies, by including the effects of local magnetic moments, the electron scattering increases with respect to the nonmagnetic vacancies case and hence, the current-voltage characteristic of the system changes. In addition, a high value for the electron-spin polarization can be obtained by applying a suitable gate voltage.Comment: 6 pages, 6 figure

Quantum Transport with Spin Dephasing: A Nonequilibrium Green's Function Approach

A quantum transport model incorporating spin scattering processes is presented using the non-equilibrium Green's function (NEGF) formalism within the self-consistent Born approximation. This model offers a unified approach by capturing the spin-flip scattering and the quantum effects simultaneously. A numerical implementation of the model is illustrated for magnetic tunnel junction devices with embedded magnetic impurity layers. The results are compared with experimental data, revealing the underlying physics of the coherent and incoherent transport regimes. It is shown that small variations in magnetic impurity spin-states/concentrations could cause large deviations in junction magnetoresistances.Comment: NEGF Formalism, Spin Dephasing, Magnetic Tunnel Junctions, Magnetoresistanc

Displaced Higgs production in type III seesaw

We point out that the type III seesaw mechanism introducing fermion triplets predicts peculiar Higgs boson signatures of displaced vertices with two b jets and one or two charged particles which can be cleanly identified. In a supersymmetric theory, the scalar partner of the fermion triplet contains a neutral dark matter candidate which is almost degenerate with its charged components. A Higgs boson can be produced together with such a dark matter triplet in the cascade decay chain of a strongly produced squark or gluino. When the next lightest supersymmetric particle (NLSP) is bino/wino-like, there appears a Higgs boson associated with two charged tracks of a charged lepton and a heavy charged scalar at a displacement larger than about 1 mm. The corresponding production cross-section is about 0.5 fb for the squark/gluino mass of 1 TeV. In the case of the stau NLSP, it decays mainly to a Higgs boson and a heavy charged scalar whose decay length is larger than 0.1 mm for the stau NLSP mixing with the left-handed stau smaller than 0.3. As this process can have a large cascade production $\sim 2$ pb for the squark/gluino mass $\sim 1$ TeV, one may be able to probe it at the early stage of the LHC experiment.Comment: 10 pages, 5 figure

A multideterminant assessment of mean field methods for the description of electron transfer in the weak coupling regime

Multideterminant calculations have been performed on model systems to emphasize the role of many-body effects in the general description of charge quantization experiments. We show numerically and derive analytically that a closed-shell ansatz, the usual ingredient of mean-field methods, does not properly describe the step-like electron transfer characteristic in weakly coupled systems. With the multideterminant results as a benchmark, we have evaluated the performance of common ab initio mean field techniques, such as Hartree Fock (HF) and Density Functional Theory (DFT) with local and hybrid exchange correlation functionals, with a special focus on spin-polarization effects. For HF and hybrid DFT, a qualitatively correct open-shell solution with distinct steps in the electron transfer behaviour can be obtained with a spin-unrestricted (i.e., spin-polarized) ansatz though this solution differs quantitatively from the multideterminant reference. We also discuss the relationship between the electronic eigenvalue gap and the onset of charge transfer for both HF and DFT and relate our findings to recently proposed practical schemes for calculating the addition energies in the Coulomb blockade regime for single molecule junctions from closed-shell DFT within the local density approximation